Tesi sul tema "RAFT"
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1
Fleet, Reda. "RAFT mediated polysaccharide copolymers". Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/1025.
Testo completo
2
Suwattana, Siripan. "Biodegradable polymers via RAFT". Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549765.
Testo completoAbstract (sommario):
This research has shown that biodegradable monomer (5,6-benzo-2- methylene-1,3-dioxepane) (BMOO) can be achieved. Also its homo-and-eo- polymerisation can be successfully realised via RAFT and ROP polymerisation techniques. BMOO was synthesised with the modification via the dehydrobrornination of 5,6-benzo-2-(bromomethyl)-1,3-dioxepane in a good yield (95% yields). The homopolymerisation of BMOO were designed to produce a target OP of 200 via living "polymerisation" and complete ring-opening polymerisation. A narrow POI (1.09) and an M n= 4,697 g mol' were observed after 24 hours for the reaction in the presence of the CT A(MCPDB)' The copolymerisation of MMA and BMOO in the presence of the CT A(CPDB) gave better control over the polymerisation than that achieved using the CT A(MCPDB) and the CTA(ETSPE), at 120 "C. A narrow POI (1.36) and an Mn= 16,662 g mol' were observed after 24 hours. The copolymer was shown to be results of a combination of 1,2-addition polymerisation and of ring-opening copolymerisation. The reactivity ratio of the monomers was calculated using the Kelen- Tudos method (rMMA= 1.12 and rBMDO= 0.43). The copolymerisation of styrene with BMOO in the presence of the CTA(cPDB) gave the better control than that given by the CT A(MCPDB) and the CTA(ETSPE), at 120aC (Sty:BMOO, with an initial feed of 33%:67%). A narrow POI (1.18) and M n= 9,684 g rnol' were obtained after 24 hours. The % ratio of BMOO that was incorporated into the final polymeric chain was Sty:BMOO= 64.3%:35.7% and the copolymer was formed from ring-opening polymerisation only. The reactivity ratio of the monomers was calculated using the Kelen-TOdos method (rsty= 2',56 and rBMDO= 0.64). NMR, FTIR and UVlVis spectroscopy provided further evidence that the final polymers were the product of a ring-opening polymerisation. As required, thermal analysis techniques were used to ascertain the consequences of the copolymerisation, with respect to thermal consequences (decomposition) and compositional features.
3
Antus, Joakim. "Reaching Consensus Using Raft". Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-301332.
Testo completoAbstract (sommario):
This thesis project implements and evaluates log replication using the Raft consensus algorithm. Raft presents a new and easier to understand consensus protocol for log replication in a distributed system. This thesis aims to evaluate the correctness and robustness of Raft by implementing a scalable system that is easy to maintain and test for further development. This thesis gives an in-depth description of Raft as well as a detailed explanation of the implemented system together with an evaluation of the system performance with focus on correctness.
4
Zong, Mengmeng. "RAFT polymerisation in supercritical CO2". Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537644.
Testo completo
5
Nozari, Samira. "Towards understanding RAFT aqueous heterophase polymerization". Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2005/580/.
Testo completoAbstract (sommario):
Reversible addition-fragmentation transfer (RAFT) was used as a controlling technique for studying the aqueous heterophase polymerization. The polymerization rates obtained by calorimetric investigation of ab initio emulsion polymerization of styrene revealed the strong influence of the type and combination of the RAFT agent and initiator on the polymerization rate and its profile. The studies in all-glass reactors on the evolution of the characteristic data such as average molecular weight, molecular weight distribution, and average particle size during the polymerization revealed the importance of the peculiarities of the heterophase system such as compartmentalization, swelling, and phase transfer. These results illustrated the important role of the water solubility of the initiator in determining the main loci of polymerization and the crucial role of the hydrophobicity of the RAFT agent for efficient transportation to the polymer particles. For an optimum control during ab-initio batch heterophase polymerization of styrene with RAFT, the RAFT agent must have certain hydrophilicity and the initiator must be water soluble in order to minimize reactions in the monomer phase.
An analytical method was developed for the quantitative measurements of the sorption of the RAFT agents to the polymer particles based on the absorption of the visible light by the RAFT agent. Polymer nanoparticles, temperature, and stirring were employed to simulate the conditions of a typical aqueous heterophase polymerization system. The results confirmed the role of the hydrophilicity of the RAFT agent on the effectiveness of the control due to its fast transportation to the polymer particles during the initial period of polymerization after particle nucleation. As the presence of the polymer particles were essential for the transportation of the RAFT agents into the polymer dispersion, it was concluded that in an ab initio emulsion polymerization the transport of the hydrophobic RAFT agent only takes place after the nucleation and formation of the polymer particles. While the polymerization proceeds and the particles grow the rate of the transportation of the RAFT agent increases with conversion until the free monomer phase disappears.The degradation of the RAFT agent by addition of KPS initiator revealed unambigueous evidence on the mechanism of entry in heterophase polymerization. These results showed that even extremely hydrophilic primary radicals, such as sulfate ion radical stemming from the KPS initiator, can enter the polymer particles without necessarily having propagated and reached a certain chain length. Moreover, these results recommend the employment of azo-initiators instead of persulfates for the application in seeded heterophase polymerization with RAFT agents.
The significant slower rate of transportation of the RAFT agent to the polymer particles when its solvent (styrene) was replaced with a more hydrophilic monomer (methyl methacrylate) lead to the conclusion that a complicated cooperative and competitive interplay of solubility parameters and interaction parameter with the particles exist, determining an effective transportation of the organic molecules to the polymer particles through the aqueous phase. The choice of proper solutions of even the most hydrophobic organic molecules can provide the opportunity of their sorption into the polymer particles. Examples to support this idea were given by loading the extremely stiff fluorescent molecule, pentacene, and very hydrophobic dye, Sudan IV, into the polymer particles.
Finally, the first application of RAFT at room temperature heterophase polymerization is reported. The results show that the RAFT process is effective at ambient temperature; however, the rate of fragmentation is significantly slower. The elevation of the reaction temperature in the presence of the RAFT agent resulted in faster polymerization and higher molar mass, suggesting that the fragmentation rate coefficient and its dependence on the temperature is responsible for the observed retardation.
Um neue Materialien mit außergewöhnlichen Eigenschaften zu erstellen, muss man in der Lage sein, die Struktur der Moleküle zu kontrollieren, aus denen die Materialien bestehen. Für das Maßschneidern solcher neuer Eigenschaften besitzen Polymere ein großes Potenzial: Dies sind sehr lange Moleküle, die aus einer großen Zahl von kleineren Einheiten aufgebaut sind. Proteine und DNS sind Beispiele für natürliche Polymere; Plastik und Gummi sind Beispiele für künstliche Polymere. Letztere werden üblicherweise durch das Zusammenfügen einer Reihe von kleineren Molekülen, den Monomeren, hergestellt. Schon lange versuchen Wissenschaftler, die Anordnung, Anzahl und Art dieser Monomere zu kontrollieren, die sich in der Struktur der Polymermoleküle widerspiegeln. Die gebräuchlichste Methode zur kommerziellen Produktion von Polymeren ist die so genannte freie radikalische Polymerisation. Die Strukturkontrolle durch diese Methode ist jedoch relativ schwierig und wurde maßgeblich erst im letzten Jahrzehnt entwickelt. Trotz der Existenz einiger effektiver Kontrollmethoden ist ihre industrielle Anwendung bislang sehr beschränkt, weil sie nicht für die Emulsionspolymerisation verwendbar sind. Die Emulsionspolymerisation ist die gängigste Technik in der industriellen Produktion von Polymeren. Es handelt sich dabei um ein vergleichsweise umweltfreundliches Verfahren, denn es werden keine organischen Lösungsmittel verwendet. Stattdessen dient Wasser als Lösungsmittel, in dem die Polymere in Form von kleinen, fein verteilten Partikeln vorliegen. In der Natur kommt dieses Prinzip beispielsweise in Pflanzen bei der Bildung von Kautschuk - allgemein als Latex bezeichnet - vor. Schließlich ist die Emulsionspolymerisation einfach durchzuführen: Das Produkt ist in vielen Fällen gebrauchsfertig, und es gibt viele technische Vorteile im Vergleich zu anderen Herstellungsprozessen.
Doch bevor die Probleme beim Einsatz von Kontrollmethoden in der Emulsionspolymerisation gelöst werden können, müssen erst ihre Ursachen geklärt werden. Dies ist eine unverzichtbare Vorraussetzung zum Übertragen von Forschungsergebnissen auf das tägliche Leben.
Ziel dieser Arbeit ist die Untersuchung der Probleme, die für die kontrollierte radikalische Polymerisation in Emulsion von Bedeutung sind. Die wichtigste Fragestellung in der Emulsionspolymerisation zielt auf die Löslichkeit der Reaktionskomponenten in den verschiedenen Phasen, wie z.B. in Wasser oder in den Polymerpartikeln. Die Kontrollmethode der Wahl für diese Arbeit ist "Reversibler Additions-Fragmentierungs Transfer" (RAFT). Die RAFT-Methode ist die modernste Kontrollmethode, und sie ist für viele Reaktionsbedingungen und viele Arten von Monomeren anwendbar.
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Conrad, Cathrin Sonja. "Polybutadien und Butadien enthaltende Copolymere mit gezielt eingebauten vulkanisierbaren Gruppen durch RAFT-Polymerisation". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5E9E-D.
Testo completoAbstract (sommario):
Die RAFT-Polymerisation ("Reversible Addition-Fragmentation Chain Transfer") ist eine radikalische Polymerisation, die auf dem Prinzip des degenerativen Kettentransfers basiert. Es können Polymere hergestellt werden, die eine niedrige Dispersität aufweisen und komplexe makromolekulare Strukturen ausbilden. Für die Funktionalisierung von Polymerketten bietet sich die RAFT-Polymerisation ebenfalls an, da idealerweise jede auf diese Art hergestellte Polymerkette eine RAFT-Einheit trägt und so eine vollständige Funktionalisierung gewährleistet ist.
Im Fokus dieser Arbeit stand die Funktionalisierung von Polybutadien und 1,3-Butadien enthaltenden Copolymeren mit gezielt eingebauten schwefelhaltigen Gruppen.
Dabei wurden zwei verschiedene Ansätze verfolgt: Die α,ω-Funktionalisierung der Polymerketten mittels modifizierter RAFT-Agenzien sowie eine Funktionalisierung entlang der Polymerkette mit Hilfe von speziellen Monomeren. Da diese Polymere in technischen Anwendungen Verwendung finden sollen, standen einfache Synthesen, die sich gut auf den Technikums- und Industriemaßstab übertragen lassen, im Vordergrund.
Da es sich bei der RAFT-Einheit auch um eine schwefelhaltige Gruppe handelt, wurden Strategien zur Funktionalisierung der Abgangsgruppe erarbeitet und experimentell untersucht, um so ein α,ω-funktionalisiertes Polymer zu erhalten. Neben klassischen RAFT-Agenzien wurden auch neuartige Makro-RAFT-Agenzien verwendet, bei denen die schwefelhaltige Gruppe während einer Polymerisation in situ angebunden wird.
Darüber hinaus konnten erfolgreich Monomere synthetisiert werden, die wegen ihrer styrolähnlichen Struktur und der Ähnlichkeit der Monomere Styrol und 1,3-Butadien in ihrem Polymerisationsverhalten gut mit 1,3-Butadien copolymerisieren und dabei die schwefelhaltige Gruppe entlang der Polymerkette einbauen. Das Hauptaugenmerk weiterer Untersuchungen lag auf den Copolymerisationseigenschaften der Monomere. Dazu wurden umfangreiche Untersuchungen mit Styrol als Modellsystem für 1,3-Butadien durchgeführt und die gewonnenen Erkenntnisse in einer Copolymerisation der funktionalisierten Monomere mit 1,3-Butadien verifiziert.
Es konnte weiterhin gezeigt werden, dass sich schaltbare RAFT-Agenzien für die Synthese von Poly(butadien)-block-poly(vinylacetat) eignen, obwohl es sich um zwei Monomere mit stark unterschiedlichen elektronischen Eigenschaften handelt, die in einer konventionellen radikalischen Polymerisation kein Copolymer bilden würden. Aufgrund der Ähnlichkeit der Monomere Vinylacetat und Ethylen eröffnet dies neue Wege in der kontrollierten radikalischen Polymerisation von Polybutadien-block-polyethylen und erweitert so das Spektrum der unpolaren Monomere in der RAFT-Polymerisation zur Herstellung von Blockcopolymeren.
7
Gemici, Hesna. "Water soluble polymers by RAFT polymerisation". Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507717.
Testo completo
8
Bray, Caroline. "Aqueous RAFT polymerisation of acrylamide monomers". Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/111296/.
Testo completoAbstract (sommario):
The challenge of this project was to control the polymerisation of acrylamide monomers, particularly sodium 2-acrylamido-2-methylpropane sulfonate (Lubrizol trademark, AMPS®2405), via reversible addition-fragmentation chain transfer (RAFT) polymerisation in aqueous solution. AMPS® based polymers are employed in a wide range of applications (e.g. medical, paint, oil recovery and water treatment), and are typically obtained via conventional radical polymerisation. Here, the use of the RAFT process to control the polymerisation of AMPS®2405 was reported, and well-defined polymeric architectures were obtained compared to materials obtained via free radical polymerisation (FRP). The chain transfer agent (CTA) of choice for this project was initially DDMAT (CTA-A, Z-group is C12H25), and a water soluble CTA synthesised by the Lubrizol corporation (USA) in tonne-scale. DDMAT is known to form aggregates in water ([CAC]DDMAT =0.005 M) and this is likely to disrupt the RAFT mechanism and consequently diminish the control over the polymerisation. To overcome this problem a chain transfer agent with a shorter alkyl chain (BDMAT, Z-group is C4H9) was used for comparison with DDMAT. The polymerisation of AMPS®2405 monomer was optimised, as discussed in CHAPTER 2, in aqueous solution using either DDMAT or BDMAT as a chain transfer agent. These conditions were found to be universal to other water soluble acrylamide monomers (N,N-dimethylacrylamide, N-hydroxyethyl acrylamide and 4-acryloylmorpholine). More complex architectures were designed, as described in CHAPTER 3, exploiting the high chain end fidelity and chain extensions. A small library of diblock copolymers using various comonomers (N,N-dimethylacrylamide, N-hydroxyethyl acrylamide, 4-acryloylmorpholine, acrylic acid and acrylamide) were first synthesised. The synthesis of star polymers using the arm first approach was further studied, and well-defined multiblock star copolymers were obtained by RAFT polymerisation. These structures synthesised were characterised, as discussed in CHAPTER 4, using diverse techniques (e.g. SAXS, DLS, SEC with triple detection and AFM). While copolymers prepared from AMPS®2405 can be used in numerous applications, the focus of this thesis, as discussed in CHAPTER 5, was to study their benefit as heparin-mimicking polymers.
9
Elnakat, Hala. "Regulation of Folate Receptor Raft Recycling". University of Toledo Health Science Campus / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=mco1174569209.
Testo completo
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Pflughaupt, Robin L. "In pursuit of RAFT-functional polyethylene : exploration of a novel class of Sn-RAFT agents and the preparation and application of RAFT-functional polyethylene-like poly(ω-pentadecalactone)". Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/64038/.
Testo completoAbstract (sommario):
This work explores the preparation of Reversible Addition-Fragmentation chain-Transfer (RAFT)-functional polyethylene (PE). Challenges in developing methods to control the polymerization of primary radicals and prepare functional polyethylene are significant. Modest control over ethylene polymerization demonstrated via F-RAFT polymerization inspired our interest in RAFT agent design and we envisaged that metallo-RAFT agents could present different reactivities towards primary radicals. Considering the challenge of attempting to develop chemistry for the controlled radical polymerization of primary radicals, preparation of RAFT-functional polyethylene-like poly(ω-pentadecalactone) (PPDL) was also investigated. We envisaged the preparation of RAFT-functional PPDL to be more convenient than reported strategies to prepare functional polyethylene all whilst being a “green” alternative to PE that may be suitable for some applications. Chapter 1 discusses challenges in preparing functional polyethylene via controlled radical polymerization techniques. Furthermore, metallo-RAFT chemistry and the ring-opening polymerization of macrocyclic esters are reviewed. Chapter 2 describes the synthesis of PPDL via enzymatic ring-opening polymerization (eROP). Using a bifunctional initiator appropriate for the RAFT polymerization of acrylic and styrenic monomers, RAFT-functional poly(ω-pentadecalactone) was prepared. Furthermore, chain extension of the macro-chain-transfer agent was utilized to prepare acrylic and styrenic block copolymers of PPDL. To our knowledge, this is the first preparation of block copolymers of poly(ω-pentadecalactone) via a combination of eROP and RAFT polymerization techniques. Chapter 3 describes the large scale synthesis and characterization of a selection of acrylic block copolymers of PPDL suitable for fuels applications. Furthermore, the fuels testing of these copolymers for cold flow applications is described. In general, all block copolymers of PPDL, in particular poly(ω-pentadecalactone)-b-poly(isodecyl acrylate) improved the cold flow performance of various diesel fuels. Chapter 4 reports the synthesis of Sn-RAFT agents and their subsequent use in the controlled radical polymerization of several vinylic monomers. Chapter 5 summarizes the findings in chapters 2 – 4 and Chapter 6 communicates the associated experimental data.
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Nguema, Edzang Ronald W. "Synthèse et caractérisation de polymères à propriétés rédox pour un contrôle des propriétés d'adhésion bactérienne". Thesis, Toulon, 2016. http://www.theses.fr/2016TOUL0006/document.
Testo completoAbstract (sommario):
En raison des propriétés redox réversibles du ferrocène et de son activité antibactérienne, les polymères à base de ferrocène sont intéressants pour synthétiser de nouveaux liants pour des revêtements anti-adhésifs bactériens. Cette étude rend compte de l’homopolymérisation et de la copolymérisation de monomères méthacryliques porteurs de groupes ferrocényles avec le méthacrylate de lauryle (LM). Le méthacrylate de méthylferrocène (FMMA) mais aussi quatre nouveaux monomères nommés méthacrylate de 2- ferrocénylméthoxyéthyle (FMOEMA), méthacrylate de 3-ferrocénylméthoxypropyle (FMOPMA), 4- ferrocénylméthoxybutyle (FMOBMA) et de 2-ferrocénylméthoxyméthyléthyle (FMOMEMA) ont d’ bord été synthétisés et ensuite polymérisés via le procédé RAFT. Les cinétiques ’homopolymérisation ont été étudiées par RMN 1H in situ. La polymérisation a été contrôlée en utilisant le 2-cyanoprop-2-yl dithiobenzoate (CPDB) comme agent de transfert de chaîne, à 70°C, dans le toluène deutéré. Ces monomères contenant le groupement ferrocényle se sont révélés très réactifs via le procédé RAFT, conduisant à des conversions de 96% et à des polymères de faibles indices de polymolécularité (Ð<1,6). La conversion des monomères suit une cinétique de premier ordre (jusqu’à 80%) avec une augmentation linéaire de la masse molaire en fonction de la conversion en monomère. En utilisant le monomère FMMA comme référence, l’ spacement entre la partie polymérisable et le groupement ferrocényle a été augmenté pour le FMOEMA, FMOPMA, FMOMEMA et FMOBMA afin d’ méliorer la mobilité des groupements latéraux. Cette mobilité se traduit par une diminution notable des températures de transition vitreuse des homopolymères entre le pFMMA et le pFMOBMA. De plus, les copolymères diblocs préparés par voie séquencée présentent deux températures de transition vitreuse spécifiques à chaque bloc, démontrant une incompatibilité de ces derniers. Les propriétés électrochimiques des monomères et celles des polymères ont été caractérisées par voltampérométrie cyclique. Enfin, les propriétés anti-adhésives de ces homopolymères et copolymères diblocs vis-à-vis d’une bactérie marine ont été évaluéesDue to the reversible redox properties of ferrocene and its antibacterial activity, ferrocenyl-based polymers are useful for the synthesis of new anti-adhesive binders for marine antifouling coatings. This study reports the homopolymerization and copolymerization with lauryl methacrylate of ferrocenyl-based methacrylic monomers. Ferrocenylmethyl methacrylate (FMMA) as well as four novel monomers, namely 2- (ferrocenylmethoxy)ethyl methacrylate (FMOEMA), 3-(ferrocenylmethoxy)propyl methacrylate (FMOPMA),4-(ferrocenylmethoxy)butyl methacrylate (FMOBMA) and 2-(ferrocenylmethoxy)methylethyl methacrylate (FMOMEMA) were first synthesized, and subsequently polymerized by the RAFT process. The homopolymerization kinetics were investigated by in situ NMR. The radical polymerization was controlled by using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a chain transfer agent, at 70 °C in deuterated toluene. These monomers containing a ferrocenyl moiety with alcoxy linkers were found to be as reactive as FMMA in RAFT polymerization, resulting in conversions of 96% and in polymers with low dispersities (ÐM < 1.6). Monomer conversion follows a first order kinetics (up to 80%) with a linear increase in the molecular mass as a function of the monomer conversion. By using the FMMA monomer as a reference, the length of the alcoxy linker between the ferrocene unit and the backbone was increased for FMOEMA, FMOPMA, FMOMEMA and FMOBMA to improve the mobility of the side groups. This increase in macromolecular mobility led to a significant decrease of glass transition temperatures of the homopolymers. In addition, diblock copolymers exhibited two glass transition temperatures indicating that the two blocks are incompatible. The electrochemical properties of the monomers and those of the polymers were characterized using cyclic voltammetry. Finally, the anti-adhesive properties of these homopolymers and diblock copolymers toward marine bacteria were evaluated
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Peng, Wentao. "Binary Planet–Satellite Nanostructure Using RAFT Polymer". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-144A-2.
Testo completo
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Banaco, Joana Filipa das Neves. "Encapsulação de nanopartículas anisotrópicas por polimerização RAFT". Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12265.
Testo completoAbstract (sommario):
Mestrado em Engenharia QuímicaOs avanços tecnológicos recentes têm vindo a gerar um enorme interesse em novos materiais, desafiando a comunidade científica a focarem a sua atenção no desenvolvimento de novos métodos de síntese para a produção, por exemplo, de nanocompósitos. O objetivo deste trabalho consistiu na otimização do procedimento de encapsulação de nanopartículas anisotrópicas (NPs) recorrendo à polimerização em emulsão e ao mecanismo de polimerização controlada por reações reversíveis de adição-fragmentação de um agente de transferência de cadeia (RAFT). No sentido de se obter um filme de polímero em torno das partículas e minimizar a formação de polímero livre, foram efetuados estudos de adsorção de um agente RAFT macromolecular (MR) à superfície de nanofibras de Gd2O3:Eu3+revestidas com sílica não calcinada cujos resultados foram monitorizados por espectroscopia UV/VIS. Nestes estudos foram analisados dois parâmetros, o pH e o tempo de contacto adsorvato/adsorvente. Estes tiveram como principal objetivo a obtenção das isotérmicas de equilíbrio de adsorção a 25 ºC, as quais forneceram informação acerca da quantidade máxima de MR adsorvida. Através desta informação, foi possível inferir que os dois parâmetros analisados afetaram significativamente os resultados. Os dados experimentais foram modelados recorrendo a alguns modelos teóricos de adsorção verificando-se que tanto os modelos de Langmuir, como o de Freundlich se ajustam bem aos resultados obtidos. Numa segunda fase, foi estudada a encapsulação das nanofibras através da polimerização em emulsão via RAFT de metacrilato de metilo (MMA) e de acrilato de n-butilo (BA). Estas polimerizações foram efetuadas a pH 7, 5,5 e 3,5 (80 ºC), e com as condições ótimas provindas dos estudos de adsorção. Os látexes obtidos foram caracterizados por dispersão de luz dinâmica (DLS) e potencial zeta (ZP). Os látexes obtidos a pH 7 foram também caracterizados por microscopia eletrónica de varrimento em modo de transmissão (STEM). A conversão foi determinada por gravimetria. Os resultados obtidos por STEM confirmaram a encapsulação das nanopartículas assim como os valores obtidos de ZP. No entanto, os valores obtidos para a conversão de monómero foram apenas de 45%.
Recent technological advances have been the basis of increasing interest in the development of new materials, challenging the scientific community to focus their attention to devise new synthesis methods for the production of e.g. nanocomposites. The purpose to this work consists in the optimization of the procedure to encapsulate anisotropic nanoparticles(NPs), using the emulsion polymerization and the polymerization mechanism controlled by reversible addition-fragmentation of a chain transfer agent (RAFT). In order to obtain a polymer film surrounding the particles and minimize the formation of free polymer, the adsorption of a macromolecular RAFT agent (MR) onto the surface of Gd2O3:Eu3+coated with uncalcined silica was studied, where results were monitored by UV / VIS spectroscopy. This study analyzed two parameters: pH and contact time of adsorbant /adsorbent. The aim of this was to obtain the equilibrium adsorption isotherms at 25ºC, which provided information about the maximum amount of adsorbed MR. This information proved that the two analyzed parameters significantly affect the results. The best values were obtained at a pH of 5.5 and a contact time of 15 hours. The experimental data were adjusted to some theoretical models of adsorption and it was verified that the Langmuir and Freundlich models fit the obtained results. In a second stage of this work, the encapsulation of nanofibres by emulsion polymerization of methyl methacrylate (MMA) and n-butyl acrylate (BA) RAFT was studied. These polymerizations were carried out at pH 7, 5,5 and 3,5 (80 ºC), using the optimal conditions previously established from adsorption studies. The obtained latexes were characterized by dynamic light scattering (DLS) and zeta potential (ZP). The latexes obtained at pH 7 were also characterized by scanning transmission electron microscopy (STEM). The conversion was determined gravimetrically. The results obtained with STEM and ZP confirmed the encapsulation of nanoparticles. However, the value obtained for monomer conversion was low (45%).
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Leswin, Joost Sieger Kaspar. "Particle Formation in RAFT-mediated Emulsion Polymerization". Thesis, The University of Sydney, 2007. http://hdl.handle.net/2123/2176.
Testo completoAbstract (sommario):
Particle formation in RAFT-mediated emulsion polymerization has been studied using reaction calorimetry. By measuring the heat flow during controlled feed ab-initio emulsion polymerization in the presence of amphipathic RAFT agents, particle formation by self-assembly of these species could be observed. Two different monomer systems, i.e. styrene and n-butyl acrylate, and various degrees of hydrophobicity of the initial macro-RAFT agents have been studied and compared. The different macro-RAFT agents were synthesized by first forming a hydrophilic block of poly(acrylic acid) that would later on act as the electrosteric stabilizing group for the particles. Subsequently, different lengths of hydrophobic blocks were grown at the reactive end of the poly(acrylic acid) hydrophilic block via the RAFT-mediated controlled radical polymerization, either comprised of n-butyl acrylate or styrene. Two processes govern particle formation: adsorption of macro-RAFT agents onto growing particles and formation of new particles by initiation of micellar aggregates or by homogeneous nucleation. Competition between these processes could be observed when monomers with a relatively high (n-butyl acrylate) or low (styrene) propagation rate coefficient were used. A model describing particle formation has been developed and the results of model calculations are compared with experimental observations. Preliminary modeling results based on a set of reasonable physico-chemical parameters already showed good agreement with the experimental results. Most parameters used have been verified experimentally. The development of the molecular weight distribution of the macro-RAFT agents has been analyzed by different techniques. Quantification of the particle formation process by analytical techniques was difficult, but qualitative insights into the fundamental steps governing the nucleation process have been obtained. The amount of macro-RAFT agents initially involved in particle formation could be determined from the increase of molecular weight. The particle size distribution has been measured by capillary hydrodynamic fractionation, transmission electron microscopy and dynamic light scattering. From the data obtained from these particle-sizing techniques, the number of particles during the reaction could be monitored, leading to an accurate estimate for the particle formation time. Upon implementation of the experimental data obtained for the surface active macro-RAFT systems, the model demonstrated to be very sensitive towards the “headgroup” area of the macro-RAFT species. Three nucleation cases based on the initial surface activity of the macro-RAFT species in the aqueous phase are proposed to explain the deviations from the assumptions of the nucleation model. Even though the macro-RAFT species have a narrow molecular weight distribution, they are nevertheless made up of a distribution of block lengths of polystyrene upon a distribution of block lengths of poly(acrylic acid). The resulting differences in initial surface activity are the most probable reason for the observed differences between model calculations and experimental results for the nucleation time and particle size distribution of the final latex product. With the procedure described above, latexes have been synthesized without using conventional surfactants and the mechanisms involved in the particle formation for these systems have been elucidated. The results of this work enable production of latex systems with well defined molecular mass distributions and narrow particle size distributions. Furthermore, the technique based on the application of amphipathic RAFT agents is promising for the production of complex polymeric materials in emulsion polymerization on a technical scale.
15
Leswin, Joost Sieger Kaspar. "Particle Formation in RAFT-mediated Emulsion Polymerization". University of Sydney, 2007. http://hdl.handle.net/2123/2176.
Testo completoAbstract (sommario):
Doctor of Philosophy(PhD)Particle formation in RAFT-mediated emulsion polymerization has been studied using reaction calorimetry. By measuring the heat flow during controlled feed ab-initio emulsion polymerization in the presence of amphipathic RAFT agents, particle formation by self-assembly of these species could be observed. Two different monomer systems, i.e. styrene and n-butyl acrylate, and various degrees of hydrophobicity of the initial macro-RAFT agents have been studied and compared. The different macro-RAFT agents were synthesized by first forming a hydrophilic block of poly(acrylic acid) that would later on act as the electrosteric stabilizing group for the particles. Subsequently, different lengths of hydrophobic blocks were grown at the reactive end of the poly(acrylic acid) hydrophilic block via the RAFT-mediated controlled radical polymerization, either comprised of n-butyl acrylate or styrene. Two processes govern particle formation: adsorption of macro-RAFT agents onto growing particles and formation of new particles by initiation of micellar aggregates or by homogeneous nucleation. Competition between these processes could be observed when monomers with a relatively high (n-butyl acrylate) or low (styrene) propagation rate coefficient were used. A model describing particle formation has been developed and the results of model calculations are compared with experimental observations. Preliminary modeling results based on a set of reasonable physico-chemical parameters already showed good agreement with the experimental results. Most parameters used have been verified experimentally. The development of the molecular weight distribution of the macro-RAFT agents has been analyzed by different techniques. Quantification of the particle formation process by analytical techniques was difficult, but qualitative insights into the fundamental steps governing the nucleation process have been obtained. The amount of macro-RAFT agents initially involved in particle formation could be determined from the increase of molecular weight. The particle size distribution has been measured by capillary hydrodynamic fractionation, transmission electron microscopy and dynamic light scattering. From the data obtained from these particle-sizing techniques, the number of particles during the reaction could be monitored, leading to an accurate estimate for the particle formation time. Upon implementation of the experimental data obtained for the surface active macro-RAFT systems, the model demonstrated to be very sensitive towards the “headgroup” area of the macro-RAFT species. Three nucleation cases based on the initial surface activity of the macro-RAFT species in the aqueous phase are proposed to explain the deviations from the assumptions of the nucleation model. Even though the macro-RAFT species have a narrow molecular weight distribution, they are nevertheless made up of a distribution of block lengths of polystyrene upon a distribution of block lengths of poly(acrylic acid). The resulting differences in initial surface activity are the most probable reason for the observed differences between model calculations and experimental results for the nucleation time and particle size distribution of the final latex product. With the procedure described above, latexes have been synthesized without using conventional surfactants and the mechanisms involved in the particle formation for these systems have been elucidated. The results of this work enable production of latex systems with well defined molecular mass distributions and narrow particle size distributions. Furthermore, the technique based on the application of amphipathic RAFT agents is promising for the production of complex polymeric materials in emulsion polymerization on a technical scale.
16
GIRETTI, Daniela. "MODELLING OF PILED RAFT FOUNDATIONS IN SAND". Doctoral thesis, Università degli studi di Ferrara, 2010. http://hdl.handle.net/11392/2389285.
Testo completoAbstract (sommario):
A piled raft is a composite foundation in which the piles are used as
settlement reducers and they share, with the raft, the load from the
superstructure. The applied load is transferred from the raft to the
shallow soil and to the pile heads, and from the piles it is diffused
through the shaft and the base to deeper soil. The pile–raft and pile–pile
interactions represent the distinctive aspect of the piled raft foundations
since they modify the load–bearing behaviour of each foundation
component, compared to an analogous isolated element, thus determining
the overall foundation behaviour.
The main aim of this thesis is to highlight the effects of the raft–soil–pile
interactions on the resistance and stiffness of axially loaded piled raft
foundations in sand.
A series of centrifuge tests on models of rigid circular piled rafts in loose
saturated sand has been performed to this end, employing both non
displacement and displacement piles. The raft settlement and the load
transmitted to the pile heads and bases were monitored during the tests,
which also included unpiled raft and isolated pile tests.
The test results have been analysed in terms of bearing capacity and
stiffness; the former according to a load efficiency method, the latter by
comparing the values obtained from centrifuge tests with those evaluated
through a simplified analytical method.
ii Modelling of Piled Raft Foundations in Sand D. Giretti
In order to clarify the effect of the pressure transmitted by the raft to the
soil on the behaviour of a single capped pile, some of the centrifuge tests
were simulated via finite element numerical analyses, using an elasto–plastic strain hardening constitutive model for the sand. The geometry
and the dimensions of the numerical models corresponded to those of the
physical ones and the simulations were carried out applying an
accelerated gravitational field to the mesh.
The influence of a granular layer, interposed between the raft and the pile
heads, on the load transfer mechanism has also been analysed, through an
additional series of centrifuge tests which was performed on square rigid
raft models on displacement piles in dry dense sand.
17
CUNATI, DIANA. "Ruolo dei lipid raft nel metabolismo della proteina prionica". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/27001.
Testo completoAbstract (sommario):
The prion protein (PrP) is a GPI-anchored protein primarily concentrated in neuronal cells. Under certain conditions, the innocuous cellular form of this protein, PrPC, can convert into the lethal scrapie isoform, PrPSc, which can aggregate with other PrP molecules and exert its neurotoxic activity.
The structure of PrPC consists of two domains: an N-terminal, glycosylated, flexible disordered domain which is capable of binding copper and a C-terminal α-helical domain.
In contrast, PrPSc is enriched in β-sheet structures and characterized by its poor solubility in non-denaturing detergents, propensity for aggregation, partial resistance to proteinase K digestion.
The conversion of PrPC into PrPSc occurs in particular regions of the cell membrane, enriched with cholesterol and glycosphingolipid, called lipid rafts; these microdomains are thought to play a crucial role both in physiological functions and in the alternative folding of the prion protein.
In addition, it’s known that:
-PrPC can be cleaved at the 110/111 peptidyl bond to produce a C-terminal fragment, C1, which remains membrane bound and a N-terminal fragment, N1, released in the extracellular space. C1 fragments can’t be converted to the scrapie isoform;
- in cell cultures, ADAM10 and ADAM17 were shown to be responsible for this processing and their activation seems PKC-dependent.
The aim of our project is to establish if the alteration of cell lipid composition can modify the membrane distribution of the prion protein within rafts or non-raft regions and promote the activity of disintegrins such as ADAM10/17 upon the prion protein.
For this reason, granule cells, from the cerebella of 8-day-old rats, were incubated after 8 days in culture with GM1 or GD1a or GT1b for 4 hours at 37°C or with GM1 for 4 hours at 4°C. Detergent resistant fractions, containing lipid rafts, were isolated and proteins in all gradient fractions were separated and analyzed by EF/WB with specific antibodies.
After cell treatments with exogenous gangliosides, a good percentage of them was found in lipid rafts; immunoblotting analysis with specific antibodies showed a significant reduction in the amount of proteins, normally localized in lipid rafts, after incubation with GT1b.
The incorporation of this ganglioside, characterized by a remarkable steric encumbrance, might be responsible for lipid rafts destabilization and proteins redistribution toward non-raft regions.
Another possibility is that GT1b incorporation reduces the number of lipid rafts on the cell membrane.
Immunoblotting analysis with three different anti-PrP antibodies showed that this protein is not selectively located in lipid rafts but it is also distributed in several intracellular compartments.
Cell treatments with GM1 or GD1a at 37°C for 4 hours were not able to promote PrPC cleavage at the 110/111 peptidyl bond; cell incubation with GM1 seemed able to induce a conformational change of the prion protein toward a “simil-scrapie” isoform, partially resistant to classical denaturation protocols. Further studies are in progress to fully demonstrate that GM1-PrP interaction results in this conformational change.
18
Nelson, Matthew D. "Lipid raft heterogeneity and dynamics in T lymphocytes". Click here for download, 2006. http://wwwlib.umi.com/cr/villanova/fullcit?p1432528.
Testo completo
19
Fischer, Thorsten. "Modelling of lipid raft formation in cell membranes". Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546490.
Testo completo
20
Luheshi, Yousef Bashir. "The fatigue characteristics of precast concrete raft units". Thesis, University of Newcastle Upon Tyne, 1997. http://hdl.handle.net/10443/1582.
Testo completoAbstract (sommario):
This research project represents a continuation of the research programme into Precast Concrete Pavement Units, "P. C. P. U. ", which is based in the Department of Civil Engineering at the University of Newcastle upon Tyne. The units were referred to as raft units throughout the thesis which focused on the use of raft units as a full concrete paving system for aircraft parking, taxiway, and other low speed areas, at airports. The physical full scale test model was designed and constructed to represent the applied loading from one of the dual wheel legs of the design aircraft, a Boeing 727-200, when it is taxiing over a raft unit paving system. It was only possible for the test model to be provided with a contact area of 200 mm square compared to the real life of 400 mm square. A theoretical correction was applied to allow for this difference. Sixteen raft units were tested in pairs using the test model. The tests were divided into three modules to investigate the effect of the raft unit dimensions, Module(M1); the reinforcement design, Module(M2); and the raft thickness, Module(M3). The twin loading assembly applied a repetitive dynamic load which was moved manually between four different loading positions to represent the aircraft moving across the raft units. The primary aim of the experimental programme was to identify for the first time the fatigue life and failure mechanisms of the raft units under the influence of twin dynamic moving loads, and provide experimental results to enable a more refined numerical design method to emerge for raft units, as well as to determine the causes of failures and to recommend remedial measures. Observations were made of vertical deflection, concrete strains, crack widths and crack patterns, failure load, and failure modes, each of which were described in detail. The test observations showed that by increasing each of the following variables, namely, the aspect ratio, the amount of steel bar reinforcement and the thickness of the raft units, resulted in each case in an extension of raft unit life. It was found that some form of uplift restraint on the raft unit should be added to improve the fatigue life for one of the loading positions and that fibre reinforcement should not be used. The ultimate load capacity of the raft units was influenced by the loading position, the applied load level and the number of load repetitions, together with the crack patterns. Using the results from the raft units that had failed within a specific module, it was possible to predict the ultimate and reserve load capacity of raft units within the modules that were only partially fatigued. Four important conclusions have been established during the research project. Firstly, based on the test results, an empirical relationship was derived using regression analysis, relating the number of load repetitions to the aspect ratio, the amount of reinforcement, the raft thickness, and the applied loading. This will need further verification, but it should eventually be very useful when estimating the fatigue life of these specific raft unit models. Secondly, a new design method has been proposed. The design methods for raft units proposed previously by Bull, Ismail, Annang, Ackroyd, and the British Port Association were reviewed. The test results enabled a new design method to be developed which was based on Bull's method but proposed new design charts and tables for each of the raft units considered in the research project which introduced the additional variables of contact pressure and the exact loading position. Thirdly, the measured strains were used to develop strain fatigue relationships for designing raft units and estimating the reserve design life in a raft unit paving system for the purpose of maintenance management by relating the accumulated number of load repetitions of a design load to the permissible concrete strain. The strain fatigue equations were generated for each of the raft units considered in this research project. Thus, the most realistic way to control raft unit distress is through the use of a predictive fatigue model. This should prove invaluable to those involved in the maintenance of raft unit paving systems. Finally, life cycle cost analysis was conducted for three types of construction pavement (paving blocks, PQC, and raft units). The analysis demonstrated that the precast concrete raft units will become a viable alternative to conventional pavement construction and a real competitive to the concrete paving blocks.
21
Johnson, Fiona Ann. "The physico-chemical characterisation of alginate raft systems". Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297175.
Testo completo
22
Hann, Monika. "Raft microdomains in myelin : an in vitro investigation". Thesis, Open University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446302.
Testo completo
23
Jeffrey, J. G. "Synthesis and chemistry of hexaosmium carbonyl 'raft' clusters". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355865.
Testo completo
24
Morse, Charlotte. "Block copolymer nanoparticles prepared by RAFT aqueous polymerisation". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19014/.
Testo completoAbstract (sommario):
This thesis describes the reversible addition-fragmentation chain transfer (RAFT) polymerisation of block copolymer nanoparticles in water. Firstly, a water-soluble poly(glycerol monomethacrylate) (PGMA) macromolecular chain-transfer agent (macro-CTA) was synthesised via RAFT solution polymerisation in ethanol. The PGMA macro-CTA is then chain-extended with 2-hydroxypropyl methacrylate (HPMA) via RAFT aqueous dispersion polymerisation. Polymerisation-induced self-assembly (PISA) occurs under these conditions, where the miscible HPMA monomer polymerises to form an insoluble poly (2-hydroxypropyl methacrylate) block, thus driving in situ formation of spheres, worms or vesicles. These PGMA-PHPMA diblock copolymers are then chain-extended with benzyl methacrylate (BzMA) via 'seeded' RAFT aqueous emulsion polymerisation to prepare PGMA-PHPMA-PBzMA triblock copolymers. In Chapter Two, a series of model framboidal PGMA-PHPMA-PBzMA triblock copolymer vesicles are synthesised with excellent control over surface roughness. Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) were utilised to characterise these nanoparticles, which were subsequently used to stabilise n-dodecane emulsion droplets in water. The adsorption efficiency, Aeff, of the nanoparticles at the n-dodecane/water interface was determined as a function of increasing vesicle surface roughness using a turbidimetry assay. A strong correlation between surface roughness and Aeff was observed, with Aeff increasing from 36 % up to 94 %. This is a significant improvement in Pickering emulsifier efficiency compared to that reported previously for similar vesicles with smooth surfaces. In Chapter Three, a series of PGMA-PHPMA-PBzMA triblock copolymer worms and spheres are synthesised. For certain block compositions, highly anisotropic worm-like particles are obtained, which are characterised by SAXS and TEM. The design rules for accessing higher order morphologies (i.e. worms or vesicles) are briefly explored. Surprisingly, vesicular morphologies cannot be accessed by targeting longer PBzMA blocks - instead only spherical nanoparticles are formed. SAXS is used to rationalise these counter-intuitive observations, which are best explained by considering subtle changes in the relative enthalpic incompatibilities between the three blocks during the growth of the PBzMA block. Finally, these PGMA-PHPMA-PBzMA worms are evaluated as Pickering emulsifiers for the stabilisation of oil-in-water emulsions. Millimetre-sized oil droplets were obtained using low-shear homogenisation (hand-shaking) in the presence of 20 % vol. n-dodecane. In contrast, control experiments performed using PGMA-PHPMA diblock copolymer worms indicated that these more delicate nanostructures did not survive even these mild conditions. In the latter two experimental Chapters of this thesis, PISA is used to design block copolymer nanoparticles as potential drug delivery vehicles. Thus, PGMA-PHPMA diblock copolymer vesicles are prepared in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. After centrifugal purification to remove excess non-encapsulated silica nanoparticles, analysis confirms encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica is a model payload: it has high electron contrast compared to the copolymer and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be obtained using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. SAXS is used to confirm silica encapsulation, because a structure factor is observed at q ~ 0.25 nm-1. A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica volume fraction within the vesicles to be determined. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes or antibodies within block copolymer vesicles for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biological tissue. Finally, by targeting a relatively short PHPMA block, PGMA-PHPMA vesicles can be obtained that lie close to the worm-vesicle phase boundary, rendering them thermo-responsive. The thermo-responsive nature of these vesicles enables thermally-triggered release of the encapsulated silica nanoparticles simply by cooling to 0-10oC, which induces a morphological transition. TEM studies confirm the change in diblock copolymer morphology and also enables direct visualisation of the released silica nanoparticles. Time-resolved small angle X-ray scattering is used to quantify the extent of silica release over time. For these experiments, the purified silica-loaded vesicles were cooled to 0oC for 30 min and SAXS patterns were collected every 15 s. For PGMA-PHPMA vesicles synthesised in the absence of silica nanoparticles, vesicles remained intact for 8 minutes before a vesicle-to-worm transition occurs. Thereafter, a worm-to-sphere transition occurs after 12 min at 0oC. For lower silica loadings, cooling induces a vesicle-to-sphere transition with subsequent nanoparticle release. For higher silica loadings, cooling to 0oC for 30 min only leads to perforation of the vesicle membranes, but silica nanoparticles are still released through the pores. For vesicles prepared in the presence of 30 % w/w silica, a new SAXS model has been developed to determine both the mean volume fraction of encapsulated silica remaining within the vesicles and also the scattering length density of the vesicle. Satisfactory data fits to the experimental SAXS patterns were obtained using this model. These results indicate that 68 % of the encapsulated silica is released from the vesicles after being held at 0°C for 30 min.
25
Cotanda, Santapau Maria José. "Amino-containing polymers for catalysis using RAFT polymerization". Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/56272/.
Testo completoAbstract (sommario):
Chapter 1 is a general introduction of the whole thesis and it features the main concepts of this project. Chapter 2 reports the synthesis and self- assembly of a temperature-responsive DMAP containing nanoreactor. The DMAP motif is incorporated in to a monomer and polymerized by RAFT with styrene in order to form the hydrophobic block of a polymeric micelle. The shell of the micelle is formed by chain extension of the styrenic block with NIPAM, which provides temperature responsive properties to the system. In Chapter 3, the concept of using polymeric micelles to catalyze organic reactions in water is presented and compared to surfactant based micelles in the context of molecular recognition, achieving enzyme-like specific catalysis by tethering the catalyst in the well-defined hydrophobic core of a polymeric micelle In Chapter 4, the incorporation of different catalytic amino motifs into a polymer backbone is investigated by RAFT polymerization in order to catalyze the reaction between polyalcohols and polyisocyanates in the formation of polyurethane foams. In the final chapter, the stimuli-responsive properties of DMAEA containing polymers are investigated. DMAEA is copolymerized by RAFT with the non-responsive MA at different loadings in order to study how the distance between amine motifs affects the polymer LCST and pKas .values
26
Wilks, Thomas R. "Synthesis of DNA-polymer conjugates using RAFT polymerisation". Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58568/.
Testo completoAbstract (sommario):
The use of reversible addition–fragmentation chain transfer (RAFT) polymerisation for the production of DNA–polymer conjugates is explored. Chapter 1 gives a general introduction to the field of DNA–polymer conjugates, their potential applications and methods for their synthesis. The need for a general, solutionphase technique for DNA–polymer conjugation is highlighted. In Chapters 2-5, the use of a number of different strategies for the production of DNA–polymer conjugates is described. Amide coupling (Chapter 2) is found to produce the desired products only under very specific reaction conditions. The thiol–alkene Michael addition reaction (Chapter 3) is found to afford DNA–polymer conjugates in aqueous solution with high yield; however, attempts to replicate this using organic solvents are not successful. The inverse electron-demand Diels–Alder reaction between tetrazine and norbornene (Chapter 4) is explored and found to produce DNA–polymer conjugates in high yield in organic solvents; however, the precursor compounds are time-consuming to prepare and so the generality of this approach is limited. Finally, the copper-catalysed azide–alkyne cycloaddition (Chapter 5) is found to be an excellent method for the production of a wide range of DNA–polymer conjugates. Chapter 6 describes the use of the DNA segment of a DNA–polymer conjugate to assemble a discrete three dimensional nanostructure – a DNA tetrahedron – incorporating the temperature-responsive polymer poly(N-isopropylacrylamide). These hybrid structures are found to be able to stabilise the formation of discrete, well-defined polymer nanoparticles at elevated temperatures. Chapter 7 describes the use of a non-covalent interaction (intercalation) to produce DNA– polymer conjugates. The effect of polymer molecular weight and structure on the strength of this interaction are explored. Finally, intercalation is exploited to template the formation of discrete polymer particles on a DNA strand.
27
Chirowodza, Helen. "Polymer-clay nanocomposites prepared by RAFT-supported grafting". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71914.
Testo completoAbstract (sommario):
Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: In materials chemistry, surface-initiated reversible deactivation radical polymerisation (SI-RDRP) has emerged as one of the most versatile routes to synthesising inorganic/organic hybrid materials consisting of well-defined polymers. The resultant materials often exhibit a remarkable improvement in bulk material properties even after the addition of very small amounts of inorganic modifiers like clay. A novel cationic reversible addition–fragmentation chain transfer (RAFT) agent with the dual purpose of modifying the surface of Laponite clay and controlling the polymerisation of monomer therefrom, was designed and synthesised. Its efficiency to control the polymerisation of styrene was evaluated and confirmed through investigating the molar mass evolution and chain-end functionality. The surface of Laponite clay was modified with the cationic chain transfer agent (CTA) via ion exchange and polymerisation performed in the presence of a free non-functionalised CTA. The addition of the non-functionalised CTA gave an evenly distributed CTA concentration and allowed the simultaneous growth of surface-attached and free polystyrene (PS). Further analysis of the free and grafted PS using analytical techniques developed and published during the course of this study, indicated that the free and grafted PS chains were undergoing different polymerisation mechanisms. For the second monomer system investigated n-butyl acrylate, it was apparent that the molar mass targeted and the monomer conversions attained had a significant influence on the simultaneous growth of the free and grafted polymer chains. Additional analysis of the grafted polymer chains indicated that secondary reactions dominated in the polymerisation of the surface-attached polymer chains. A new approach to separating the inorganic/organic hybrid materials into their various components using asymmetrical flow field-flow fractionation (AF4) was described. The results obtained not only gave an indication of the success of the in situ polymerisation reaction, but also provided information on the morphology of the material. Thermogravimetric analysis (TGA) was carried out on the polymer-clay nanocomposite samples. The results showed that by adding as little as 3 wt-% of clay to the polymer matrix, there was a remarkable improvement in the thermal stability.
AFRIKAANSE OPSOMMING: Oppervlakgeïnisieerde omkeerbare deaktiveringsradikaalpolimerisasie (SI-RDRP) is een van die veelsydigste roetes om anorganiese/organiese hibriedmateriale (wat bestaan uit goed-gedefinieerde polimere) te sintetiseer. Die produk toon dikwels ʼn merkwaardige verbetering in die makroskopiese eienskappe – selfs na die toevoeging van klein hoeveelhede anorganiese modifiseerders soos klei. ʼn Nuwe kationiese omkeerbare addisie-fragmentasie kettingoordrag (RAFT) middel met die tweeledige doel om die modifisering van die oppervlak van Laponite klei en die beheer van die polimerisasie van die monomeer daarvan, is ontwerp en gesintetiseer. Die klei se doeltreffendheid om die polimerisasie van stireen te beheer is geëvalueer en bevestig deur die molêre massa en die funksionele groepe aan die einde van die ketting te ondersoek. Die oppervlak van Laponite klei is gemodifiseer met die kationiese kettingoordragmiddel (CTA) deur middel van ioonuitruiling en polimerisasie wat uitgevoer word in die teenwoordigheid van ʼn vrye nie-gefunksionaliseerde CTA. Die toevoeging van die nie-gefunksionaliseerde CTA het ʼn eweredig-verspreide konsentrasie CTA teweeggebring en die gelyktydige groei van oppervlak-gebonde en vry polistireen (PS) toegelaat. Verdere ontleding van die vrye- en geënte PS met behulp van analitiese tegnieke wat ontwikkel en gepubliseer is gedurende die verloop van hierdie studie, het aangedui dat die vry- en geënte PS-kettings verskillende polimerisasiemeganismes ondergaan. n-Butielakrilaat is in die tweede monomeer-stelsel ondersoek en dit was duidelik dat die molêre massa wat geteiken is en die geënte polimeerkettings. ʼn Nuwe benadering tot die skeiding van die anorganiese/organiese hibriedmateriale in hulle onderskeie komponente met behulp van asimmetriese vloeiveld-vloei fraksionering (AF4) is beskryf. Die resultate wat verkry is, het nie net 'n aanduiding gegee van die sukses van die in-situ polimerisasiereaksie nie, maar het ook inligting verskaf oor die morfologie van die materiaal. Termogravimetriese analise (TGA) is uitgevoer op die polimeer-klei nanosaamgestelde monsters. Die resultate het getoon dat daar 'n merkwaardige verbetering in die termiese stabiliteit was na die toevoeging van so min as 3 wt% klei by die polimeermatriks.
28
Bailly, Nathalie. "AB diblock copolymers via RAFT-mediated miniemulsion polymerization". Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/2707.
Testo completoAbstract (sommario):
Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008.The Reversible addition fragmentation chain transfer (RAFT) technique is a robust and versatile technique that enables the synthesis of polymers of controlled molecular weight and polydispersity. The application of the RAFT technique in heterogeneous aqueous media has attracted great interest in academics and industry due to it being more environmentally friendly, besides its other advantages. To date, the synthesis of well-defined high molecular weight polymers via the RAFT process under industrially relevant conditions still remains a challenge for polymer chemists. The study addresses the application of the RAFT process in heterogeneous media, namely in miniemulsion polymerization, for the synthesis of AB diblock copolymers of n-butyl methacrylate and styrene. AB diblock copolymers of high molecular weight were successfully prepared via a twostep method. In the first step, a dithiobenzoate monofunctional RAFT agent was used in bulk polymerization with the first monomer, n-butyl methacrylate. After the polymerization, the majority of the polymer chains contained the thiocarbonyl-thio RAFT agent functionality, which makes the chains potentially active for chain extension. The polymeric RAFT agent (also referred to as the starting block) obtained in the first step was chain extended in the second step, in miniemulsion, upon further addition of fresh initiator and the second monomer, styrene. The effects of the initiator/RAFT agent concentration ratio on the miniemulsion systems were investigated. The miniemulsion systems used for the high molecular weight AB diblock copolymers exhibited living features despite the high polydispersity indices. Kinetic results showed an increase in the rate of polymerization throughout the polymerization. Size exclusion chromatography (SEC) results indicated significant broadening in the molecular weight distributions and a steep increase in the polydispersity during the polymerization. It was concluded that the broad molecular weight distributions and steep increase in the polydispersity was not only related to the initiator concentration but possibly due to other factors such as inhomogeneity in the miniemulsion system and a transition in the kinetic behavior during the polymerization. Secondary particle formation emerged from kinetic data and transmission electron microscopy (TEM) results, but this were not supported by the SEC results. The effect of the use of a water-soluble initiator on the miniemulsion system was also investigated. Results indicated a similar behavioral pattern as observed in the AIBNinitiated systems, and not much improvement in terms of the molecular weight distributions and polydispersity was seen. The effect of the molecular weight of the diblock copolymers on the miniemulsion system was investigated. Poly(n-butyl methacrylate)-b-poly(styrene) diblock copolymers of lower molecular weight were synthesized via the two-step process. Kinetic results indicated a similar behavioral trend as to that of the high molecular weight diblock copolymers synthesized, however SEC chromatograms showed narrower molecular weight distributions and low polydispersity indices.
29
Bivigou, Koumba Achille Mayelle. "Design, synthesis and characterization of novel raft agents". Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/2992.
Testo completoAbstract (sommario):
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005.This thesis begins with the description of the preparation of thirteen dithioesters (of the form Z- (C=S)-S-R) which were characterized via Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and ultraviolet spectroscopy (UV). The dithioesters were then used as reversible addition-fragmentation chain transfer (RAFT) mediating agents in the bulk polymerization of styrene, in order to observe differences in the kinetic behaviour of the polymerizations and, as a result, the efficiencies of the dithioesters in mediating the polymerizations.
30
Ng, Harald. "Distributed Consensus: Performance Comparison of Paxos and Raft". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281973.
Testo completoAbstract (sommario):
With the growth of the internet, distributed systems have become increasingly important in order to provide more available and scalable applications. Con- sensus is a fundamental problem in distributed systems where multiple pro- cesses have to agree on the same proposed value in the presence of partial failures. Distributed consensus allows for building various applications such as lock services, configuration manager services or distributed databases.Two well-known consensus algorithms for building distributed logs are Multi-Paxos and Raft. Multi-Paxos was published almost three decades before Raft and gained a lot of popularity. However, critics of Multi-Paxos consider it difficult to understand. Raft was therefore published with the motivation of being an easily understood consensus algorithm. The Raft algorithm shares similar characteristics with a practical version of Multi-Paxos called Leader- based Sequence Paxos. However, the algorithms differ in important aspects such as leader election and reconfiguration.Existing work mainly compares Multi-Paxos and Raft in theory, but there is a lack of performance comparisons in practice. Hence, prototypes of Leader- based Sequence Paxos and Raft have been designed and implemented in this thesis. The prototypes were implemented using the Rust programming lan- guage and the message-passing framework Kompact and then benchmarked in real-world scenarios to compare the performance of Leader-based Sequence Paxos and Raft.The results show that Leader-based Sequence Paxos and Raft have simi- lar performance in geographically distributed deployments. However, the un- predictable leader election in Raft could greatly affect the performance if the elected leader is in an undesired location. In our experiments, the location of the Raft leader affected the average throughput by up to 35%. Furthermore, the results indicate that implementation details could have a significant impact on performance even in the parts where the algorithms are similar. By batch- ing messages more efficiently, Leader-based Sequence Paxos achieved up to 17% higher average throughput than Raft.Med tillväxten av internet har distribuerade system blivit allt mer viktiga för att bygga mer tillgängliga och skalbara applikationer. Konsensus är ett funda- mentalt problem i distribuerade system där flera processer ska komma överens om samma föreslagna värde, samtidigt som partiella fel kan ske. Distribuerad konsensus kan appliceras till olika användningsomården som låstjänster, kon- figurationshanterare och distribuerade databaser.Två välkända konsensusalgoritmer för att bygga distribuerade loggar är Multi-Paxos och Raft. Multi-Paxos publicerades nästintill tre årtionden före Raft och blev populär. Men kritiker av Multi-Paxos anser att algoritmen är svår att förstå. Av denna anledning publicerades Raft med motivationen att vara en konsensusalgoritm som är enkel att förstå. Raft delar likheter med Leader- based Sequence Paxos, en praktisk version av Multi-Paxos. Dock skiljer sig algoritmerna i viktiga aspekter som leaderval och rekonfigurering.Befintliga arbeten jämför i huvudsak Multi-Paxos och Raft i teorin, men det saknas jämförelse av prestandan i praktiken. Av denna anledning har pro- totyper av Leader-based Sequence Paxos och Raft blivit designade och imple- menterade i denna avhandling. Dessa prototyper implementerades i program- meringsspråket Rust och message-passing ramverket Kompact, som sedan tes- tades i verkliga situationer för att jämföra Leader-based Sequence Paxos och Raft.Resultaten visar att Leader-based Sequence Paxos och Raft har liknande prestanda i geografiskt distribuerade sammanhang. Dock kan det oförutsäga- bara ledarvalet i Raft påverka prestandan avsevärt ifall den valde ledaren befin- ner sig på en oönskad plats. I våra experiment påverkade Raft ledarens plats den genomsnittliga kapaciteten med upp till 35%. Resultaten visar även att implementationsdetaljer kan ha en signifikant effekt på prestandan även i de delar där algoritmerna är liknande. Genom att sammanfoga meddelanden mer effektivt uppnådde Leader-based Sequence Paxos 17% högre genomsnittlig kapacitet än Raft.
31
Lagarde, Antoine. "Birth, life and death of a granular raft". Thesis, Sorbonne université, 2020. http://www.theses.fr/2020SORUS054.
Testo completoAbstract (sommario):
Nous étudions le devenir d'une monocouche de particules à une interface huile-eau, appelée radeau granulaire, depuis sa formation jusqu'à son naufrage. Nous nous attaquons d'abord à l'interaction capillaire entre deux particules, que nous généralisons ensuite à deux radeaux granulaires. Cette force dépend fortement du nombre de particules, une conséquence directe de la déformation que chacun des radeaux impose à l'interface. Nous explorons ensuite l'interaction entre de nombreux radeaux granulaires répartis aléatoirement à l'interface. Leur agrégation est d'autant plus rapide que la distance initiale qui les sépare est faible. Le mouvement de chaque radeau ne peut être résolu analytiquement, mais l'agrégation dans son ensemble peut être décrite statistiquement. La distribution des tailles de radeaux évolue ainsi de manière auto-similaire. Nous nous tournons ensuite vers les changements structuraux qu'un radeau granulaire peut subir au cours de son mouvement, à savoir son érosion. Sa cohésion est bien supérieure à ce que prédit la théorie classique, un résultat que nous retrouvons également pour deux billes en contact. La description précise de la géométrie de la ligne de contact permet d'expliquer cette résistance étonnement grande à l'érosion. Pour finir, nous nous concentrons sur le naufrage d'un radeau granulaire, lorsque la déflexion verticale de l'interface devient trop grande. Le filament d'huile formé s'amincit en suivant un régime transitoire inhabituel, ce qui retarde l'apparition du régime final attendu. Ce résultat met l'accent sur le rôle décisif que les conditions aux limites peuvent jouer dans la transition entre deux régimes auto-similairesWe study the life of an axisymmetric monolayer of particles called a granular raft floating at an oil-water interface, from its formation to its sinking. We first look at the capillary interaction between a pair of beads, and generalize the result to a pair of granular rafts. The force strongly depends on the number of particles in each raft, a result that we understand by looking at the interfacial deformation each individual raft creates. Then, we explore the interaction between numerous granular rafts of different sizes randomly distributed. The aggregation is faster when the particles are initially more concentrated at the interface. The individual motion of each bead cannot be solved, but the overall clustering can be described statistically. The cluster-size distribution appears to answer to a self-similar evolution that we characterize. After that, we focus on the structural changes a granular raft can experience during its motion, and more precisely to its erosion. The cohesion of an entire raft is far higher than expected by the usual capillary theory. The same high cohesion is found between two beads in contact. A precise description of the position of the contact line accounts for the unexpectedly high resistance to erosion. Finally, we explore the dynamics of sinking of a granular raft, which happens when the vertical deflection of the interface exceeds a critical deformation. The oil thread formed during the sinking thins following an unusual path between the two classical self-similar regimes, delaying the onset of the final regime. This result emphasizes the decisive role boundary conditions can play in the transition between self-similarities
32
Wilkinson, Dorothy Kate. "Functional characterisation of the lipid raft protein stomatin". Thesis, University of Leeds, 2005. http://etheses.whiterose.ac.uk/448/.
Testo completoAbstract (sommario):
The function of the integral membrane protein stomatin is as yet poorly understood. Stomatin is deficient from the erythrocyte membrane of patients suffering with Overhydrated Hereditary Stomatocytosis (OHSt). Patient erythrocytes have altered morphology and are known as stomatocytes. It is believed that stomatin is mistrafficked in the developing stomatocyte. These patients suffer grossly abnormal cation fluxes in the stomatocyte membrane which causes increased osmotic fragility of the cell and results in haemolytic anaemia. This study set out to characterise further stomatin and to investigate its role in the cell. The membranes and lipid rafts of stomatocytes were found to have reduced actin levels as compared to erythrocytes, suggesting that stomatin may function as a structural protein linking the cytoskeleton to the membrane. Overexpression of stomatin in nucleated cells caused enhanced actin association with cell membranes and lipid rafts, further confirming the findings from stomatocytes. Calcium-induced vesiculation was found to be significantly enhanced from the stomatocyte as compared to the erythrocyte, with defective partitioning of the flotillin proteins into the vesicles. This suggests that stomatin may function as a negative regulator in this vesiculation, possibly due to its interaction with actin and that the flotillins may substitute for stomatin in this process within the stomatocyte. Mutating the principle cysteine residue for palmitoylation within stomatin caused the protein to show less affinity for the membrane and lipid rafts but an increased affinity for the nucleus. This suggests that palmitoylation of stomatin affects the affinity of stomatin for the membrane and that this modification may be involved in regulating the shuttling of stomatin between the plasma membrane and the nucleus. Prokaryotic stomatin exists in an operon with a serine protease, suggesting a functional link between the two. Using a reporter gene construct approach the potential for mammalian stomatin to be proteolytically processed was investigated. Stomatin was found to be proteolytically processed in the membrane by a serine protease with the subsequent release of a C-terminal fragment.
33
Noble, Gavin Thomas. "Modelling glycocluster effects using artificial lipid rafts". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/modelling-glycocluster-effects-using-artificial-lipid-rafts(10686397-b8ea-473d-ab27-8fc79b4c424b).html.
Testo completoAbstract (sommario):
The interaction of carbohydrates with carbohydrate-binding proteins is key to a multitude of important biological events, such as cell-cell interactions and signal transduction. Carbohydrates are also essential for energy storage and transfer. Binding to the three-dimensional display of carbohydrates at the cell surface (the glycocalyx) is known to play a role in many disease states, such as carbohydrate binding by viruses. Furthermore, changes in the distribution and type of oligosaccharides is known to occur at tumour cell surfaces. The importance of these natural events at the cell membrane surface provided the motivation for their study in a biomimetic environment. Inspired by previous work in the field of carbohydrate-lectin binding and work in the Webb group into mimicry of cellular processes using supramolecular chemistry, vesicular structures of synthetic glycolipids in natural phospholipids were created. Several synthetic glycolipids were synthesised and found to be capable of lateral phase separation in ordered-phase phospholipid bilayers, forming artificial lipid rafts in the bilayer. The glycolipid vesicle systems were used to study the effects of the lateral clustering of glycolipids on two different biochemical events at the membrane surface: Binding of mannosyl-lipids by concanavalin A (ConA) and the enzymatic galactosylation of N-acetylglucosamine (GlcNAc)-lipids by bovine β-(1,4)-galactosyltransferase (β4GalT1). Fluorescence quenching titrations revealed that clustering of mannosyl-lipids had little effect on the strength of ConA binding. However, HPLC measurements showed that lateral clustering of GlcNAc-lipids could enhance their enzymatic galactosylation by β4GalT1. The work presented in this thesis represents the formulation of these vesicle systems and their study with ConA and β4GalT1. Further investigation with other phase-separating glycolipid-lectin/enzyme pairs is necessary to establish whether the effects of clustering observed herein are exclusive to ConA and β4GalT1, or are general phenomena observed at the membrane surface.
34
Seifert, Denis. "Synthese und Charakterisierung von sensitiven vernetzungsfähigen Blockcopolymeren mittels RAFT". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1132231440987-09334.
Testo completoAbstract (sommario):
In vorangegangenen Arbeiten im eigenen Arbeitskreis wurden sensitive Hydrogelpartikel im mm- und &#956;m-Bereich synthetisiert. Die Reaktion dieser Gele auf Änderung des einwirkenden Stimulus war jedoch nicht schnell genug für die gewünschten Anwendungen in Mikroventilen. Die verwendeten Polymere waren statistische Copolymere aus einem Chromophor (DMIAAm) und einem sensitiven Monomer (NIPAAm) und wiesen daher sehr breite Molmassenverteilungen auf. Mit Hilfe des Chromophores wurde es möglich, Hydrogele im Submikrometerbereich zu synthetisieren. Bei der Vernetzung dieser Polymere mit UVBestrahlung musste immer ein Tensid (SDS) zugesetzt werden, um die Bildung kleiner Aggregate zu unterstützen und gleichzeitig die Bildung großer zu unterdrücken. Ein solches Tensid kann die Anwendung dieser Hydrogele in bestimmten Bereichen, wie in der Medizin, verhindern. Es sollen daher tensidfrei Hydrogele synthetisiert werden. Für die Vernetzung sollte auf die photochemische Variante mit DMIAAm als Chromophor zurückgegriffen werden. Als Ausgangspolymere wären Di- bzw. Triblockcopolymere denkbar, die in wässriger Lösung zu einer Mizellbildung neigen. Aus den oben genannten Problemen ergab sich die folgende Zielstellung für die Arbeit. Es sollten sensitive Hydrogelpartikel erzeugt werden, die in der Lage sind, schnell auf eine Änderung der Temperatur zu reagieren. Eine kurze Reaktionszeit ist nur von Gelpartikeln mit kleinen Dimensionen im nm-Bereich zu erwarten. Weiterhin sollen diese Partikel mit einer Hülle umgeben werden, die für eine Stabilisierung sorgt und die Bildung größerer Aggregate unterbindet. Die Hülle muss so beschaffen sein, dass die Volumenänderung des sensitiven Blocks nicht beeinflusst wird. In dieser Dissertation wurde die kontrollierte radikalische Polymerisation von Acrylaten und Acrylamiden untersucht. Als Methode kam die Reversible-Addition-Fragmentation-chain-Transfer (RAFT) Polymerisation zum Einsatz. Die RAFT wurde gewählt, weil diese im Gegensatz zur ATRP metallionenfrei verläuft und die NMRP nicht für Acrylate geeignet ist. Bei den RAFT-Polymerisationen der verschiedenen Monomere wurden vier unterschiedliche Kettenüberträger verwendet (Schema 33) und folgende Ergebnisse erhalten. Als Lösungsmittel kam 1,4-Dioxan in den Polymerisationen zum Einsatz.
35
Özyürek, Zeynep. "Thermoresponsive Glycopolymers via Controlled Radical Polymerization (RAFT) for Biomolecular Recognition". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1190291104620-73670.
Testo completoAbstract (sommario):
Stimuli responsive polymers (SRP) have attracted a lot of attention, due to their potential and promising applications in many fields, as protein-ligand recognition, on-off switches for modulated drug delivery or artificial organs. Poly(N-isopropylacrylamide) (PNIPAM) is one of the most widely studied polymers due to its lower critical solution temperature (LCST) at ~ 32° C in aqueous solution. Additionally, glycopolymers, where free sugar units are present, have potentially interesting applications especially in bio-recognition where sugars play an important role. In this work, our interest was focused on the synthesis of glycomonomers and its block- and random- copolymers with NIPAM. NIPAM homopolymers with an active chain transfer unit at the chain end could be prepared by RAFT. They were used as macro-chain transfer agents to prepare a variety of sugar containing responsive block copolymers from new glycomonomers by the monomer addition concept. The LCSTs of the aqueous solutions of the copolymers are affected strongly by the comonomer content, spacer chain length of the glycomonomer and the chain architecture of the copolymers. These polymers were coated on a solid substrate by spin coating and crosslinked by plasma immobilization. Characterization of the polymers was performed by nuclear magnetic resonance spectroscopy (NMR), ultraviolet (UV), dynamic light scattering (DLS, detection of aggregation behaviour) and gel permeation chromatography (GPC). Polymer films were investigated by ellipsometry, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) regarding their surface properties. Afterwards sulfation of sugar – OH groups was performed in order to obtain heparin like structure, as heparin exhibits numerous important biological activities, like good interaction with diverse proteins. Finally, affinity of the polymers (sulfated and non sulfated form) on a solid support to the endothelial cells was investigated.
36
Hentschel, Jens. "Synthese und kontrollierte Mikrostrukturbildung funktionaler Peptid-Polymerkonjugate in organischen Lösungsmitteln". Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/1984/.
Testo completoAbstract (sommario):
In der vorliegenden Arbeit wurde ein Ansatz verfolgt, die besonderen Eigenschaften der Strukturbildung sequenzdefinierter Peptide mit den vielseitigen Materialeigenschaften synthetischer Blockcopolymere zu kombinieren.
Dazu wurde ein synthetisches Polymer kovalent mit einer definierten Peptidsequenz verknüpft. Der Peptidblock (die Organisationseinheit) wurde speziell designt, um später die Strukturbildung des Peptid-Polymerkonjugates induzieren und leiten zu können. Als Organisationsmotiv diente hierbei das aus der Natur bekannte β-Faltblatt Strukturmotiv.
Das Peptidsegment wurde in einer festphasengebundenen Synthese aufgebaut. Dabei wurden temporäre Stör-Segmente (Switch-Segmente) in die Peptidsequenz integriert. Diese Segmente unterdrücken die Aggregationstendenz während der Synthese und können durch einen pH-abhängigen Schaltvorgang in das natürliche Peptidrückgrat überführt werden. Zusätzlich zu der verbesserten Ausbeute und Reinheit der entsprechenden Peptide war auf diese Weise eine kontrollierte Aktivierung der Mikrostrukturbildung möglich.
Mit Hilfe zwei verschiedener Synthesestrategien (Kupplungs- bzw. Polymerisationsstrategie) wurde ein Satz von definierten Peptid-Polymerkonjugaten mit unterschiedlich großen Polymersegmenten synthetisiert. Diese wurden anschließend im Hinblick auf ihre Strukturbildungseigenschaften in organischen Lösungsmitteln untersucht. Durch mikroskopische Verfahren (AFM, TEM), konnte für alle Konjugate, die Bildung faserartiger Aggregate mit Dimensionen im Nano- bis Mikrometerbereich beobachtet werden. Genauere Untersuchungen zeigten, dass die Peptidsegmente in diesen Faserstrukturen ein β-Faltblatt ausbilden. Dies ist ein deutlicher Hinweis darauf, dass die Strukturbildung der Konjugate tatsächlich durch den Peptidblock gesteuert und kontrolliert wurde.The aim of this work was to combine the particular structuring properties of sequence-defined peptides with the versatile material properties of synthetic block-copolymers. Therefor, synthetic polymers were linked covalently to a defined oligopeptide-sequence using varying synthetic approaches. The oligopeptide was designed to guide and control the microstructure formation of the peptide-polymer conjugate. For this reason a peptide sequence with a high propensity to adopt the β-sheet motif was chosen. Thus, highly attractive, anisometric tape, fibrillar or fibre-like nanostructures can be accessed. However, such peptide-sequences are very difficult to synthesize and handle, as a result of their strong aggregation tendency. Therefore, temporary structure breaking units, so called switch-segments, were integrated into the peptide sequence, disturbing the peptide backbone and thus, temporarily suppressing the peptide properties. The controlled rearrangement of these defects reestablishes the native peptide backbone, switching the aggregation tendency of the peptide segment on, and triggers the assembly process. A set of defined peptide-polymer conjugates with different polymer block-lengths was synthesized either by an coupling approach or by RAFT polymerization using a switch-peptide macro chain transfer agent. Afterwards, the structure formation properties of these conjugates were investigated. By the use of microscopic techniques (AFM, TEM), the formation of densely twisted tape-like microstructures was observed for all conjugates. The formation of extended β-sheets was confirmed by different techniques (FT-IR, TEM-SAED), indicating a peptide guided microstructure formation process. Thus, it could be demonstrated that the peptide guided organization of synthetic polymers can be successfully transferred into organic solvents.
37
Yilmaz, Beren. "An Anlaytical And Experimental Study On Piled Raft Foundations". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611500/index.pdf.
Testo completoAbstract (sommario):
Two different concepts and design procedures namely settlement reducing piles and piled raft foundations have been studied independently in this thesis.
A laboratory study is conducted on model rafts with differing number of model settlement reducing piles. Pile length, pile diameter, type of soil and size of raft are kept constant and settlements are measured under sustained loading. Remolded
kaolin is consolidated under controlled stresses before tests are performed in model boxes. The tests are conducted under two sustained loadings of 75 kPa and 40 kPa. 0(raft), 16 and 49 number of piles are used. During the tests, all of the skin friction is mobilized. Several tests are conducted for each combination to see the variability. It is concluded that increasing the pile number beyond an optimum value is inefficient as far as the amount of settlement is considered. Also an analytical procedure has been followed to calculate settlements with increasing number of piles. In the second part of this thesis, finite element analyse have been performed on a piled raft foundation model, using Plaxis 3D Foundation Engineering software. This analyse are supported with analytical methods. The piled raft model is loaded with
450 kPa raft pressure. The studies are conducted in two sets in which different pile lengths are used25 m and 30 m respectively. The numbers of piles are increased from 63 to 143. All other parameters are kept constant. The results showed that again an optimum number of piles will be sufficient to reduce the settlement to the acceptable level. The analytical methods indicate a similar behavior. The comparison and results are presented in the study.
38
Peng, Wentao [Verfasser]. "Binary Planet–Satellite Nanostructure Using RAFT Polymer / Wentao Peng". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1234846802/34.
Testo completo
39
Giannopoulos, Konstantinos. "Numerical analysis of the reuse of piled raft foundations". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9101.
Testo completoAbstract (sommario):
This thesis considers the reuse and the optimum design of piled raft foundations using numerical analysis. The solution proposed for reusing foundations is the design of a piled raft foundation capable of supporting successive buildings. A raft foundation, with a limited number of piles located strategically beneath the raft and utilising a high proportion of the ultimate load capacity, is considered the most efficient design when the raft foundation alone provides sufficient load capacity, but at the same time settlements are excessive. This is the case in high plasticity stiff clays such as London Clay. When building on old piles, these piles had to sustain a certain load from the previous structure over a period of time, during which the soil is subjected to the time-related processes of consolidation and creep. A time dependent constitutive model, capable of reproducing several aspects of the time dependent behaviour of soils including creep and isotach viscosity, is employed in the finite element analyses. The model parameters are calibrated with the results of laboratory tests on London Clay, whose time dependent behaviour in its natural state is characterised by isotach viscosity, rate dependent peak strength and rate independent critical state line. Preliminary analyses of single piles indicate that the consolidation processes in the ground result in little gain in capacity in the long term, whereas creep results in increased capacity. A back-analysis of documented piled load tests in London Clay is performed, where the effects of pile installation are quantified. Numerical model calibration is performed with the documented observations of a well instrumented piled raft foundation at Stonebridge Park, London. 3D parametric analyses of piled raft foundations are then performed, in order to assess the appropriate location and dimensions of piles and raft thickness. The performance of piled raft foundations with time is assessed parametrically at different levels of preloading. Optimisation of the performance of the piled raft foundation at Stonebridge Park is attempted by examining several pile arrangements, where a central pile support with a limited number of piles is more cost-effective than the original design.
40
Bowes, Angela. "Novel synthesis of block copolymers via the RAFT process". Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/976.
Testo completo
41
Johnson, Iain Joseph. "Synthesis and characterisation of polymeric materials via RAFT polymerisation". Thesis, Durham University, 2013. http://etheses.dur.ac.uk/8452/.
Testo completoAbstract (sommario):
Well-defined polymeric materials incorporating N-vinylpyrrolidone (NVP), vinyl acetate (VAc) and / or N-vinylcaprolactam (NVCL) were synthesised using reversible addition fragmentation chain transfer (RAFT) polymerisation. Chapter 1 is a general introduction on controlled / living radical polymerisation methods, in addition to a brief background on poly(N-vinylpyrrolidone) (PNVP), poly(vinyl acetate) (PVAc) and poly(N-vinylcaprolactam) (PNVCL). Chapter 2 describes the synthesis of RAFT agents (RAFT agents 1-7) used within this study comprising either a dithiocarbamate (RAFT agent 1) or xanthate (RAFT agents 2-7) structure. Several novel RAFT agents with pyrrolidone functionality and based on xanthates (RAFT agents 4-7) were synthesised to improve the RAFT polymerisation of “less activated” monomers (LAMs). Furthermore, multi armed RAFT agents (RAFT agents 9-11) based on xanthates were also synthesised with the aim of generating star-like polymeric structures incorporating LAMs. 1H and 13C nuclear magnetic resonance (NMR) spectroscopy methods were used to characterise the RAFT agents synthesised. Chapter 3 involves the use of RAFT agents 1-8, to mediate the polymerisation of NVP, VAc and NVCL in order to synthesise linear homopolymers with controlled molecular weight and narrow PDI. The kinetics of NVP RAFT mediated polymerisations using novel RAFT agents 5-7 were also investigated and showed that the polymerisations had controlled / living characteristics. Furthermore, the effect of having either primary, secondary or tertiary R groups was explored, for the controlled polymerisation of NVP. RAFT agent 4 which incorporates a primary R group was found to be ineffective in controlling the polymerisation of NVP, whereas RAFT agents with a secondary or tertiary R groups were found to be effective. The resulting polymers were characterised by 1H NMR spectroscopy and size exclusion chromatography (SEC). Chapter 4 focuses on the synthesis of linear block and novel random copolymers incorporating various combinations of PNVP, PVAc and PNVCL. PNVP macroCTA’s (12-14) were used to synthesise PNVP-block-PVAc and PNVP-block-PNVCL, whereas PVAc macroCTA’s (15-17) were used to synthesise PVAc-block-PNVP and PVAc block-PNVCL. Bimodal molecular weight distributions were observed in all the block copolymers synthesised. Novel linear PNVP ran PVAc, PNVCL ran PVAc and PNVP-ran-PNVCL were also synthesised in the presence of RAFT agent 5, with monomodal molecular weight distributions and narrow PDI’s. Chapter 5 describes the synthesis of more complex polymeric structures using multi-armed RAFT agents prepared in Chapter 2 (RAFT agents 9-11). A “core first” R group approach was implemented instead of a “core first” Z group approach to synthesise the polymeric stars, in order to maintain the integrity of the star structure. NVP, VAc and NVCL were polymerised via RAFT in the presence of RAFT agents 9 11, to synthesise Star 1-6. PNVP and PVAc three and four armed stars (Star 1-4) were found to exhibit monomodal molecular weight distributions and low PDI. However, PNVCL three and four armed stars (Star 5 and 6) were found to show bimodal molecular weight distributions. Star 3 (4 arm star of PNVP) and Star 4 (4 arm star of PVAc) were then subsequently used as star macroCTA’s and chain extended with NVP, VAc and NVCL to synthesise novel Star-block 1-4. Star block copolymers were found to either have broad or bimodal molecular weight distributions. In addition, novel three and four armed star random copolymers (Star-random 1-6) were also synthesised via RAFT using RAFT agents 9 and 11, respectively. All Star-random copolymers were observed to have monomodal molecular weight distributions and narrow PDI. Chapter 6 investigates the temperature responsive behaviour of polymeric materials containing NVCL using UV-Visible spectroscopy and optical microscopy. PNVCL synthesised via conventional free radical polymerisation, with a Mn of 9.97 x 104 gmol-1, was found to exhibit an LCST at 33°C. In comparison, linear PNVCL samples prepared via RAFT polymerisation, with Mn ranging from 1.02 x 104 to 2.62 x 104 gmol-1 were observed to exhibit higher LCST’s in the region of 38-40°C. This suggests that the LCST of PNVCL is dependent on the polymer chain length; i.e. “classical” (Type 1) Flory Huggins behaviour. Furthermore, PNVCL synthesised using RAFT agents 2-5 exhibited LCST’s in the region of 39-40°C, which is known as fever temperature. Novel linear PNVCL-ran-PNVP, PNVCL-ran-PVAc and Star-random 2, 3, 5-6 were also analysed to determine their temperature responsive behaviour. The introduction of a hydrophobic (PVAc) and hydrophilic (PNVP) entities into PNVCL is shown to significantly decrease and increase the LCST, respectively. Comparison of the LCST transition range for PNVCL-ran-PVAc synthesised via RAFT and conventional FRP, indicated that the former showed a much narrower transition. Novel Star-random 5 and 6 (four armed random copolymers) were found to have a lower LCST compared to Star random 2 and 3 (three armed random copolymers) despite having similar monomer compositions. A thermal hysteresis was found to be present in all polymer samples, which was attributed to the possibility of weak cross-linking interactions between water molecules and PNVCL carbonyl groups. Chapter 7 is a general conclusion of the work discussed in Chapters 1-6 and future work.
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Sasso, Barbara. "Synthesis of ω-end functional polymers by raft polymerization". Thesis, University of Manchester, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492065.
Testo completo
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Rettig, Hartmut Arnim. "Methoden zur Synthese von definierten bioorganisch-synthetischen Blockcopolymeren". Phd thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982242581.
Testo completo
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Mertoglu, Murat. "The synthesis of well-defined functional homo- and block copolymers in aqueous media via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization". Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/233/.
Testo completoAbstract (sommario):
New chain transfer agents based on dithiobenzoate and trithiocarbonate for free radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT) were synthesized. The new compounds bear permanently hydrophilic sulfonate moieties which provide solubility in water independent of the pH. One of them bears a fluorophore, enabling unsymmetrical double end group labelling as well as the preparation of fluorescent labeled polymers. Their stability against hydrolysis in water was studied, and compared with the most frequently employed water-soluble RAFT agent 4-cyano-4-thiobenzoylsulfanylpentanoic acid dithiobenzoate, using UV-Vis and 1H-NMR spectroscopy. An improved resistance to hydrolysis was found for the new RAFT agents, providing good stabilities in the pH range between 1 and 8, and up to temperatures of 70°C. Subsequently, a series of non-ionic, anionic and cationic water-soluble monomers were polymerized via RAFT in water. In these experiments, polymerizations were conducted either at 48°C or 55°C, that are lower than the conventionally employed temperatures (>60°C) for RAFT in organic solvents, in order to minimize hydrolysis of the active chain ends (e.g. dithioester and trithiocarbonate), and thus to obtain good control over the polymerization. Under these conditions, controlled polymerization in aqueous solution was possible with styrenic, acrylic and methacrylic monomers: molar masses increase with conversion, polydispersities are low, and the degree of end group functionalization is high. But polymerizations of methacrylamides were slow at temperatures below 60°C, and showed only moderate control. The RAFT process in water was also proved to be a powerful method to synthesize di- and triblock copolymers including the preparation of functional polymers with complex structure, such as amphiphilic and stimuli-sensitive block copolymers. These include polymers containing one or even two stimuli-sensitive hydrophilic blocks. The hydrophilic character of a single or of several blocks was switched by changing the pH, the temperature or the salt content, to demonstrate the variability of the molecular designs suited for stimuli-sensitive polymeric amphiphiles, and to exemplify the concept of multiple-sensitive systems. Furthermore, stable colloidal block ionomer complexes were prepared by mixing anionic surfactants in aqueous media with a double hydrophilic block copolymer synthesized via RAFT in water. The block copolymer is composed of a noncharged hydrophilic block based on polyethyleneglycol and a cationic block. The complexes prepared with perfluoro decanoate were found so stable that they even withstand dialysis; notably they do not denaturate proteins. So, they are potentially useful for biomedical applications in vivo.Ziel der vorliegenden Arbeit war es, neue Kettenübertragungs Agenzien, basierend auf Dithiobenzoat- und Trithiocarbonatderivaten zu synthetisieren, welche in der "Reversiblen Additions-Fragmentierungs Kettenübertragungs-Polymerisation" (RAFT) eingesetzt werden können. Die neu synthetisierten Verbindungen zeichnen sich durch permanent hydrophile Sulfonatgruppen aus, welche eine pH-unabhängige Löslichkeit in Wasser ermöglichen. Eine dieser Verbindungen trägt ein Fluorophore, wodurch eine asymmetrische doppelte Endgruppenmarkierung sowie die Herstellung von Fluoreszenzmarkierten Polymeren möglich ist. Die Hydrolysestabilität dieser Verbindungen in wässriger Lösung im Vergleich mit dem z. Zeit bekanntesten wasserlöslichen RAFT Agenz (4-Cyano-4-thiobenzoylsulfanylpentansäuredithiobenzoate) wurde unter Anwendung spektroskopischer Methoden (UV-Vis, 1H-NMR) untersucht. Dabei wurde festgestellt, dass diese neue Verbindungen deutlich bessere Hydrolysestabiltäten im pH-Bereich von 1-8 und bis zu einer Temperatur von 70°C besitzen. Die neuen RAFT-Verbindungen wurden ebenfalls bezgl. Ihrer Eignung in der Polymerisation von wasserlöslichen nichtionischen, anionischen und kationischen Monomeren in wässrigem Medium bei 48°C und 55°C getestet. Unter diesen Bedingungen konnten Vinylverbindungen wie z. B. Styrenderivate. Acrylate und Methacrylate kontrolliert polymerisiert werden: Die Molmasse stieg mit dem Umsatz, die Polydispersitäten waren niedrig und die isolierten Polymere zeigten Grad an Endgruppenfunktionalität. Bei der Polymerisation von Methacrylamiden wurde bei Polymerisationstemperaturen unter 60°C nur eine mäßige Kontrolle gefunden.
Es konnte weiterhin die RAFT Polymerisation in Wasser als leistungsstarke Methode zur Herstellung definierter Di- und Triblockcopolymere, einschließlich der Synthese von funktionalen Polymeren mit komplexer Struktur – beispielsweise amphiphiler- und schaltbare (stimuli responsive) Blockcopolymere entwickelt werden. Dies beinhaltet auch Polymere, die einen oder zwei schaltbare hydrophile Polymerblöcke enthalten. Der hydrophile Eigenschaft eines oder mehrer Blöcke kann durch äußere Reize wie pH-Änderung, Temperatur oder Salzgehalt geändert werden. Diese Beispiele demonstrierten die Variabilität des für schaltbare Polyamphiphile notwendigen Designs und zeigten exemplarisch das Konzept für multi-sensitive Systeme.
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Chakraborty, Sourav. "Synthesis of magnetic polymer nanoparticles using RAFT mediated miniemulsion polymerization in presence of amphiphilic ionic liquid as surfactant". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-164920.
Testo completoAbstract (sommario):
Polymer magnetic composite (PMC) nanoparticles have gained a large attention due to their potential use in several biomedical applications from biomedical to engineering field. Among the different heterogeneous polymerization techniques that are generally used to prepare hybrid polymer particles, miniemulsion polymerization is proved to be an efficient one. The occurrence of preferential droplet nucleation in case of miniemulsion polymerization results in a 1:1 copy of monomer droplets to the polymer particles and such a mechanistic pathway offers a suitable environment for the preparation of hybrid polymer nanoparticles in the range between 50 to 500 nm.
The surfactant in miniemulsoin plays a significant role to stabilize the droplets/particles and also in the encapsulation of nanoparticles. In the present study, a new class of surfactant, called amphiphilic ionic liquid, has been employed in the field of miniemulsion. The amphiphilic ionic liquid has amazing ability to impart surface tunable characteristics to the polymer particles when present on the surface of the particles. Thus the aim of the present work is to synthesize polymer magnetic composite nanoparticles with good colloidal stability, high content of magnetic nanoparticles as well as the chance for further surface functionality. Such magnetic nanoparticles may find applications in various fields.
At first, the aim of the work was to establish a suitable recipe with ionic liquid as surfactant for the execution of miniemulsion polymerization. Monodisperse polystyrene nanoparticles were possible to be synthesized reproducibly. The established recipe was utilized to carry out the synthesis of PMC nanoparticles. Iron oxide (Fe3O4) was taken as magnetic nanoparticles (MNP) and it was hydrophobized with oleic acid to disperse in styrene. The concentration of feed MNP was varied to observe its influence on the characteristics of PMC nanoparticles. Stable dispersion of magnetic polystyrene particles was possible to be synthesized up to 8 wt% feed MNP. But feeding 12 wt% MNP resulted in the development of large amount of coagulum associated with instability in the dispersion. TGA investigation confirmed a significantly lower MNP content (8.2 wt%) of the composite compared to the feed amount. TEM investigation showed inhomogeneous distribution of MNP among polystyrene particles and agglomeration of MNP was observed on the surface of polystyrene particles.
Considering the inability of the single step miniemulsion polymerization for the preparation of high MNP content polymer particles, it was aimed to find a new strategy which can produce such material. Inspired from the affinity of carboxylic acid group towards the surface of MNP, it was aimed to synthesize carboxyl functionalized polystyrene which was expected to improve the interaction between polymer and magnetic nanoparticles. For this purpose, RAFT mediated miniemulsion polymerization was performed in presence of a carboxyl functionalized chain transfer agent (CTA). The colloidal stability was much better compared to the previous case of non-RAFT experiments. From a feed MNP of 8 wt%, a high final MNP content up to ~27 wt% could be achieved and all the dispersions were highly stable. The higher MNP content in the final composites compared to the feed ratio was a result of the low monomer conversion and could be adjusted by a proper tuning of AIBN to CTA mole ratio.
Another significant influence of the carboxyl functionalized CTA was observed on the morphology of the composite nanoparticles. The MNP were distributed homogeneously among the PS particles. Regarding the dispersion of MNP in the individual polystyrene particles, it was observed that higher amount of CTA resulted in a homogeneous dispersion of MNP whereas higher amount of initiator ended up producing asymmetric Janus like morphology.
Apart from that, due to the involvement of CTA in the polymerization, much lower molecular weight of the polystyrene chains was developed compared to the free radical process and the molecular weight distribution of PS in the composite nanoparticles became much narrower through the RAFT polymerization. Thus a relatively good control over the polymerization process was achieved through RAFT polymerization which was confirmed by a nearly linear increase of molecular weight (Mn) with time of polymerization and thus, monomer conversion.
In the recipe of miniemulsion, costabilizer plays an important role to retard monomer diffusion from smaller to larger droplets. Hexadecane, being the most frequently used costabilizer for miniemulsion, has been employed in this study so far. But its volatile nature restricts its utilization in several applications. For the replacement of hexadecane, a carboxyl functionalized polystyrene is employed as a costabilizer as well as a macro CTA in miniemulsoin polymerization of styrene. For this purpose, low molecular weight carboxyl bi-functionalized polystyrene (9000 g/mole) was synthesized by thermal bulk RAFT polymerization. The carboxylated polystyrene worked successfully as a costabilizer in miniemulsion and molecular weight investigation confirmed the integration of the carboxyl functionalized macro CTA into the developing polystyrene chain via RAFT polymerization. This strategy was employed successfully to synthesize stable dispersion of PMC nanoparticles with a reasonable content of MNP in the system. A homogeneous morphology was observed regarding the distribution of MNP among the polystyrene particles.
The strategy of using macro CTA as costabilizer can be utilized to synthesize various functional copolymers with control architecture without any added monomer and CTA in the system. Moreover, presence of functionality within the monomer droplets can be effective to encapsulate several nanomaterials using miniemulsion polymerization.
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Hemp, Sean Taylor. "From N to P: Examining Structure-Property Relationships of Ammonium- and Phosphonium-Containing Macromolecules". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/51560.
Testo completoAbstract (sommario):
An unprecedented comprehensive study of ammonium and phosphonium polyelectrolytes probed and examined structure-property relationships with a focus on different macromolecular properties. Conventional free radical polymerization readily generated a large library of ammonium- and phosphonium-containing polyelectrolytes. Along with the two different cationic atoms, the alkyl substituent lengths and counterions were varied to generate a thorough structure-property relationship analysis. Phosphonium macromolecules displayed improved thermal stabilities and improved ionic conductivities compared to ammonium analogs. Longer alkyl substituent lengths systematically decreased the glass transition temperatures of all polyelectrolytes; the larger, bulkier counterions also resulted in lower glass transition temperatures. Counterion also impacted the thermal stability of the polymerized ionic liquids with less basic counterions leading to improved thermal stability. For the first time, the efficacy of phosphonium macromolecules for nonviral nucleic acid delivery was examined. Phosphonium macromolecules more efficiently complexed nucleic acids than ammonium analogs and butyl-containing phosphonium macromolecules delivered nucleic acids more effectively than the ammonium analog. Controlled radical polymerization generated unprecedented phosphonium-containing diblock copolymers and these diblock copolymers displayed enhanced colloidal stability and lower cytotoxicity compared to the phosphonium homopolymer for nucleic acid delivery.
Step-growth polymerization techniques enabled the synthesis of well-defined, high molecular weight phosphonium ionenes for the first time. Phosphonium ionenes exhibited higher thermal stability and alkaline stability compared to ammonium ionenes. Due to their high thermal stability and relatively low glass transition temperatures, unprecedented melt rheology studies on polyelectrolytes probed the melt flow characteristics of phosphonium ionenes. Novel phosphonium gemini surfactants displayed interesting solution properties in aqueous and chloroform solutions. Electrospinning of the phosphonium gemini surfactants created uniform fibers. The synthesis and characterization of sulfonium polyelectrolytes enabled the first examination of sulfonium macromolecules for nonviral nucleic acid delivery. Sulfonium polyelectrolytes successfully bound nucleic acids and delivered them in vitro. Controlled radical polymerization generated innovative AB diblock and ABA triblock copolymers that displayed salt- and temperature-responsive properties suitable for biological applications such as drug delivery vehicles and hydrogels. Finally, adenine-containing polyelectrolytes were synthesized and they were successfully electrospun to generate adenine-decorated nanofibers appropriate for filtration and nonwoven applications.Ph. D.
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Arrington, Kyle. "Sustainable Polymers Through Creative Design". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/96220.
Testo completoAbstract (sommario):
Plastics have changed the world of materials due to their high durability, low price, low density, and ease of processing. Unfortunately, the majority of plastic goods produced are discarded instead of recycled, leading to a massive accumulation of plastic waste in landfills and natural habitats. To decrease the impact of plastic waste, sustainable materials and synthetic methods are needed. This dissertation focuses on new strategies for developing renewable and degradable polymers with minimal energy input as well as new methods to blend legacy polyolefins with renewable polymers. The first half of the dissertation focuses on synthesizing polymers using light while the second section focuses on combining traditional polyolefins with renewable polymers.
Photo-mediated polymerizations are an attractive alternative to traditional thermal polymerizations due to their ease of setup and the spatiotemporal control afforded by light. Using LED lights also affords a synthetic technique that requires little energy input, thus decreasing the overall environmental impact of the material. In this work, coupling LEDs with a trithiocarbonate allowed for the synthesis of many different polymers and topologies. Bottlebrush polymers synthesized with light afforded molar masses in excess of 11 million Da without the oligomerization of the bottlebrush polymers. These bottlebrush polymers were then used to make reversibly crosslinkable adhesives, allowing for a new example of recyclable adhesives.
The second half of the dissertation focuses on developing sustainable polymers using ring-opening metathesis polymerization (ROMP) to combine the properties of polyolefins with renewable polymers. First, polyketones synthesized by ROMP were developed for their potential use as photodegradable polymers. This initial study probed the synthesis of different polyketone monomers and the properties of their respective polymers. Next, a photodegradable and biodegradable thermoplastic elastomer (TPE) was synthesized that incorporated a ketone containing polybutadiene (PB) flanked by polylactide (PLA). The thermomechanical properties were controlled based on the relative length of each block while the rate of photodegradation was controlled by the mol% of ketone incorporated into the PB block. Finally, ABA triblock copolymers of cellulose derivatives and polyolefins were developed for their uses as compatibilizers for blends. With the addition of as little as 1 wt% of the ABA triblock copolymer, the respective blends showed large impPHD
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Emiliani, Laura. "Raft miniemulsion (co)polymerization of methyl methacrylate and n-butyl acrylate". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8606/.
Testo completoAbstract (sommario):
This thesis work is part of a larger synthesis project about alkyd resins from natural sources, copolymerized with methyl acrylate and n-butyl acrylates, which wil be used for coatings purpose.
The aim is to control the copolymerization of methyl acrylate and n-butyl acrylate in RAFT miniemulsion. The research was divided into three parts. First the homopolymerization of methyl methacrylate and n-butyl acrylate was studied by varying different parameters such as the amount of surfactant, the amount of initiator, pH, and especially the RAFT agent. Then two macro RAFT agents were synthesized, as suggested by the existing literature. Finally, the two monomers were copolymerized using both the RAFT used for the homopolymerization and those synthesized in the second stage.
To verify the obtained control over the polymerization, the synthesized polymers were analyzed by gel permeation chromatography, GPC, thus finding their molecular weight and its polydispersity.
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Roßner, Christian. "High-Precision Particle Arrangement in Gold‒Polymer-Nanocomposites using RAFT Polymerization". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-002B-7CAD-0.
Testo completo
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Möhrke, Julia. "Kinetik der konventionellen radikalischen und der RAFT-Polymerisation an Nanopartikeloberflächen". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-87D3-9.
Testo completoAbstract (sommario):
Diese Arbeit gibt neue Einblicke in die kinetischen und mechanistischen Aspekte der konventionellen radikalischen und der Reversible-Addition–Fragmentation-chain-Transfer- (RAFT-)Polymerisation von der Oberfläche von Silica-Nanopartikeln.
Die Terminierungskinetik der oberflächeninitiierten Polymerisation von n-Butylmethacrylat (n-BMA) wurde mit Hilfe der Single-pulse–pulsed-laser-Polymerisation (SP–PLP) in Kombination mit der Elektronenspinresonanzspektroskopie (ESR-Spektroskopie) analysiert. Die Polymerisation wurde dabei durch den neu entwickelten oberflächengebundenen Photoinitiator 2,2-Dimethoxy-2-phenyl-1-(2-(2-(trimethoxysilyl)-ethyl)phenyl)-1-on (DMPTS) initiiert. Die erhaltenen Geschwindigkeitskoeffizienten der Terminierung kt, die ausschließlich der Terminierungsreaktion zwischen zwei oberflächengebundenen Radikalen zugeordnet werden konnten, waren signifikant kleiner als die Literaturwerte für das entsprechende homogene Polymerisationssystem. Erstaunlicherweise konnte außerdem keine Kettenlängenabhängigkeit von kt gefunden werden. Dies zusammen mit der Tatsache, dass bei temperaturabhängigen Untersuchungen eine Aktivierungsenergie für kt gefunden wurde, die in exzellenter Übereinstimmung mit der des Propagationsgeschwindigkeitskoeffizienten von n-BMA ist, lässt das Bild einer reaktionsdiffusionskontrollierten Terminierung oberflächengebundener Makroradikale entstehen.
Die Entwicklung des oberflächengebundenen Photoinitiators DMPTS erlaubte weiterhin neue Einblicke in die Propagationskinetik – insbesondere deren Temperaturabhängigkeit betreffend – oberflächengebundener Makroradikale. Mittels der PLP von n-BMA in Kombination mit der Größenausschlusschromatographie (engl. size-exclusion chromatography, SEC) wurden Werte für den Geschwindigkeitskoeffizienten der Propagation kp und die entsprechende Aktivierungsenergie ermittelt, die exzellent mit den Daten der International Union of Pure and Applied Chemistry (IUPAC) für die Polymerisation von n-BMA in homogenem Reaktionsmedium übereinstimmen, sodass kein Einfluss der Oberflächenverankerung der Makroradikale auf die Propagationskinetik ersichtlich ist.
Weiterhin wurde die Kinetik der RAFT-Polymerisation von n-Butylacrylat (BA) von Oberflächen bei –40 °C mit Hilfe verschiedener ESR-spektroskopischer Methoden für den R- und den Z-Gruppen-Ansatz unter Verwendung oberflächengebundener Trithiocarbonate als RAFT-Agenzien untersucht.
Die kinetischen Analysen des R-Gruppen-Ansatzes mittels stationärer ESR-Experimente lieferten Gleichgewichtskonstanten Keq, die um eine Größenordnung kleiner sind als die Literaturwerte für entsprechende homogene Polymerisationssysteme, was darauf hindeutet, dass die Oberflächenverankerung des RAFT-Agens einen signifikanten Einfluss auf die Kinetik der RAFT-Polymerisation hat. Durch die Aufnahme zeitlicher Konzentrationsverläufe der Intermediatspezies und der propagierenden Radikale nach Einzelpulsinitiierung mittels der hochaufgelösten zeitabhängigen ESR-Spektroskopie (SP–PLP–ESR–RAFT) in Kombination mit PREDICI®-Simulationen wurden diese Ergebnisse bestätigt, da eine Abnahme des Geschwindigkeitskoeffizienten der Addition eines Makroradikals an die RAFT-Gruppe mit zunehmender Anzahl beteiligter oberflächengebundener Makromoleküle gefunden wurde. Dieser Befund ist im Einklang mit der Vorstellung, dass die Additionsreaktion bei Beteiligung verankerter Makromoleküle diffusionskontrolliert abläuft, was auf die unterdrückte Translations- und die eingeschränkte Segmentdiffusion oberflächengebundener Polymerketten zurückzuführen ist.
Ein noch kleinerer Wert von Keq wurde für den Z-Gruppen-Ansatz gefunden und kann darauf zurückgeführt werden, dass die in Lösung wachsenden Ketten für die Additionsreaktion mit der RAFT-Gruppe, die sich über den gesamten Verlauf der Polymerisation in unmittelbarer Nähe zur Partikeloberfläche befindet, durch die Polymerschicht auf der Oberfläche diffundieren müssen. Die Wahrscheinlichkeit dafür, dass eine Additionsreaktion stattfindet, nimmt mit zunehmender Polymerschichtdicke ab, was durch einen kleineren Wert von Keq bei Verwendung von einem RAFT-Agens, das über die Z-Gruppe verankert war und über eine makromolekulare anstatt einer niedermolekularen R-Gruppe verfügte, gezeigt werden konnte.
Die vorgestellten Ergebnisse geben einen umfangreichen Überblick über den Einfluss der Oberflächenverankerung von Komponenten, die am Prozess der radikalischen Polymerisation beteiligt sind, auf die Kinetik der oberflächeninitiierten radikalischen Polymerisation und ebnen den Weg für detaillierte, systematische Untersuchungen der Zusammenhänge zwischen der Kinetik von radikalischen Polymerisationen an Oberflächen und der molekularen Struktur der erhaltenen oberflächengebundenen Polymere.