Dissertations / Theses on the topic 'Polymerization mechanisms'
To see the other types of publications on this topic, follow the link: Polymerization mechanisms.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Polymerization mechanisms.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Bandtock, J. "An investigation into mechanisms of termination in anionic polymerization." Thesis, De Montfort University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370511.
Full text
2
Bergenudd, Helena. "Understanding the mechanisms behind atom transfer radical polymerization : exploring the limit of control." Doctoral thesis, KTH, Kärnkemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32104.
Full textAbstract:
Atom transfer radical polymerization (ATRP) is one of the most commonly employed techniques for controlled radical polymerization. ATRP has great potential for the development of new materials due to the ability to control molecular weight and polymer architecture. To fully utilize the potential of ATRP as polymerization technique, the mechanism and the dynamics of the ATRP equilibrium must be well understood. In this thesis, various aspects of the ATRP process are explored through both laboratory experiments and computer modeling. Solvent effects, the limit of control and the use of iron as the mediator have been investigated. It was shown for copper mediated ATRP that the redox properties of the mediator and the polymerization properties were significantly affected by the solvent. As expected, the apparent rate constant (kpapp) increased with increasing activity of the mediator, but an upper limit was reached, where after kpapp was practically independent of the mediator potential. The degree of control deteriorated as the limit was approached. In the simulations, which were based on the thermodynamic properties of the ATRP equilibrium, the same trend of increasing kpapp with increasing mediator activity was seen and a maximum was also reached. The simulation results could be used to describe the limit of control. The maximum equilibrium constant for controlled ATRP was correlated to the propagation rate constant, which enables the design of controlled ATRP systems. Using iron compounds instead of copper compounds as mediators in ATRP is attractive from environmental aspects. Two systems with iron were investigated. Firstly, iron/EDTA was investigated as mediator as its redox properties are within a suitable range for controlled ATRP. The polymerization of styrene was heterogeneous, where the rate limiting step is the adsorption of the dormant species to the mediator surface. The polymerizations were not controlled and it is possible that they had some cationic character. In the second iron system, the intention was to investigate how different ligands affect the properties of an ATRP system with iron. Due to competitive coordination of the solvent, DMF, the redox and polymerization properties were not significantly affected by the ligands. The differences between normal and reverse ATRP of MMA, such as the degree of control, were the result of different FeIII speciation in the two systems.QC 20110406
3
Kowatz, Thomas. "Mechanisms of silicate polymerisation, carbohydrate epimerisation and metalloprotease inhibition." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/771.
Full text
4
Thickett, Stuart Craig Vincent. "The Kinetics of Electrosterically Stabilized Emulsion Polymerization Systems." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/2380.
Full textAbstract:
The kinetics of electrosterically stabilized emulsion systems was studied. The aim of this was to understand the impact that steric and electrosteric stabilizers have on the kinetics of particle growth and particle formation in the area of emulsion polymerization. The well-established mechanisms that govern these processes for emulsions stabilized by conventional low molecular weight surfactants were used as a reference point for comparative purposes. Model latexes were synthesized that comprised of a poly(styrene) core stabilized by a corona of poly(acrylic acid). The advent of successful controlled radical polymerization techniques in heterogeneous media (via RAFT polymerization) allowed for latexes to be synthesized under molecular weight control. For the first time, the degree of polymerization of the stabilizing block on the particle surface was able to be controlled and verified experimentally using mass spectrometry techniques. Three latexes were made with different average degrees of polymerization of the stabilizing block; five, ten and twenty monomer units respectively. A methodology was developed to remove the RAFT functionality from the polymer chains present in the emulsion while retaining the desired particle morphology. Oxidation with tertbutylhydroperoxide (TBHP) was proven to be successful at eliminating the living character provided by the thiocarbonyl end-group. Extensive dialysis and cleaning of the latex was performed to ensure no residual TBHP or reaction by-products remained. Latexes with poly(styrene) cores were chosen for this work as poly(n-butyl acrylate) latexes were shown to be influenced by chain transfer to polymer, providing an additional kinetic complication. The three electrosterically stabilized emulsions were used as seed latexes in carefully designed kinetic experiments to measure the rate of polymerization as a function of time. Two independent techniques (chemically initiated dilatometry and γ-relaxation dilatometry) were used to measure the rate coefficients of radical entry (ρ) and exit (k) in these systems – the two parameters that essentially govern the rate of particle growth. The latexes were chosen such that they satisfied ‘zero-one’ conditions (i.e. that any given latex particle contains at most one growing radical at any given time) in order to simplify data analysis. Three different chemical initiators were used, each yielding a radical with a different electric charge. Results from γ-relaxation experiments demonstrated that the three electrosterically stabilized latexes gave very long relaxation times when removed from the radiation source, ultimately yielding very small k values. These values were up to a factor of 10 smaller than that predicted by the ‘transfer-diffusion’ model for exit for particles of that size. This reduction was attributed to a ‘restricted diffusion’ effect, where the exiting monomeric radical has to diffuse through a dense layer of polymer on the particle surface, where its mobility will be restricted. Modification of the Smoluchowski equation for diffusion-controlled adsorption/desorption to account for this postulate led to the development of a model that gave excellent semi-quantitative agreement with experiment. Chemically initiated dilatometric experiments (using three different types of initiator) gave the unusual result of very low reaction rates and low steady-state values of 'nbar', the average number of radicals per particle. Using the standard kinetic equations for styrene-based systems (where it is assumed that an exited monomeric radical undergoes re-entry), this led to the calculation of impossibly small values of the entry rate coefficient ρ (far below any background or ‘thermal’polymerization rate). However upon removing the assumption of re-entry and assuming that exited radicals undergo termination, the obtained values of ρ were in almost perfect agreement with the values predicted from the ‘control by aqueous phase growth’ entry mechanism. This unexpected result was attributed to chemical reaction with the poly(acrylic acid) stabilizers through chain transfer to polymer (via hydrogen-atom abstraction). This postulate was verified by separate experiments that demonstrated that poly(acrylic acid) could act as a reasonably efficient chain transfer agent for styrene polymerization. The addition of poly(acrylic acid) to the aqueous phase of a conventionally stabilized emulsion also led to the rate reduction seen previously. NMR experiments demonstrated the existence of poly(acrylic acid-graft-styrene), which could only be formed through termination of a poly(styrene) chain with a poly(acrylic acid) chain bearing a mid-chain radical (as the product of a chain transfer reaction). These additional terms of transfer and termination were included in the governing kinetic equations of emulsion systems (the Smith-Ewart equations) to develop a model to account for the behaviour of electrosterically stabilized latexes. The ultimate fate of an exiting radical was now shown to be a competition between fates; successful desorption into the aqueous phase, or chemical reaction (through transfer or termination) within the hairy layer. These additional terms were shown to significantly reduce the theoretical value of nbar, and were in excellent agreement with experiment. For small electrosterically stabilized particles with a densely packed ‘hairy layer,’ it was seen that transfer/termination is the dominant loss mechanism as opposed to desorption. The developed model showed that as the particle size was increased, the dominant loss mechanism once again became successful desorption into the aqueous phase. The model was shown to give excellent agreement with experimental data from ‘uncontrolled’ emulsion systems. To explain the highly unusual secondary nucleation behaviour seen in systems such as these, it was postulated that beta-scission of a poly(acrylic acid) chain bearing a mid-chain radical is an important mechanistic step in the nucleation mechanisms of these systems. Modelling (both steady-state and time-dependent) gave good agreement with experiment with a minimal number of adjustable parameters. Theory (and supporting experimental evidence) demonstrated that this nucleation mechanism is only significant at high particle numbers; under other conditions the well-known ‘homogeneous nucleation’ mechanism is once again dominant.
5
Devlin, Glyn L. "The mechanisms of serpin misfolding and its inhibition." Monash University, Dept. of Biochemistry and Molecular Biology, 2003. http://arrow.monash.edu.au/hdl/1959.1/9469.
Full text
6
Müller, Jonathan Benedikt [Verfasser], and M. [Akademischer Betreuer] Wegener. "Exploring the Mechanisms of Three-Dimensional Direct Laser Writing by Multi-Photon Polymerization / Jonathan Benedikt Müller. Betreuer: M. Wegener." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1072464608/34.
Full text
7
XUE, YUAN. "Quantum Mechanical Calculations on Ring-opening Reactions of Hexachlorophosphazenes." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627595429444473.
Full text
8
Tchernook, Ivan. "Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum Mechanics." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-198756.
Full textAbstract:
This thesis presents computational studies of problems in the organic and polymer chemistry. The state-of-the art quantum chemical methods are used to gain further insight into the origin and the nature of the reactions in three different organic and polymer systems. The research questions are conceptually approached by identifying the key aspects. Then an appropriate strategy for the quantum chemical modeling is developed.
In the scope of the polymer chemistry, the novel synthesis technique of nanostructured materials, the so-called twin polymerization, is investigated. Using three model systems of increasing complexity the influence of the anion (trifluoroacetate) in the reaction system is investigated. The effect of the solvent polarity as well as the effect of the entropic contributions are also considered.
The rearrangement reaction of the volatile cyanotritylcarbenes is another topic. These carbenes readily rearrange to ethene main products, however also small amount of the unexpected heptafulvenes is formed. This unprecedented heptafulvene formation is modeled in detail and the energetics is systematically evaluated to identify most reasonable rearrangement pathways of the probable multiple alternative routes. Computational investigation of other tritylcarbenes with varying spectator substituents results in sophisticated data base for experimental investigations.
At last, some controversial observations in experimental studies concerning the kinetics of the electrophilic alkylation of the barbiturate anion are studied. To interpret the kinetic measurements, different alkylation pathways are analyzed with respect to their energetics. Further, the influence of microsolvation is demonstrated.
9
Huang-Hobbs, Helen. "Dissecting the mechanism of ETV6 polymerization." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45691.
Full textAbstract:
ETV6 (or TEL), a member of the ETS family of eukaryotic transcription factors, normally functions as a transcriptional repressor and putative tumor suppressor. ETV6 is modular, containing a SAM (or PNT) domain and a DNA-binding ETS domain joined by a flexible linker sequence. The ETV6 SAM domain self-associates in a head-to-tail fashion, forming helical polymers proposed to generate extended repressive complexes at target DNA sites. ETV6 is also frequently involved in chromosomal translocations yielding unregulated chimeric oncoproteins with the SAM domain fused to the catalytic domain of a tyrosine receptor kinase such as NTRK3. Cellular transformation likely results from SAM domain-mediated polymerization and constitutive activation of the kinase domain. In the case of the ETV6- NTRK3 fusion (EN), this transformation is linked to congenital fibrosarcomas. Our goal is to investigate via mutations within its SAM domain, the thermodynamic and dynamic mechanisms underlying the altered transformation properties of ETV6-NTRK3. These studies have been carried out using monomeric variants of the isolated SAM domains with "head" or "tail" point mutations that prevent self-association, yet allow for formation of a mixed dimer with a native binding interface. Specifically, we used a combination of NMR spectroscopy and isothermal titration calorimetry to study the effects of additional mutations on their dimerization. Consistent with its involvement in a crystallographically-observed interdomain salt bridge, mutation of Lys99 was found to weaken the association of ETV-SAM monomers in solution, and to disrupt cellular transformation by EN. This supports the role of the SAM domain self-association in the activation of ETV6-NTRK3, and helps define the mechanisms underlying cellular transformation by similar chimeric oncoproteins.
10
Kashirsagar, Ravindra S. "Study of entry mechanism in emulsion polymerization." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/11747.
Full text
11
Koss, Hans. "Mechanism of actin polymerization with yeast formin Bni1p." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-149371.
Full text
12
Hibi, Yusuke. "Sequence Regulation in Radical Polymerization via Template Mechanism." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188611.
Full text
13
Prehl, Janett, and Constantin Huster. "Morphology on Reaction Mechanism Dependency for Twin Polymerization." MDPI, 2019. https://monarch.qucosa.de/id/qucosa%3A34346.
Full textAbstract:
An in-depth knowledge of the structure formation process and the resulting dependency of the morphology on the reaction mechanism is a key requirement in order to design application-oriented materials. For twin polymerization, the basic idea of the reaction process is established, and important structural properties of the final nanoporous hybrid materials are known. However, the effects of changing the reaction mechanism parameters on the final morphology is still an open issue. In this work, the dependence of the morphology on the reaction mechanism is investigated based on a previously introduced lattice-based Monte Carlo method, the reactive bond fluctuation model. We analyze the effects of the model parameters, such as movability, attraction, or reaction probabilities on structural properties, like the specific surface area, the radial distribution function, the local porosity distribution, or the total fraction of percolating elements. From these examinations, we can identify key factors to adapt structural properties to fulfill desired requirements for possible applications. Hereby, we point out which implications theses parameter changes have on the underlying chemical structure.
14
Sendall, Timothy James. "Investigating the molecular mechanism of serpin polymerisation." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610868.
Full text
15
Li, Xiaopei. "Elucidation of the Termination Reaction Mechanism of Radical Polymerization." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263689.
Full text
16
Abdollahi, Banouei Zohreh. "Inverse emulsion polymerization of acrylamide: synthesis, mechanism and monitoring." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12661.
Full textAbstract:
Polyacrylamides (PAAMs) including both homo- and copolymers of acrylamide constitute the largest group of water soluble polymers which are used in various industrial applications. The common industrial method for the synthesis of high molecular weight PAAMs is inverse emulsion polymerization (IEP); however, considerable disagreement exists regarding the mechanism of IEP. Besides, the high polymerization rate of acrylamide has made the controllability of this system challenging for the industry. A new IEP recipe for synthesis of polyacrylamide using an industrial solvent (D80) and oil soluble initiator azobisiosbutyronitrile (AIBN) was developed in this study. The samples from the IEP reactor were monitored using TEM and optical microscopy for particle size and structure of latex while gravimetric method was applied for monitoring monomer conversion. The results indicated that the locus of reaction is micelles; however, with an increase in initiator concentration or a decrease in emulsifier concentration, the droplets also serve as loci of polymerization. As the alteration of electrical properties with any reaction is rapid, the novel idea of following IEP reactor using electrical impedance spectroscopy (EIS) was examined. Firstly, EIS successfully could detect critical micelle concentration of the emulsifier in the oils. We found that at the CMC a transition in conductance-concentration graph of the emulsifier/oils mixture at 1Hz occurs. From the slope of the graph after CMC, characteristics of the micelles were deduced. More importantly, we found that by using EIS it is feasible to monitor the key parameters of polymerization, such as monomer conversion and particles size and their number. The comparison of electrical responses of IEP using the oil soluble initiator with the redox initiator with definite droplet nucleation confirmed that droplet or micellar nucleation can be distinguished from electrical response of the reaction
17
Leswin, Joost Sieger Kaspar. "Particle Formation in RAFT-mediated Emulsion Polymerization." Thesis, The University of Sydney, 2007. http://hdl.handle.net/2123/2176.
Full textAbstract:
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.
18
Leswin, Joost Sieger Kaspar. "Particle Formation in RAFT-mediated Emulsion Polymerization." University of Sydney, 2007. http://hdl.handle.net/2123/2176.
Full textAbstract:
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.
19
Xu, Jie. "Polymerization mechanism, micro-macro properties, and carbonization of polyurethane foams." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/43925/.
Full textAbstract:
Polyurethane is one of the most diversified macropolymers with versatile properties for many applications including construction, transportation, personal wear, household appliance, etc. The research of this PhD study covers many aspects of polyurethane, including modelling on urethanisation and foaming mechanism, cell microstructure and packing polyhedrons, macroscopic properties and performance, and functional carbon materials developed from carbonisation of polyisocyanurate (PIR) foams. The work contains both theoretical modelling and experimental measurements. Urethanisation Kinetics The catalysed polyisocyanurate reaction kinetic model was developed based on generalized copolymerization scheme. PIR/PUR ratio was derived from mathematical manipulation on rate equations. The structural unit effects of isocyanurate, urethane and urea were evaluated based on Mayo-Lewise tercopolymerization scheme. Two reaction scenarios – bifunctional and macropolyol – were taken into consideration. Two ratios of isocyanate/polyol and urethane/urea rather than isocyanurate concentration were found to have impact on isocyanate conversion. Cell Growth and Foaming Process The cell microstructural configuration model was developed based on FOAMAT reactivity profiling (FOAMAT is a foam qualification system to measure the formation by curing and foaming parameters). The cell constructions were well understood by characterization of interstitial border area between cells. The cell anisotropic degree was calculated based on 2D cell shapes deformation comparison between free rising and stress stretching. The foaming process of continuous line panel production was further modelled based on cell anisotropic stretching. Plateau Borders The geometric Plateau border model for closed cell polyurethane foam was developed based on volume integrations of approximated 3D four-cusp hypocycloid structure. The tetrahedral structure of convex struts was orthogonally projected into 2D three-cusp deltoid with three central cylinders. The idealized single unit strut was modeled by superposition. The volume of each component was calculated by geometric analyses. The strut solid fraction f_s and foam porosity coefficient δ were calculated from developed strut model based on representative elementary volume (REV) of Kelvin and Weaire-Phelan structures. The specific surface area Sv derived from packing polyhedra model and deltoid approximation model respectively were put into contrast against strut dimensional ratio ε. The characteristic parameters modeled from this semi-empirical method were further employed to predict foam thermal conductivity. The correlation results show good agreement with actual measurement. The deviation gap can be caused by disorderedness and irregularity of actual cells. The periodical numerical method still has limit in predicting foam mechanics. Foam Defect Microstructure Streak and blister cell defects pose extensive surface problems for rigid polyurethane foams. In this study, these morphological anomalies were visually inspected using 2D optical techniques, and the cell microstructural coefficients including degree of anisotropy, cell circumdiameter, and the volumetric isoperimetric quotient were calculated from the observations. A geometric regular polyhedron approximation method was developed based on relative density equations, in order to characterize the packing structures of both normal and anomalous cells. The calculated cell volume constant, C_c, from polyhedron geometric voxels was compared with the empirical polyhedron cell volume value, C_h. The geometric relationship between actual cells and approximated polyhedrons was characterized by the defined volumetric isoperimetric quotient. Binary packing structures were derived from deviation comparisons between the two cell volume constants and the assumed partial relative density ratios of the two individual packing polyhedrons. The modelling results show that normal cells have a similar packing to the Weaire-Phelan model, while anomalous cells have a dodecahedron/icosidodecahedron binary packing. Insulation Performance Polyurethane (PU) is a commonly used insulation material for cold storage warehouses. The insulation performance of PU sandwich panels made from blended blowing agents were re-assessed by k-factor measurements and the insulation thickness was calculated based on cold warehouse design standard. The purposes of this study is test the impact of thermal conductivity value from experimental measurements on insulation barrier thickness calculation, and try to identity the gap between experimental data and empirical data in real practice and its impact on insulation design. The building design standard of cold warehouse can be a good benchmark to showcase this difference in aggressive cooling environment. The results have confirmed significant positive impact of blowing agents for energy saving. Post-curing Stability Problem The foam post-curing stability was evaluated by mathematic manipulation. The developed 3D paraboloid model based on gridding measurements has provided a scientific solution to foam panel shrinkage problem. Cell microstructure characterisation and post-growth angle coefficients calculation were further performed in this study. The results show the cell microstructure undergoes severe contraction during cooling and some cell destruction has happened on foam defects. Meanwhile, the cell anisotropic degree is getting more uniformed and this phenomenon is considerably prominent in central position. Thermal Degradation The thermal degradation of polyisocyanurate foam samples were studied by TG/DTA, FTIR, and SEM. All samples with different isocyanate index (NCO/OH = 100, 200, 300) were pre-treated by H2SO4, K2CO3, and NaOH before heating. The measurements of DTG and DTA presented corresponding variability for different acidic and alkaline treatments. The activation energy of thermal decomposition was calculated based on kinetic reaction evaluation. The pronounced polyol and isocyanate regenerations were observed over degradation. Further FTIR measurements at elevated temperatures suggested the possibility of acidic hydrogen bonding catalyzation and alkaline reversible amide regeneration during degradation by chemical treatments. The morphology study by SEM show localized corrosion is severe for high temperature carbonisation by acidic treatment (H2SO4) and microcrystallization occurs for alkalic treatments (K2CO3 and NaOH). The microcrystals vary by geometric shape. Carbonization The isocyanate index (NCO/OH) of diisocyanate and macropolyol can dictate the carbonisation of polyisocyanurate (PIR) foams. The carbon amorphousness was characterized by DSC which suggests the disorderedness can be aggravated by acidic pre-treatment. XRD investigation on crystallography suggests intercalation layered structure was created during carbonisation. Synchrotron-based X-ray photoelectron spectroscopy (XPS) analyses of all carbonaceous residues reveal that N-doping carbonisation has been realized by isocyanate dipolar cycloaddition. The N-doping structures with pyridinic (N-6) and pyrrolic (N-5) nitrogen atoms were found in carboncyclic rings, but no graphitic (N-Q) structure was identified. Higher isocyanate index (NCO/OH) can increase the opportunity for N-doping by creating more pyrrolic (N-5) nitrogen structure. The acidic treatment by H2SO4 can promote pyridinic (N-6) structure formation by cyanic acid trimerization. The derived carbons from higher isocyanate index (NCO/OH) were further found from electrochemical tests to possess improved capacitance but with negative resistivity which is attributed to more capacitive but amorphous N-doping carbon structure.
20
Sörensen, Nicolai. "Kinetics and Mechanism of Cu-Catalyzed Atom Transfer Radical Polymerization." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0023-9662-7.
Full text
21
Ando, Tsuyoshi. "DESIGN AND MECHANISM OF TRANSITION METAL-MEDIATED LIVING RADICAL POLYMERIZATION." Kyoto University, 2000. http://hdl.handle.net/2433/180981.
Full text
22
Hayat, Soytas Serap. "Living Carbocationic Polymerization of Isobutylene by Epoxide/Lewis Acid Systems: The Mechanism of Initiation." Akron, OH : University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1239650255.
Full textAbstract:
Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2009."May, 2009." Title from electronic dissertation title page (viewed 11/29/2009) Advisor, Judit E. Puskas; Committee members, Roderic P. Quirk, Joseph P. Kennedy, Li Jia, Chrys Wesdemiotis; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
23
Bassi, Mitchell Brian 1963. "The mechanism of the ring-opening polymerization of ε-caprolactone using tin(IV) carboxylates." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/291748.
Full textAbstract:
The polymerization of epsilon-caprolactone using tin(IV) carboxylates has been investigated and related to literature research. Polymers with broad MWD were obtained in quantitative yield. At 100% conversion polymer molecular weights ranged from 50,000 to almost 60,000. After an initial induction period, the polymerization shows zero order kinetics with respect to monomer and near first order kinetics with respect to catalyst. The mechanism of the polymerization is coordination-type, and is dependent on the presence of water or an alcoholic initiator. Added water decreases polymer molecular weight to approx. 30,000 at 100% conversion. The polymer has a terminal hydroxyl group and a terminal carboxyl group. The hydroxyl end is the reactive end in propagation. The carboxyl end and free carboxylic acid produced by the hydrolysis of the catalyst are responsible for the induction period.
24
Meiser, Wibke. "Investigation of the Kinetics and Mechanism of RAFT Polymerization via EPR Spectroscopy." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-FB50-3.
Full text
25
Lu, Alvin Z. "Assembly and Regulation of the Inflammasome Governed by a Unified Polymerization Mechanism." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493513.
Full textAbstract:
The innate immune system employs a diverse set of pattern recognition receptors to detect intrinsic and extrinsic danger signals for host protection. Inflammasomes represent an important class of receptors that elicit inflammatory response through the maturation of pro-inflammatory cytokines and the induction of a form of cell death known as pyroptosis. Assembly of a functional inflammasome typically involves an upstream sensor component, an adaptor component, and an effector caspase. The upstream sensor oligomerizes upon detection of pro-inflammatory triggers to recruit the adaptor, which in turn drives caspase activation. The assembled inflammasome proteolytically cleaves interleukin-1β (IL-1β) and interleukin-18, which are the cytokines responsible for downstream signaling events. Previously, our understanding of this assembly process had been limited by the lack of biochemical data and high-resolution structures.
In this dissertation, I present key findings that provide novel perspectives on the assembly and regulation of inflammasomes using structural and biochemical approaches. More specifically, a two-step nucleated polymerization mechanism governs the assembly and activation of inflammasomes that require the filamentous scaffold of an adaptor known as Apoptosis-associated Speck-like protein containing a CARD (ASC). Upstream sensors oligomerize to nucleate the formation of ASC filaments, which in turn nucleate the effector caspase-1 to form another set of filaments. These signaling filaments coalesce into a micron-sized perinuclear puncta, which could be observed under light microscopes. Moreover, I also present evidence to support a capping mechanism for inflammasome regulation. Inhibitor of CARD (INCA) terminates caspase-1 filaments by binding to their ends, which effectively blocks proximity-driven activation of pro-caspase-1 and dampens IL-1β maturation. Both activation and regulation of the inflammasome rely on the special properties of homotypic interaction domains that belong to the death domain superfamily.
Collectively, these studies support a novel paradigm in which the innate immune system exploits signaling filaments for the desired functional outcomes. By understanding the structural and biophysical properties of these supramolecular complexes, we may begin to identify novel targets for therapeutic intervention. In the last chapter, I will also discuss some remaining questions of the inflammasome field, particularly the ones that could be addressed by structural and biochemical methods.Chemical Biology
26
Si, Kun. "Kinetics and Mechanism of Vinyl Chloride Polymerization: Effects of Additives on Polymerization Rate, Molecular Weight and Defect Concentration in the Polymer." online version, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1168382967.
Full text
27
Gillan, Eileen Marie Danielle. "The mechanism of initiation and propagation of ring-opening metathesis polymerization of norbornene." Thesis, Queen's University Belfast, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335961.
Full text
28
Yang, Qizhi. "Development & study of a new photocatalyzed mechanism of atom transfer radical polymerization." Thesis, Mulhouse, 2016. http://www.theses.fr/2016MULH9453.
Full textAbstract:
Plusieurs mécanismes de polymérisation radicalaire contrôlée (PRC) sous irradiation lumineuse ont récemment été développés. Ces approches offrent potentiellement de nombreux avantages, en permettant notamment d’introduire dans le mécanisme des PRCs certaines caractéristiques propres aux photopolymérisations, tels que les contrôles spatial et temporel de la réaction. Les travaux de thèse présentés dans ce manuscrit s’inscrivent dans ce contexte, en ayant pour objectif le développement et l’étude d’un nouveau mécanisme de polymérisation radicalaire par transfert d’atome (ATRP) photocatalysée. Après une étude bibliographique présentant l’état de l’art dans le domaine des PRCs sous irradiation lumineuse (chapitre 1), un complexe de bis(1,10-phenanthroline) cuivre (I) (Cu(I)) est utilisé comme catalyseur pour la synthèse de poly(méthacrylate de méthyle)s bien définis par ATRP menée sous l’irradiation d’une lampe LED bleue de faible intensité (chapitre 2). Le mécanisme proposé implique la formation de l’état excité Cu(I)* à partir de Cu(I) sous irradiation, suivie de sa désactivation oxydative par les composés bromés, générant les espèces actives propagatrices et la forme désactivante du complexe Cu(II). Le cycle catalytique est ensuite complété par l’ajout de triethylamine comme agent réducteur permettant la régénération in situ de la forme activante Cu(I) du complexe et conduisant ainsi à une polymérisation plus rapide. Le méthacrylate de glycidyle est ensuite considéré comme comonomère jouant simultanément le rôle d’un agent réducteur (chapitre 3). Des copolymères fonctionnels bien définis, avec une distribution contrôlée de groupes latéraux époxydes, sont ainsi synthétisés. Enfin, le mécanisme d’ATRP photocatalysé est amélioré en développant une procédure permettant la génération in situ de la forme activante Cu(I) en partant d’un complexe Cu(II) stable en présence d’air (chapitre 4). Le mécanisme ainsi développé présente une bonne tolérance à la présence d’oxygène ou d’inhibiteur dans le milieu réactionnel. Les effets de plusieurs paramètres (intensité lumineuse, concentration en ligand et nature du solvant ou du contre-ion) sont étudiés, suggérant un échange de ligand photo-induit comme processus photochimique additionnel impliqué dans le mécanisme d’ATRP photocatalysé étudiéSeveral mechanisms of controlled radical polymerization (CRP) under light irradiation have been recently developed. These approaches offer potentially numerous advantages, enabling especially to introduce in the mechanism of CRPs some features characteristic of photopolymerizations, such as the spatial and temporal controls of the reaction. The PhD work presented in this manuscript comes in this framework, aiming at developing and studying a new mechanism of photocatalyzed atom transfer radical polymerization (ATRP). After a bibliographic study presenting the state-of-the-art in the domain of CRPs under light irradiation (chapter 1), a bis(1,10-phenanthroline) copper (I) complex (Cu(I)) is used as catalyst for the synthesis of well-defined poly(methyl methacrylate)s by ATRP carried out under the irradiation of a low intensity blue LED lamp (chapter 2). The proposed mechanism implies the formation of the excited state Cu(I)* from Cu(I) under irradiation, followed by its oxidative quenching by the brominated compounds, generating the growing active species and the deactivator form of the complex Cu(II). The catalytic cycle is then completed by the addition of triethylamine as a reducing agent enabling the in situ regeneration of the activator form of the complex Cu(I), therefore leading to a faster polymerization. Glycidyl methacrylate is then considered as a comonomer playing simultaneously the role of a reducing agent (chapter 3). Well-defined functional copolymers, with a controlled distribution of epoxide side groups, are thus synthesized. Finally, the photocatalyzed ATRP mechanism is improved by developing a procedure permitting the in situ generation of the activator Cu(I) starting directly from an air-stable Cu(II) complex (chapter 4). The mechanism developed in this way exhibits a good tolerance to the presence of oxygen or inhibitor in the reaction medium. The effects of several parameters (light intensity, ligand concentration and nature of the solvent or counter-ion) are studied, suggesting a photo-induced ligand-exchange as an additional photochemical process implied in the studied photocatalyzed ATRP mechanism
29
Congdon, Erin Elizabeth. "Insights into the mechanism of Tau polymerization and the effects of small molecules." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1185397658.
Full text
30
Zhong, Yongliang. "Development of Controlled Ring-Opening Polymerization of O-Carboxyanhydrides." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100736.
Full textAbstract:
The aim of my Ph.D. thesis is to summarize my research on the development of ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) to synthesize functionalized, degradable polyesters. Biodegradable polyesters are promising alternatives to conventional petroleum-based non-degradable polyolefins and they are widely used in everyday applications ranging from clothing and packaging to agriculture and biomedicine. Commercially available polyesters, such as poly(lactic-co-glycolic acid), poly(lactic acid), and polycaprolactone, hydrolyze in physicochemical media. They have been approved by FDA and widely used for medical applications. However, the lack of side-chain functionality in polyesters and in corresponding monomers greatly plagues their utility for applications that demand physicochemical properties such as high stiffness, tensile strength and elasticity. Increasing efforts have been devoted to the introduction of pendant groups along the polymer chain in order to modify and modulate the physicochemical properties of polyesters and thereby to expand their applications.
Over the last decade, OCAs have emerged as an alternative class of highly active monomers for polyester polymerization. OCAs are prepared from amino acids and thus have a richer range of side chain functionalities than lactone or lactide. Like lactones, OCAs can undergo ROP to obtain polyesters. Unfortunately, current ROP methods, especially those involving organocatalysts, result in uncontrolled polymerization including epimerization for OCAs bearing electron-withdrawing groups, unpredictable molecular weights (MWs), or slow polymerization kinetics. Based on our recent success of Ni/Ir photoredox catalysis allowing for rapid synthesis of high-MWs polyesters, we further explore new polymerization chemistry to use earth-abundant metal complexes to replace expensive rare-earth metal photocatalysts, and practice the polymerization in moderate and energy-efficient reaction conditions.
II
This thesis introduces novel photoredox and electrochemical earth-abundant metal catalysts that overcome above difficulties in the ROP chemistry of OCAs, and allow for the preparation of stereoregular polyesters bearing abundant side-chain functionalities in a highly controlled manner. Specifically, various highly active metal complexes have been developed for stereoselective ROP of OCAs, either using light or electricity, to synthesize syndiotactic or stereoblock copolymers with different thermal properties. Additionally, simple purification protocols of OCAs have also been initially studied, which potentially paves the way to bulk production of functional monomers.
In this thesis, I first describe newly-developed photoredox Co/Zn catalysts to achieve a controlled ROP of enantiopure OCAs under mild reaction conditions (Chapter 2). Such discovery is extended to the combination use of Co catalysts with various Zn/Hf complexes that enable stereoselective controlled ROP of racemic OCAs for the preparation of stereoregular polyesters (Chapter 3). The mechanistic studies of the aforementioned developments lead to the application of such a catalytic system in controlled electrochemical ROP of OCAs (Chapter 4). Such chemistry can also be translated to stereoselectively electrochemical ROP of racemic OCAs to either syndiotactic or stereoblock polyesters, allowing precise control of polyester's tacticity and sequence (Chapter 5). An overview future work has been summarized (Chapter 6).Doctor of Philosophy
Polyesters are widely used in everyday applications ranging from clothing and packaging to agriculture and biomedicine. Different from conventional unrecyclable plastics, polyesters are usually biocompatible and biodegradable, and can be synthesized from renewable resources. A few commercially available polyesters have been approved by FDA and widely used for medical applications. However, their utility for applications that demand various mechanical and chemical properties is greatly limited by the lack of side-chain functional groups in polyesters and in their monomers—lactones. Increasing efforts have been devoted to the introduction of pendant groups along the polymer chain in order to modify and modulate the desired properties of polyesters and thereby to expand their applications. Over the last decade, O-carboxyanhydrides (OCAs) have emerged as an alternative class of highly active monomers for polyester polymerization. OCAs can be prepared from renewable source amino acids and thus have a richer range of side chain functional groups. Like lactones, OCAs can undergo ring-opening polymerization (ROP). Unfortunately, current ROP methods usually result in uncontrolled polymerization of OCAs including loss of stereoregularity, unpredictable molecular weights, or slow polymerization rate. To address the above-described polymer chemistry and materials challenges, I have been motivated to develop a new polymer chemistry knowledge base when starting my Ph.D. program. I was first involved in the development of a controlled photoredox polymerization of OCAs produces polyesters with various side chain functional groups. By using photoredox Ni/Zn/Ir catalysts, stereoregular high molecular weight polyesters can be synthesized from racemic OCAs in a rapid, controlled manner. IV However, this catalytic system has to be used at -20 oC despite so successful in preparing stereoblock polyesters. Encouraged by our recent success in this area, I started to work on the discovery of other transition metal complexes such as the Co complexes used in N-carboxyanhydride polymerization. Ultimately, innovative photoredox Co/Zn catalysts has been successfully developed, and applied to our protocol to achieve the controlled ROP of enantiopure OCAs under mild reaction condition (Chapter 2). The Co catalyst can replace both Ni and Ir in aforementioned photoredox system. Meanwhile, the combination of Co catalysts and various Zn/Hf complexes has also been developed to undergo photoredox ROP of racemic OCAs to efficiently produce polyesters with different microstructures (Chapter 3). Although photoredox ROP is an efficient method for synthesizing degradable polyesters, great decrease in photonic flux with the depth of the reaction medium makes it less energy efficient compared to electricity. Therefore, we then extended our protocol to electrochemical reaction, which is one of the most energy-efficient chemical reactions. The newly identified Co/Zn catalytic system can be activated by electric current to mediate rapid electrochemical ROP (eROP) of enantiopure OCAs, allowing for the synthesis of isotactic polyesters in a highly controlled manner (Chapter 4). Additionally, stereoselective eROP of racemic OCAs has been firstly achieved by using various combinations of Co and Zn/Hf complexes (Chapter 5). In summary, my research produces unique and transformative insights into the innovative photoredox and electrochemical ROP mediated by metal catalysts. Given the importance and versatility of biodegradable and biocompatible polyester materials, the chemistry invented by our team can be expected to serve as a new platform for various applications in material and biomedical engineering.
31
Downey, Jeffrey S. "Precipitation polymerization of divinylbenzene to monodisperse microspheres : an investigation of the particle formation mechanism /." *McMaster only, 2000.
Find full text
32
Ri, Tokusyoku. "Studies on Mechanism of Polymerization of Food Proteins by Transglutaminases from Mammalian and Microbial Origins." Kyoto University, 1997. http://hdl.handle.net/2433/202385.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第6902号
農博第920号
新制||農||739(附属図書館)
学位論文||H9||N3026(農学部図書室)
16019
UT51-97-H286
京都大学大学院農学研究科食品工学専攻
(主査)教授 森 友彦, 教授 佐々木 隆造, 教授 廣瀬 正明
学位規則第4条第1項該当
33
Di, Stefano Luciano Héctor. "Development of New Photoiniator Systems for Polymerization with Visible Light." Thesis, Mulhouse, 2015. http://www.theses.fr/2015MULH9439.
Full textAbstract:
La photopolymérisation est une technologie qui gagne de plus en plus d’importance de par ses nombreuses applications et ses énormes avantages par rapport à la polymérisation thermique tels que le respect de l’environnement, des coûts économiques maitrisés car la technologie est mise en œuvre à température ambiante et ne requiert qu’une faible consommation d'énergie. De plus, elle n'utilise pas ou très peu de solvants, d'où la réduction d’émission de produits polluants. Le processus de polymérisation photochimique présente également l’avantage d’être très rapide : en effet les réactions de photopolymérisation sont souvent rapides voire même quasi instantanées. De plus le procédé de polymérisation devient photolatent : la polymérisation impliquant les formulations actives seulement en présence de lumière, la réaction peut être déclenchée « quasi à la demande ». Ce processus chimique nécessite des composants nommés « photoamorceurs », lesquels absorbent la lumière et produisent le démarrage de la réaction de polymérisation. En particulier, le développement de systèmes photoamorceurs capables d’absorber de la lumière visible a un intérêt croissant pour différentes applications industrielles, notamment l’holographie. Dans la cadre de cette thèse, des diverses systèmes photoamorceurs contenant un colorant et un ou deux co-amorceurs, qui après réaction avec les états excités des colorants génèrent les radicaux actifs, ont été étudiés, depuis leurs propriétés photophysiques fondamentales et moléculaires, jusqu’aux applications et performances pour la polymérisation des résines acrylates. Cette thèse est articulée autour de six chapitres. Dans le premier chapitre une introduction et une étude bibliographique des différents systèmes photoamorceurs développés ces dernières années sont présentées et comparés. Les chapitres deux et trois sont consacrés à l’étude des propriétés photochimiques et photophysiques réalisés sur des photoamorceurs absorbant de la lumière ultraviolette et visible respectivement. Les techniques utilisés dans ces chapitres incluent, mais ne sont pas limités à, la spectroscopie d’absorption UV-Vis stationnaire, la fluorescence, la photolyse éclaire (LFP), la fluorescence résolue en temps par comptage de photon unique (TC-SPC), la spectroscopie ultrarapide nanoseconde et femtoseconde, la spectroscopie de résonance paramagnétique électronique (EPR), entre autres. Le chapitre deux porte sur l’étude de la photophysique d’un colorant de type cyanine : l’astrazone Orange R (AO R). La photophysique de ce colorant n’est pas connue et une étude exhaustive a été menée avec des spectroscopies ultra rapides (femtoseconde) ainsi que par modélisation moléculaire. Malgré sa photophysique compliquée ce colorant, fonctionne comme un photoamorceur très efficace dans la région bleue du spectre électromagnétique. Les chapitres suivants forment une deuxième partie de la thèse dédiée à l’étude des mécanismes d’amorçage de photopolymérisation, dont le chapitre quatre aborde le cas d’irradiation le plus « traditionnel », qui est l’irradiation en mode continu (ou CW). Est ensuite abordé l’étude de la polymérisation sous irradiation pulsée ultra-courte : dans cette partie la source d’irradiation continue classique est remplacée par un laser Nd :Yag qui produit des impulsions lumineuses d’une durée de quelques 9-10 nanosecondes. Cette polymérisation avec laser pulsé ou PLP est très originale et sera étudiée par spectroscopie infrarouge à transformée de Fourier résolue en temps (RT-FTIR). Dans le chapitre trois, donc, on retrouve les études réalisés avec différents types de systèmes photoamorceurs visibles. Ainsi, les propriétés des colorants capables d’absorber de la lumière visible à différentes longueurs d’onde ont été étudiées dans des systèmes photoamorceurs à deux et trois composantsPhotopolymerization is a technology that is gaining more and more importance due to its numerous applications and its advantages compared to thermic polymerization. This chemical process requires compounds called photoinitiators, which absorb light and produce the initiation of the radical polymerization. The development of photoinitiating systems (PIS) which are able to absorb visible light have an increasing interest due to its industrial applications, such as holographic recording. During this thesis, many PIS were studied, from its photophysical properties to its application in acrylate polymerization. There are many different types of photoinitiators. The most classical ones are Type I PI, which are molecules that overcome homolytic cleavage from their excited state, generating initiating radicals immediately after photon absorption. Type II PI, in contrast, are composed by two molecules: one that absorbs the photon, and other that will react with the excited state of the first via electron transfer or hydrogen transfer, generating radicals that will be able to initiate polymerization. In last place, there are the most efficient Photocyclic Initiating Systems (PCIS) whose mechanism is more complicated and will be widely discussed within these pages. A state of the art of the PIS available up to date is made in the first chapter. Given the importance of the properties of the molecules involved in the photoinitiating process, the studies of the photophysical properties of a Photoinitiator, the Astrazone Orange (AO), are shown. It was found that this molecule suffers an isomerization process from its excited state, which then comes slowly back to the more stable conformer. This process being viscosity-dependent makes AO a suitable photoinitiator for polymerization with visible light in highly viscous media. The last three chapters of this thesis are devoted to the study of a novel technique called Pulsed Laser Polymerization (PLP). This technique consists in the irradiation of the samples with a short duration pulsed laser, which allows the separation of the initiation steps of the polymerization reaction from the steps of propagation and termination. A simple Type I PI was used as a model to study the properties of this technique of polymerization. The monomer conversion was registered by RT-FTIR and analyzed. To a better understanding of these results, a mathematical model was developed. Thanks to it, it was possible to collect valuable information about propagation and termination rate constants (kp and kt, respectively), the variation of viscosity with conversion and other aspects relatives to PLP mechanism. Furthermore, the efficiency of many visible light PIS was studied by PLP. Their performance was compared and studied and contrasted with the classical continuous irradiation mode (CW). The characteristics that a PIS must have in order to show efficient polymerization in PLP mode were found and discussed. Finally, the effect of formulation viscosity in PLP and CW was analyzed by diluting the sample with different amounts of DMSO. In PLP, it was seen that the highest conversion is found for the most concentrated samples, while the opposite effect is noticed in CW. This result is attributed to the different conditions given by the difference in irradiation methods
34
Primpke, Sebastian. "Mechanism and Kinetics of Catalyzed Chain Growth." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://hdl.handle.net/11858/00-1735-0000-0022-5DA6-1.
Full text
35
Cihaner, Atilla. "Electrochemical Synthesis Of Crowned Conducting Polymers: Nature Of Radical Cations In Polymerization And Mechanism Of Conductivity." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605054/index.pdf.
Full textAbstract:
ABSTRACT
ELECTROCHEMICAL SYNTHESIS OF CROWNED CONDUCTING POLYMERS: NATURE OF RADICAL CATIONS IN POLYMERIZATION AND MECHANISM OF CONDUCTIVITY
Cihaner, Atilla
Ph. D., Department of Chemistry
Supervisor: Prof. Dr. Ahmet M. Önal June 2004, 96 Pages Poly(dibenzo-18-crown-6) (Poly(DB18C6)) was synthesized by electrochemical oxidation of dibenzo-18-crown-6 (DB18C6) using a mixture of acetonitrile and dichloromethane as solvent and tetrabutylammonium tetrafluoroborate (TBABF4) or tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. The anodic polymerization of DB18C6 was investigated using in-situ ESR and in-situ UV-VIS spectroscopic techniques. Spectroelectrochemical (SPEL) properties and thermal analysis of the resulting polymers have been investigated using UV-VIS, Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). Furthermore, new compounds consisting of bis(2-thienyl) methyl (I and II) and bis(2-thienyl) ethyl (III) units linked by polyether bridges have been synthesized and their electrochemical polymerization was performed via constant potential electrolysis (CPE) in an electrolytic solution containing 0.1 M TBAPF6 dissolved in CH3CN. Also, I and II were polymerized via chemical oxidation which yielded broken &
#61552
-conjugated polymers except for III. The polymers were characterized using 1H-NMR and FT-IR spectroscopic techniques. In addition, copolymers of III with thiophene (Th) and pyrrole (Py) were studied with cyclic voltammetry (CV). SPEL behaviors of the products were investigated using UV-VIS spectroscopic technique.
36
Yang, Ning. "Polystyrene-based cationic copolymers : a study of their synthesis, characterization, and sizing mechanism." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/7074.
Full text
37
Stegmann, Jacobus Christiaan. "RAFT-mediated synthesis of graft copolymers via a thiol-ene addition mechanism." Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/18700.
Full textAbstract:
Thesis (MSc)--University of Stellenbosch, 2007.ENGLISH ABSTRACT: The main objective of this project was the controlled synthesis of graft copolymers via a thiol-ene addition mechanism. The Reversible Addition-Fragmentation chain Transfer (RAFT) process was used in all polymerization reactions with the aim to achieve a certain degree of control over the molecular weight. Several synthetic steps were required in order to obtain the final graft copolymer and each step was investigated in detail. Firstly, two RAFT agents (cyanovaleric acid dithiobenzoate and dodecyl isobutyric acid trithiocarbonate) were synthesized to be used in the various polymerization reactions of styrene and butyl acrylate. This was done successfully and the RAFT agents were used to synthesize low molecular weight polystyrene branches of the graft copolymer. Different molecular weights were targeted. It was found that some retardation phenomena were present especially at high RAFT agent concentrations. The polystyrene branches that were synthesized contained RAFT end-groups. Various pathways were explored to modify these RAFT end-groups to form thiol end-groups to be used in the thiol-ene addition reaction during the grafting process. The use of sodium methoxide for this purpose proved most successful and no evidence of the formation of disulfide bridges due to the initially formed thiols was detected. Allyl methacrylate (AMA) was chosen as monomer to be used for the synthesis of the polymer backbone because it has two double bonds with different reactivities. For the first time, RAFT was used to polymerize AMA via the more reactive double bond to obtain linear poly(allyl methacrylate) (PAMA) chains with pendant double bonds. However, at higher conversions, gelation occurred and the molecular weight distributions were uncontrolled. NMR was successfully used to study the tacticity parameters of the final polymer. Finally, the synthesis of the graft copolymer, PAMA-g-polystyrene, was carried out by means of the “grafting onto” approach. The thiol-functionalized polystyrene branches were covalently attached to the pendant double bonds of the PAMA polymer backbone via a thiol-ene addition mechanism in the presence of a free radical initiator. A Multi- Angle Laser Light Scattering (MALLS) detector was utilized in conjunction with Size- Exclusion Chromatography (SEC) to obtain molecular weight data of the graft copolymer. The percentage grafting, as determined by 1H-NMR, was low.
AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie projek is die beheerde sintese van ‘n entkopolimeer via ‘n merkaptaan-een addisiereaksie. Die sogenaamde “Reversible Addition-Fragmentation chain Transfer” (RAFT) proses is in al die polimerisasiereaksies gebruik met die doel om ‘n mate van beheer oor die molekulêre massa van die polimere te verkry. Verskeie stappe (waarvan elkeen ten volle ondersoek is) was nodig om die finale entkopolimeer te verkry. Eerstens is twee RAFT-agente (sianovaleriaansuur ditiobensoaat en dodekielisobottersuur tritiokarbonaat) gesintetiseer vir gebruik in verskeie polimerisasiereaksies van stireen en butielakrilaat. Hierdie stap was suksesvol en die RAFT-agente is toe gebruik vir die sintese van lae molekulêre massa polistireensytakke vir die entkopolimeer. Die molekulêre massas van die sytakke is gevarieer en daar is gevind dat vertragings in die polimerisasiereaksies voorgekom het, veral by hoë konsentrasies van die RAFT-agente. Die polistireensytakke wat gemaak is, besit almal ‘n RAFT-eindgroep. Verskeie roetes is bestudeer ten einde die RAFT-eindgroepe tot merkaptaan-eindgroepe te modifiseer om sodoende tydens ‘n merkaptaan-een addisiereaksie gebruik te word. Die gebruik van natriummetoksied was hier die suksesvolste en daar was geen teken van die vorming van disulfiedbrûe as gevolg van die oorspronklik gevormde merkaptane nie. Allielmetakrilaat (AMA) is gekies as die monomeer wat gebruik sou word vir die sintese van die polimeerruggraat omdat die monomeer twee dubbelbindings met verskillende reaktiwiteite besit het. Vir die eerste keer is RAFT gebruik vir die polimerisasie van AMA via die meer reaktiewe dubbelbinding om lineêre poli(allielmetakrilaat) (PAMA) kettings met dubbelbindings in die sygroepe te verkry. Gelvorming en onbeheerde molekulêre massaverspreiding het egter by hoër monomeeromsettings voorgekom. KMR is susksekvol gebruik om die taktisiteitsparameters van die finale polimeer te bestudeer. Ten slotte is die sintese van die entkopolimeer, PAMA-g-polistireen, uitgevoer deur die aanhegting van voorafgevormde sytakke. Die polistireensytakke met die merkaptaaneindgroepe is kovalent geheg aan die dubbelbindings in die sygroepe van die PAMA-polimeerruggraat via ‘n merkaptaan-een addisiemeganisme in die teenwoordigheid van ‘n vrye radikaalinisieerder. ‘n Kombinasie van gelpermeasiechromatografie en multi-hoeklaserligverstrooiing is gebruik om die molekulêre massa van die entkopolimeer te bepaal. Die persentasie sytakke soos bepaal deur 1H-KMR was laag.
38
Wright, Trevor. "NMR studies on the mechanism of iodine mediated polymerisation." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17967.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2011.ENGLISH ABSTRACT: In reverse iodine transfer polymerisation (RITP), chain transfer agents (CTAs) are generated in situ from the reaction between 2,2’-azobis(isobutyronitrile) (AIBN) and molecular iodine. This stage of RITP is the inhibition period, which ends when all iodine has been consumed. The evolution of CTAs was studied for the polymerisation reactions of n-butyl acrylate and styrene respectively. RITP of n-butyl acrylate was performed at 70 °C. In situ 1H nuclear magnetic resonance (NMR) experiments were carried out to study the evolution of CTAs during the inhibition period of n-butyl acrylate polymerisation and the structures A-I and A-Mn-I (where A represents the moiety originating from AIBN, M represents the monomer unit and n is the mean number degree of polymerisation) were observed. A polymer with the general structure A-Mm-I is formed. The molecular weight of poly(n-butyl acrylate) (PnBA) was evaluated with size exclusion chromatography (SEC) and NMR. Structural analysis of PnBA was done using NMR spectroscopy and matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) mass spectrometry. Similar conditions to those used for n-butyl acrylate polymerisation were used for RITP of styrene. The evolution of CTAs during the inhibition period of styrene polymerisation was studied using in situ 1H NMR. The inhibition period of styrene polymerised by RITP was much shorter than expected. This is due the consumption of iodine in the reaction between styrene and iodine which reversibly forms 1,2-diiodo-ethyl benzene. The CTAs A-I and A-Mn-I are formed, as well as 1-phenylethyl iodide (1-PEI). The molecular weight of polystyrene (PS) was determined using SEC and NMR and the functionality was evaluated using 1H NMR. The structure of PS was confirmed with 1H NMR and MALDI-ToF mass spectrometry. By increasing the temperature of the reaction, the inhibition period can be shortened. Both polymerisation systems retain control over molecular weight with an increase in temperature, however, n-butyl acrylate is limited due to the possible formation of mid-chain radicals. The formation of an A–Mm–A population (direct combination of the initiator and styrene) in RITP of styrene results in more initiator being consumed than for n-butyl acrylate, despite limited conversion of styrene to polymer.
AFRIKAANSE OPSOMMING: In omgekeerde-jodium-oordrag polimerisasie, is die kettingoordragagente gegenereer in situ van die reaksie tussen 2,2’-azobis(isobutironitriel) (AIBN) en molekulêre jodium. Hierdie fase van RITP is die inhibisie tydperk wat eindig wanneer alle jodium verbruik is. Die evolusie van kettingoordragagente is vir die polimerisasiereaksies van butielakrilaat en stireen onderskeidelik bestudeer. Omgekeerde-jodium-oordrag polimerisasie van butielakrilaat was uitgevoer by 70 °C. In situ 1H kernmagnetieseresonans (KMR) eksperimente is uitgevoer om die evolusie van die kettingoordragagente te bestudeer tydens die inhibisie van butielakrilaat polymerisasie en die strukture A-I en A-Mn-I (waar A die gedeelte voorstel wat afkomstig is van AIBN, M die monomeer-eenheid en n die gemiddelde aantal polymerisasiegraad verteenwoordig) is ge-identifiseer. 'n Polimeer met die algemene struktuur A-Mm-I is gevorm. Die molekulêre gewig van poli(butielakrilaat) (PnBA) was geëvalueer deur grootte-uitsluitings chromatografie en KMR spektroskopie. Strukturele ontleding van PnBA is gedoen deur die KMR spektroskopie en matriks ge-assisteerde laser desorpsie/ionisasie tyd-van-vlug massaspektroskopie. Soortgelyke kondisies as dié wat gebruik word vir butielakrilaat polymerisasie, is gebruik vir omgekeerde-jodium-oordrag polimerisasie van stireen. Die evolusie van die ketting oordrag agente gedurende die inhibisie periode van stireen polymerisasie is deur in situ 1H KMR bestudeer en die inhibisie periode is baie korter as verwag. Dit is as gevolg van die opname van jodium in die reaksie tussen stireen en jodium wat omkeerbare stireen-di-jodied tot gevolg hê. Die ketting oordrag agente A-I en A-Mn-I is gevorm, sowel as 1-feniel-etiel jodied. Die molekulêre massa van polistireen (PS) is bepaal met behulp van grootte-uitsluitings chromatografie en KMR spektroskopie en die funksioneering is geëvalueer met behulp van 1H KMR. Die struktuur van PS is bevestig deur 1H KMR en matriks ge-assisteerde laser desorpsie/ionisasie tyd-vanvlug massaspektroskopie. Deur die verhoging van die temperatuur van die reaksie, kan die inhibisie periode verkort word. Beide polimerisasie sisteme behou beheer oor die molekulêre massa met 'n toename in temperatuur, alhoewel butielakrilaat beperk word as gevolg van die moontlike vorming van middel kettingradikale. Die vorming van die A-Mm-A spesie (direkte kombinering van AIBN en stireen) in omgekeerdejodium- oordrag polimerisasie van stireen veroorsaak dat meer AIBN verbruik word as butielakrilaat, ten spyte van die beperkte omskakeling van stireen tot polimeer.
39
Münter, Sylvia Gabriele. "Analysing the role of a cellular mechanism in HIV infection and evaluation of novel antiviral compounds." Paris 11, 2004. http://www.theses.fr/2004PA112103.
Full textAbstract:
VIH est responsable du syndrome d'immunodéficience acquise (SIDA). L'étape fondamentale pour découvrir de nouvelles stratégies antivirales reste la compréhension de la pathogénie du SIDA ainsi que les mécanismes moléculaires de l'interaction du virus avec l'hôte. Une caractéristique des lentivirus est le transport actif du complexe de pré-intégration (PIC) dans le noyau de la cellule hôte. Le mécanisme de ce transport n'est pas connu, mais Vpr (viral protein R) pourrait être impliqué dans ce processus. Vpr reste associée au PIC jusqu'à la translocation du génome à travers la membrane nucléaire. Par ailleurs, il a été montré que Vpr est capable d'intéragir avec le complexe du pore nucléaire (NPC). Cela laisse soupçonner que cette interaction est à la base de l'import nucléaire du PIC. Il a également été montré que le cytosquelette joue un rôle prépondérant dans le transport de particules virales. Dans cette perspective, nous avons observé que la membrane nucléaire est entourée d'actine. Nous avons mis au point une nouvelle approche pour visualiser l'actine dans les cellules vivantes, ce qui nous a permis de visualiser un réservoir d'actine qui polymérise autour de l'enveloppe nucléaire ainsi que dans les invaginations de cette membrane. Nous avons montré que des enveloppes nucléaires isolées suffisent à initier la polymérisation de filaments d'actine in vitro. Nos résultats démontrent que la dynamique de l'actine périnucléaire est orchestrée par l'enveloppe nucléaire elle-même. C'est donc via la liaison de Vpr au NPC que le virus pourrait exploiter la présence de l'actine comme stratégie pour pénétrer dans le noyau en dépit de la barrière que constitue l'enveloppeHIV is the causative agent of the acquired immunodeficiency syndrome (AIDS). For the development of novel antiviral compounds, understanding of the lifecycle as well as the molecular mechanisms of host pathogen interactions are a prerequisite. A particular feature of lentiviruses is the active transport of the pre-integration complex (PIC) into the nucleus. The mechanism remains elusive, yet in the case of HIV Vpr is one candidate possibly implicated in the process. The protein stays associated to the PIC until nuclear translocation. It has been shown, that Vpr binds to the nuclear pore complex. This interaction might therefore be the link mediating import of the PIC. Moreover the cytoskeleton has been shown to play a major role in cytoplasmic transport of viral particles. In this context, we observed the nuclear envelope (NE) to be embedded in a perinuclear actin shell and displaying highly dynamic nuclear invaginations. We developed a novel approach to visualize actin inside living cells and thus we could show a high turnover actin pool around the NE and inside NE invaginations of living cells. Although reported in different cell types, the possible role of perinuclear actin filaments in the dynamic structural plasticity of the NE remains unresolved. We could show that NE-membranes alone are sufficient to nucleate polymerizing actin filaments in vitro, involving both actin recruitment to their surface, and filament growth. Accordingly, our results demonstrate that perinuclear actin dynamics are orchestrated by the NE itself. By binding of Vpr to the NPC, the virus could possibly exploit this pool of polymerizing actin as a new strategy to overcome the nuclear membrane
40
Sörensen, Nicolai [Verfasser], Michael [Akademischer Betreuer] Buback, and Philipp [Akademischer Betreuer] Vana. "Kinetics and Mechanism of Cu-Catalyzed Atom Transfer Radical Polymerization / Nicolai Sörensen. Betreuer: Michael Buback. Gutachter: Michael Buback ; Philipp Vana." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://d-nb.info/107815080X/34.
Full text
41
Sörensen, Nicolai Verfasser], Michael [Akademischer Betreuer] [Buback, and Philipp [Akademischer Betreuer] Vana. "Kinetics and Mechanism of Cu-Catalyzed Atom Transfer Radical Polymerization / Nicolai Sörensen. Betreuer: Michael Buback. Gutachter: Michael Buback ; Philipp Vana." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://nbn-resolving.de/urn:nbn:de:gbv:7-11858/00-1735-0000-0023-9662-7-2.
Full text
42
Virtanen, Otto L. J. [Verfasser], Walter [Akademischer Betreuer] Richtering, and Sebastian [Akademischer Betreuer] Seiffert. "Insight into precipitation polymerization of N-isopropylacrylamide : reaction mechanism, particle formation and particle structure / Otto L. J. Virtanen ; Walter Richtering, Sebastian Seiffert." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130792501/34.
Full text
43
Meiser, Wibke [Verfasser], Michael [Akademischer Betreuer] Buback, and Philipp [Akademischer Betreuer] Vana. "Investigation of the Kinetics and Mechanism of RAFT Polymerization via EPR Spectroscopy / Wibke Meiser. Gutachter: Michael Buback ; Philipp Vana. Betreuer: Michael Buback." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1044074043/34.
Full text
44
Meiser, Wibke Verfasser], Michael [Akademischer Betreuer] [Buback, and Philipp [Akademischer Betreuer] Vana. "Investigation of the Kinetics and Mechanism of RAFT Polymerization via EPR Spectroscopy / Wibke Meiser. Gutachter: Michael Buback ; Philipp Vana. Betreuer: Michael Buback." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://nbn-resolving.de/urn:nbn:de:gbv:7-11858/00-1735-0000-000D-FB50-3-1.
Full text
45
Koss, Hans [Verfasser], and Michael [Akademischer Betreuer] Schleicher. "Mechanism of actin polymerization with yeast formin Bni1p : effect of the KCI concentration on the FH2 mediated actin nucleation / Hans Koss. Betreuer: Michael Schleicher." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/102966160X/34.
Full text
46
Huser, Julien. "FUI Ecoating. Comprehension of the Scale Formation Mechanism during the Suspension Polymerization of Vinyl Chloride Monomer and Development of a Durable Protective Polymer Coating." Thesis, Mulhouse, 2013. http://www.theses.fr/2013MULH4032.
Full textAbstract:
La production de poly(chlorure de vinyle) (PVC) sous forme de suspension chez INEOS ChlorVinyls est réalisée en réacteur fermé agité, dont les parois sont en émail ou en acier inoxydable. Il se forme en cours de polymérisation un dépôt de PVC (croûte) sur les parois du réacteur qui génère de nombreux inconvénients. Afin de limiter cet encroûtement, INEOS ChlorVinyls et l’ensemble des producteurs de PVC appliquent à chaque batch (par exemple pour INEOS ChlorVinyls 50 fois par jour pour ses 22 réacteurs) un revêtement organique. L’application systématique du revêtement et la formation de croûtes ont des conséquences économiques non négligeables (arrêts de production, coût de main d’œuvre et matière, coût de traitement des déchets, qualité du PVC contaminé par le revêtement…).La compréhension du phénomène d’encroûtement en vue de développer un revêtement permanent devient donc nécessaire pour améliorer la qualité des produits, diminuer les coûts et dégager un avantage concurrentiel favorable à INEOS vis-à-vis de ses concurrents. Le sujet de thèse a été divisé en deux parties bien distinctes avec premièrement l’étude du mécanisme d’encroûtement et la mise en place d’un scénario permettant d’expliquer de manière physique et chimique la formation de la croûte sur les parois du réacteur. Une seconde partie a été dédiée au développement d’un revêtement polymère avec la sélection d’un système résistant au milieu réactionnel de polymérisation en suspension du chlorure de vinyle puis à l’optimisation de l’adhésion du revêtement polymère sur acier inoxydable afin d’obtenir des performances maximales et durablesThe suspension synthesis of PolyVinyl Chloride (S-PVC) at the INEOS ChlorVinyls facility in Mazingarbe (FRANCE) is realized thanks to a closed-reactor technology with reactor walls made of stainless steel or enamel. One of the major problems during the production of PVC by suspension polymerization is the formation of a deposit (called crust or scale) on the reactor walls. The formation of scale leads to numerous sorts of drawbacks like a decrease of the reactors’ productivity, the need to clean the reactors after each batch, the exposure of the operators to VinylChloride Monomer (VCM) which is classified CMR, some quality issues… At the moment, a coating is applied before each batch (50 times per day for the 22 reactors at Mazingarbe) in order to lower the amount of scale formed during the S-PVC batch. The application of the coating added to the formation of scale leads to important extra costs. The comprehension of the scale formation mechanism with the aim of then developing a durable protective coating becomes a priority in order to increase the final product quality, lower the costs and gain a competitive advantage for INEOS ChlorVinyls. The Ph.D. subject was divided into two parts with the first year dedicated to the comprehension of the scale formation mechanism and the establishment of a complete scenario explaining the formation of scale from a chemical and physical point of view. The second part of this project was dedicated to the development of a polymer coating with the selection of an adapted polymer candidate and then the optimization of its adhesion onto stainless steel in order to obtain the optimal performances and the durability of the coating
47
Branka, Pilić. "Perkolacioni procesi pri polimerizaciji olefina pomoću jedinjenja prelaznih metala." Phd thesis, Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, 2006. https://www.cris.uns.ac.rs/record.jsf?recordId=71274&source=NDLTD&language=en.
Full textAbstract:
Prema postojećem tumačenju Ziegler-Natta polimerizacije, smatra se da se prekursor prelaznog metala (Mt) aktivira pomoću alkila metala, a da se rast polimernog lanca ostvaruje umetanjem monomera između Mt i rastućeg polimernog lanca. Postoje mnoga neslaganja eksperimentalnih činjenica sa tumačenjem polimerizacije mehanizmom insertacije. U ovom radu predložen je novi mehanizam polimerizacije olefina pomoću jedinjenja prelaznih metala perkolacijom naelektrisanja (CPM): makromolekulski lanac nastaje polimerizacijorm grozda monomera (nM) koji je adsorbovan na nosaču (S) između dva adsorbovana prelazna metala, jednog u višem (Mt+4), a drugog u nižem oksidacionom stanju (Mt+2):( Mtn+1...nM...Mtn+1)/S →(MtnMtn)/S + polimer.Novi mehanizam polimerizacije perkoracijom naelektrisanja potvrđen je eksperimentalnim podacima, matematičkim proračunima i kompjuterskim simulacijama. U radu je prvo ukazano na značaj dosadašnjih istraživanja i dat je prikaz pojedinih eksperimentalnih činjenica koje potvrđuju perkolacioni model polimerizacije. Po principu Monte-Carlo simulacija, napravljen je novi specijalni kompjuterski program "Lattice" koji omogućuje simulaciju polimerizacije olefina pomoću CPM. U radu je dat detaljan opis kompjuterskog programa "Lattice" i ojašnjeno je na koji način se eksperimentalni parametri prevode u parametre perkolacionog modela polimerizacije. Na osnovu matematičkog proračuna i kompjuterske simulacije (primenom teorije Kobozeva) predviđen je uticaj sadržaja prelaznog metala na nosaču na produktivnost metala i nosača, što je potvrđeno eksperimentalnim podacima. U radu je prikazano na koji način promene: tipa nosača, početne površinske koncentracije monomera, koncentracije prelaznim metala redosledu dodavanja reagujućih komponenti, utiču na grafiku brzina polimerizacije - vreme. Primenom perkolacionog modela polimerizacije objašnjene su eksperimentalne činjenice koje do sad nisu mogle biti potpuno objašnjene primenom mehanizma insertacije.According the current explanation of Ziegler-Natta polymerization, transition metal (Mt)is activated by alkyl group and vacant orbital are formed. It is belived that polymerchain propagates by monomer insertion between Mt and growing polymer chain. It has also been known that by using existing insertion mechanism of the polymerization,some experimentally proved facts cannot be explained completely. In this paper newcharge percolation mechanism (CPM) of olefin polymeiization by supported Mtcomplexes is presented: a macromolecular chain is formed polymerization ofmonomer cluster (nM) adsorbed at the support (S) between two immobilised Mt ions,one in the higher (Mt+4) and the other in the lower (Mt+2) oxidation state:( Mtn+1...nM...Mtn+1)/S →(MtnMtn)/S + polymer.New CPM has been confirmed by published experimental data, by calculating and by computer simulation. First it has been clarified the signifigance of the existingexperiment and some experimental facts wich are confrlmed by CPM are shown. A special computer program "Lattice" has been developed to simulate olefinpolymerization based on CPM using Monte Carlo procedure. In this work it is explaniedhow the polymerization parametar from real experiments are transfered to percolationand simulation parametars. The effects of thesurface concentration of active centres onmetal productivities and support productivites has been predicted by the calculating and computer simulation (using catalytic theory of Kobozev) and confirmed by realexperimental data. In this work it is also shown how the polymer structure and tipe ofthe curve polymerization rate/time depend on reaction conditions (Mt concentration, tipe of the support, Mt/S ratio, sequence of chemical components addition, time). At the end the experimental facts which couldn't have been explained completaly ty insertionmechanism are explanied using CpM.
48
Alsharaeh, Edreese Housni. "Gas Phase Studies of Molecular Clusters Containing Metal Cations, and the Ion Mobility of Styrene Oligomers." VCU Scholars Compass, 2004. http://scholarscompass.vcu.edu/etd/1200.
Full textAbstract:
This study is divided into three parts. Part I deals with the mechanism of the self-initiated polymerization (or thermal polymerization) of styrene in the gas phase. In this work, we present the first direct evidence for the thermally self-initiated polymerization of styrene in the gas phase. Our approach is based on on-line analysis of the gas phase Oligomers by mass-selected ion mobility. The mobility measurements provide structural information on the ionized oligomers based on their collision cross-sections (Ω) which depend on the geometric shapes of the ions. Theoretical calculations of possible structural candidates of the Oligomers ions are then used to compute angle averaged Ω for comparison with the measured ones. The agreement between the measured and calculated Ω of the candidate structures provides reliable assignments to the structures of the oligomers. Furthermore, collisional-induced dissociations of the mass-selected oligomer ions provide further support for the structures obtained from the mobility measurements. Our results indicate that the gas phase polymerization of styrene proceeds via essentially the same initiation mechanism (the Mayo mechanism) as in condensed phase polymerization. The structural evidence, the mechanism of formation and the observed fragmentation pathway of the growing dimers and trimers in the gas phase are presentedIn Part II the solvation of a variety of metal cations by benzene clusters have been studied using laser vaporization, cluster beam and time-of-flight mass spectrometry techniques. In this work strong magic numbers were observed for clusters containing 10, 13 and 14 benzene molecules depending on the nature of the metal cation involved. The metal cations exhibiting preference solvation by 14 benzene molecules show a strong tendency to form sandwich structures with two benzene molecules. The interpretation of these results in view of the proposed structures and the growth patterns of the clusters are presented. In Part III, the work is focused on the investigation of the intracluster ion molecule reactions following the generation of Mg+ within the polar clusters (water, methanol, ether and acetonitrile).
49
Brown, Nicole Robitaille. "Understanding the Role of N-Methylolacrylamide (Nma) Distribution in Poly(Vinyl Acetate) Latex Adhesives." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/26446.
Full textAbstract:
This work addresses the distribution of N-methylolacrylamide (NMA) units in crosslinking poly(vinyl acetate) (PVAc) adhesives. In this case, distribution refers to the three potential locations of polymerized NMA units in a latex: the water-phase, the surface of polymer particles, and the core of the polymer particles. The objective is to identify the distribution of NMA in three latices and to determine whether NMA distribution correlates with durability related performance. NMA distribution was studied via a series of variable temperature solution NMR experiments, while the durability-related performance was studied via mode I fracture mechanics tests.
Studying the distribution of NMA required the use of isotopically labeled NMA. Both 15N-NMA and 13C, 15N-NMA were synthesized. Three NMA/vinyl acetate (VAc) latices were prepared. The NMA feed strategy was varied during each of the three emulsion copolymerizations. Latex characterization methods including differential scanning calorimetry (DSC), rheometry, particle size analysis, and scanning electron microscopy (SEM) were used to study the three latices.
The solution NMR method to identify NMA distribution was performed on untreated latices and on washed latices. Washing techniques included membrane dialysis and centrifugation. Results revealed that the three latices had different NMA distributions, and that the distributions were related to the expected differences in microstructure. Latex 3 had ~ 80% core-NMA, while Latex 2 had ~ 80% surface-NMA. Latex 1 had a high proportion of surface-NMA (~60%), but also had the highest proportion of water-phase NMA (~ 20%). This high proportion of water-phase NMA could be responsible for the unique morphology Latex 1 exhibited in SEM studies.
Mode I opening fracture mechanics studies were used to study adhesive performance. Specimens were analyzed after exposure to accelerated aging treatments. Latex 2 and Latex 3 exhibited very similar results, despite having very different NMA distributions. All three latices showed good durability related performance. In Latex 2 and Latex 3, the critical strain energy release rates (Gc) after accelerated aging treatments were statistically the same as the Gc of the control specimens. The most interesting finding was that the Latex 1 Gc values were significantly higher after accelerated aging. Latex 1 also had the highest proportion of water-phase NMA. Bondline images and SEM micrographs both indicated that the integrity of Latex 1 was least affected by the accelerated aging treatments.Ph. D.
50
Dentzer, Laetitia. "Compréhension du suivi de polymérisation d’un système réactif phénolique fortement dilué en présence d’une phase latex pour l'élaboration d’un adhésif sans formaldéhyde." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI043.
Full textAbstract:
Un nouveau système réactif de type phénolique plus respectueux de l’environnement, c’est-à-dire sans phénol, résorcinol ou formaldéhyde a été caractérisé lors de ces travaux de thèse. Ce système implique la copolymérisation du phloroglucinol et du téréphthalaldéhyde (TPA) en solution aqueuse très diluée. Dans un premier temps, une recherche bibliographique a permis de sélectionner les techniques expérimentales pertinentes pour suivre l’avancement de ces systèmes évolutifs complexes en solution. La combinaison d’analyses chromatographiques et spectroscopiques a été nécessaire pour la caractérisation de la partie soluble du système phloroglucinol-TPA. Un mécanisme de polymérisation conduisant à des espèces linéaires a été proposé pour des temps courts de réaction. L’augmentation de la fraction insoluble lors de la réaction dans les analyses nécessitant une étape de solubilisation met en évidence un second mécanisme de réaction des oligomères entre eux. Une méthode de suivi de l’état du système par mesures rhéologiques a été également développée pour le contrôle de production. Dans un deuxième temps, ce système a été utilisé pour la conception d’un adhésif Phloroglucinol-TPA-Latex. Celui-ci a été étudié à l’état liquide lors du ‘mûrissement’ et à l’état solide après réticulation sous la forme de films libres pour différentes situations modèles. La stabilité de l’adhésif lors du ‘mûrissement’ a été vérifiée même si des réactions de condensation au sein du système Phloroglucinol-TPA se poursuivent. Après réticulation, la morphologie à deux phases des films observée est spécifique à la nature de la phase latex. Il a été conclu que le nouveau système phloroglucinol-TPA a un comportement similaire à celui du système résorcinol-formaldéhyde en termes de mécanismes de réaction et lors de son utilisation en présence de latex. Celui-ci a donc la capacité de remplacer le système initial dans l’élaboration d’un nouvel adhésif plus respectueux de l’environnementA new phenolic-type reactive system more environment friendly, namely phenol-, resorcinol- or formaldehyde-free, was characterized during this Ph.D. This system consists in the copolymerization of Phloroglucinol and Terephthalaldehyde (TPA) in highly diluted water solution conditions. First, a literature study allowed a selection of relevant experimental technics in order to follow the advancement of these complex systems in solution. The combination of chromatographic and spectroscopic analyses is required to characterize the soluble part of the Phloroglucinol-TPA based system. A mechanism of reaction to synthesize linear oligomers was proposed for short reaction times. The increase of the non-soluble part during the reaction in the analyses made after a solubilization step leaded to the conclusion of another type of mechanism where the oligomers are involved. A monitoring method to follow the state of the system by rheological measurement was also developed for the production process. Secondly, this system was used in the preparation of an adhesive based on Phloroglucinol, TPA and Latex. This adhesive was studied in a liquid state during it ‘maturation’ and in a solid state after curing resulting in films from several model systems. The stability of the system during maturation was checked even if condensation reactions of the Phloroglucinol-TPA still took place. After curing, a two-phase morphology of the films was observed which was found to be specific to the nature of the latex phase. It was concluded that the new Phloroglucinol-TPA system has a similar behavior to the one of Resorcinol-Formaldehyde in terms of mechanism and use in presence of latex. It showed the capability to replace the initial system in the preparation of a new adhesive more environment friendly