Littérature scientifique sur le sujet « Atom Transfer Radical Polymerization Techniques »

Electrochemistry may seem an outsider to the field of polymer science and controlled radical polymerization. Nevertheless, several electrochemical methods have been used to determine the mechanism of atom transfer radical polymerization (ATRP), using both a thermodynamic and a kinetic approach. Indeed, electron transfer reactions involving the metal catalyst, initiator/dormant species, and propagating radicals play a crucial role in ATRP. In this mini-review, electrochemical properties of ATRP catalysts and initiators are discussed, together with the mechanism of the atom and electron transfer in ATRP.1 Introduction2 Thermodynamic and Electrochemical Properties of ATRP Catalysts3 Thermodynamic and Electrochemical Properties of Alkyl Halides and Alkyl Radicals4 Atom Transfer from an Electrochemical and Thermodynamic Standpoint5 Mechanism of Electron Transfer in ATRP6 Electroanalytical Techniques for the Kinetics of ATRP Activation7 Electrochemically Mediated ATRP8 Conclusions

Abstract Electron spin resonance (ESR, aka electron paramagnetic resonance, EPR) investigations have been conducted on radicals formed during radical polymerizations and provide a detailed characterization of the active radical species. Active propagating radicals can be observed during actual radical polymerizations by ESR/EPR. The chain lengths of the observed radicals were estimated by a combination of atom transfer radical polymerization (ATRP) and ESR/EPR. The structures of the chain end radicals were determined by analysis of the ESR/EPR spectra. An increase in the dihedral angles between terminal p-orbital of radical and Cβ–H bonds was observed with increasing chain lengths of methacrylate polymers. Radical transfer reactions were observed during radical polymerization of acrylates. A combination of ATRP and ESR/EPR clarified a 1,5-hydrogen shift mechanism of the radical transfer reactions using model adamantyl acrylate radicals. Penultimate unit effects were also observed. Time-resolved ESR/EPR (TR ESR) spectroscopy clarified the initiation processes of an alternating copolymerization of styrene with maleic anhydride and the copolymerization of styrene with 1,3-butadiene. Several unsolved problems in conventional radical polymerization processes have been clarified using combinations of ATRP with ESR/EPR and TR ESR. Characterization of the radicals in radical polymerizations using various ESR techniques would definitely provide interesting and useful information on conventional radical polymerizations.

Catalysts are essential for mediating a controlled polymerization in atom transfer radical polymerization (ATRP). Copper-based catalysts are widely explored in ATRP and are highly efficient, leading to well-controlled polymerization of a variety of functional monomers. In addition to copper, iron-based complexes offer new opportunities in ATRP catalysis to develop environmentally friendly, less toxic, inexpensive, and abundant catalytic systems. Despite the high efficiency of iron catalysts in controlling polymerization of various monomers including methacrylates and styrene, ATRP of acrylate-based monomers by iron catalysts still remains a challenge. In this paper, we review the fundamentals and recent advances of iron-catalyzed ATRP focusing on development of ligands, catalyst design, and techniques used for iron catalysis in ATRP.

The ability to conduct controlled radical polymerizations (CRP) in homogeneous aqueous media is discussed. Three main techniques, namely stable free radical polymerization (SFRP), with an emphasis on nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) are examined. No examples exist of homogeneous aqueous NMP polymerization, but mixed water/solvent systems are discussed with specific reference to the NMP of sodium 4-styrenesulfonate. Aqueous ATRP is possible, although monomer choice is limited to methacrylates and certain styrenics. Finally, homogeneous aqueous RAFT polymerizations are examined. We demonstrate the greater versatility of this technique, at least in terms of monomer variety, by discussing the controlled polymerization of charged and neutral acrylamido monomers and of a series of ionic styrenic monomers. Many of these monomers cannot/have not been polymerized by either NMP or ATRP.

Atom transfer radical polymerization (ATRP) is one of the most successful techniques for the preparation of well-defined polymers with controllable molecular weights, narrow molecular weight distributions, specific macromolecular architectures, and precisely designed functionalities. ATRP usually involves transition-metal complex as catalyst. As the most commonly used copper complex catalyst is usually biologically toxic and environmentally unsafe, considerable interest has been focused on iron complex, enzyme, and metal-free catalysts owing to their low toxicity, inexpensive cost, commercial availability and environmental friendliness. This review aims to provide a comprehensive understanding of iron catalyst used in normal, reverse, AGET, ICAR, GAMA, and SARA ATRP, enzyme as well as metal-free catalyst mediated ATRP in the point of view of catalytic activity, initiation efficiency, and polymerization controllability. The principle of ATRP and the development of iron ligand are briefly discussed. The recent development of enzyme-mediated ATRP, the latest research progress on metal-free ATRP, and the application of metal-free ATRP in interdisciplinary areas are highlighted in sections. The prospects and challenges of these three ATRP techniques are also described in the review.

AbstractDuring the last decade, atom transfer radical polymerization (ATRP) received significant attention due to its exceptional capability of synthesizing polymers with pre-determined molecular weight, well-defined molecular architectures and various functionalities. It is economically and environmentally attractive to adopt ATRP to aqueous dispersed media, although the process is challenging. This review summarizes recent developments of conducting ATRP in aqueous dispersed media. The issues related to retaining “controlled/living” character as well as colloidal stability during the polymerization have to be considered. Better understanding the ATRP mechanism and development of new initiation techniques, such as activators generated by electron transfer (AGET) significantly facilitated ATRP in aqueous systems. This review covers the most important progress of ATRP in dispersed media from 1998 to 2009, including miniemulsion, microemulsion, emulsion, suspension and dispersed polymerization.

Telechelic polymers have been explored widely because they are precursors for preparing multi-block copolymers, grafted polymers, star polymers, and polymer networks [1-2]. A variety of telechelic polymers with terminals like hydroxy, carboxylic, epoxy groups and carbon–carbon double bond have been prepared by controlled radical polymerization (CRP) techniques including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT)[3-5].The CRP techniques can not only control the molecular weight but also can be carried out in the presence of many functional groups from monomers, initiators, or chain transfer agents (CTA).

Controlled/living radical polymerization (LRP) is a field of special interest because it allows tailoring well-defined macromolecular architectures such as telechelic, block, graft or star copolymers. Since the eighties, several techniques have been reported [such as the iniferter method, nitroxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), iodine transfer polymerization (ITP), and reversible addition-fragmentation chain transfer (RAFT)] giving rise to a huge number of publications and patents. This review aims at illustrating the contribution of fluorinated organic compounds in this area of research through the use of fluorinated initiators (dithiocarbamates, xanthates, tetraphenylethanes, alkoxyamines, fluorinated alkyl halides, and dithioesters) or other fluorinated molecules (ligands, solvents). Another point depicts the LRP of various fluorinated monomers (methacrylates, acrylates, styrenics, and alkenes). Finally, fluorinated block and graft copolymers prepared by LRP have been reported. A review with 165 references.

Self-assembled monolayers and surface-initiated polymer, or polymer brushes, have attracted attention as they form dense layers with much higher structural order than bulk or solution polymers. Another field of research which has emerged over the last two decades is the field of organic and polymer electronics. In this field molecular order and surface modification are of major influence on the device performance, hence that both self-assembled monolayers as polymer brushes have been investigated to find applications in organic electronic devices. After an introduction into the field self-assembled monolayers, polymer brushes and organic electronics, the first part of this thesis focusses on three applications of surface modification techniques for applications in devices. Alignment of the active material is crucial for high mobilities in organic electronics. Chapter 2 discusses the synthesis of a liquid crystalline surface-initiated polymer and its application to induce strong homeotropic alignment. The alignment is homogeneous over large areas and can be patterned by combining the polymerization with soft lithographic techniques. Mobilities of organic electronic materials can also be strongly influenced by dopants in the material. In field-effect transistors the positioning of the dopant is thought to be crucial, as the conductance predominantly takes place in only a small channel near the dielectric interface. In chapter 3 dopant functionalized monolayers and polymer brushes are presented which enable the localized deposition of dopants in the channel of organic transistors. It is shown that the mobility of charges and hence the device performance is affected by the introduction of this dopant layer. Polymer brushes have been suggested for the fabrication of highly ordered semiconducting polymers. In chapter 4 the use of a thiophene functionalized polymer brush is shown, that can be used as a template for the subsequent growth of highly conjugated surface grafted polythiophene layers. Thick polythiophene layers are obtained, that are low in roughness and show photoluminescence and polychromism upon doping. The second part (chapter 5 and 6) of this thesis presents new techniques for surface polymerizations. It is attractive to investigate reduction of reactor volume for polymer brush growth. Chapter 5 discusses a method to achieve volume reduction by back-filling the superfluous volume with beads. It is found that this influences the polymerization kinetics significantly. The combined advantages of less volume and enhanced reaction speeds enable reduction of the total amount of monomer needed by up to 90%. Chapter 6 presents a controlled way to convert initiators for atom transfer radical polymerization into initiators for nitroxide mediated polymerization. In this way mixed polymer brushes and block co-polymer brushes become accessible. This combination makes it an attractive tool to fabricate complex polymer architectures. The technologies used in this thesis show that the synthesis of polymer brushes enable the fabrication of complex architectures without the wastes normally associated with surface-initiated polymers. Combined with several functionalized polymer brushes with properties that enhance order, influence mobility or serve as template for the growth of surface attached conjugated polymers this shows the high potential for the application of surface-initiated polymers in organic electronics.

Ce travail concerne la modification de surface de nanoparticules magnétiques (MNP) par des copolymères réactifs renfermant des cycles azlactone, aux fins de l’élaboration de nano-supports destinés à l’immobilisation de biomolécules. Trois stratégies basées sur des techniques de polymérisation radicalaire contrôlée ont été mises en œuvre.Dans la première, un copolymère poly(méthacrylate de poly(éthylène glycol)-stat-2-vinyl-4,4-diméthylazlactone) (poly(PEGMA-stat-VDM)) a été préparé par polymérisation radicalaire par transfert d’atome (ATRP) selon la technique « grafting from » à partir des MNP et utilisé pour la bioconjugaison de thymine peptide nucleic acid (PNA). La présence de l’écorce polymère et l’immobilisation du PNA ont été confirmées par différentes techniques complémentaires (FTIR, VSM).La deuxième stratégie est basée sur l’élaboration de MNP greffées pour la bioconjugaison de l’acide folique, via l’ARTP du PEGMA et de la VDM. L’analyse par microscopie électronique à transmission (TEM) a montré qu’après bioconjugaison les MNP possèdent une très bonne aptitude à la dispersion en milieu aqueux.La troisième stratégie met en œuvre la technique «grafting onto » de copolymères poly(oxyde d’éthylène)-bloc-poly(2-vinyl-4,4-dimethylazlactone) (PEO-b-PVDM) pour la préparation de nanosupports magnétiques recyclables. Des copolymères à blocs PEO-b-PVDM ont été préparés par la technique de polymérisation RAFT puis greffés sur des MNP fonctionnalisées amino-silane. Les analyses en TEM et par spectroscopie de corrélation de photons ont révélé l’aptitude à la dispersion aqueuse et à la formation de nanoclusters. Les clusters ainsi obtenus ont été utilisés en tant que nanosupports magnétiques recyclables pour l’adsorption d’anticorps
We herein report the surface modification of magnetite nanoparticle (MNP) with copolymers containing active azlactone rings via a grafting ‘from’ and grafting ‘onto’ controlled radical polymerization (CRP) for use as a nano-solid support for immobilization with biomolecules. Three different approaches were presented as following. First, synthesis of poly(poly(ethylene glycol) methyl ether methacrylate-stat-2-vinyl-4,4-dimethylazlactone) (PEGMA-stat-VDM)-grafted MNP via a grafting ‘from’ atom transfer radical polymerization (ATRP) and its application as a platform for conjugating thymine peptide nucleic acid (PNA) monomer were presented. The presence of polymeric shell and the immobilization of thymine PNA on MNP core were confirmed by fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM) techniques. The second strategy is based on the synthesis of MNP grafted with PEGMA and VDM via ATRP for conjugation with folic acid (FA). The existence of PEGMA and VDM in the structure was characterized by FTIR, TGA and VSM. After the FA conjugation, Transmission Electron Microscopy (TEM) results indicated that the FA-conjugated MNP having high VDM content exhibited good dispersibility in water.Third, the synthesis of MNP grafted with poly(ethylene oxide)-block-poly(2-vinyl-4,4-dimethylazlactone) (PEO-b-PVDM) block copolymer via a grafting ‘onto’ strategy and its application as recyclable magnetic nano-support for adsorption with antibody were studied. PEO-b-PVDM diblock copolymers were first synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and then grafted onto amino-functionalized MNP. TEM images and photo correlation spectroscopy (PCS) indicated an improvement in the particle dispersibility in water after coating with the copolymers. The nanoclusters with PEO-b-PVDM copolymer coating were used as recyclable magnetic nano-supports for adsorption with antibody

Atom transfer radical polymerization (ATRP) has proven to be a powerful technique to obtain polymers with narrow polydispersities and controlled molecular weight. It also offers control over chain-ends. The technique is the most studied and utilized of thecontrolled/”living” radical polymerization techniques since a large number of monomerscan be polymerized under simple conditions. ATRP can be used to obtain polymer graftsfrom multifunctional substrates. The substrates can be either soluble (i. e. based ondendritic molecules) or insoluble (such as gold or silicon surfaces). The large number ofgrowing chains from the multifunctional substrates increases the probability of inter-and intramolecular reactions. In order to control these kinds of polymerizing systems, andsuppress side-reactions such as termination, the concentration of propagating radicalsmust be kept low. To elaborate such a system a soluble multifunctional substrate, based on 3-ethyl-3-(hydroxymethyl)oxetane, was synthesized. It was used as a macroinitiatorfor the atom transfer radical polymerisation of methyl acrylate (MA) mediated byCu(I)Br and tris(2-(dimethylamino)ethyl)amine (Me6-TREN) in ethyl acetate at room temperature. This yielded a co-polymer with a dendritic-linear architecture. Since mostsolid substrates are sensitive to the temperatures at which most ATRP polymerisations are performed, lowering the polymerization temperatures are preferred. ATRP at ambienttemperature is always more desirable since it also suppresses the formation of thermally formed polymer. The macroinitiator contained approximately 25 initiating sites, which well mimicked the conditions on a solid substrate. The polymers had low polydispersity and conversions as high as 65% were reached without loss of control. The solid substrateof choice was cellulose fibers that prior to this study not had been grafted through ATRP.As cellulose fibers a filter paper, Whatman 1, was used due to its high cellulose content.The hydroxyl groups on the surface was first reacted with 2-bromoisobutyryl bromidefollowed by grafting of MA. Essentially the same reaction conditions were used that hadbeen elaborated from the soluble substrate. The grafting yielded fibers that were very hydrophobic (contact angles>100°). By altering the sacrificial initiator-to-monomer ratiothe amount of polymer that was attached to the surface could be tailor. PMA with degreesof polymerization (DP’s) of 100, 200 and 300 were aimed. In order to control that thepolymerizations from the surface was indeed “living” a second layer of a hydrophilicmonomer, 2-hydroxymethyl methacrylate (HEMA), was grafted onto the surface. Thisdramatically changed the hydrophobic behavior of the fibers.

QC 20100524

Surface tethered bottle-brush co-polymers are prepared by ATRP grafting of the macroinitiator brush backbone onto plasmachemical deposited poly(vinylbenzyl chloride) initiator nanofilms, followed by ATRP growth of the side chains (bristles). Lateral force scanning probe microscopy demonstrates that poly(glycidyl methacrylate)-graft-poly(sodium 4-styrenesulfonate) bottle-brush decorated surfaces give rise to an enhancement in lubrication. Patterned polymer brushes are fabricated using molecular scratchcard lithography, where a functional top nanolayer (acting as a resist) is selectively removed using a scanning probe tip to expose underlying ATRP initiator sites. The lateral spreading of grafted polymer brush patterns across the adjacent functional resist surface is reversibly actuated by solvent exposure. Macroporous poly(vinylbenzyl chloride) scaffolds are used for ATRP initiation to generate polymer brushes and thereby actuate pore size. These functionalised macroporous scaffolds are fabricated by a decoupled two-step approach comprising plasmachemical deposition of the host material followed by spontaneous emulsion formation using amphiphilic species. Finally, charge nanopatterning onto polymer film surfaces is accomplished by using an SPM probe tip to create localised corona discharge electrification. The efficacy of surface charging is shown to correlate strongly to the polymer substrate hydrophilicity. Localised plasma generation using a scanning probe microscope tip is then demonstrated to actuate the movement of ATRP surface grafted polyelectrolyte and polyzwitterionic brushes. The raising or retraction of polymer brushes can be controlled by varying the SPM tip polarity.

Controlled radical polymerizations (CRPs) are among the most powerful methods to obtain polymers with well-defined properties and high commercial value. Atom transfer radical polymerization (ATRP) is probably the most widely used CRP, in academia and industry, thanks to its versatility and simplicity. In ATRP, a metal complex in a low oxidation state, MtzLm (typically a copper-amine system, [CuIL]+) reacts with a dormant polymeric chain Pn–X (where X = Cl, Br) to produce radicals Pn• that can propagate, in the bulk of the solution, by addition to monomer units. In this reaction, the copper complex is oxidized and binds to X–, generating the deactivating species [X-CuIIL]+, which traps the propagating species. ATRP equilibrium is shifted towards the dormant species Pn-X, so that Pn• concentration is very low, and the probability of radical-radical termination events is minimized. Growth of all chains begins virtually at the same time, thanks to the use of alkyl halide (RX) initiators that are more reactive than the dormant species, Pn-X. In such conditions, chain growth is homogenous, and it is possible to obtain polymers with predetermined molecular weight, narrow molecular-weight distribution and high chain-end fidelity. ATRP allows to tailor macromolecules with specific compositions, architectures and position of functional groups. The aim of this thesis is to contribute to both the understanding and development of ATRP catalyzed by copper complexes, using electrochemical methods as equally analytical tools and efficient means of triggering and controlling the polymerization. The work focused on spreading the use of such systems to efficiently control the polymerization of a series of important monomers. Moreover, the investigated ATRP systems can be considered also “green” for several reasons: (i) most of the work regards the study and development of the reaction in green solvents in which copper complexes generally have high catalytic activity; (ii) electrochemical methods for catalyst regeneration (electrochemically mediated ATRP, eATRP) allowed triggering the polymerization with low loadings of copper complexes; (iii) ionic liquids, a class of non-flammable and easily recyclable solvents, were explored as potential media for eATRP; (iv) the mechanism of catalytic halogen exchange was investigated and defined, abridging the synthesis of block copolymers. ATRP catalysts were investigated in the ionic liquid 1-butyl-3-methylimidazolium triflate ([BMIm][OTf]). Both Cu/L speciation and reactivity were found to be suitable for a well-controlled polymerization process. Polymerizations were conducted with electrochemical (re)generation of the active [CuIL]+ complex (eATRP). eATRP of methyl acrylate was investigated in detail by varying a series of parameters such as applied potential, temperature, degree of polymerization and catalyst load ([CuIITPMA]2+, TPMA = tris(2-pyridylmethyl)amine). Application of an electrochemical switch and chain extension with acrylonitrile via catalytic halogen exchange (cHE) proved the livingness of the polymerizations. Experiments triggered in recycled ionic liquid proved that eATRP tolerates well the recycled solvent; polymerizations exhibited good control and high conversion. Block copolymers (BCP) have relevance in a vast range of applications in everyday life. BCP of acrylonitrile (AN) and butyl acrylate (BA) were investigated as precursors for mesoporous carbons. Thus, eATRP of acrylonitrile was studied considering several aspects, including the effect of applied potential, degree of polymerization, C-X nature and initiator structure. A macroinitiator of PAN was then extended with BA to form PAN-b-PBA copolymer as a precursor for mesoporous carbons. BCP can be obtained also by extension of a PBA chain with AN via cHE, thus avoiding purification procedures and reactivity mismatch when crossing from a less reactive monomer to a more reactive one. cHE was proved to be an efficient tool of polymerization by both SARA and eATRP, in a range of solvents, including water. Methyl methacrylate (MMA) was polymerized thanks to cHE in [BMIm][OTf] and ethanol, to solve the issue of penultimate effect. Fine tuning of the electrolysis conditions afforded PMMA with low dispersion. Further improvements were obtained by using [CuIIPMDETA]2+ as an inexpensive and efficient catalyst in alternative to [CuIITPMA]2+. Tacticity analysis of PMMA obtained in [BMIm][OTf] and ethanol confirmed the poor ability of the ionic solvent to induce stereocontrol to the polymerization. Pyridinic complexes such as [CuIITPMA]2+ are stable in very acid conditions (pH = 1). This allowed unprecedented control over conditions of macromolecular growth in water. In addition, it opened a new avenue for the polymerization of ionic liquid monomers (ILMs), a class of building blocks that can give a plethora of new materials. The main reason preventing ATRP of ILM is a cyclization reaction involving the chain-end with the terminal halogen as a leaving group, as in the case of methacrylic acid. Application of three strategies previously developed for ATRP of methacrylic acid allowed to dramatically improve conversion and control over ILMs polymerization. (i) Using C-Cl chain end functionality, which is much more stable than C-Br, (ii) lowering further the pH to completely convert free carboxylate ions to carboxylic acid, which is a much weaker nucleophile, and (iii) enhancing the polymerization rate to avoid the negative contribution of the cyclization side reaction, allowed synthesis of well-controlled high molecular weight poly(ionic liquids), PILs, with degree of polymerization > 500. A simple (poly)halogenated organic initiator such as 2,2-dichloropropionic acid was used to produce linear homotelechelic PILs. Electrochemically mediated ATRP allowed exceptional control over CuI (re)generation. For this reason, it was decided to study the eATRP of vinyl chloride, which was considered impossible until now. The polymerization, triggered in a pressure-resistant electrochemical reactor, was controlled, fast and afforded an acceptable conversion. In addition to linear PVC, a star PVC was also synthesized, highlighting the flexibility of eATRP. In the star architecture, the electrochemical polymerization was by far superior to the chemical one (SARA ATRP). The success of this polymerization has categorically denied the SET-LRP mechanism and its assumptions. One of the crucial properties of electrochemical eATRP is the inert role played by the cathode material used for the regeneration of [CuIL]+. Any electrode material with good stability in the reaction medium can be used as a cathode. It was therefore decided to study the polymerization of an acrylate using the surface of a stainless steel (SS304) reactor exposed to the polymerization mixture as a cathode. In this way, the reactor has the dual function of electrode and place where the reaction takes place. The results showed that polymerization is fast, controlled and reaches high conversions. Moreover, the absence of release of metal ions during the reaction (Fe, Ni, Cr) confirmed that the polymerization takes place via electrochemical reduction of CuII to CuI, while SS304 acts only as an electron reservoir, not chemically involved in ATRP activation. Such simple and cheap electrochemical setup can make the scale-up of the eATRP a reality in the short term and open new economic prospects.
Le polimerizzazioni radicaliche controllate (CRP) sono riconosciute come i metodi più potenti per ottenere polimeri con struttura macromolecolare ben definita e alto valore commerciale. La polimerizzazione radicalica a trasferimento atomico (ATRP) è probabilmente la CRP più utilizzata, in accademia e industria, grazie alla sua versatilità e semplicità. Nell’ATRP, un complesso metallico a basso stato di ossidazione, MtzLm (tipicamente un sistema rame-ammina, [CuIL]+) reagisce con una catena polimerica dormiente Pn-X (dove X = Cl, Br) per produrre radicali Pn•. Questi propagando nel bulk della soluzione, crescono aggiungendo unità monomeriche. In questo processo, il complesso di rame viene ossidato e si lega a X-, generando la specie disattivante [X-CuIIL]+, che intrappola la specie propagante. L'equilibrio di ATRP è fortemente spostato verso la specie dormiente Pn-X, cosicché la concentrazione di radicali sia molto bassa e la probabilità di eventi di terminazione bimolecolare sia ridotta al minimo. La crescita inizia praticamente allo stesso tempo per tutte le catene grazie a iniziatori (alogenuro alchilico) molto efficienti (RX). In tali condizioni, la crescita delle catene è omogenea ed è possibile ottenere polimeri con peso molecolare predeterminato, distribuzione stretta dei pesi molecolari e alta ritenzione della funzionalità di fine catena. L’ATRP consente di costruire dunque macromolecole con specifiche composizioni, architetture e posizionamento dei gruppi funzionali. Lo scopo di questa tesi è di contribuire alla comprensione e allo sviluppo dell’ATRP catalizzata da complessi di rame, utilizzando metodi elettrochimici sia come strumenti analitici che come strumenti per eseguire e controllare la polimerizzazione. Il lavoro si è concentrato sulla diffusione dell'uso di tali sistemi per controllare in modo efficiente la polimerizzazione di una serie di monomeri rilevanti. I sistemi investigati per ATRP possono essere considerati anche "green" per diversi motivi: (i) la maggior parte del lavoro riguarda lo studio e lo sviluppo della reazione in solventi green, generalmente caratterizzati da un'elevata attività catalitica; (ii) i metodi elettrochimici per la rigenerazione del catalizzatore (ATRP mediata elettrochimicamente, eATRP) permette la polimerizzazione con limitata quantità di complessi di rame; (iii) i liquidi ionici, una nuova classe di solventi non infiammabili e facilmente riciclabili, sono stati esplorati come potenziali solventi per eATRP; (iv) il meccanismo di halogen exchange catalitico (cHE) è stato studiato e sviluppato, facilitando la sintesi di copolimeri a blocchi. I catalizzatori ATRP sono stati studiati nel liquido ionico 1-butil-3-metilimidazolio triflato. Sia la speciazione che la reattività di Cu/L sono risultate in linea per un processo di polimerizzazione ben controllato. Le polimerizzazioni sono state condotte con la (ri)generazione elettrochimica del complesso attivo [CuIL]+ (eATRP). L'eATRP del metil acrilato è stata studiata in dettaglio variando una serie di parametri come: potenziale applicato, temperatura, grado di polimerizzazione e carico di catalizzatore di Cu/TPMA (TPMA = tris(2-piridilmetil)ammina). Un interruttore elettrochimico e l'estensione della catena con acrilonitrile (grazie al meccanismo di halogen exchange catalitico) hanno dimostrato la presenza della funzionalità di fine catena. Le polimerizzazioni ottenute tramite liquido ionico riciclato hanno dimostrato che eATRP tollera bene anche un solvente riciclato. I copolimeri a blocchi (BCP) hanno rilevanza in una vasta gamma di applicazioni nella vita di tutti i giorni. BCP di acrilonitrile (AN) e butil acrilato (BA) sono stati studiati come precursori di carbonio mesoporoso. Pertanto, eATRP di acrilonitrile è stata introdotta e studiata nei diversi aspetti, come: effetto del potenziale applicato, del grado di polimerizzazione, della natura di C-X e della struttura dell'iniziatore. Un macroiniziatore di PAN è stato quindi esteso con BA per formare il copolimero PAN-b-PBA come precursore del carbonio mesoporoso. I BCP possono essere ottenuti anche via cHE, evitando così le procedure di purificazione e la differenza di reattività quando si passa da un monomero meno reattivo a uno più reattivo. Il cHE si è dimostrato strumento efficace di polimerizzazione sia da SARA che da eATRP, in una gamma di solventi incluso DMSO e acqua. Il metil metacrilato (MMA) è stato polimerizzato grazie al cHE in liquido ionico ed etanolo, per risolvere il problema dell’effetto del penultimo. La messa a punto delle condizioni di elettrolisi ha permesso di ottenere PMMA a bassa dispersione. Ulteriori miglioramenti sono stati ottenuti utilizzando [CuIIPMDETA]2+ come catalizzatore come alternativa economica ed efficiente a Cu/TPMA. L'analisi della tatticità del PMMA ottenuta in [BMIm][OTf] e l'etanolo ha confermato la scarsa capacità del solvente ionico di indurre stereocontrollo durante la polimerizzazione. I complessi piridinici, come Cu/TPMA, stabili fino a condizioni molto acide (pH ⁓1) hanno permesso di ottenere poli(liquidi ionici). Hanno aperto infatti una nuova strada per la polimerizzazione di monomeri liquidi ionici, una classe di molecole che può dare una pletora di nuovi materiali polimerizzati mediante ATRP. La ragione principale che impedisce l'ATRP di ILM è una reazione di ciclizzazione che coinvolge l'estremità della catena, con l'alogeno terminale come gruppo uscente, come nel caso dell'acido metacrilico. Le stesse tre strategie usate per l’acido metacrilico hanno permesso di migliorare drasticamente la conversione e il controllo sulla polimerizzazione di ILM: (i) usando la funzionalità di fine catena C-Cl, che è molto più stabile di C-Br; (ii) abbassando il pH per convertire completamente gli ioni carbossilato liberi in acido carbossilico, che è un nucleofilo molto più debole; (iii) migliorare la velocità di polimerizzazione per evitare il contributo negativo della reazione di ciclizzazione. Tali condizioni hanno permesso la sintesi di poli(liquidi ionici) (PIL) ben controllati ad alto peso molecolare fino a grado di polimerizzazione 1000. Un semplice iniziatore organico (poli)alogenato come acido 2,2-dicloropropionico è stato utilizzato per produrre un PIL lineare telechelico. L’insieme di questi risultati può consentire una più facile implementazione e scalabilità industriale dell’eATRP. Per questo motivo, è stato deciso di studiare l’eATRP del cloruro di vinile, considerata finora impossibile. La polimerizzazione, effettuata in un reattore elettrochimico resistente alla pressione, è controllata, veloce e con una conversione buona in tempi ragionevoli. Oltre al classico PVC lineare, è stato anche sintetizzato un PVC a stella, evidenziando la flessibilità dell'eATRP. Nell'architettura a stella, la polimerizzazione elettrochimica si è dimostrata di gran lunga superiore a quella chimica (SARA ATRP). Il successo di questa polimerizzazione ha smentito il meccanismo SET-LRP e le sue assunzioni. Una delle proprietà dell’eATRP è la tolleranza al materiale catodico utilizzato per la rigenerazione di [CuIL]+. Si è deciso dunque di studiare la polimerizzazione di un acrilato usando la superficie del reattore esposto alla miscela di polimerizzazione come elettrodo. In questo modo il reattore ha la duplice funzione di elettrodo e luogo fisico in cui avviene la reazione. I risultati hanno mostrato che la polimerizzazione è veloce e controllata, raggiungendo conversioni elevate in breve tempo. Inoltre, l'assenza di rilascio di ioni metallici durante la reazione (Fe, Ni, Cr) da parte dell’acciaio conferma che la polimerizzazione avviene elettrochimicamente, l'acciaio agisce solo come un serbatoio di elettroni e non è chimicamente coinvolto. Una tale impostazione elettrochimica, semplice ed economica, può rendere l'eATRP una tecnica commerciale a breve termine e aprire nuove prospettive economiche.

In this work, methylmethacrylate, MMA was polymerized by ATRP method to obtain low molecular weight living polymers. The initiator was p-toluenesulfonylchloride and catalyst ligand complex system were CuCl-4,4&rsquo
dimethyl 2,2&rsquo
bipyridine. Polymers with controlled molecular weight were obtained. The polymer chains were shown by NMR investigation to be mostly syndiotactic. The molecular weight and molecular weight distribution of some polymer samples were measured by GPC method. The K and a constants in [h]=K Ma equation were measured as 9.13x10-5 and 0.74, respectively. FT-IR and X-Ray results showed regularity in polymer chains. The molecular weight-Tg relations were verified from results of molecular weight-DSC results.

Polymer Chemistry: A Practical Approach in Chemistry has been designed for both chemists working in and new to the area of polymer synthesis. It contains detailed instructions for preparation of a wide-range of polymers by a wide variety of different techniques, and describes how this synthetic methodology can be applied to the development of new materials. It includes details of well-established techniques, e.g. chain-growth or step-growth processes together with more up-to-date examples using methods such as atom-transfer radical polymerization. Less well-known procedures are also included, e.g. electrochemical synthesis of conducting polymers and the preparation of liquid crystalline elastomers with highly ordered structures. Other topics covered include general polymerization methodology, controlled/"living" polymerization methods, the formation of cyclic oligomers during step-growth polymerization, the synthesis of conducting polymers based on heterocyclic compounds, dendrimers, the preparation of imprinted polymers and liquid crystalline polymers. The main bulk of the text is preceded by an introductory chapter detailing some of the techniques available to the scientist for the characterization of polymers, both in terms of their chemical composition and in terms of their properties as materials. The book is intended not only for the specialist in polymer chemistry, but also for the organic chemist with little experience who requires a practical introduction to the field.

Magneto-rheologiacal Fluid (MRF), suspensions of polarizable micron size particles, is synthesized from suspensions of iron particles (micron and nano size) in phosphate buffered saline (PBS). The iron particles have been surface coated using atom transfer radical polymerization (ATRP) with various polymers, such as poly(N-isopropylacrylamide) (poly(NIPAAm)), and poly(acrylamide) (poly(AAm)). The surface grafted polymer has been characterized using differential scanning calorimetry (DSC), and properties of resulting fluid have been measured using a rheometer. A mathematical model is developed to explore the force induced by the particles on the neighboring tissue under externally applied magnetic field. This force results in the damage of the tumor cell lines and trigger the immune system response. The effect of MRF on primary and metastasized tumor growth were evaluated by using an orthotopic murine breast cancer model (4T1). Tumors were evaluated by growth measurements and histological changes following injection of MRF or carrier fluid alone into the tumor and the effects of subsequent application of a magnetic field to the site. Results indicate slowed tumor growth and increased dendritic cell activation with this therapy and they are encouraging.