Controlled radical polymerization kinetics

The preparation of polymer brushes by controlled radical polymerization from appropriately functionalized polymer chains, surfaces or particles by a grafting from approach has recently attracted a lot of attention.742 743 The advantages of growing a polymer brush directly on a surface include well-defined grafts, when the polymerization kinetics exhibit living character, and stability due to covalent attachment of the polymer chains to the surface. Most work has used ATRP or NMP, though papers on the use of RAFT polymerization in this context also have begun to appear. 

This book will be of major interest to researchers in industry and in academic institutions as a reference source on the factors which control radical polymerization and as an aid in designing polymer syntheses. It is also intended to serve as a text for graduate students in the broad area of polymer chemistry. The book places an emphasis on reaction mechanisms and the organic chemistry of polymerization. It also ties in developments in polymerization kinetics and physical chemistry of the systems to provide a complete picture of this most important subject. 

Using NMP [114, 115] or reversible addition-fragmentation chain transfer (RAFT) [ 119,120,127], agents with ammonium groups for the ion exchange allowed the attachment of initiators on the clay surface for controlled radical polymerizations (NMP, RAFT). Samakande et al. investigated the kinetics of RAFT-mediated living polymerization of styrene [120] and styrene/BA [119] mixtures in miniemulsion. 

TABLE 3.1 Differences and Common Features of Living Anionic and Controlled Radical Polymerization Processes (Kinetic Constants According to Fig. 3.4)... 

FT-NIR spectroscopy in combination with a fiber-optic probe was successfully used to monitor living isobutylene, ethylene oxide and butadiene polymerizations using specific monomer absorptions. In the case of EO a temperature dependent induction period was detected when 5ec-BuLi/ BuP4 were used as an initiating system. This demonstrates the usefulness of this technique because this phenomenon had not been observed so far by other methods. We have also successfully conducted experiments in controlled radical polymerization. Then we were able to monitor the RAFT polymerization of A -isopropylacrylamide (NIPAAm). Thus it can be expected that with the help of online NIR measurements detailed kinetic data of many polymerization systems will become available which will shed more light onto the reaction mechanisms. Consequently, FT-NIR appears to be a method, which can be applied universally to the kinetics of polymerization processes. 

Controlled radical polymerization techniques are suitable for synthesizing polymers with a high level of architectural control. Notably, they not only allow a copolymerization with functional monomers (as shown previously for free-radical polymerization), but also a simple functionalization of the chain end by the initiator. Miniemulsion systems were found suitable for conducting controlled radical polymerizations [58-61], including atom transfer radical polymerization (ATRP), RAFT, degenerative iodine transfer [58], and nitroxide-mediated polymerization (NMP). Recently, the details of ATRP in miniemulsion were described in several reviews [62, 63], while the kinetics of RAFT polymerization in miniemulsion was discussed by Tobita [64]. Consequently, no detailed descriptions of the process wiU be provided at this point. 

The polymerization rate is directly proportional to the monomer concentration for ideal free radical polymerization kinetics. Deviations from this first-order kinetics can be caused by a whole series of effects which must be checked by separate kinetic experiments. These effects include cage effects during initiator free radical formation, solvation of or complex formation by the initiator free radicals, termination of the kinetic chain by primary free radicals, diffusion controlled termination reactions, and transfer reactions with reduction in the degree of polymerization. Deviations from the square root dependence on initiator concentration are to be primarily expected for termination by primary free radicals and for transfer reactions with reduction in the degree of polymerization. 

The fourth SML meeting (September 3-8, 2006) was organized by Michael Buback and by Alex van Herk from the Technical University of Eindhoven. As has been foreseen in the last meeting, the number of contributions on controlled radical polymerization (CRP) has significantly increased. Four out of the eight sessions were devoted to CRP and the organizers consequently decided to remove the word Free from the conference heading. The symposium nevertheless remains the number one forum where kinetic and mechanistic issues are addressed in detail and depth for the entire field of radical polymerization. Several important aspects of radical polymerization have first been presented at SML con-... 

K. Matyjaszewski, T. E. Patten, J. Xia, Controlled/ living radical polymerization, kinetics of the homogeneous atom transfer radical... 

Strategies for controlling the copolymer composition and MWD of latices based on linear and non-linear copolymers, such as styrene/butyl acrylate copolymers and methyl methacrylate/n-butyl acrylate copolymers, are described. These strategies involve on-line procedures based on calorimetric measurements and open-loop processes employing a mathematical model for determining the trajectories of the manipulated variables, such as monomer feed flow rates and chain transfer agent. 35 refs. (3rd lUPAC-Sponsored International Symposium on Free-Radical Polymerization Kinetics and Mechanism, II Ciocco (Lucca), Tuscany, Italy, 3rd-9th June, 2001)... 

As mentioned above, the term controlled radical polymerization is sometimes used to describe a radical or ionic polymerization in which reversible deactivation of the chain carriers is an essential component of the mechanism. It increases the time of propagation, securing control of one or more kinetic features of the polymerization or one or more structural aspects of the macromolecules, or both. The adjective... 

KINETIC MODELING OF POLYSTYRENE CONTROLLED RADICAL POLYMERIZATION... 

The kinetic modeling of styrene controlled radical polymerization, initiated by 2,2 -asobis(isobutimitrile) and proceeding by a reversible ehain transfer meeha-nism was carried out and accompanied by addition-fragmentation in the presenee dibenzyltiitiocarbonate. An inverse problem of determination of the unknown temperature dependences of single elementary reaction rate eonstants of kinetic scheme was solved. The adequacy of the model was revealed by comparison of theoretical and experimental values of polystyrene molecular-mass properties. The influence of process controlling factors on polystyrene molecular-mass properties was studied using the model. 

Kinetic Modeling of Polystyrene Controlled Radical Polymerization... 

Kinetic scheme, introduced for description of styrene controlled radical polymerization process in the presence of trithio carbonates, includes the following phases. 

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