Controlled/living radical mechanism

The fifty chapters submitted for publication in the ACS Symposium series could not fit into one volume and therefore we decided to split them into two volumes. In order to balance the size of each volume we did not divide the chapters into volumes related to mechanisms and materials but rather to those related to atom transfer radical polymerization (ATRP) and to other controlled/living radical polymerization methods reversible-addition fragmentation transfer (RAFT) and other degenerative transfer techniques, as well as stable free radical pol5mierizations (SFRP) including nitroxide mediated polymerization (NMP) and organometallic mediated radical polymerization (OMRP). 

Controlled/ Living radical polymerization (CRP) of vinyl acetate (VAc) via nitroxide-mediated polymerization (NMP), organocobalt-mediated polymerization, iodine degenerative transfer polymerization (DT), reversible radical addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) is summarized and compared with the ATRP of VAc catalyzed by copper halide/2,2 6 ,2 -terpyridine. The new copper catalyst provides the first example of ATRP of VAc with clear mechanism and the facile synthesis of poly(vinyl acetate) and its block copolymers. 

Scheme 1. General mechanisms of controlled/" living radical polymerizations. (Reproduced with permission from American Chemical Society).

RAFT polymerization is another powerful controlled/living radical polymerization technique for surface modification.The generally accepted mechanism of the RAFT polymerization is depicted in Scheme 5.4. The... 

In this article, two examples of the application ESR to conventional radical polymerizations, especially to both kinetics and mechanism, based on materials prepared by controlled/living radical polymerizations will be demonstrated. The first example is the estimation of the effect of chain length on propagating radicals. The second is the detection of chain transfer reactions on propagating radicals in the polymerization of rert-butyl acrylate. 

A benefit of the relatively stable end groups of polymers prepared by controlled/ living polymerizations, is that they can be isolated and stored as macroinitiators with relative ease. Such is not the case for polymers prepared by ionic polymerizations the active anion or cation will be quenched by advantageous moisture. This also allows one to modify polymers prepared by other methods so that they can become macroinitiators for controlled/ living radical polymerization. Such mechanism transformation can be used to prepare a wide array of novel polymers block copolymers of combinations of radically prepared polymers with those synthesized by step-growth polymerizations [160,276], ROMP [159,277], cationic [161,278] and anionic polymerizations [255,279] have been prepared (Table 3). 

Greszta, D., and Matyjaszewski, K. (1996). Mechanism of controlled/ living radical polymerization of styrene in the presence of nitroxyl radicals. Kinetics and simulations. Macromolecules, 29(24) 7661-7670. 

The polymerization of MA with 7 was carried out in the presence of 13, i.e., 7 and 13 were used as two-component iniferters [175]. When an identical amount of 13 to 7 was added to the system, the polymerization proceeded according to a mechanism close to the ideal living radical polymerization mechanism. Similar results were also obtained for the polymerization of VAc. These results indicate that the chain end of the polymer was formed by the competition of primary radical termination and/or chain transfer to bimolecular termination, and that it could be controlled by the addition of 13. 

The living radical polymerization of some derivatives of St was carried out. The polymerizations of 4-bromostyrene [254], 4-chloromethylstyrene [255, 256], and other derivatives [257] proceed by a living radical polymerization mechanism to give polymers with well-controlled structures and block copolymers with poly(St). The random copolymerization of St with other vinyl... 

In contrast to the above polymerizations via anionic and/or coordination anionic mechanisms, radical polymerization initiated with metalloporphyrins remains to be studied. The only example of controlled radical polymerization by metalloporphyrins has been reported by Wayland et al. where the living radical polymerization of acrylic esters initiated with cobalt porphyrins was demonstrated. In this section the radical polymerization of MMA initiated with tin porphyrin is discussed. 

A series of so-called Grubbs ruthenium—carbene complexes (Ru-12) can mediate living radical polymerization of MMA and styrene to afford controlled polymers with narrow MWDs (MJMn 1.2).63 66 The polymerization apparently proceeds via a radical mechanism, as suggested by the inhibition with galvinoxyl. For example, a novel ruthenium—carbene complex (Ru-13) carries a bromoisobutyrate group and can thus not only initiate but also catalyze living radical polymerization of MMA without an initiator.67... 

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