Synthesis of poly(chloromethylstyrene-b-styrene) block copolymers by controlled free-radical polymerization

The controlled free-radical polymerization of styrene and chloromethylstyre ne monomers in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO ) has been studied with the aim of synthesizing block copolymers with well- defined structures. First, TEMPO-capped poly(chloromethylstyrene) was prepa red. Among several initiating systems [self-initiation, dicumyl peroxide, a nd 2,2'-azobis(isobutyronitrile)], the last offered the best compromise for obtaining a good control of the polymerization and a fast polymerization r ate. The rate of the TEMPO-mediated polymerization of chloromethylstyrene w as independent of the initial concentration of TEMPO but unexpectedly highe r than the rate of the thermal self-initiated polymerization of chloromethy lstyrene. Transfer reactions to the chloromethyl groups were thought to pla y an important role in the polymerization kinetics and the polydispersity i ndex of the resulting poly(chloromethylstyrene). Second, this first block w as used as a macroinitiator in the polymerization of styrene to obtain the desired poly(chloromethylstyrene-b-styrene) block copolymer. The kinetic mo deling of the block copolymerization was in good agreement with experimenta l data. The block copolymers obtained in this work exhibited a low polydisp ersity index (weight-average molecular weight/number-average molecular weig ht < 1.5) and could be chemically modified with nucleophilic substitution r eactions on the benzylic site, opening the way to a great variety of archit ectures. (C) 2000 John Wiley & Sons, Inc.