Synthesis of Poly(chloromethylstyrene-b-styrene) Block Copolymers by Controlled Free-Radical Polymerization PATRICK LACROIX-DESMAZES, 1 THIERRY DELAIR, 2 CHRISTIAN PICHOT, 2 BERNARD BOUTEVIN 1 1 UMR-CNRS 5076, Ecole Nationale Supe ´rieure de Chimie de Montpellier, 8 Rue de l’Ecole Normale, 34296 Montpellier Cedex 5, France 2 Unite ´ Mixte CNRS-BioMe ´rieux, ENS Lyon, 46, Alle ´e d’Italie, 69364 Lyon Cedex 07, France Received 1 February 2000; accepted 14 July 2000 ABSTRACT: The controlled free-radical polymerization of styrene and chloromethylsty- rene 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 struc- tures. First, TEMPO-capped poly(chloromethylstyrene) was prepared. Among several initiating systems [self-initiation, dicumyl peroxide, and 2,2'-azobis(isobutyronitrile)], the last offered the best compromise for obtaining a good control of the polymerization and a fast polymerization rate. The rate of the TEMPO-mediated polymerization of chloromethylstyrene was independent of the initial concentration of TEMPO but un- expectedly higher than the rate of the thermal self-initiated polymerization of chloro- methylstyrene. Transfer reactions to the chloromethyl groups were thought to play an important role in the polymerization kinetics and the polydispersity index of the resulting poly(chloromethylstyrene). Second, this first block was used as a macroini- tiator in the polymerization of styrene to obtain the desired poly(chloromethylstyrene- b-styrene) block copolymer. The kinetic modeling of the block copolymerization was in good agreement with experimental data. The block copolymers obtained in this work exhibited a low polydispersity index (weight-average molecular weight/number-average molecular weight  1.5) and could be chemically modified with nucleophilic substitu- tion reactions on the benzylic site, opening the way to a great variety of architectures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3845–3854, 2000 Keywords: block copolymers; nitroxide; controlled free-radical polymerization; chlo- romethylstyrene INTRODUCTION Block copolymers are useful for a wide range of applications, such as the compatibilization of non- miscible polymers, the dispersion of mineral fill- ers in a polymer matrix, and the stabilization of colloids. Anionic 1 and cationic 2 polymerizations allow the synthesis of such polymers, but the pu- rity of the reagents is often restrictive and the variety of monomers polymerizable in this man- ner is rather limited. Free-radical polymerization can be applied to a wide range of monomers; how- ever, it does not permit the synthesis of block copolymers because of the predominance of termi- nation reactions over propagation ones. Never- theless, a few methods have been developed to obtain block copolymers by radical polymeriza- tion, 3 including the use of multifunctional initia- tors 4–7 or macroinitiators, 8,9 the bis-telomeriza- tion technique 10 or telomerization with chemical modification, 11,12 and, more recently, living or controlled free-radical polymerization. 13 For ni- troxide-mediated polymerization, a thermally re- Correspondence to: P. Lacroix-Desmazes (E-mail: lacroix@ cit.enscm.fr) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 38, 3845–3854 (2000) © 2000 John Wiley & Sons, Inc. 3845