Synthesis and Chain Extension of Nitroxide-Terminated Styrene–Maleimide Copolymers J. Lokaj, 1 I. Krakovsky ´, 2 P. Holler, 1 L. Hanykova ´ 2 1 Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,162 06 Prague 6, Czech Republic 2 Faculty of Mathematics and Physics, Charles University, 180 00 Prague 8, Czech Republic Received 22 May 2003; accepted 20 November 2003 ABSTRACT: Thermal radical copolymerization of styrene (S) and maleimide (MI) at 125°C in diglyme in the presence of 2,2,6,6-tetramethylpiperidin-1-yloxyl radical (TEMPO) was studied. Mole fractions of maleimide in the feed, F MI , varied in the range 0.1– 0.9. A quasiliving reaction process proceeded yielding copolymers with a low polydispersity (M w /M n = 1.17–1.41). The found azeotropic composition, (F MI ) A = 0.46, did not differ substantially from that (0.5) in the conventional radical S-MI copolymerization. At a higher conversion or MI content in the feed, deactivation of the copolymer chains occurred. The obtained TEMPO-termi- nated S-MI copolymers readily initiated polymerization of styrene; chain extension of the macroinitiators took place, giving poly(S-co-MI)-block-poly(S) diblock copolymers. The synthesized copolymers containing S and MI units were characterized by elemental analysis, NMR spectroscopy, size-exclusion chromatography, and differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1863–1868, 2004 Key words: styrene–maleimide copolymers; nitroxide-medi- ated radical copolymerization; chain extension reaction; diblock copolymers INTRODUCTION In recent years, the synthesis of polymers have achieved remarkable success due to new techniques such as nitroxide-mediated radical polymerization (NMRP). 1–22 In the presence of a nitroxide stable rad- ical or N-alkoxyamine-based unimolecular initiator, a quasiliving radical polymerization proceeds at ele- vated temperatures (usually 100°C) in mixtures consisting of a thermal initiator [2,2'-azobis(isobuty- ronitrile), dibenzoyl peroxide] and monomer. Some monomers and comonomer couples (styrene and sty- rene-N-butyl- or N-phenylmaleimide) polymerize in the quasiliving manner even without any added initi- ator. 12,23,24 The mediating role of the nitroxide consists of reversible termination of growing polymer radicals under formation of thermally unstable N-alkoxyamine bond. Dissociation of the bonds regenerates the poly- mer radicals, which can add more monomer units before being trapped again with the nitroxide. The obtained nitroxide-terminated polymers have well-de- fined structure and properties. They can be employed in chain extension reactions for the synthesis of block copolymers. Convenient monomers for the NMRP are styrene or its derivatives; the most widely used nitroxide is 2,2,6,6- tetramethylpiperidin-1-yloxyl radical (TEMPO). How- ever, by using TEMPO, the structure and process control of polymerization are generally not achievable with monomer units containing functional groups. Neverthe- less, the functional monomers can be introduced into polymer chains by the controlled copolymerization with excess styrene. 10,25 In most cases, the nitroxide-mediated radical copo- lymerization of styrene and monomers having 1- or 1,1-substituted polymerizable double bond was stud- ied. Recently, the copolymers with incorporated het- erocyclic derivatives of maleic acid (maleic anhydride, N-substituted maleimides) were reported. 21,23,24,26 The present work is focused on the copolymerization of maleimide by using the nitroxide technique. Func- tional groups in maleimide molecule (i.e., NH and carbonyls) are favorable to supramolecular interac- tions based on triple hydrogen bonding. 27 This can be used in the formation of polymer blends, 28 liquid crys- talline polymers, 29 and polymer networks. 30 Our aim was to prepare TEMPO-terminated copolymers of sty- rene with maleimide (C) and to synthesize related poly(styrene-co-maleimide)-block-polystyrene copoly- mers (BC) by the chain extension of C with styrene (Scheme 1). Investigation of the prepared maleimide copolymers as components of supramolecular aggre- gates is envisaged. EXPERIMENTAL Materials Styrene (Kauc ˘uk Group Co., Kralupy, Czech Republic) [boiling point (bp) 36°C/1.56 kPa] was distilled prior Correspondence to: J. Lokaj (lokaj@imc.cas.cz). Contract grant sponsor: Grant Agency of the Czech Re- public; contract grant number: 203/02/0653. Journal of Applied Polymer Science, Vol. 92, 1863–1868 (2004) © 2004 Wiley Periodicals, Inc.