Thermal radical copolymerization of styrene (S) and maleimide (MI) at 125degreesC in diglyme in the presence of 2,2,6,6-tetrametliylpiperidin-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), = 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-terminated 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. (C) 2004 Wiley Periodicals, Inc.