A series of block copolymers comprising poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEW end-functionalized with a quaternary ammonium group (R-Q) was synthesized by free-radical polymerization of N-isopropylacrylamide with well-defined RQPEO macroazoinitiators. The radical termination occurred mainly by disproportionation, as confirmed by combining the data from size exclusion chromatography (SEC) and rheology measurements. The copolymers denoted RQExNy differ in type of the terminal group [F-Q = C8F17(CH3)(2)N+ or M-Q = (CH3)(3)N+] and in the length of the PEO (Ex; x = 4, 6, or 10 K) and PNIPAM (N-y; y = 7 or 17-19 K) blocks. The type of the terminal group determined the behavior of the block copolymers in the dilute and semidilute regime. Self-assembled species formed by both F-Q and M-Q modified block copolymers were detected by static light scattering measurements at 25degreesC and above the lower critical solution temperature (LCST). The LCST of the block copolymers depended on the type of the R-Q group and the length of the blocks. F-Q-modified copolymers form elastic gels below and above the LCST. It was inferred that the F-Q groups and the PNIPAM blocks form segregated microdomains that serve as junctions to maintain a viscoelastic network. (C) 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42:5736-5744,2004.