Associative block copolymers comprising poly(<i>N</i>‐isopropylacrylamide) and poly(ethylene oxide) end‐functionalized with a fluorophilic or hydrophilic group. Synthesis and aqueous solution properties

Abstract

Abstract A series of block copolymers comprising poly( N ‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) end‐functionalized with a quaternary ammonium group (R Q ) was synthesized by free‐radical polymerization of N ‐isopropylacrylamide with well‐defined R Q PEO 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 R Q E x N y differ in type of the terminal group [F Q = C 8 F 17 (CH 3 ) 2 N + or M Q = (CH 3 ) 3 N + ] and in the length of the PEO (E x ; 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 25 °C 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. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5736–5744, 2004