Synthesis of Miktoarm Star Amphiphilic Block Copolymers via Combination of NMRP and ATRP and Investigation on Self-Assembly Behaviors

The novel trifunctional initiator, 1-(4-methyleneoxy-2,2,6,6-tetramethyl-pip-eridinoxyl)-3,5-bi(bromomethyl)-2,4,6-trimethylbenzene (TEMPO-2Br), was successfully synthesized and used to prepare the miktoarm star amphiphilic poly(styrene)-(poly(N-isopropylacrylamide))(2) (PS(PNIPAAM)(2)) via combination of atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP) techniques. Furthermore, the star amphiphilic block copolymer, poly (styrene)-(poly(N-isopropylacrylamide-b-4-vinylpyridine))(2) (PS(PNIPAAM-b-P4VP)(2)), was also prepared using PS(PNIPAAM)(2) as the macroinitiator and 4-vinylpyridine as the second monomer by ATRP method. The obtained polymers were well-defined with narrow molecular weight distiibutions (M-w/M-n <= 1.29). Meanwhile, the self-assembly behaviors of the miktoarm amphiphilic block copolymers, PS(PNIPAAM)(2) and PS(PNIPAAM-b-P4VP)(2), were also investigated. Interestingly, the aggregate morphology changed from sphere-shaped micelles (4.7 < pH < 3.0) to a mixture of spheres and rods (1.0 < pH < 3.0), and rod-shaped nanorods formed when pH value was below 1.0. The LCST of PS(PNIPAAM)(2) (pH 7) was about 31 degrees C and the LCST of PS(PNIPAAM-b-P4VP)(2) was about 35 degrees C (pH 3). (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6304-6315, 2009