Synthesis of star thermoresponsive amphiphilic block copolymer nano-assemblies and the effect of topology on their thermoresponse

Cao, MJ (Cao, Mengjiao)^[ 1 ] ; Nie, HJ (Nie, Huijun)^[ 1 ] ; Hou, YW (Hou, Yuwen)^[ 1 ] ; Han, G (Han, Guang)^[ 2 ] ; Zhang, WQ (Zhang, Wangqing)^[ 1,3 ]

POLYMER CHEMISTRY, 2019, 10(3): 403-411

DOI: 10.1039/c8py01617h

Abstract

Well-defined multi-arm star thermoresponsive block copolymer nano-assemblies of [poly(N-isopropylacrylamide)-block-polystyrene](n) [(PNIPAM-b-PS)(n)] with n = 1, 2, 3 and 4 arms were synthesized by RAFT dispersion polymerization via polymerization-induced self-assembly. By carefully changing the degree of polymerization (DP) of the polystyrene (PS) block and modulating the polymerization conditions, (PNIPAM-b-PS)(n) nano-assemblies with similar DP and similar chain density but different topology structures of the tethered poly(N-isopropylacrylamide) (PNIPAM) chains were obtained. By comparatively studying the thermoresponse via turbidity analysis, dynamic light scattering, variable-temperature H-1 NMR and rheological analysis, it was found that the phase transition temperature of the tethered PNIPAM chains in the (PNIPAM-b-PS)(n) nano-assemblies correlates to the number of arms, n, demonstrating that the topology of the tethered PNIPAM chains exerts a significant influence on the thermoresponsive phase transition.