Synthesis and self-assembly behaviors of four-armed amphiphilic polystyrene-b-poly(N-isopropylacrylamide) copolymers |
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| Authors: | N Hu J H Li D J Shi X Y Liu M Q Chen |
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| Institution: | 1. The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, Jiangnan University, Jiangsu Province, Wuxi, 214122, China
2. School of Chemical and Material Engineering, Jiangnan University, Jiangsu Province, Wuxi, 214122, China
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| Abstract: | Four-armed amphiphilic block copolymers polystyrene-b-poly(N-isopropyl acrylamide) (PSt-b-PNIPAAM)4 were synthesized by atom transfer radical polymerization (ATRP) in two steps. Star narrow dispersed polystyrene, (PSt-Br)4, with controlled number-average molecular weight was firstly synthesized by ATRP of styrene (St) using pentaerythritol tetrakis (2-bromoisobutyrate) (4Bri-Bu) as four-armed initiator. Then, (PSt-b-PNIPAAM)4 was prepared using (PSt-Br)4 as macroinitiator by ATRP. The structures of (PSt-Br)4 and (PSt-b-PNIPAAM)4 were confirmed by characterization by nuclear magnetic resonance (1H NMR). The apparent viscosity of the four-armed (PSt-b-PNIPAAM)4 was significantly lower than that of the linear PSt-b-PNIPAAM with the same amount of repeat units of PSt and PNIPAAM. The self-assembly behavior of the four-armed amphiphilic block copolymers (PSt-b-PNIPAAM)4 in mixed solution (DMF/H2O) and the lower critical solution temperature (LCST) of the resulting micelles were investigated by scanning electron microscopy (SEM), dynamic light scattering (DLS) and UV-VIS spectroscopy. The results show that the size of the mono-dispersed spherical micelles decreased with the increment of the chain length of PNIPAAM in the block copolymers, while LCST increased. |
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