Thermoresponsive core cross-linked star-shaped poly(N-isopropylacrylamide) for reversible and controlled aggregation of nanoscale molecular units

Core cross-linked star-shaped poly(N-isopropylacrylamide) (PNIPAAm), which was prepared via an arm-first method by reversible addition-fragmentation chain-transfer polymerization, was shown to exhibit unique thermoresponsive behavior in water. Star polymers with ~20–35 arms with narrow molecular weight distributions apparently had a more hydrophilic nature compared with that of linear PNIPAAm, judging from their thermoresponsive behavior. Most importantly, an aqueous solution of the star PNIPAAm with carboxy ends remained transparent even at 70 °C.