Synthesis and aggregation behaviors of well-defined thermoresponsive pentablock terpolymers with tunable LCST

Abstract

A series of thermoresponsive pentablock terpolymers, poly(N- isopropylacrylamide)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(N-isopropylacrylamide), is prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of NIPAM and PPO block lengths on lower critical solution temperature (LCST), critical micelle concentration (cmc), and aggregation number (N agg) is investigated via UV-Vis spectroscopy and steady-state fluorescence spectroscopy. The results show that upon increasing the block lengths, LCST and cmc decrease, while N agg increases. TEM observation shows that associated spherical-like particles are evidenced below the LCST of the terpolymers, and regular or irregular spherical micelles or even intermicellar aggregates are observed above the LCST. A series of thermoresponsive pentablock terpolymers, PNIPAM n-PEO-PPO-PEO- PNIPAM n, is synthesized by RAFT polymerization. In the dilute aqueous solution, they possess spherical-like particle structures below LCST, and irregular shape micelles or even intermicellar aggregates are obtained above LCST. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.