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

摘要

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.