Thermo-responsive ABA triblock copolymer of PVEA-b-PNIPAM-b-PVEA showing solvent-tunable LCST in a methanol–water mixture

Abstract

The thermo-responsive triblock copolymers of poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-poly(N-isopropylacrylamide)-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine] containing two outer thermo-responsive blocks of poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PVEA) and a central thermo-responsive block of poly(N-isopropylacrylamide) (PNIPAM) with different block lengths are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The PVEA block of the triblock copolymer shows the lower critical solution temperature (LCST) in a methanol-rich methanol–water mixture, while the PNIPAM block exhibits the LCST-type phase transition in a water-rich methanol–water mixture. It is found that the LCST of the PVEA block in the triblock copolymer increases with the polymerization degree (DP) of the PNIPAM block and decreases with the DP of the PVEA block, and the PNIPAM chain length exerts no obvious influence on the LCST of the PNIPAM block. By adjusting the water content in the methanol–water mixture and the solvent temperature, the triblock copolymer exhibits various morphologies including soluble polymer chains, flowerlike micelles containing a dehydrated PVEA core and a looped PNIPAM corona, and micellar aggregates.