Effect of block order of ABA- and BAB-type NIPAAm/HEMA triblock copolymers on thermoresponsive behavior of solutions

Abstract

ABA and BAB triblock thermoresponsive copolymers (A = N- isopropylacrylamide, B = 2-hydroxyethyl methacrylate) have been synthesized by atom transfer radical polymerization (ATRP). BAB is shown to exhibit a higher transition temperature and a good solubility in water compared to ABA with the same composition and concentration. The differences are attributed to the distinct micellar structure, which is regulated by the block order of the copolymers. It is speculated that ABA and BAB copolymers separately form branch and flower micelles in water, which mainly influence the course of phase transition. The moduli of the ABA copolymer solution are higher than those of the BAB above gel point. In terms of hypothesized micelle models, it is proposed that the 'branch' micelles of the ABA solution preferably form more physical interconnections. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.