Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block-like to gradient-like behavior

Abstract

Stimuli-responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N-acryloylpyrrolidine)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PAPy-b-P(APi-co-APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature-induced self-assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT1) can indeed be precisely adjusted while the temperature-induced collapse upon heating leads to a fully reversible well-defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block-like to rather gradient-like behavior. This means the micellization onset at PTT1 and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT2) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on-demand” switchable materials.