Double thermoresponsive pentablock copolymers: synthesis by one-pot RAFT polymerization and self-assembly in aqueous solutions

Abstract

In this study, well-defined hydrophilic pentablock copolymers with iterative blocks of poly(2-hydroxyethyl methacrylate) (pHEMA) and poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) were synthesized by three-step one-pot RAFT polymerization in the presence of difunctional RAFT CTA. Two types of pentablock copolymers with central blocks of either pHEMA or pDMAEMA were synthesized and thermoresponsive self-assembly of these copolymers in aqueous solutions was studied by DLS, SEM, and zeta potential measurements. It was determined that these copolymers are double thermoresponsive, with temperature-induced aggregation at about 26–36 °C and 59–65 °C. Upon heating, these copolymers form micellar aggregates with pHEMA blocks in the core, while above the LCST of pDMAEMA the micellar aggregates gradually lose their previous core–shell form and convert to aggregates with more or less evenly distributed pDMAEMA and pHEMA blocks. Aggregation behaviour of the pentablock copolymers depends on the position of the blocks and content of HEMA units.