CO2-Triggered UCST transition of amphiphilic triblock copolymers and their self-assemblies
A well-defined thermo- and CO2-responsive triblock copolymer, poly[(ethylene glycol)methyl ether]-block-poly(acrylamide-co-acrylonitrile)-block-poly(N,N-diethylamino ethyl methacrylate) (PEG-b-P(AAm-co-AN)-b-PDEAEMA), was synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. It contains a temperature responsive segment based on P(AAm-co-AN), which exhibits an upper critical solution temperature (UCST) in water, and a CO2-responsive segment derived from PDEAEMA. Most importantly, the temperature responsive behavior (UCST) of this triblock copolymer could be controlled by the amount of CO2 in aqueous solution because the UCST of the polymer decreased with the increasing amount of CO2 in aqueous solution. Additionally, the prepared amphiphilic triblock copolymer could self-assemble into vesicles in aqueous solution. These vesicles showed good stability in aqueous medium even at high temperatures (up to 80 °C) in the absence of CO2. Purging of CO2 into the solution induced a morphological transition from vesicles to micelles, which further disassembled into unimers above the UCST of the polymer. Subsequently, triblock copolymer assemblies were assessed as vehicles for drug delivery and release by using Nile red as a model. The results showed that the released amount of Nile red could be regulated via CO2 content and temperature in aqueous solution.