Dually responsive multiblock copolymers via reversible addition- fragmentation chain transfer polymerization: Synthesis of temperature- and redox-responsive copolymers of poly(N-isopropylacrylamide) and poly(2-(dimethylamino)ethyl methacrylate)

We report the synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl) benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multibrock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)- terminated PNIPAM and PDMAEMA. The copolymers and their stimulusresponsive behavior were characterized by size exclusion chromatography, NMR, light scattering, and atomic force microscopy. Because of the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as the core and eationic PDMAEMA as the stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH, while the molecular weight of the assemblies decreased.