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)

摘要

We report the synthesis of temperature-and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization.Well-defined alpha,omega-bis(dithioester)-functionalized poly(N-isopropylacrylafnide) (PNIPAM) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) were prepared using l,4-bis(thiobenzoylthiomethyl)benzene and l,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents,respectively,Dually responsive multiblock copolymers were synthesized in 4 single arninolysis/oxidation step from the alpha,omega-bis(dithioester)-terminated PNIPAM and PDMAEMA.the copolymers and their stimulus-responsive 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 arid cationic PDMAEMA as the stabilizing shell when above the phase transition temperatures of PNTPAM.The tempgrature-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.