Comb-Type Grafted Hydrogels of PNIPAM and PDMAEMA with Reversed Network-Graft Architectures from Controlled Radical Polymerizations

Dual thermo- and pH-responsive comb-type grafted hydrogels of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropylacrylamide) (PNIPAM) with reversed network-graft architectures were synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization and click chemistry. Two kinds of macro-cross-linkers with two azido groups at one chain-end and different chain length [PNIPAM–(N(3))(2) and PDMAEMA–(N(3))(2)] were prepared with N,N-di(β-azidoethyl) 2-halocarboxylamide as the ATRP initiator. Through RAFT copolymerization of DMAEMA or NIPAM with propargyl acrylate (ProA) using dibenzyltrithiocarbonate as a chain transfer agent, two network precursors with different content of alkynyl side-groups [P(DMAEMA-co-ProA) and P(NIPAM-co-ProA)] were obtained. The subsequent azido-alkynyl click reaction of macro-cross-linkers and network precursors led to the formation of the network-graft hydrogels. These dual stimulus-sensitive hydrogels exhibited rapid response, high swelling ratio and reproducible swelling/de-swelling cycles under different temperatures and pH values. The influences of cross-linkage density and network-graft architecture on the properties of the hydrogels were investigated. The release of ceftriaxone sodium from these hydrogels showed both thermal- and pH-dependence, suggesting the feasibility of these hydrogels as thermo- and pH-dependent drug release devices.