Synthesis of rapid responsive gels comprising hydrophilic backbone and poly(N-isopropylacrylamide) graft chains by RAFT polymerization and end-linking processes

A thermosensitive poly(N-isopropylacrylamide) (PNIPAM) grafted gel, which comprises hydrophilic backbone and freely mobile PNIPAM graft chains, was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and end-linking processes. Functional PNIPAM bearing dithiobenzoate end group (-C(S)S-R) was prepared first, and then it was reacted with divinyl compounds to obtain gel. In order to adjust the composition of the gels, two divinyl compounds, N,N-methylenebisacrylamide (BIS) and poly(ethylene glycol) diacrylate (PEGDAC), were used. The cross-linking polymerization mechanism was proposed. The swelling and deswelling kinetics of the hydrogels were measured. The gels exhibit rapid deswelling kinetics. At the same time, they show rapid swelling kinetics within 30 min, whereas a conventional PNIPAM-co-PEG-co-BIS gel with the same feed composition requires more than 10 h to reach swelling equilibrium.