Synthesis and swelling behavior of comb-type grafted hydrogels by reversible addition-fragmentation chain transfer polymerization

The comb-type grafted hydrogels poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide) (PNIPAM-g-PNIPAM) and poly(acrylic acid)-g-poly(N-isopropylacrylamide) (PAAc-g-PNIPAM) were prepared by reversible addition-fragmentation chain transfer polymerization. A macromolecular chain-transfer agent was prepared first. Then, hydrogels were obtained by a reaction with a comonomer (N-isopropylacrylamide or acrylic acid) in the presence of N,N-methylenebisacrylamide as a crosslinker. The equilibrium swelling ratios and the swelling and deswelling kinetics of PNIPAM-g-PNIPAM were measured. The effects of the chain length and amount on the swelling behavior were investigated. The deswelling mechanism was illustrated. Meanwhile, the PAAc-g-PNIPAM hydrogel was used to confirm the versatility of this novel method. It was prepared in an alcoholic medium, whereas hydrogen-bonding complexes formed in 1,4-dioxane, which was chosen as the reaction medium for the PNIPAM-g-PNIPAM hydrogel. (c) 2005 Wiley Periodicals, Inc.