Synthesis and Property of Temperature-Responsive Hydrogel with Movable Cross-Linking Points

A novel water-soluble cyclic macromonomer, AAm- c -PEG, based on a cyclic poly(ethylene glycol) (PEG) was prepared. Radical copolymerizations of N -isopropylacrylamide (NIPAAm) with the cyclic macromonomer were carried out to obtain mechanically cross-linked poly(NIPAAm) hydrogels with movable cross-linking points. For comparison, chemically cross-linked PEG-grafted poly(NIPAAm) hydrogels were prepared by radical copolymerization of NIPAAm with a PEG-based linear macromonomer, AAm- l -PEG, using methylenebis(acrylamide) (MBAAm) as a cross-linking agent. Shrinking experiment of these hydrogels revealed poly(NIPAAm) gels with movable cross-linking points exhibited faster volume shrinking than those of chemically cross-linked ones. Further, threading efficiency for cyclic PEG segment was estimated by measuring the swelling ratio in isopropyl alcohol (IPA) which is a nonsolvent for PEG.