Rapid deswelling response of poly(N-isopropylacrylamide) hydrogels by the formation of water release channels using poly(ethylene oxide) graft chains

Poly(ethylene oxide) (PEO) chains are introduced as graft chains maintaining freely mobile ends in thermo-responsive cross-linked poly(N-isopropylacrylamide) (PLPAAm) hydrogels by copolymerization of IPAAm with alpha-acryloyl-omega-methoxy-PEO. The deswelling response on raising the temperature of this gel above the gel phase transition temperature (Tp) takes place within 10 min, whereas a conventionally cross-linked PIPAAm gel of the same dimensions requires 1 month for deswelling. This difference is due to the formation of water release channels within the skin layer by the hydrophilic PEO graft chains. The rapid deswelling of the grafted gel is compared with the deswelling changes of random copolymer gels composed of IPAAm and hydrophilic acrylic acid (AAc), which also accelerates gel deswelling. Deswelling is fastest in copolymers containing 1.3 wt % AAc and in grafted gels containing 13 wt % PEO. These results were interpreted as reflecting the gel structure.