Synthesis and characterization of porous poly(N-isopropylacrylamide) hydrogels prepared in ethanol-water mixtures

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by free-radical polymerization in different ethanol-water mixtures. A scanning electron microscopy study revealed that the resulting hydrogels were macroporous. The swelling ratios of the resultant hydrogels in water at 20°C followed this order: X0.34 â X0.68 > X 0.48 > X0.09 > X0.04 > X0, where Xa denotes a gel prepared in an ethanol-water solvent mixture with an ethanol molar fraction of a. Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with increasing temperature. The complete collapse of the PNIPAM chain of all of these gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all of the PNIPAM gels with different molar fractions of ethanol at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.34 > X0.48 > X0.68 > X 0.09 > X 0.04 > X0. The reswelling rates of these hydrogels decreased in the following order: X0 > X0.04 â X0.48 > X0.09 â X0.68 > X 0.34. The freeze-drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels. © 2011 Wiley Periodicals, Inc.