SWELLING OF POLY(N-ISOPROPYLACRYLAMIDE) GELS IN WATER-ALCOHOL (C1-C4) MIXED-SOLVENTS

The swelling volume of poly(N-isopropylacrylamide) gels in alcohol-water mixtures (C1-C4) was measured at 25-degrees-C. The swollen gel in water shrank first with addition of a small amount of alcohol and then reswelled on further addition of alcohol showing a typical reentrant transition. The swelling behavior of the gels was correlated with the properties of the aqueous alcohol mixtures (i.e., the change of alcohol molar volume and thermodynamic activities of alcohol and water). The uptake of ethanol and water in the equilibrated gels was measured at 25-degrees-C. Ethanol was found to be selectively taken up in all aqueous alcohol mixtures. The strength of hydrogen bonding around amide groups of the linear polymer in aqueous ethanol solution was examined by Fourier transform infrared spectroscopy (Ff -IR). Stretching frequencies of the carbonyl group (amide I) of the polymer were sensitive to hydrogen bond strength which depended on the alcohol composition. These FT-IR spectroscopic studies suggested that the polymer networks may take a compact conformation in the reentrant transition region where the PIPAAm chains interact with themselves through hydrogen bonding.