EFFECT OF CROSS-LINKS ON THE THERMODYNAMICS OF POLY(VINYL ALCOHOL) HYDROGELS

The Flory-Huggins interaction parameter chi(gel) was determined for ch emically crosslinked poly(vinyl alcohol) (PVA) hydrogels from swelling pressure and elastic modulus measurements. The PVA gels were prepared in aqueous solutions of different molecular weight (22 000 < M(w) < 3 46 000). Crosslinks were introduced at different polymer concentration s (3% w/w less than or equal to c(0) less than or equal to 12% w/w). I t is found that in all systems the values of chi(gel) for the crosslin ked polymer are greater than the values of chi(sol) for the uncrosslin ked material at identical concentrations. The chi(gel) data reported h ere seem to be a function only of the polymer concentration and are in dependent of the details of the network structure. The results are dis cussed in relation to other work on the crosslink dependence and volum e fraction dependence o chi(gel).