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

The Flory-Huggins interaction parameter chi(gel) was determined for chemically 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) < 346 000). Crosslinks were introduced at different polymer concentrations (3% w/w less than or equal to c(0) less than or equal to 12% w/w). It is found that in all systems the values of chi(gel) for the crosslinked polymer are greater than the values of chi(sol) for the uncrosslinked material at identical concentrations. The chi(gel) data reported here seem to be a function only of the polymer concentration and are independent of the details of the network structure. The results are discussed in relation to other work on the crosslink dependence and volume fraction dependence o chi(gel).