THERMODYNAMIC PROPERTIES OF SWOLLEN POLYMER NETWORKS CONTAINING FREE POLYMER-CHAINS

Osmotic and small-angle X-ray and neutron scattering (SAXS and SANS) m easurements are reported for poly(vinyl acetate)-toluene solutions and gels containing a controlled amount of free poly(vinyl acetate) (PVAc ) chains. The thermodynamic response of the gel was found to differ si gnificantly from that of the corresponding polymer solution. This devi ation is interpreted in terms of a reduction in the volume fraction of the network polymer participating in the thermodynamic concentration fluctuations. No significant difference was detected in the thermodyna mic properties of PVAc gels containing different amounts of free PVAc chains. The radius of gyration of the free chains trapped in the swoll en network, determined by SANS, was found to be significantly smaller than their unperturbed dimension. The observed chain contraction is co nsistent with predictions of the theory of random media.