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A relation that represents "solid-liquid coexistence" curves in binary equilibrium phase diagrams of solvent crystal-noncrystalline polymer systems is deduced on a more general theoretical basis, which is a counterpart of the Flory-Huggins equation representing a solution curve. The relation deduced is expressed as a function of concentration in terms of the interfacial free energy and crystal size. Next, on this relation basis, a melting point depression analysis is made by using certain experimental results on lightly chemically cross-linked NR-benzene systems whose degree of chemical crosslinking is so small that they can be regarded as uncrosslinked systems. The relation is revised when considering an elastic term by chain entanglements in the good solvent and a certain concentration-temperature dependent polymer-solvent interaction parameter. Consequently, in the higher concentration range, part of the previous data of crystal size determined from X-ray fit fairly well within the upper and lower limits of the data points calculated from the relation revised.

The entanglement model, which was proposed previously on the melting point depression of a crystalline low molecular weight diluent in an un-cross-linked amorphous polymer, was modified so as to be consistent with a frozen tube model. In the latter model, the crystallization of the diluent occurs within the entangled polymer chains, which act as a confining frozen and hard tube involving an unfrozen solvent within. The new model accounts reasonably for the experimental observations and provides estimates of the diluent crystal size, frozen tube size, and other well-defined parameters for the un-cross-linked systems. The calculation based on the new model for two different cases of lightly cross-linked and un-cross-linked rubber mixtures can explain well the crystal sizes determined by X-ray and NMR measurements for some relevant concentrations.

SYNOPSISThe properties of poly(viny1 alcohol) (PVA) hydrogels containing saccharose were examined. The effect of the addition of saccharose to atactic PVA (a-PVA) gels on their melting temperatures was larger than that for syndiotacticity-rich PVA (s-PVA) gels and the melting temperature was above 100°C for a-PVA gels with saccharose contents of 60 wt %. However, the fusion enthalpy ( A H ) of the a-PVA gels was at most 100 kJ/mol. The release of solvent (water/saccharose) from gels in air decreased with an increase in the saccharose content and the equilibrium was achieved after standing for 20 days for the a-PVA and s-PVA gels with saccharose contents above 40 and 20 wt %, respectively.

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