COEXISTENCE CURVE OF DILUTE POLYMER-SOLUTION IN A MIXED-SOLVENT HAVING CRITICAL DEMIXING POINT

The coexistence curves of dilute solutions of Poly(vinyl methyl ether) (PVME) in a solvent mixture methanol/cyclohexane which has a critical demixing point were measured. We found that in the methanol-rich regi on the presence of a small amount of PVME does not cause any appreciab le change in the phase boundary of binary methanol/cyclohexane mixture , whereas in the cyclohexane-rich region it gives rise to a marked shi ft of phase boundary toward higher temperature region. It is shown tha t this characteristic phase behavior can be well explained qualitative ly on the basis of Flory-Huggins solution theory, together with the in teraction parameters deduced from small angle neutron and X-ray scatte ring experiments, as due to the smallness of the interaction parameter , chi13, between methanol and PVME. The smallness of chi13 can be inte rpreted as a manifestation of the association of methanol molecules.