Phase diagrams of ethylene-vinyl acetate copolymers

The miscibility of ethylene-vinyl acetate copolymers of different compositions was studied by X-ray microanalysis over a wide temperature range, and phase diagrams were obtained. The dependences of critical temperature and compositions of coexisting phases on the difference in compositions of blended copolymers were determined. The data obtained were analyzed in terms of the Flory-Huggins-Scott concept. It was shown that the predictive power of the Scott equation is rather low. A more general expression that takes into account the difference in the molecular mass of copolymers was proposed. The interaction parameters were calculated and their enthalpy and entropy terms were estimated. It was found that the deviations in the experimental critical temperatures from the values calculated with the proposed equation are due to the contribution of the entropic term to the interaction parameter.