Thermodynamic investigation of the phase separation behaviour of ethylene‐vinyl acetate copolymers in diphenyl ether

Abstract

AbstractLiquid‐liquid phase separation in solutions of ethylene‐vinyl acetate (EVA) random copolymers is investigated for different VA content using diphenyl ether (DPE) as the solvent. Cloud‐point curves (CPC's), spinodal curves (SC's) and critical conditions (CC's) were experimentally established by visual observation, pulse‐induced critical scattering (PICS) and phase‐volume ratio method, respectively. It is found that the miscibility gap, which is of the Upper Critical Solution Temperature (UCST) type, shifts to lower temperatures as the VA content in the copolymer increases. The limits of thermodynamic stability (spinodals) could be reasonably well described by means of the classical rigid lattice model, provided allowance is made for the various constitutional repeating units (CRU's) to differ in nearest‐neighbour contacts. Using this description, CC's and SC's could be predicted in a qualitative way. Further, measured CPC's can be nearly described in a quantitative sense when the value of the higher molecular weight average M̄z is adjusted well above the value suggested by GPC measurements.