Miscibility of propylene-ethylene copolymer blends

Miscibility of homogeneous propylene/ethylene (P/E) copolymers of relatively narrow molecular weight distribution was studied as a function of constituent comonomer content. Polymers with up to 31 mol % ethylene were blended in pairs in order to vary the comonomer content difference. Binary blends were rapidly quenched from the melt to retain the phase morphology, and the phase volume fractions were obtained from AFM images. Copolymers of molecular weight about 200 kg mol(-1) were miscible if the difference in ethylene content was less than about 18 mol % and immiscible if the ethylene content difference was greater than about 20 mol %. Blends with constituent composition difference in the range of 18-20 mol % exhibited partial miscibility in the melt as indicated by a phase volume fraction that was different from the blend volume fraction. The temperature dependence of blend morphology confirmed the UCST behavior of P/E copolymer blends. The phase composition and the X interaction parameter were extracted by using an approach that considered the molecular weight distribution. The compositional dependence of X conformed to the copolymer equation and depended on comonomer content difference only, not on comonomer content per se.