Thermodynamics and phase separation in melt blends of polyethylene and model copolymers

Binary blends of linear polyethylene (PE) and hydrogenated polybutadiene (HPB) are employed to evaluate the interaction parameter chi between chains containing different relative amounts of linear and ethyl-branched C sub 4 H sub 8 repeat units. Conditions for liquid--liquid phase separation in the melt are determined unambiguously from the appearance of quench-crystallized blends which have been etched to define HPB-rich domains. For polyethylene and random poly(ethylene-co-butene-1) at 150 deg C, chi = 0.022Y sub br exp 2 , where Y sub br is the fraction of branched C sub 4 H sub 8 repeat units. Domain sizes range from 0.1-16 mu m, increasing with chi / chi sub c and the time permitted for phase separation. Sizes observed for blends near the critical point compare favorably to those predicted by the linearized theory for spinodal decomposition. Photomicrographs. 37 ref.--AA