THE COMPOSITIONAL DEPENDENCE OF THERMODYNAMIC INTERACTIONS IN BLENDS OF MODEL POLYOLEFINS

We have investigated the thermodynamic interactions as functions of co mponent volume fraction phi and temperature T in six binary polymer bl end systems. The components in all cases were model polyolefins, made by saturating the double bonds of nearly monodisperse polydienes. Smal l-angle neutron scattering measurements for single-phase melts, analyz ed with the incompressible random phase approximation, were expressed in terms of the Flory-Huggins interaction parameter chi for 27 degrees C less than or equal to T less than or equal to 167 degrees C and 0.1 less than or equal to phi greater than or equal to 0.9. In most syste ms we found a characteristic upturn in chi at the composition extremes that diminished with increasing temperature. We also found that the c omponent chain dimensions were unaffected by the strength of the inter actions. Several theoretical attempts to explain the dependence of chi on component volume fraction were examined. Most were qualitatively i nconsistent with the results, and none were fully satisfactory.