The compositional dependence of thermodynamic interactions in blends of model polyolefins

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Abstract
We have investigated the thermodynamic interactions as functions of component volume fraction φ and temperature T in six binary polymer blend systems. The components in all cases were model polyolefins, made by saturating the double bonds of nearly monodisperse polydienes. Small‐angle neutron scatteringmeasurements for single‐phase melts, analyzed with the incompressible random phase approximation, were expressed in terms of the Flory–Huggins interaction parameter χ for 27 °C≤T≤167 °C and 0.1≤φ≤0.9. In most systems we found a characteristic upturn in χ at the composition extremes that diminished with increasing temperature. We also found that the component chain dimensions were unaffected by the strength of the interactions. Several theoretical attempts to explain the dependence of χ on component volume fraction were examined. Most were qualitatively inconsistent with the results, and none were fully satisfactory.