ANOMALOUS MIXING BEHAVIOR OF POLYISOBUTYLENE WITH OTHER POLYOLEFINS

Mutual solubilities and liquid-state interactions of polyisobutylene ( PIB) with other polyolefins were investigated by a variety of techniqu es. Near room temperature PIB was found to be miscible with a limited range of polyolefin structures. The interactions for several blends in this range were determined by small-angle neutron scattering. The Flo ry-Huggins parameter chi was found to be large and negative at room te mperature in all cases, contrary to expectations and to previous exper ience with blends of other saturated hydrocarbon polymers. However, ch i diminished rapidly in magnitude with increasing temperature, eventua lly becoming positive and culminating finally in phase separation. Mol ecular weight independence of chi, volume change on mixing, glass tran sition temperature vs blend composition, and a phase diagram were esta blished for one PIB/polyolefin system. The insensitivity of phase sepa ration temperature to both blend composition and component molecular w eight was shown to be a natural qualitative consequence of the unusual ly strong temperature dependence of chi. The volume changes and T-g be havior are also unusual and remain to be explained, along with the fun damental source of attractive interactions (negative chi) in blends of saturated hydrocarbon polymers.