ANOMALOUS ATTRACTIVE INTERACTIONS IN POLYPROPYLENE BLENDS

Some new results on thermodynamic interactions in blends of model poly olefins are reported, including more examples of the anomalous attract ion found earlier for polyisobutylene (PIE) blends. Small-angle neutro n scattering (SANS) data demonstrate a significant suppression of conc entration fluctuations in two polypropylene (PP) blends, meaning a net attraction between components relative to the pure liquid states and corresponding to negative values of the Flory-Huggins interaction para meter chi. As in the PIB blends, the temperature dependencies indicate LCST phase behavior but with much higher critical temperatures for th e PP blends. The two PP blends with net attraction also differ from PI B blends in that all their components behave conventionally (net repul sion, positive chi) in blends with other species. The other five PP bl ends in the study exhibit net repulsion but a wide range of mixing beh avior, regular to highly irregular, depending on the second species.