Some new results on thermodynamic interactions in blends of model polyolefins are reported, including more examples of the anomalous attraction found earlier for polyisobutylene (PIE) blends. Small-angle neutron scattering (SANS) data demonstrate a significant suppression of concentration 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 parameter chi. As in the PIB blends, the temperature dependencies indicate LCST phase behavior but with much higher critical temperatures for the PP blends. The two PP blends with net attraction also differ from PIB blends in that all their components behave conventionally (net repulsion, positive chi) in blends with other species. The other five PP blends in the study exhibit net repulsion but a wide range of mixing behavior, regular to highly irregular, depending on the second species.