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In this article, we report the results of molecular dynamics simulations for models of poly(ethylene), isotactic poly(propylene), and mixtures of the two to understand the possible origin of melt state incompatibility. At temperatures well above the crystal melting points of the homopolymers, isolated poly(ethylene) and poly(propylene) chains formed high-density collapsed states. The poly(ethylene) and poly(propylene) chains were found to segregate into distinct domains even when the initial state was highly interpenetrating. The poly(ethylene) phase shows a significant amount of local order at the simulation temperature. In the case of poly(propylene), some helical segments were found in the collapsed structure. We speculate that the immiscibility of these two nonpolar polymers, in the melt state, may be due to the differences in local morphology that are present in the melt state.

Blends of monodisperse polystyrene were recovered from chloroform solutions and dried. Large variations in the mean entanglement molecular weight and in the zero shear viscosity were observed. The steady state compliance was dependent only on sample polydispersity and did not vary with sample history. The results could be rationalized using a modification of the theory of Kavassalis and Noolandi. It is concluded that the prior treatment of the polymers alterd the the entanglement spacing. This may be the result of a change in the spatial dimensions of the polymer moleculs in the bulk

Monodispersed polystyrenes were precipitated from chloroform solutions and dried. Residual solvent was present only in trace quantities. Large variations were observed in the mean molecular weight between entanglements and in the zero-shear viscosity. The steady-state compliance was not affected by sample history. Trends predicted by reptation scaling laws were indeed observed, but the data for all the samples did not fit a unique curve. The data could be resolved into a single plot by using a modification of the theory of Kavassalis and Noolandi. It is concluded that the prior treatment of the polymer altered the entanglement spacing as well as the nature of the entanglements