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Mutual solubilities and liquid-state interactions of polyisobutylene (PIB) with other polyolefins were investigated by a variety of techniques. 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 Flory-Huggins parameter was found to be large and negative at room temperature in all cases, contrary to expectations and to previous experience with blends of other saturated hydrocarbon polymers. However, diminished rapidly in magnitude with increasing temperature, eventually becoming positive and culminating finally in phase separation.Molecular weight independence of , volume change on mixing, glass transition temperature vs blend composition, and a phase diagram were established for one PIB/polyolefin system. The insensitivity of phase separation temperature to both blend composition and component molecular weight was shown to be a natural qualitative consequence of the unusually strong temperature dependence of . The volume changes and Tg behavior are also unusual and remain to be explained, along with the fundamental source of attractive interactions (negative ) in blends of saturated hydrocarbon polymers.

Much is known about the structure and order-disorder transitions of linear block copolymers.1-3 Detailed information about the kinds of microphase domain morphologies that can be found in block polymers, the composition of copolymer that display each structure, and the conditions for the transitions between these morphologies, as well as into a disordered state, is available. For graft polymers, there has been only one theoretical treatment

In this paper, we report on how interaction strength varies with pressure and temperature for several polyolefin mixtures. We find that the interaction energies that govern phase behavior in polymer blends are only a function of density for UCST polyolefin blends far from a critical point. As a result, the effects of pressure on miscibility can be predicted for such blends from knowledge of the effects of temperature on the interactions combined with PVT data. This remarkable simplification appears to be related to the van der Waals nature of the interactions between saturated hydrocarbons. Density dependence predicts the trends correctly for LCST polyolefin blends, but for these mixtures the interactions depend in a more complex way on T and P.

The morphological development in blends of bisphenol-A polycarbonate (PC) and poly(methylmethacrylate) (PMMA) blends during isothermal annealing above 200 °C has been investigated where competition between liquid–liquid phase separation by spinodal decomposition and interchange reactions take place. Interchange reactions between PC and PMMA occurs at temperatures above 200 °C and leads to the formation of in situ graft copolymers from an ester–ester interchange reaction. During spinodal decomposition, graft copolymers are produced mainly at the interface region between the interconnected microphase domains. Instead of the usual ‘‘coarsening’’ process which is characteristic of the late-stage of spinodal decomposition, the mixture exhibits nearly monodisperse spherical domains as revealed by optical microscopy. This phenomenon is further studied through extensive small angle light scattering measurements. Resonance peaks up to fourth order are noted, a rare observation. The result clearly demonstrates that graft copolymers are formed in situ and can act as very effective ‘‘surfactants’’ in polymer blends. Furthermore, an attempt is made to analyze the angular dependence of the scattering intensity from this morphology with the Percus–Yevick hard sphere liquid theory. These results are believed to be general and therefore applicable to a wide variety of blends containing one or more components capable of an interchange reaction.