Abstract
The phase behavior of blends of poly(isobutylene) (PIB) having different molecular weights and its carbosilane analog poly(dimethylsilylenemethylene) (PDMSM) is studied by optical microscopy, differential scanning calorimetry (DSC) and pressure-volume-temperature (PVT) measurements. DSC and microscopy measurements reveal that PDMSM with M w = 721000 g/mol is miscible at all blend ratios with a PIB of M w = 1500 g/mol, and immiscible at virtually all blend ratios and temperatures with PIBs of higher molecular weight. PVT measurements of the neat blend components are evaluated in terms of the Flory-Orwool-Vrij equation-of-state and Patterson theory. Free volume and interactional contributions to the overall X parameter are of comparable size, but have opposing trends in temperature dependence. This leads to a X(T) function that does not obey the proportionality between X and 1/T observed for systems with dominating repulsive enthalpic interactions. The miscibility as a function of blend ratio and molecular weight is successfully described by the Patterson theory with the parameter X 12 = 0.4 J/cm 3 .
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