Observations and thermodynamic interpretations of polymer blend phase behavior
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The phase behavior of binary mixtures of several different homopolymers and copolymers was investigated and compared to the phase behavior predicted while using the Flory-Huggins theory, mean field approximation, and Sanchez-Lacombe Equation of State. Blends were prepared by a variety of methods to achieve equilibrium phase behavior and to simulate critical point miscibility criteria. The resulting blend phase behavior was evaluated by observation of glass transitions and scattered light. Collected blend phase behavior was used to characterize the enthalpic interaction between various polymer repeat units based on styrene, acrylonitrile, maleic anhydride, n-alkyl acrylates, benzyl acrylate, pentabromobenzyl acrylate, and polycarbonates. These interactions were iv analyzed for consistency with related polymer miscibility regions, suggested binary interactions reported by other researchers, and predicted interactions obtained through regular solution theory. Of special interest were interactions with poly(styrene-coacrylonitrile), which appears to contain a substantially larger intramolecular repulsion than some researchers have suggested. The implied styrene-acrylonitrile interaction and the interactions derived while using that interaction were closer to their predicted values than previous estimates. Interactions derived from blends with poly(styrene-co-maleic anhydride) were consistent when the alternating nature of the copolymer was accounted for. The phase behavior and optical properties of blends of poly(styrene-statacrylonitrile) and a polycarbonate copolymer were studied. These blends were not miscible, but appeared clear in certain conditions of composition and temperature. The light scattering behavior of these blends as a function of temperature was investigated. The phase behavior of blends containing copolymers made from benzyl acrylate and pentabromobenzyl acrylate was investigated. A set of interactions between styrene, methyl methacrylate, benzyl acrylate, pentabrombenzyl acrylate, and acrylonitrile was determined that could be used to predict the phase behavior in blends of copolymers.