A Binary Interaction Model for Miscibility of Copolymers in Blends

Abstract Miscibility windows often exist in polymer blend systems when the chemical structure of one of the components is systematically varied, e.g. a random copolymer may be miscible with another polymer when neither limiting homopolymer is. A binary interaction model is developed which explains such behaviour. From this prediction, the general notion is advanced that many cases exist where the net exothermic heat of mixing required for miscibility of high molecular weight polymer mixtures may result from appropriate considerations of both intermolecular and intramolecular interactions of component units without an exothermic interaction existing between any individual pair of units. However, it is shown that for a net exothermic mixing the individual interaction parameters for the pairs of units must differ from those predicted by solubility parameter theory. Moreover, the departures from the geometric mean assumption of the solubility parameter theory need not be large to achieve conditions for miscibility. Several examples of the use of such a model are given including one where the homologous series of aliphatic polyesters is treated as ‘copolymers’ by considering their CH x and COO constituents as the ‘monomers’.

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