VAPOR-LIQUID-EQUILIBRIA FOR COPOLYMER SOLVENT SYSTEMS - EFFECT OF INTRAMOLECULAR REPULSION/

The role of intramolecular interactions in blend miscibility is well d ocumented for polymer+copolymer mixtures (ten Brinke et al., 1983; Pau l and Barlow, 1984). Some copolymer+polymer mixtures are miscible alth ough their corresponding homopolymers are not miscible; for example, o ver a range of acrylonitrile content, styrene/acrylonitrile copolymers are miscible with poly(methyl methacrylate) but neither polystyrene n or polyacrylonitrile is miscible with poly(methyl methacrylate). Simil arly, over a composition range, butadiene/acrylonitrile copolymers are miscible with poly(vinyl chloride) while none of the binary combinati ons of the homopolymers [polybutadiene, polyacrylonitrile, and poly(vi nyl chloride)] are miscible. This behavior has been attributed to ''in tramolecular repulsion'' between unlike copolymer segments. We have ob served similar behavior in vapor-liquid equilibria (VLE) of copolymersolvent systems. We find that acrylonitrile/butadiene copolymers have higher affinity for acetonitrile solvent than do polyacrylonitrile or polybutadiene. We attribute this non-intuitive behavior to ''intramole cular repulsion'' between unlike segments of the copolymer. This repul sive interaction is weakened when acetonitrile molecules are in the vi cinity of unlike copolymer segments, favoring copolymer+solvent miscib ility. We find similar behavior when acetonitrile is replaced by methy l ethyl ketone. To our best knowledge, this effect has not been report ed previously for VLE. We have obtained VLE data for mixtures containi ng a solvent and a copolymer as a function of copolymer composition. I t appears that, at a given solvent partial pressure, there may be copo lymer composition that yields maximum absorption of the solvent. This highly non-ideal VLE phase behavior may be useful for optimum design o f a membrane for a separation process.