Phase behavior and binary interaction energies of copolymer blends

The phase behavior of blends with copolymers have been investigated experimentally. The polymer systems studied focused on three areas: the influence of depolymerization stabilizers on polymer blend miscibility, reactive compatibilization, and the incorporation of flame retardants (bromine) as monomers. Small amounts of an acrylate comonomer are incorporated in commercial methyl methacrylate (MMA)-based polymers to increase their stability against depolymerization. Blends of styrene-acrylonitrile (SAN) copolymers with MMA-n-butyl acrylate copolymers had a larger miscibility window than with MMA-ethyl acrylate copolymers. The functional monomers 2-hydroxyethyl methacrylate (HEMA) and 4-methacryloxyethyl trimellitic anhydride (4META) could be incorporated into MMA copolymers in small amounts and maintain miscibility with SAN copolymers. Blends containing tribromostyrene (TBS) were investigated and compared to the corresponding non-brominated blend. The miscibility regions for blends of STBS copolymers with the homopolymers polystyrene (PS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), tetramethyl bisphenol A polycarbonate (TMPC), as well as blends of MMA-TBS copolymers with poly(methyl methacrylate) (PMMA) were determined. Blends of MMA-TBS copolymers with styrene-methyl methacrylate (SMMA) copolymers, and blends of both TBS copolymers with SAN and styrene-maleic anhydride (SMA) copolymers were also investigated. Binary interaction energies were determined using the miscibility data with the Flory-Huggins theory and the binary interaction model. Lower critical solution temperature (LCST) behavior was found with some blends, and agreed well with the spinodal temperatures predicted using the interaction energies in conjunction with the lattice-fluid theory developed by Sanchez and Lacombe. All interaction energies found were consistent with values from the literature and thus can be added to the database of interaction energies for use in predicting miscibility behavior.