Upper critical solution temperature type phase behavior of poly(styrene-co-acrylonitrile) blends with poly(styrene-co-n-phenyl maleimide) and their interaction energies

Abstract

To enhance the heat resistance of poly(styrene-co-acrylonitrile-co-butadiene), ABS, miscibility of poly(styrene-co-acrylonitrile), SAN, with poly(styrene-co-n-phenyl maleimide), SNPMI, having a higher glass transition temperature than SAN was explored. SAN/SNPMI blends casted from solvent were immiscible regardless of copolymer compositions. However, SNPMI copolymer forms homogeneous mixtures with SAN copolymer within specific ranges of copolymer composition upon heating caused by upper critical solution temperature, UCST, type phase behavior. Since immiscibility of solvent casting samples can be driven by solvent effects even though SAN/SNPMI blends are miscible, UCST-type phase behavior was confirmed by exploring phase reversibility. When copolymer composition of SNPMI was fixed, the phase homogenization temperature of SAN/SNPMI blends was increased as AN content in SAN copolymer increased. To understand the observed phase behavior of SAN/ SNPMI blend, interaction energies of blends were calculated from the UCST-type phase boundaries by using the lattice-fluid theory combined with a binary interaction model.