Interactions between polystyrenes of different tacticities and thermal evidence for miscibility

Various evidence of thermal behavior was probed to discuss the miscibility in atactic polystyrene (a-PS) with syndiotactic polystyrene (s-PS), which w as not trivial owing to the small difference of only 10 degrees C between t he T(g)s of these two isomeric polystyrenes. The preliminary morphology cha racterization using optical and scanning electron microscopies indicated th at no discernible heterogeneity existed in the a-PS/s-PS blend. Composition dependence of peak temperature of cold crystallization for the quenched a- PS/s-PS blend samples also supported that inter-segmental interactions exis ted. The crystallinity of s-PS in a-PS/s-PS mixtures showed a minor negativ e deviation from linearity, which suggests favorable, albeit weak, interact ions between the chain segments of s-PS and a-PS. These results provide evi dence that this isomeric pair of polystyrenes of different tacticities are mixed in the molecular scales. The melting behavior of semicrystalline s-PS in the a-PS/s-PS mixtures was analyzed using the Flory-Huggins approach. I n measuring the equilibrium melting point of s-PS in the a-PS/s-PS mixtures , the complex multiple melting peaks of s-PS were also discussed. A small n egative value for the interaction parameter (chi=similar to-0.11) was found , further suggesting that miscibility is likely favored. (C) 1999 Elsevier Science Ltd. All rights reserved.