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 was not trivial owing to the small difference of only 10°C between the T(g)s of these two isomeric polystyrenes. The preliminary morphology characterization using optical and scanning electron microscopies indicated that 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 existed. The crystallinity of s-PS in a-PS/s-PS mixtures showed a minor negative deviation from linearity, which suggests favorable, albeit weak, interactions between the chain segments of s-PS and a-PS. These results provide evidence 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. In 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 negative value for the interaction parameter (X=~-0.11) was found, further suggesting that miscibility is likely favored.