ON THE STATE OF MISCIBILITY OF ISOTACTIC POLY(PROPYLENE) ISOTACTIC POLY(1-BUTENE) BLENDS - COMPETITIVE LIQUID-LIQUID DEMIXING AND CRYSTALLIZATION PROCESSES

The miscibility behavior of blends of high molecular weight isotactic poly(propylene) (it-PP) and isotactic poly(1-butene) (it-P1B) has been investigated by a combination of optical and scanning electron micros copies, differential scanning calorimetry, and dynamic mechanical anal ysis. The results of these investigations demonstrate that for the mol ecular weights investigated, it-PP and it-P1B form blends that are par tially miscible in the liquid state. Liquid-liquid demixing is observe d by optical microscopy at temperatures above the melting temperature of the it-PP component and is also inferred from scanning electron mic rographs of the freeze fracture surface of quenched blends after extra ction of the it-P1B component with cyclohexane. It-PP spherulites grow through both liquid phases at relative rates that depend markedly on the crystallization temperature. The complex multiple-melting behavior of the isotactic poly(propylene) component in the blend is explained in terms of a bimodal distribution of it-PP lamellar crystals which re sults from crystal growth in the phase-separated liquid. The heterogen eous nature of the mixed liquid is consistent with the upper critical solution temperature behavior observed in our previous study of blends of atactic poly(propylene) and atactic poly(1-butene). Finally, the d ynamic mechanical analysis data are explained in terms of a liquid-liq uid demixing process that results in a significant degree of phase mix ing.