Crystallization of Isotactic Polypropylene from Prequenched Mesomorphic Phase

Abstract

The crystallization process of isotactic polypropylene (iPP) by heating from the prequenched mesomorphic phase has been studied using wide-angle X-ray diffraction, small-angle X-ray scattering, and optical microscopy. Mesomorphic iPP as quenched shows the well-known nodular structure of ca. 100 Å. In heating process the nodules grew larger keeping self-similarity, with the mesomorphic phase partially transforming into the crystalline phase inside the nodules. After reaching the isothermal process, the nodules stopped to grow at a certain quasi-equilibrium size depending on the annealing temperature. During the long annealing, the interface among the nodules became obscure, and the nodules in nanometer scale merge into larger structure of pure α-phase in micrometer scale. The relation between the quasi-equilibrium nodule size and the annealing temperature leads an extrapolated melting temperature of the mesomorphic phase, which is located above the equilibrium melting temperature of the α-crystal.