Stacking Faults and Growth of Syndiotactic Polypropylene Crystals

Abstract

Lamellar crystals of syndiotactic polypropylene (sPP) with three different stereoregularities were grown isothermally in thin films, and the growth rates in the b-direction were estimated. Melting of the isothermally crystallized samples was also investigated with DSC, and equilibrium melting temperatures of the samples were estimated. Because of the existence of stacking faults, the (010) surface of sPP crystals should have a considerable amount of steps in the range of crystallization temperature (T c ) adopted in this study. Nucleation at such steps should be advantageous according to the nucleation theory. Because the amount of the faulted boundary, and hence the steps, increases with increasing supercooling (ΔT), the growth of sPP should be accelerated at the lower T c compared with other polymers, such as polyethylene. However, the accelerating trend was not recognized. At the same time, the existence of Regime I growth, as modeled in the original nucleation theory, is doubtful on the growth surface with the steps. However, the discontinuity that should be attributed to the Regime II to Regime I transition was observed in the plot of logarithmic growth rate vs. 1/T c (ΔT). According to these results, it is doubtful that the formation of a new surface is the barrier for secondary nucleation, at least for sPP.