Crystallization mechanism of syndiotactic polypropylene analyzed by time-dependent light scattering

Monitoring the time dependence of polarized (vv) and depolarized (hv) light scattering during the crystallization of a polymer can be used to characterize the development of the size and internal structure of the growing spherulites or hedrites. In particular, it is possible to distinguish between a growth of objects with a fixed inner structure and cases of a subsequent inner structure modification. We report here on the crystallization of a sample of syndiotactic polypropylene from the melt. The vv- and hv-scattering patterns are indicative for the growth of hedrites and enable a specific direct evaluation procedure to be applied. We determined for several crystallization temperatures the final size of the hedrites, the crystallization time and observed, in particular, changes with time in the mean inner anisotropy and density. Observations speak in favor of an in-filling process of crystalline lamellae accompanying the hedrite's growth. From a complementary dilatometric determination of the specific volume change and its agreement with kinetical data of the light-scattering experiments it follows that the number of growing hedrites is constant.