CRYSTALLIZATION KINETICS OF SYNDIOTACTIC POLYPROPYLENE STUDIED BY TIME-DEPENDENT LIGHT ATTENUATION

Abstract

Crystallization kinetics of syndiotactic polypropylene ( sPP) was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering. Initial time and growth time of crystallization were obtained, and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated. of polymer crystallization are usually carried out by differential scanning calorimetry or X-ray scattering in the wide- and small-angle range, sometimes also by light scattering, dilatometry or time dependent vibrational spectroscopy. Although based on different properties there is not much difference in the sensitivity of all these methods. Reliable data are only obtained from values of the crystallinity in the range of some percent of the final values. This means that for growing spherulites, which usually reach end sizes in the order of several micrometers, measurements start only at sizes of several hundred nanometers. This, however, is already far away from the initial stages. Nuclei have sizes in the order of several to ten nanometers and these, together with the small hedrites and spherulites existing at the beginning, cannot be observed. To study the objects in these initial stages, one can now use atomic force microscopy (AFM), but this technique has also some shortcomings. Observations by AFM principally refer to the development and growth of spherulites at the free surface of a melt, and conditions here may differ from those in the bulk. In addition, deriving global properties from observations of the development of single objects is sometimes difficult, because a certain selectivity is usually involved. Presently, the work on polymer crystallization has given considerable attention to the possibility that the crystal phase in the final semicrystalline state could be preceded by a transient liquid phase with density different from that of the initial quenched bulk isotropic melt or annealed glassy state. A number of papers have explicitly criticized the spinodal hypothesis and associated experimental studies, favoring the traditional picture of nucleation and growth. Various studies have suggested that the denser transient phase involves chain orientation, and there are good reasons to assume a crystal nucleation and growth which include an intermediate phase in the form of a coverage of the whole volume by a prior mesomorphic phase developing by a mechanism which resembles a spinodal process (7) , or a nucleation into a mesomorphic phase (8) , or the existence of a