STEREOCHEMICAL COMPOSITION PROPERTIES RELATIONSHIPS IN ISOTACTIC POLYPROPYLENES OBTAINED WITH DIFFERENT CATALYST SYSTEMS

The influence of stereochemical composition of the radial growth rate of spherulites, the nucleation density, the overall rate of crystallization and the thermal behavior of fractions of iPP samples synthesized with different catalyst systems was investigated. The study used **1**3C n. m. r. , differential scanning calorimetry and optical microscopy. The **1**3C n. m. r. analysis showed that due to the presence of catalytic sites with different stereoregulating capability the catalyst system produces polypropylene with different stereoregularity. It was found that the growth rate of spherulites and the overall rate of crystallization are strictly related to the stereochemical structure of the polypropylene. Moreover, for the low yield iPP, phenomena of secondary crystallization were observed by Avrami analysis of the overall kinetics. Values of the equilibrium melting temperature, energy of nucleation, and surface free energy of folding of iPP lamellar crystals have been determined according to the kinetic theory of polymer crystallization.