INVESTIGATION ON THE PARTICLE GROWTH-MECHANISM IN PROPYLENE POLYMERIZATION WITH MGCL2-SUPPORTED ZIEGLER-NATTA CATALYSTS

To elucidate the particle growth mechanism in propylene polymerization with high-yield MgCl2-supported Ziegler-Natta catalysts, observations have been carried out by electron microscopy on a series of samples h aving different degrees of polymer growth (from 0.1 to 1000 g/g of cat alyst). Topics such as surface and bulk morphology, catalyst fragmenta tion, as well as distribution of the catalyst residues in the polymer have been investigated. The experimental data suggest that if the site distribution in the catalyst is uniform and the polymerization condit ions are mild, the polymer growth starts uniformly throughout the cata lyst particle, which then undergoes an even and progressive fragmentat ion into very fine units homogeneously dispersed in the polymer matrix . The above results thus provide further experimental support to the p article growth mechanism outlined in the multigrain or polymeric flow models. (C) 1994 John Wiley and Sons, Inc.