X-RAY MICROTOMOGRAPHY STUDIES OF NASCENT POLYOLEFIN PARTICLES POLYMERIZED OVER MAGNESIUM CHLORIDE-SUPPORTED CATALYSTS

Drastic changes occur during the initial stages of the alpha-olefin po lymerization over heterogeneous catalysts. Fragmentation of the suppor t takes place as polymer is formed at the active sites within the void s of the support/catalyst. Magnesium chloride-supported titanium catal yst/polymer particles have been analyzed employing high-resolution com puted microtomography (CMT) using synchrotron radiation at Brookhaven National Laboratory. The changes in morphology, the spatial distributi on of the support/catalyst fragments, porosity, and polymer distributi on in single growing polypropylene and polyethylene particles have bee n studied. These studies documented considerable macroporosity (> 2 mu m in size) within the growing catalyst/support/polymer particles. The largest pores may be due to agglomeration of smaller subparticles. Our results confirm that the initial fragmentation of the support proceed s readily and uniformly to yield a multi-grain growth of subparticle a gglomerates. The support/catalyst fragments appear to be distributed r elatively uniformly within the growing polymer particle. The surface o f the subparticle agglomerates is accessible through the void-space be tween growing catalyst/particle grains. This may facilitate monomer tr ansport to the activate sites through the polymer/catalyst particles. (C) 1993 John Wiley & Sons, Inc.