Fragmentation Behavior of Silica-Supported Metallocene/MAO Catalyst in the Early Stages of Olefin Polymerization

Abstract

Polymer particle growth in the early stages of olefin polymerization has been investigated using metallocene/methylaluminoxane (MAO)/silica catalyst systems. Scanning electron microscopy (SEM) has been used to characterize the surface and cross-sectional morphology of polymer particles at different stages of particle growth. The aluminum distribution in various MAO-impregnated supports has been determined by energy-dispersive X-ray (EDX) analysis, revealing that the homogeneity of the distribution is dependent on both the silica calcination temperature and the impregnation conditions used. Depending on the impregnation routes and polymerization conditions applied, two fragmentation behaviors have been observed: main polymerization at the surface with coarse fragmentation at the core of the support particles in the case of propylene polymerization and a heterogeneous (co)catalyst distribution, and a layer-by-layer fragmentation of the support in ethylene polymerization using a homogeneously immobilized catalyst.