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.

Investigation of the characteristics and performance in propylene polymerization of silica-immobilized methylaluminoxane (MAO), in combination with a moderately and a highly isospecific zirconocene catalyst, has revealed that a simple impregnation of silica with MAO at ambient temperature is insufficient to obtain uniform distribution of MAO throughout the support particle. Homogeneous Al distribution throughout the support, giving increased catalyst activity, was achieved by a more rigorous impregnation of silica with MAO at elevated temperatures. The highest catalyst activities were obtained by precontacting the MAO with the zirconocene to generate the activated species before immobilization on silica. Polymer particle morphology was strongly dependent on the characteristics of the silica used for catalyst immobilization. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43

An investigation of the polymer particle growth characteristics and polymer molecular weight and composition distributions in ethylene homopolymerization and ethylene/1-hexene copolymerization has been carried out with a catalyst comprising a zirconocene and methylaluminoxane immobilized on a silica support. The presence of 1-hexene leads to higher productivity and easier fragmentation of the support during particle growth. Crystallization analysis fractionation and gel permeation chromatography analysis of ethylene/1-hexene copolymers prepared at different polymerization times reveals a broadening of the chemical composition distribution with increasing polymerization time as a result of the gradual formation of a relatively high-molecular-weight, ethylene-rich fraction. The results are indicative of significant monomer diffusion effects in both homopolymerization and copolymerization.