Abstract: The gas-phase polymerization of ethylene with prepolymerized Ti-Mg supported catalyst was studied. The results showed that catalytic activity and bulk density of the prod uct particles increased and the size distributions of the product particles narrowed with the using of prepolymerization method. The morphology of catalyst particles, prepolymer and the polymerization product particles were studied by SEM and image analysis. From these investigation, it was found that the prepolymerization makes catalyst particles puff with fis sure. The particles of prepolymer and polymerization product are composed of bound ag glomerates of fine secondary polymer globules, while the secondary polymer globules consist of smaller primary particles. The average values of diameters (DAV) of catalyst particles,prepolymer and the product particles by image analysis are 33um, 168 um and 263 um, re-spectively, and the ratios of the large axis to small axis(D/d) are 1. 524, 1. 540 and 1. 514,respectively.

Key words: Ti-Mg catalyst, Prepolymerization, Gas-phase polymerization of ethylene, Mor phology of particles