Morphological development of impact polypropylene produced in gas phase with a TiCl4/MgCl2 catalyst

This article reports on a comprehensive study of the reaction kinetics, particle morphology development, and polymer properties of impact polypropylene produced in gas phase with a TiCl4/MgCl2 catalyst. Experiments were conducted over a range of copolymerization times, temperatures, monomer compositions, and hydrogen levels. The catalyst was found to exhibit a decay-type reaction rate for ethylene and propylene, but the presence of both monomers together caused an activation of the catalyst. Copolymer composition was constant over reaction time. Hydrogen was found to reversibly enhance the rate of propylene polymerization but to have no effect on ethylene. Microscopy provided evidence that the copolymer phase segregates from the homopolymer during polymerization. As copolymer content increased, product bulk density decreased because of the presence of sticky material on the particle surface. However, even at 70 wt % copolymer, enough pores were present in the particle to prevent monomer diffusion limitations. (C) 2001 John Wiley & Sons, Inc.