A sequence of experimental steps was perfected to produce high-impact modified polypropylene (PP), and to study the influence of particle morphology and rubber content on the reaction kinetics, especially in terms of mass transfer limitations. It was found that after a critical copolymer content at approximately 40% (with respect to total weight), it was impossible to obtain high reaction rates. This is thought to be the result of a fundamental change in particle morphology attributed to the presence of a soft EPR copolymer phase in the micropores.

SUMMARY Propene polymerizations were performed using the two ansa-zirconocene catalyst systems dimethylsilylbis( 1 -indenyl)zirconium dichloride/methylaluminoxane and dimethylsilylbis(2-methyl-1 -indeny1)zirconium dichloride/methylaluminoxane. The polymerization rate was observed by continuously monitoring the monomer consumption. Reaction rate profiles were obtained in the temperature range from 40 "C to 130°C at pressures between 1 and 2.5 bar and catalyst concentrations from 4.6-10" M to 4.2. lCr5 M. Isotacticity, as measured by NMR, melting point and molecular weight decreases markedly at higher temperatures. Small amounts of 1,3-inserted monomer (el mol-%) was observed at polymerization temperatures above 80 "C. No 2,1-inserted monomer was detected. A kinetic model was developed that describes the polymerization rate for Me2Si(Ind)2ZrC12 as the catalyst over the entire observed temperature range, and the polymerization rate for Me&Si(2-Me-Ind)&C12 in a limited temperature range. The model includes an activation reaction, latent sites that may revert to active sites and a permanent deactivation that is second order with respect to the active sites. The activation energy for the propagation reaction was found to be 37 kT/mol for Me2Si(Ind)2ZrC12 and 32 kJ/mol for Me2Si(2-Me-Ind)2ZrClJMAO. Several kinetic models are compared and discussed.

The catalyst particle fragmentation process is an important step in determining the final morphology of olefin polymer particles. Understanding the different phenomena that influence it is, therefore, essential in optimizing polymerization processes and in obtaining the desired quality of polymer. A new ®iscoelastic model of the fragmentation process de®eloped is demonstrated. The model relates the magnitude and generation rate of physical forces and the physical characteristics of the polymer and support. In this way, the effects of different parameters, such as reaction rate, polymer properties, and support characteristics, can be related to changes in the morphology of polymer particles. A faster reaction rate makes the particle become more porous, and a more ®iscous polymer will make particles with less porosity. It is discussed why larger pores will break before smaller on the same catalyst.

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