Improving Impact Poly(propylene) Morphology and Production: Selective Poisoning of Catalyst Surface Sites and the Use of Antistatic Agents

Selective poisoning has been studied as a means of improving the morphology and rheological properties of high-impact poly(propylene) copolymer particles. Two different methods of poisoning the catalyst surface in order to avoid the accumulation of ethylene-propylene rubber (EPR) without influencing the reaction kinetics were tested: a slurry-phase poisoning step using ethylene glycol dimethyl ether between the homopolymerisation and copolymerisation reaction steps; and direct poisoning via the use of a commercial antistatic agent during the gas-phase copolymerisation reactor. It was observed that both methods eliminated the formation of rubber on the particle surface without noticeably influencing the kinetics. On the other hand, the use of the products directly in the gas-phase reaction also contributed to the reduction of static electricity. It can be concluded from these experiments that industrial antistatic agents derive at least part of their effect from poisoning of the active sites on the surface of the catalyst. Furthermore, it appears that in the case of the catalyst used in this study, EPR does not appear to flow out of the growing particles. Most of the EPR found at the surface of the particles is formed close to it.