Properties of ethylene-propylene copolymers synthesized by a supported Ziegler-Natta catalyst based on TiCl 4/MgCl 2/PCl 3

Abstract

Enthylene-propylene copolymers were synthesized through Ziegler-Natta catalysts based on TiCl 4, MgCl 2 and PCl 3. The catalyst system TiCl 4/MgCl 2/PCl 3 was prepared by impregnating the support, obtained by ball milling of MgCl 2 with varied amounts of PCl 3, with TiCl 4. The addition of PCl 3 has, remarkably, increased MgCl 2 surface area and, according to plasma spectrometry data, promoted the PCl 3 incorporation in the catalyst. The effect of PCl 3 on the ethylene homopolymerization, ethylene-propylene copolymerization and on the copolymer properties was studied. The employed catalyst system produced propylene-ethylene copolymers up to 75% (w/w) of propylene. The reduction on the copolymer molecular weight distribution suggested the PCl 3 acted as an internal donor, poisoning some catalytic active sites. The effect of Al Ti ratio on the copolymer structures was investigated. Low ratio caused increase of propylene incorporation in the copolymer and high Al Ti ratio promoted overreduction of titanium as shown by EEE triad content. The reactivity ratio data indicated the ethylene-propylene copolymerization present a tendency to produce block copolymers.