Ethylene-propylene-diene terpolymerization using metallocene catalysts

Abstract

Ethylene and propylene homopolymerization were carried out using different metallocene catalysts in three types of reactor systems i.e. semibatch, batch, and continuous gas flow system. Effects of reaction conditions i.e. catalyst concentration, [Al][subscript MAO]/[Metal] ratio, reaction temperature in propylene polymerization are summarized. The ansa-metallocene catalyst Et[Ind][subscript 2]ZrCl[subscript 2] showed the highest activity in ethylene/propylene/diene terpolymerization among the commercially available metallocene catalysts chosen. Rate enhancement from the comonomer addition or so-called comonomer effect was observed in this metallocene catalyst system. No significant effect of the types of diene i.e. ENB, HD, VCH on the activity was observed. Diene addition has both positive and negative effect on the catalytic activity by enhancing the propagation reaction or promoting the deactivation process. More adverse effect was observed in the reaction carried out under lower pressure. In silica-supported system, effect on activity of MAO was more obvious than TMA. TMA may be useful as a scavenger while MAO is required in forming the active species. An increase of TMA and MAO in the system reduced Mw only slightly; this suggested that chain transfer to alkylaluminum is not the major chain transfer reaction for this copolymerization system. In-situ supported system, in which the metallocene catalyst was injected directly to the reactor, exhibit higher activity than preformed supported system without effect on the copolymer properties suggesting another promising heterogeneous process. The modification of silica with silicon tetrachloride increased the copolymerization activity. The copolymer produced had lower molecular weight but no significant effect on the microstructure of the copolymer chain was observed.