The influence of cocatalysts on 1-hexene polymerization with various supported magnesium – titanium catalysts

Abstract

The influence of various cocatalysts on the activity and stereospecificity of a supported magnesium–titanium catalyst, generated by in situ reduction of titanium (IV) chloride using a Grignard reagent (MgCl2/TiCl3) or prepared by the recrystallization method (MgCl2/2M2P/ED/TiCl4, 2M2P= 2-methyl-2-pentanol, ED= dibutyl phthalate or ethyl benzoate), in the 1-hexene polymerization was investigated. The MgCl2/TiCl3 catalyst showed the highest activity but the lowest stereospecificity in the 1-hexene polymerization with all investigated cocatalysts. The MgCl2/2M2P/ED/TiCl4 catalyst with dibutyl phthalate as an internal electron donor was characterized by the highest stereospecificity and led to the polymers with high molecular weight. All catalysts showed the highest activity and stereospecificity when triisobutylaluminium was used as a cocatalyst. The addition of a small amount of ethyl benzoate as an external electron donor ([Al]/[ED] 10:1) led to considerable improvement of the stereospecificity of the MgCl2/TiCl3 catalyst in comparison with the catalysts prepared by the recrystallization method.