Enhanced activity of clays and its crucial role for the activity inethylene polymerization

Abstract

This paper presents a study of the effects of different treatments on the polymerization activity of mod-ified clays as cocatalysts. To achieve this goal, an intercalating cation was introduced into two smectitesand these clays were then modified with trimethyl aluminium. The results for ethylene polymeriza-tion, when a zirconocene complex was used as catalyst, and the structure analysis, allow us to obtaininteresting deductions about the generation mode of the active species. All active materials employedas support activators presented aluminium in a pentahedral environment together with acidic hydrogenatoms. These two features were detected only after TMA treatment and they seem to be crucial elementsin active cocatalyst generation. Moreover, a material without structural aluminium displayed the bestactivity pointing to the new aluminium species generated in the solid matrix as the determining factorfor the activity. We proposed a synergic effect between Lewis acid aluminium centres and acidic Brönstedprotons that generate the SiOHAl groups that activate the zirconium compound.