6533b835fe1ef96bd129e8b3

RESEARCH PRODUCT

Two-step polymerization of propylene over MgCl2-supported titanium catalyst

subject

description

The prepolymerization effect on propylene polymerization in the presence of a MgCl 2 -supported titanium catalyst was studied. The catalyst was pre-activated by polymerizing a small amount of propylene in the presence of Et 3 Al and cyclohexylmethyldimethoxysilane under mild conditions, and then it was used in a second step of propylene polymerization. Comparative studies of the polymerization process involving the investigated catalyst and its unmodified counterpart showed the rate-enhancement effect of prepolymerization and the same molecular weights, MWD's and isotacticities of the polymers obtained. Concentrations of active sites and propagation rate as well as transfer rate constants were found from detailed kinetic studies. The findings revealed that the activating effect of catalyst prepolymerization resulted from the increased concentration of active sites. This in turn is the result of the slow and uniform fragmentation of initial catalyst agglomerates with the prepolymer created under mild conditions. The prepolymerization process causes no change in the reactivity of active sites since the chain propagation and chain transfer rates are the same for single-step and two-step polymerization reactions; similarly, the properties of the polymers produced are unchanged.