DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Abstract

Distribution of active centers (ACD) of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl2/TiCl4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components. Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducing α-olefin on ethylene polymerization. On the other hand, ACD of ethylene-1- hexene copolymer with very low ethylene incorporation was compared with that of 1-hexene homopolymer. Adding small amount of 1-hexene in ethylene polymerization caused marked activation of all the Flory components of the polymer, in which the low molecular weight components are activated more than the high molecular weight components. In 1-hexene polymerization system, the activity can also be greatly enhanced by introducing small amount of ethylene, but the different Flory components (or active centers) are activated with similar extent, except a newly emerged active center producing polymer with the lowest molecular weight. The total number of active centers is markedly increased by adding small amount of ethylene in 1-hexene polymerization, but the average catalysis efficiency of the active centers decreased. The broad composition distribution of the ethylene-1-hexene copolymer can be well understood from the ACD of catalyst and its dependence on the monomer.