Effect of hydrogen on the chain structure of ethylene-propylene copolymer synthesized by supported high-activity Ziegler-Natta catalyst

Ethylene-propylene copolymers were synthesized using a TiCl4/MgCl2/SiO2/diester type supported Ziegler-Natta catalyst with or without the presence of hydrogen in a slurry polymerization process. The copolymer was inhomogeneous in composition and can be fractionated into two parts, fractions soluble and insoluble in n-octane at room temperature, respectively. The soluble part is a nearly random copolymer, while the insoluble part is a kind of segmented copolymer, as revealed by C-13-NMR and DSC analyses. Adding H-2 in the reaction system caused an increase of copolymer yield and a decrease of the insoluble part, but the propylene content and average length of propylene segments of the insoluble part were markedly increased, meanwhile the average length of ethylene segments of the insoluble part was markedly decreased. Copolymer sequence distribution of the soluble part was only slightly changed by H-2. The segmented copolymer fraction present in this ethylene-propylene copolymer has the similar structure as the segmented copolymer fractions found in polypropylene/poly(ethylene-co-propylene reactor alloy. Mechanism of the hydrogen effect on copolymer structure is discussed.