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Indexed by:期刊论文

Date of Publication:2017-11-01

Journal:CHINESE JOURNAL OF CHEMISTRY

Included Journals:SCIE、Scopus

Volume:35

Issue:11

Page Number:1731-1738

ISSN No.:1001-604X

Key Words:polymerization mechanism; density functional theory (DFT); half-tianocene; copolymerization; selective insertion

Abstract:The copolymerization of ethylene and styrene can be efficiently carried out by using Cp* TiCl2(N= (CBu2)-Bu-t)/MAO (Cp*=eta(5)-C5Me5) system, yielding the poly(ethylene-co-styrene) s with isolated styrene units. In order to investigate the reasons for formation of the structure, the mechanism of copolymerization, especially the selective insertion of ethylene and styrene, is studied in detail by density functional theory (DFT) method. At the initiation stage, insertion of ethylene is kinetically more favorable than insertion of styrene, and insertion of styrene kinetically and thermodynamically prefers 2,1-insertion. That is different from the conventional half-titanocene system, in which the 1,2-insertion is favorable. At chain propagation stage, the computational results suggest that the continuous insertion of styrene is hard to occur at room temperature due to the high free energy barriers (28.90 and 35.04 kcal/mol for 1,2-insertion, and 29.15 and 34.00 kcal/mol for 2,1-insertion) and thermodynamically unfavorable factors in two different conditions. That is mainly attributed to the steric hindrance between the coming styrene and chain-end styrene or ketimide ligand. The computational results are in good agreement with the experimental data.