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Selective Insertion in Copolymerization of Ethylene and Styrene Catalyzed by Half‐Titanocene System Bearing Ketimide Ligand: A Theoretical Study
Author(s) -
Xu Xiaowei,
He Gaohong,
Wei NingNing,
Hao Ce,
Pan Yu
Publication year - 2017
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.201700282
Subject(s) - styrene , copolymer , ethylene , chemistry , polymer chemistry , steric effects , chain propagation , insertion reaction , ligand (biochemistry) , catalysis , density functional theory , photochemistry , computational chemistry , organic chemistry , polymerization , polymer , biochemistry , receptor
The copolymerization of ethylene and styrene can be efficiently carried out by using Cp* TiCl 2 (N = C t Bu 2 )/ MAO (Cp*= η 5 ‐ C 5 Me 5 ) 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.