Systheisis of Vanadium Complexes Bearing Tridentate β-Ketoimine Ligands and Their Catalytic Capabilities towards Ethylene (Co)polymerization
作者：Ling-pan Lu, Kai-ti Wang*, Yi Liu, Jia-jun Wu
關鍵字：Vanadium?complexs,?Olefin?polymerization,?Polyethylene,?Cyclic?olefin?copolymers
論文來源：期刊
具體來源：ACTA?POLYMERICA?SINICA
發表時間：2020年
Vanadium catalysts always show outstanding catalytic properties towards ethylene (co)polymeriztaion, while the high-valent vanadium species would be deactivated because of the generation of inactive or less active low-valent species at elevated temperature and/or in prolonged time. As proved, introducing of bulky groups into the ligands is benefit to improving the catalytic properties of vanadium complexes. Herein, in order to well control the oxidation state of vanadium species, a series of tridentate β-ketoimine type vanadium(III) complexes bearing cyclic skeleton {[(R)X(C6H4)N＝CH(C6H5)C10H7O]VCl2(THF): 2a, R = CH3, X = S; 2b, R =CF3, X = S; 2c, R = Ph, X = S; 2d, R = tBu, X = S; 2e, R = Ph2, X = P; 2f, R = Ph, X = O}, were synthesized and characterized. Because of the constrained effects of the cyclic skeleton and the stabilizing effects of the bichelating ring, these synthesized catalysts showed high activities and improved stabilities in ethylene (co)polymerization. In the presences of Et2AlCl and ethyl trichloroacetate, catalysts 2a ? 2f showed 8.16 ? 19.9 kgpolymer/(mmolV·h), 7.68 ? 26.9 kgpolymer/(mmolV·h) and 4.80 ? 42.2 kgpolymer/(mmolV·h) of catalytic activities towards ethylene polymerization, ethylene/norbornene (NBE) copolymerization and ethylene/exo-1,4,4a,9,9a,10-hexahy-dro-9,10(1′,2′)-benzeno-1,4-methanoanthracene (HBM) copolymerization, respectively. All of the resultant polymers exhibited a unimodal distribution, indicating that these vanadium catalysts showed single-site catalytic behaviour, even at elevated temperatures (50 ? 70 °C). Catalysts 2b, 2d, 2e and 2f showed “positive” comonomer effects in both ethylene/NBE copolymerization and ethylene/HBM copolymerization. Besides, 2a and 2c also exhibited “positive” comonomer effects in ethylene/HBM copolymerization. Cyclic olefin copolymers possessing high molecular weights (NBE: 43.1 ? 66.4 kg/mol; HBM: 90.2 ? 138 kg/mol) and high comonomer incorporations (NBE: 30.9 mol% ? 42.1 mol%; HBM: 14.7 mol% ? 25.0 mol%) were obtained facilely via direct copolymerization. The glass transition temperature is dominantly affected by the cyclic olefin incorporations and the steric hindrance of the cyclic olefin. Compared with the ethylene/NBE copolymers, the obtained ethylene/HBM copolymers showed much higher glass transition temperatures (NBE: 84 ? 105 °C versus HBM:173 ? 188 °C).