作者：Ling-pan Lu, Kai-ti Wang*, Yi Liu, Jia-jun Wu
关键字：Vanadium?complexs,?Olefin?polymerization,?Polyethylene,?Cyclic?olefin?copolymers
论文来源：期刊
具体来源：ACTA?POLYMERICA?SINICA
发表时间：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).