Hexacoordinated nickel catalysts containing salicylaldbenzhydrylimine ligand and tetrahydrofuran heterocycle: High catalytic activity and high 1-hexene insert ratios for norbornene (Co)polymerization

Abstract

Three novel hexacoordinated nickel catalysts containing salicylaldbenzhydrylimine ligand and tetrahydrofuran heterocycle, Ni{(THF) (3-R1) (5-R2)C6H2(O)CHNCH(C6H5)2}2, (R1 = Br, R2 = H, Ni1; R1 = Br, R2 = Br, Ni2; R1 = Cl, R2 = Cl, Ni3.), were synthesized and their molecular structures were confirmed by X-ray crystallography. Ni1–Ni3 catalysts exhibited high activities (0.53–2.11 × 106 gpolymer/molNi·h) toward norbornene homopolymerization and high activity (0.29–2.62 × 105 gpolymer/molNi·h) to copolymerization of norbornene and 1-hexene. When the 1-hexene feed ratio was changed from 10 to 70%, the 1-hexene content in the obtained copolymers could be controlled to 8.23–26.58%. The Ni3 with R1 and R2 were both electron withdrawing groups (-Cl) on the aromatic ring of salicylaldehyde, showed the highest activity as well as the highest 1-hexene insert ratios. At the same time, only a small amount of B(C6F5)3 cocatalyst (5 × 10−5 mol) need to be consumed in the copolymerization process. In addition, the obtained copolymers had a high thermal decomposition temperature (Td > 386 °C) and a low glass transition temperature (Tg = 208.67–237.42 °C), which showed that the processability of these polymers was improved while the high thermal decomposition temperature was kept. The copolymers also exhibited good solubility in general organic solvents and high optical transparency in the visible region.