Imidazolidin-2-iminato vanadium complexes for the synthesis of ethylene/propylene/5-ethylidene-2-norbornene (ENB) terpolymers with high ENB incorporation and ultra-high molecular weight

Abstract

A series of imidazolidin-2-iminato vanadium complexes VOCl₂[1,3-R₂-(CH₂N)₂CN], Vi1, R = 2,6-Me₂C₆H₃; Vi2, 2,4,6-Me₃C₆H₂; Vi3, R = 2,6-ⁱPr₂C₆H₃; Vi4, R = cyclohexanyl, were synthesized and fully characterized by NMR (¹H, ¹³C and ⁵¹V) and elemental analysis. The copolymerizations of ethylene with propylene using the imidazolidin-2-iminato vanadium complexes were conducted in the presence of Et₃Al₂Cl₃. The catalytic activity increased in the order of Vi4 < Vi1 < Vi2 < Vi3, probably due to the different electron donating natures of the imidazolidin-2-iminato ligands. Both high catalytic activity of 2.44 × 10⁶ g copolymer per mol of V per h and incorporation ratio of propylene (up to 32.5 mol%) were afforded by using the Vi3/Et₃Al₂Cl₃ catalytic system in the copolymerization of ethylene with propylene. An ethylene–propylene copolymer with ultra-high molecular weight (M_w = 2660 kg mol⁻¹) could be also synthesized by using the Vi3/Et₃Al₂Cl₃ catalytic system. Importantly, the highly efficient terpolymerizations of ethylene, propylene with 5-ethylidene-2-norbornene (ENB) were also achieved by using this catalytic system, affording ethylene–propylene–ENB terpolymers (EPDMs) with high contents of ENB units up to 9.8 mol% (29.8 wt%) and ultra-high molecular weight (M_w = 1521–2537 kg mol⁻¹). This work offers a unique catalytic system of vanadium complexes for the synthesis of EPDM with both high content of ENB units and ultra-high molecular weight.