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
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 (Mw = 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 (Mw = 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.
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