Synthesis of ultra-high-molecular-weight ethylene-propylene copolymer via quasi-living copolymerization with N-heterocyclic carbene ligated vanadium complexes

The quasi-living copolymerization of ethylene with propylene was achieved by using N-heterocyclic carbene (NHC) ligated vanadium complex (V3, VOCl₃[1,3-(2,6-ⁱPr₂C₆H₃)₂(NCH)₂C:]) due to the stabilization of active center by the introduction of bulky and electron rich NHC ligand with bulky isopropyl substituents at the ortho positions of the phenyl rings. The weight-average molecular weight (M_w) of the resulting copolymer increases linearly with its weight in 20 min. The ultra-high-molecular-weight (UHMW) ethylene-propylene copolymer (M_w = 1612 kg mol⁻¹) can be synthesized with V3/Et₃Al₂Cl₃ catalytic system. The novel complex V4′ (VCl₃[1,3-(2,4,6-Me₃C₆H₂)₂(NCH)₂C:]·2THF) was constructed by the introduction of two coordinated tetrahydrofuran molecules and decrease in steric hindrance at the ortho positions of phenyl rings. The UHMW ethylene-propylene copolymer (M_w = 1167 kg mol⁻¹) can also be synthesized by using V4′/Et₃Al₂Cl₃ catalytic system.