Preparation of polyethylene thermoplastic elastomers using CS-symmetric nickel catalysts in ethylene polymerization

Abstract

Recently, the structural symmetry of α-diimine nickel catalysts was demonstrated to have a pronounced effect on the microstructure of the resulting polyethylene. In this study, two plane symmetric α-diimine Ni(II) complexes were designed and used in ethylene polymerization. The plane-symmetric Ni(II) complexes exhibited very high activities (well above 106 g mol−1 h−1) and yielded high molecular weight (up to 1088 kg/mol) polyethylenes with tunable branching density (49–87/1000C). Compared to the corresponding centrosymmetric Ni(II) complex, the plane-symmetric Ni(II) complex yielded significantly higher branched polyethylene (77 vs 29/1000C) under the same conditions. The polyethylene products obtained by plane-symmetric Ni(II) complexes exhibited low to moderate stress (3.7–21.6 MPa) and high strain (617–4058%) at break values as well as tunable recovery values (SR = 35–79%). Compared to the centrosymmetric Ni(II) complex, the plane-symmetric Ni(II) complexes yielded polyethylene materials with higher strain and lower stress at break values, and most importantly, significantly higher SR values (68% vs. 28%) under the identical conditions. Anyway, elastomer-like polyethylene materials were obtained from plane-symmetric Ni(II) complexes while centrosymmetric Ni(II) complex yielded linear low-density polyethylene-like materials.