Methyl-Branched Polyethylene Synthesized by Thermostable Nickel Anilinonaphthoquinone Complexes

Linear low-density polyethylene (LLDPE) is widely used, ranging from flexible film packaging to rigid applications such as covers and pipes. Compared to the classic copolymerization of ethylene and α-olefin, as well as tandem catalysis, branched polyethylene (PE) bearing similar properties to LLDPE has been getting more attention recently. Several cationic and neutral nickel catalysts have been established while most of them produce LLDPE-grade polymer at temperatures lower than 80 °C. In this work, we developed a series of anilinonaphthoquinone nickel complexes that catalyze ethylene polymerization effectively at 90-100 °C. Tensile property studies reveal that PE synthesized in this work displays stress-at-break values of 26-33 MPa and strain-at-break values of 900-1100%, which are very similar to those of commercial LLDPE 1018-MA. The crystallinities of the PENi2 (44.5%) and PENi3 (45.3%) are also consistent with that of LLDPE 1018-MA (45.0%). Quantitative 13C NMR studies suggest that PENi2 and PENi3 have only methyl branch microstructures.