Facile access to diverse polyethylenes via neutral salicylaldiminato nickel catalysts

Abstract

A new family of neutral salicylaldiminato nickel(II) catalysts (Ni1–Ni5) is developed with various well-designed ortho substituents to the phenoxy moiety and these show moderate to high catalytic activity for ethylene polymerization as single-component catalysts. Compared to the classical Grubbs-type neutral nickel(II) catalyst Ni-An, the polymer obtained has lower molecular weight and significantly higher (2–5 times, up to 110 branches/1000C) branching degree. Polyethylene materials from solid semi-crystalline plastic (T_m = 108 °C) to polyethylene wax and polyethylene oil can thus be facilely accessed. In particular, through the cooperative work of N-aryl groups and ortho substituents, the upgraded catalysts Ni6 and Ni7 produce polymers with high molecular weight while retaining high branching degree, thus leading to polyethylenes with excellent elastic properties (tensile strength: 4.3 and 18.4 MPa, strain at break: ∼1500%, strain recovery value (SR): 54% and 67%). This work overcomes the established difficulty in simultaneously improving polymer molecular weight and branching degree using neutral nickel(II) catalysts, enlightening new ideas for catalyst design.