Access to polyethylene elastomers via ethylene homo-polymerization using N,N′-nickel(II) catalysts appended with electron withdrawing difluorobenzhydryl group

Abstract

A library of five hither-to-unknown unsymmetrical N,N′-diiminoacenaphthylenes, 1-[2,4,6-{(4-FC6H4)2CH}3C6H4N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2Ph L1, 2,6-Et2Ph L2, 2,6-i-Pr2Ph L3, 2,4,6-Me3Ph L4 and 2,6-Et2-4-Me-Ph L5), have been synthesized and used to prepare their corresponding nickel(II) halide complexes of the type LNiBr2 (Ni1–Ni5) and LNiCl2 (Ni6–Ni10). Single-crystal structures of Ni1 and Ni2 reveal the nickel center and coordination atoms formed distorted tetrahedral geometry. Upon activation with either methylaluminoxane (MAO) or diethylaluminum chloride (Et2AlCl), Ni1–Ni10 displayed high activities towards ethylene polymerization with the optimal performance being observed using Ni5 in combination with MAO (1.29 × 107 g of PE (mol of Ni)−1 h−1 at 30 °C), which produced high molecular weight elastomeric polyethylene (Mw = 4.6 × 105 g mol−1, Tm = 47.13 °C) with narrow polydispersity (Mw/Mn = 2.6). Dynamic mechanical analysis (DMA) and monotonic stress–strain test has been employed on the obtained polymeric materials and reveal high tensile strength, good elastomeric recovery (up to 93.6%) and high elongational break (up to 1037.1%), which indicates a promising equivalent material to currently commercial thermoplastic elastomers (TPEs).