Methylene‐bridged bis(8‐arylimino)‐5,6,7‐trihydro‐quinolylinickel precatalysts for ethylene polymerization

Abstract

AbstractA series of binuclear nickel complexes bearing N‐(5,6,7‐trihydroquinolin‐8‐ylidene)amino CH(C6H4‐4‐R2){4‐C6H2‐2,6‐R12N‐(C5H3NC4H6)}2 [R1 = Me, R2 = OH L1, R1 = Et, R2 = OH L2, R1 = Me, R2 = H L3, R1 = Me, R2 = OCH3L4] has been synthesized and characterized. In the presence of either methylaluminoxane (MAO) or Et2AlCl, all nickel complexes exhibited high activities up to 3.33 × 106 g (PE)·mol−1(Ni)·hr−1 toward ethylene polymerization, producing high branched polyethylenes (PEs). The aluminum cocatalysts have significantly affected the properties of resultant PE; with MAO as the cocatalyst, the resultant PE shows higher molecular weight and possesses only one Tm value, meanwhile Et2AlCl as the cocatalyst, the obtained PE indicates lower molecular weight and two melting points. The microstructures of those PEs determined by their 13C NMR spectra illustrate the similar densities but different types of branches, in which the PE obtained with Et2AlCl shows high methyl branch selectivity (>80%), and the PE produced by MAO has 50% methyl and another half of longer branches. The branched PEs are consistent to the chain migration happened in the ethylene polymerization.