Effect of alkylaluminum structure and aggregation state on the micro-kinetics of ethylene polymerization catalyzed by α-diimine nickel complex

2-thiophenecarbonyl chloride (TPCC) quenching method was used into the study of alkylaluminum activation behavior on α-diimine nickel catalysts. The influence of alkylaluminum structure (AlEt2Cl, Al2Et3Cl3, AlEtCl2 and modified methylaluminoxane (MMAO)) and polymerization temperature on the kinetic factors (active center concentration [C*] and chain propagation rate constant kp) of ethylene polymerization catalyzed by the system was systematically studied. It was found that, compared with MMAO, alkyl aluminum chloride could better activate catalyst and produced more active centers in the polymerization system, but the value of kp was lower than MMAO. Unexpectedly, as the polymerization temperature increased, [C*] in the polymerization system with AlEtCl2 as cocatalyst gradually increased, and kp decreased. But the change of [C*] and kp of the polymerization system with MMAO as cocatalyst was opposite. It was proposed that cocatalyst is one of the factors affecting the thermal stability of catalyst.