The curious case of the molecular catalysts that behaved like a dual-site catalyst

Conference Dates

May 20-25, 2018


Semi-batch, solution copolymerizations of ethylene and 1-hexene were performed using both dichloride (Hf-Cl2) and dimethyl (Hf-Me2) analogues of the bis(n-propylcyclopentadienyl) hafnium precatalyst. Either tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C6F5)4]-[Me2NHPh]+) (B) or methyl aluminoxane (MAO) was employed as the activator, and tri-n-octylaluminum (TOA) was used as the scavenger for the borate-activated experiments. For the copolymerization study using Hf-Cl2/B/TOA, 1-hexene, borate and TOA concentrations were varied systematically. Crystallization analysis fractionation (CRYSTAF) or crystallization elution fractionation (CEF) profiles were used interchangeably to compare the chemical composition distributions (CCD) of the copolymers. Above a minimum threshold 1-hexene level, the CCD profiles of all the copolymers were bimodal and the areas under the peaks depended on the B/Hf-Cl2 and B/Al ratios. Decreasing the TOA concentration reduced the weight fraction of the higher crystallinity polymer component.

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