Synthesis of Alumina-Terminated Linear PE with a Hafnium Aminopyridinate Catalyst

Five different Ap (aminopyridinato) ligand stabilized hafnium complexes were synthesized and characterized through NMR spectroscopy, elemental analysis, and (to some extent) by X-ray crystal structure analysis. Moreover, a tunable ethylene polymerization catalyst system based on these complexes was tested in CCTP (coordinative chain transfer polymerization) with TEA (triethylaluminum) as the chain transfer agent. The catalyst precursor giving the highest degree of control, [Cp*Hf(Ap(H)DIP)Me-2] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl ligand, Ap(H)DIP-H = N-(2,6-diisopropylpheny)pyridine-2-amine, Me = methyl), in the presence of high amounts of TEA was investigated regarding different parameters: e.g., temperature, ethylene pressure, catalyst/chain transfer agent ratio, and reaction time. The results showed that the new catalyst system is able to tolerate up to 5000 equiv of TEA and was able to produce linear alumina-terminated polyethylene with polydispersities down to 1.2.