Aluminoxane co-catalysts for the activation of a bis phenoxyimine titanium (IV) catalyst in the synthesis of disentangled ultra-high molecular weight polyethylene

New activation systems for the bis[n-(3-tert-butylsalicylidene)pentafluoroanilinato] ti (iv) dichloride catalyst (fi) for the synthesis of ultra-high molecular weight polyethylene (uhmwpe) with reduced entanglement density are explored. Together with the well-studied fi catalyst-methylaluminoxane (mao) catalytic system, different aluminoxanes, namely polymethylaluminoxane-improved performance (pmao), modified methylaluminoxane type 12 (mmao12) and type 3a (mmao3a) have been used. The catalyst activity increases with the addition of a co-catalyst modifier (2,6-di-tert-butyl-4-methylphenol, bht). For an example when using mmao3a as co-catalyst in combination with bht the catalyst activity increases by tenfold. The synthesized uhmwpes have been characterized via rheology, differential scanning calorimetry and uniaxial solid-state deformation to evaluate the influence that the different co-catalysts have on the catalyst activation and the entangled state of the polymer. Entanglement density increases when pmao is used as a co-catalyst influencing the rheological response of the polymer melt and melting kinetics of nascent powder. Mechanical properties increase when mmao12 is used in place of mmao3a as co-catalyst. However, the earlier reported mechanical properties of uhmwpe synthesized using the fi/mao are found to be better than those obtained using the co-catalysts investigated in this study.