Effect of cocatalysts on ethylene polymerization with fluorinated bisphenoxyimine titanium as a catalyst

Abstract

In this study, we examined various alkylaluminums, including triethylaluminum (TEA), triisobutylaluminum (TIBA), and diethylaluminum chloride (DEAC), as cocatalysts for the activation of ethylene polymerizations in the presence of a fluorinated Fujita group invented titanium (FI-Ti) catalyst, bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride (complex 1). DEAC, because of the strong Lewis acidity, was an efficient cocatalyst for activating complex 1 for the ethylene polymerizations, whereas TEA and TIBA as cocatalysts could hardly polymerize ethylene. The effects of the polymerization temperature and Al/Ti molar ratio on the formation of active species, properties, and molecular weight of the resulting polyethylene were investigated. In the complex 1/ DEAC catalyst system, the oxidation states of Ti active species were determined by electron paramagnetic resonance. The results demonstrated that Ti(IV) active species were inclined to polymerize ethylene and yielded high-molecular-weight polyethylene. Comparatively, Ti(III) active species resulted from the reduction of Ti(IV) by DEAC and afforded oligomers. Moreover, the bigger steric bulk for the cocatalysts was necessary to achieve ethylene living polymerization with the fluorinated FI-Ti catalyst.

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

“…The catalytic system, formed by the combination of FI catalyst and MMAO3A, has an activity of one order of magnitude lower compared to the rest of catalytic systems studied here. In agreement to previous finding [22], this result suggests that the catalyst can be modified by the TiBAl (which is present in the MMAO3A solution), leading to nonactive species toward ethylene polymerization. The low yield of the run 7 leads to high catalytic ashes content and the rheological response of the polymer was affected.…”

“…The resulting active species are capable of synthesizing UHMWPE with M w in a range of 5 million g/mol up to 11 million g/mol. The catalytic system formed by the combination of FI catalyst+MMAO3A shows considerably depressed activity, probably due to the presence of TiBAl that modifies the catalyst [22].…”

“…The same catalyst used in this study has been tested by Li et al in the presence of TiBAl and also in this case no catalytic activity is reported [ 22 ]. Because of the steric hindrance it is reasonable to think that bigger trialkylaluminums, in combination with the catalyst considered in this study, will preferentially not act as chain transfer agent.…”

Structural modification of phenoxyimine titanium complexes and activation studies with alkylaluminum compounds

“…Due to its large size (weak interaction with the positively charged activated catalyst), strong Lewis acidity and weak reduction ability, MAO and modified methylaluminoxane (MMAO) are commonly employed co-catalysts for Ti(IV) systems, including the FI complexes. [16] Scattered information on the use of FIÀ Ti complexes using different co-catalyst can be found in literature. Therefore, understanding the chemistry/interactions between the two components is of critical importance.…”

“…The difference in Lewis acidity of the four different co-catalysts is also taken into account and used to understand in more detail their activation ability. Complex 4 is unreactive in the presence of alkylaluminum such as TiBA, [16] and an interest is stimulated in the reactivity of other synthesized complexes with such co-catalysts. The nuclear magnetic resonance (NMR) study of the activity of the synthesized complexes with different alkylaluminum co-catalysts (TEM and TiBA) by different Al/Ti ratio is also reported.…”