Reactivity of zirconium and titanium alkoxides bidentade complexes on ethylene polymerization

Flavone complexes of Ti and Zr active in ethylene polymerization

“…This decrease in catalytic activity with increasing Al/Ti ratio may be related to steric hindering caused in the complex due to the excessive amount of MAO used, which can hinder the insertion of ethylene. Studies on Ti complexes of methylmaltol ligand also showed that the catalytic activity of the Ti complex decreased with increasing Al/Ti ratio and that reduction was attributed to the equilibrium shift in the direction of the ionic pair association between the cationic species and MAO [8]. Moreover, there is also the possibility that the reduction process in the Ti center, observed by voltammetry, generates inactive species for polymerization.…”

“…This theoretical study is consistent with the results obtained in 1 H NMR spectra of the complexes, which show signs of a main isomer, probably cis 2, in greater proportion. Furthermore, the higher possibility of obtaining complexes with cis structure is favorable for our purposes because only cis isomers are capable of polymerizing ethylene [8].…”

“…7a) correspond to redox processes centered on the metallic center, as illustrated in Scheme 2. The proposed electrode process was based on the followed by analogous complexes with pyrone ligands [8,9]. These signals are not present in the DPV profile of 3HF ligand.…”

“…In fact, the effect of Al/M ratio (Al/M = 1000, 1500 and 2500) and ethylene pressure (2.8, 4 and 6 bar) in catalytic activity were studied. The polymerization reactions with complex 1 were performed at 40 • C while the reaction with complex 2 was made at 60 • C. At high temperatures the Zr complexes are more stable and active than complexes based on Ti [8,29]. Table 1 shows the set of evaluated polymerization conditions as well as polymer melting temperature and crystallinity.…”

Titanium(III, IV)-Containing Catalytic Systems for Production of Ultrahigh Molecular Weight Polyethylene Nascent Reactor Powders, Suitable for Solventless Processing—Impact of Oxidation States of Transition Metal

“…This is not surprising given the results of all early works on Ziegler catalysis, starting with metallocene and nonmetallocene systems containing groups 4 and 5 metals, as well as a significantly higher reduction potential M 4+ /M 3+ for zirconium and hafnium compounds (for metallocene Cp 2 MCl 2 : −E 12 = 1.4 (Ti), 1.6-2.3 (Zr) and 2.7 (Hf) [33][34][35] and titanium and zirconium nonmetallocene compounds with a pyrone ligand: −E 1\2 = 0.48 (Ti); 1.3 (Zr)) [36].…”