Trialkylaluminum cocatalyst

Isohexides exhibit excellent properties as plasticizers for polyvinyl alcohol polymers.2 Compounds obtained from isosorbide and trialkylaluminum proved to be highly active cocatalysts for polymerization of alkenes. Such derivatives, which were supposed to be oligomeric O-aluminum-isosorbides, are of glass-like appearance and exhibit pyrophoric properties.255 Isosorbide is a component of mixtures used for water-based pigment inks, having excellent dispersion stability, which is necessary for ink-jet printing.256 257... 

A Theory of Initiation and Propagation of Carbonium Ion Polymerizations with Trialkylaluminum Catalysts. Trialkylaluminums or dialkylaluminum halides in conjunction with suitable cocatalysts in polar solvent are active polymerization catalysts. For example, when cocatalytic amounts of tert-butyl chloride are added to a quiescent mixture of trialkylaluminums or dialkylaluminum halides in methyl chloride solvent in the temperature range —30° to —100°C., immediate polymerization commences (2, 3, 4, 5, 6). 

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

The solid studies have also shown that all trialkylaluminum compounds are more or less equivalent as cocatalysts. Thus with a good solid, such as the 0.9 i-Bu3Al solid, trialkyls—as far apart as the trimethyl- and trioctyl-aluminum—are essentially equivalent. This indicates that the poorer activity of unseparated catalysts prepared from the lower alkyls (trimethyl-, triethyl-aluminum) must be directly related to the resulting reaction products with TiCl4, i.e., the reduced and/or alkylated Ti species (expected to be found in the solid phase) and the alkylaluminum chlorides (unless strongly adsorbed, expected to be found in the liquid phase). 

A well-known problem in the preparation of MAO is the inevitable presence of trimethylaluminum in the MAO product or trialkylaluminum species in the MMAO product. The quantity of residual R3-A1 has major effects on the catalytic activity of MAO. Very low activities have been reported in the literature when TMA is used alone as the cocatalyst for Cp2ZrR2-catalyzed ethylene polymerization. The effect of free TMA on polymerization activity and polymer molecular weight has been studied by altering [TMA]/[MAO] ratios in zirconocene-catalyzed ethylene polymerization. as well as by replacing TMA with TEA or TIBA in combination with the... 

Polymerization was conducted at 0.2-0.7MPa ethylene and 60°C in the presence of a trialkylaluminum. The best activity, 1643 kg PE/(mol -Fe-h), was obtained using catalyst XXIII with AbBug as cocatalyst. The catalyst produced highly linear polyethylene with a melting point of 134°C and a broad molecular weight distribution = 7.1). 

Some support materials can be rendered Lewis acidic enough to ionize dialkyl metallocenes. Marks and co-workers have reported (33) that alnmina dried at very high temperatures can react at least to some small degree with both thorium-and zirconium-based metallocene dimethyl species to yield active catalysts for polyethylene. The resulting cationic metal center is believed to remain coordinated to the surface through an Al-O-M Lewis acid/base linkage, at least prior to exposure to ethylene. Hybrid surface/cocatalyst systems based on aluminum alkyl-treated clays have been developed (34) in which the solid substrate appears to play some role in promoting polymerization activity far beyond that expected for non-methyl aluminoxane- or trialkylaluminum-activated catalysts. 

Looking at the preparation of supported metallocenes, synthesis of the metallocene on the carrier is found as well as fixing a metallocene either via functionality at the ligand or by direct reaction with the carrier, in both cases followed by activation with MAO or trialkylaluminum, but more common is heterogenization of the cocatalyst prior to mixing the modified carrier with the metallocene and activation by trialkylaluminum. 

The most investigated homogeneous catalyst systems are based on bis(cyclopenta-dienyl)titanium(lV), bis(cyclopentadienyl)zirconium(rV), tetrabenzyltitanium, vanadium chloride, and trialkylaluminum or alkylaluminum halides as cocatalysts. Subsequent research on these and other systems with various alkyl groups has been conducted by Patat and Sinn [4], Shilov [5], Hemici-Olive and Olive [6], Reichert and Schoetter [7], and Fink et al. [8]. 

Shiono T (2013) Trialkylaluminum-free modified methylaluminoxane as a cocatalyst for living polymerization of olefins. Adv Polym Sci. doi 10.1007/12 2013 211... 

Trialkylaluminum-Free Modified Methylaluminoxane as a Cocatalyst for Living Polymerization of Olefins... 

The first coordination epoxide polymerization catalytic system was reported by Pmitt and Baggett in 1955. It was based on iron tricbloride. Since that time, metal-based catalysts bave been widely exploited for epoxide polymerization. Tbe most studied systems are those based on zinc or aluminum derivatives. A first group consists of diethylzinc or trialkylaluminum associated to a cocatalyst, wbicb is generally water or an organic compound (alcohol, amine, and other compoimds) that reacts with the alkyl metal to form in situ new metal derivatives as the true catalytic system exploited (see Table 6). For a detailed review on the coordination polymerization of epoxides, see Kman. ... 

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