Trialkylaluminum polymerization catalysts

The use of bulky trialkylaluminum reagents, such as Al( Bu)3, with various group 4 metallocenes led to olefin-polymerization catalysts that rivaled those formed with MAO as the co-catalyst. 

Ziegler, Gellert, Holzkamp, Wilke, Duck and Kroll (72) have shown that the hydride transfer reaction of alkylaluminum occurs much more easily with trialkylaluminum than with the more electrophilic diethylaluminum chloride. Catalysts must be more anionic in order to produce oligomers which involve large amounts of hydride transfer than with polymerization catalysts where hydride chain transfer must be minimized. Thus the oligomerization catalyst employed by Bestian and Clauss was more anionic, or less cationic, than the usual polymerization catalyst where anionic chain transfer is minimized. 

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). 

TRIALKYLALUMINUM (CAS varies) Flash point and other properties may vary because these chemicals are generally supplied as a solution in a hydrocarbon solvent. They react with many materials, including air, water, alcohols, halocarbons, titanocene dichloride (polymerization catalyst), arachidyl alcohol, triethyl borane. Pyrophoric may ignite spontaneously in air. Water-reactive. Decomposes in heat at about 350°F/177°C. See also triethyl aluminum (97-93-8). 

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. 

The trialkylaluminum-water catalyst used in these systems is believed to initiate cationic polymerization reactions. Two possible mechanisms have been suggested for these reactions, either the Sf i and S 2 paths, as shown in Equation 3. 

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

Lal (8) has studied the polymerization of vinylisobutylether using a catalyst composed of titanium tetrachloride and trialkylaluminum. He concluded that this catalyst combination produced polyvinylethers by a cationic mechanism similar to that of borontrifiuoride-etherate catalysis. The stereoregular polymerization of isobutylvinylether in... 

How does the anionic alkyl of the original trialkylaluminum or of the dialkylaiuminum chloride, which has sufficient anionic character to undergo anionic hydride exchange or CH3OT reaction, form a catalyst which becomes cationic under certain polymerization conditions No studies of this have been reported. One possibility is an internal oxidation-reduction reaction that converts an anionic alkyltitanium trichloride to a cationic alkyltitanium trichloride (Equation 10). Basic and electrophilic catalyst components would determine the relative contributions of the anionic and cationic forms. This type of equilibrium or resonance structures could also explain the color in transition metal compounds such as methyltitanium trichloride (73). 

It is known that the polymerization of ethylene by trialkyl aluminum is not a rapid reaction at normal pressures and temperatures. Ziegler, Gellert, Holzkamp, Wilke, Duck and Kroll (72) have found that ethylene was polymerized to higher trialkylaluminums only at elevated temperatures and pressures. Anionic hydride transfer commonly occured under these conditions. However, the addition of a transition metal halide such as titanium tetrachloride, the classical Ziegler catalyst, polymerized ethylene rapidly under mild conditions. 

Karapinka, Smith, Carrick (79) studied the use of methyltitanium trichloride as a catalyst for polyethylene. Alone it was inactive for the polymerization of polyethylene. It required the predecomposition to titanium trichloride at 120° or the addition of titanium trichloride to produce an active catalyst. Vanadium tetrachloride also produced an active catalyst. Aluminum bromide failed to activate the catalyst, whereas trialkylaluminum which reacts to produce alkylaluminum chlorides was effective. 

Ashikari, Kanemitsu, Yanagisawa, Nakagawa, Okomoto, Ko-bayashi and Nishioko (59) have studied the copolymerization of propylene and styrene. They found decreasing styrene content and conversion of the copolymer by increasing aluminum to titanium ratios with triisobutyl aluminum and titanium trichloride catalysts. The trialkylaluminum titanium tetrachloride catalyst had relatively low steric control on the polymerization while trialkylaluminum-titanium trichloride had higher steric control. The ionicity which is required for atactic polymerization is more cationic for styrene than for propylene which is more cationic than that for ethylene. Some of the catalyst systems for these three monomers are shown on the ionicity chart in Fig. 9. 

From the time that isoprene was isolated from the pyrolysis products of natural mbber (1), scientific researchers have been attempting to reverse the process. In 1879, Bouchardat prepared a synthetic rubbery product by treating isoprene with hydrochloric acid (2). It was not until 1954—1955 that methods were found to prepare a high ar-polyisoprene which duplicates the structure of natural rubber. In one method (3,4) a Ziegler-type catalyst of trialkylaluminum and titanium tetrachloride was used to polymerize isoprene in an air-free, moisture-free hydrocarbon solvent to an all t /s- 1,4-polyisoprene. A polyisoprene with 90% 1,4-units was synthesized with lithium catalysts as early as 1949 (5). 

Al-Tl Catalyst for cis-1,4-Poly isoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces />mf-l,4-polyisoprene. A second is a lithium alkyl which produces 90% j -l,4-p olyis oprene. Very high (99%) cis- 1,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl4, plus a trialkylaluminum, R3A1, or a combination ofTiCl4 with an alane (aluminum hydride derivative) (86—88). 

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