Aluminum alkyl co-catalyst

A unique variant of catalyst preformation in the absence of dienes was described by Enichem in an early patent on Nd-BR. The active Nd catalyst was prepared by the reaction of neodymium oxide with carboxylic acid and (BuCl in vaseline at 80 °C. Subsequently, aqueous HC1 was added at 80 °C. Finally, the addition of the aluminum alkyl co catalyst yielded the active Nd catalyst [389,390]. 

In addition to titanium-based Ziegler-Natta catalysts, vanadium-based systems have also been developed for PE and ethylene-based co-polymers, particularly ethylene-propylene-diene rubbers (EPDM). Homogeneous (soluble) vanadium catalysts produce relatively narrow molecular mass distribution PE, whereas supported V catalysts give broad molecular mass distribution.422 Polymerization activity is strongly enhanced by the use of a halogenated hydrocarbon as promoter in combination with a vanadium catalyst and aluminum alkyl co-catalyst.422,423... 

Homogeneous ylide-nickel systems were combined with heterogeneous surface chromium(II) catalysts. Both separate catalyst systems work in the absence of aluminum alkyl co-catalysts. In this process the nickel complex is supported on the chromium contact, resulting in a new heterogeneous catalyst, which is active in the ediylene polymerization and where two different catalytic centers co-operate [14a, b]. 

Because this chapter focuses on molecular transition metal complexes that catalyze the formation of polyolefins, an extensive description has not been included of the heterogeneous titanium systems of Ziegler and the supported chromium oxide catalysts that form HDPE. However, a brief description of these catalysts is warranted because of their commercial importance. The "Ziegler" catalysts are typically prepared by combining titanium chlorides with an aluminum-alkyl co-catalyst. The structural features of these catalysts have been studied extensively, but it remains challenging to understand the details of how polymer architecture is controlled by the surface-bound titanium. This chapter does, however, include an extensive discussion of how group(IV) complexes that are soluble, molecular species polymerize alkenes to form many different types of polyolefins. 

Most Ziegler-Natta catalysts for high vinyl 1,2-polybutadiene delds syndiotactic polymer with a melting temperature that ranges between 90 and 220°C depending on the degree of crystallinity. The microstructure of this material was first recognized by Natta (272) in 1955 and can be prepared with cobalt (275-280), vanadium (281), molybdenum (282,283), chromium (274,284), and titanium (285) salts treated with aluminum alkyl co-catalysts. 

This phenomenon is rather specific. That is, a Cr/silica catalyst is preferred, not a Cr/silica-titania or a Cr/silica-alumina. It must be activated at a high temperature or treated with fluoride, perhaps to reduce potential ligands. Then it must be reduced in CO. When contacted with some cocatalysts, especially aluminum alkyls, the catalyst then becomes highly sensitive to H2. As illustrated in Table 60, in this series of experiments there was a huge jump in MI only when all of these treatments were combined. Activation at 600 °C does not work unless the catalyst also contains fluoride. Activation at 800 °C is effective without fluoride, but the effect is more pronounced with fluoride. The data shown in Figure 214 illustrate the huge shift in the MW distribution resulting from this combination of catalyst and reaction variables. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Zieglei-type catalysts based upon Co, Ni, and Fe and in the presence of aluminum alkyls codimeiize butadiene with olefins such as ethylene. 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

Nametkin and co-workers hrst reported the alkylation of benzene derivatives with allylchlorosilanes in the presence of aluminum chloride as catalyst. " 2-(Aryl)propylsilanes were obtained from the alkylation of substituted benzenes (Ph—X X = H, CL Br) with allylsilanes such as allyldichlorosilane and allyltrichlo-rosilane.The yields ranged from 34 to 66% depending upon the substituents on the benzene ring, but information concerning reaction rates and product isomer distribution was not reported. 

Activation of the catalyst is usually performed by exposure to a co-catalyst, namely an aluminum alkyl. The model catalysts were successfully activated by trimethylalumimun (TMA) and triethylaluminum (TEA), commonly used for this purpose. The compounds were dosed from the gas phase either at room temperature for a prolonged time or for a much shorter time at a surface temperature of 40 K. Nominal 3400 L of TMA or TEA were exposed at room temperature. The chemical integrity of the co-catalyst was verified by IR spectroscopy of condensed films grown at low temperature on the substrates. The spectra were typical for condensed and matrix isolated species [119]. 

Cobalt compounds, - particularly salts of organic acids, such as cobalt(II) octanoate369-371 with aluminum alkyls, are also suitable catalysts in hydrocarbon solvents. An A1 Co ratio higher than 1 and water370-372 are essential to obtain high catalytic activity and high cis selectivity.184,363 Polybutadiene with a high cis content can also be synthesized by nickel-based catalysts. Of the... 

Breslow (139) discovered a homogeneous system well suited for kinetic analysis. He realized that bis(cyclopentadienyl)titanium(IV) compounds, which are very soluble in aromatic hydrocarbons, could be used instead of titanium tetrachloride as the transition-metal compound together with aluminum alkyls to give Ziegler catalysts. Subsequent research on this and other systems with various alkyl groups has been conducted by Natta et al. (140, 141), Belov el at. (142-144), Patat (145), Patat and Sinn (146) Sinn et al. (119, 147), Shilov and co-workers (148-150), Chien and Hsieh (20), Adema (151), Clauss and Bestian (152), Henrici-Olive and Olive (153), and Reichert and Schoetter (154) and Fink (155). 

As discussed in Sects. 2.1 and 2.2.8 control of molar mass is an important aspect in the large-scale polymerization of dienes. In Nd-catalyzed polymerizations the control of molar mass is unique amongst Ziegler/Natta catalyst systems as standard molar mass control agents such as hydrogen, 1,2-butadiene and cyclooctadiene which are well established for Ni- and Co-systems do not work with Nd catalysts [82,206,207]. The only known additives which allow for the regulation of molar mass without catalyst deactivation are aluminum alkyls, magnesium alkyls, and dialkyl zinc. 

Trialkyl boron was first claimed as a new anionic initiator for the polymerization of vinyl compounds (264), although it was rather improbable in view of the low ionic character of the boron-carbon bond. The error was quickly corrected when it was shown that free radicals were involved (265, 266) and that oxygen, peroxides, silver salts and copper salts were co-catalysts (262, 267). Aluminum alkyls can also initiate radical polymerizations in the presence of oxygen (267,262) but, as in the case of zinc, cadmium or boron alkyls, the products were not stereoregular. Thus, complexing between catalyst and monomer probably does not occur. 

A second method of production utilizes the Ziegler-Natta TiCl4 catalyst with liquid cocatalysts such as an alkyl aluminum halide. This is a reactive catalyst that must be prepared at the exclusion of air and water. The alkyl group of the co-catalyst coordinates with the Ti+3 site. The polymer grows by insertion of the ethylene into the double bond of the adsorbed polymer on another site. 

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