Synthetic rubber catalysts

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The conjugated diene 1 3 butadiene is used m the manufacture of synthetic rubber and IS prepared on an industrial scale m vast quantities Production m the United States is currently 4 X 10 Ib/year One industrial process is similar to that used for the prepara tion of ethylene In the presence of a suitable catalyst butane undergoes thermal dehy drogenation to yield 1 3 butadiene... 

The original recipe adopted by the U.S. Government Synthetic Rubber Program was known as the "Mutual Recipe" and is shown iu Table 4. As can be seen, the reaction temperature was set at 50°C, which resulted iu 75% conversion to polymer iu about 12 h. The reaction was then stopped by addition of a "shortstop," such as 0.1 parts hydroquinone, which destroyed any residual catalyst (persulfate), and generated quiuone, which helped inhibit any further polymerisation. 

The revolutionary development of stereospecific polymerization by the Ziegler-Natta catalysts also resulted ia the accomplishment ia the 1950s of a 100-year-old goal, the synthesis of i7j -l,4-polyisoprene (natural mbber). This actually led to the immediate termination of the U.S. Government Synthetic Rubber Program ia 1956 because the technical problem of dupHcating the molecular stmcture of natural mbber was thereby solved, and also because the mbber plantations of the Far East were again available. 

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. 

The process of anionic polymerisation was first used some 60 or more years ago in the sodium-catalysed production of polybutadiene (Buna Rubbers). Typical catalysts include alkali metals, alkali metal alkyls and sodium naphthalene, and these may be used for opening either a double bond or a ring structure to bring about polymerisation. Although the process is not of major importance with the production of plastics materials, it is very important in the production of synthetic rubbers. In addition the method has certain special features that make it of particular interest. 

As with polybut-l-ene and many other vinyl monomers that contain an asymmetric carbon, isotactic, syndiotactic and atactic stmctures may be drawn. Using co-ordination catalysts such as mixtures of cobalt chlorides, aluminium alkyls, pyridine and water high-1,2 (high vinyl) polymers may be obtained. One product marketed by the Japan Synthetic Rubber Company (JSR 1,2 PBD) is 91% 1,2, and 51-66% of the 1,2 units are in the syndiotactic state. The molecular mass is said to be several hundred thousand and the ratio MJM is in the range 1.7-2.6. 

World production of I2 in 1992 approached 15 000 tonnes, the dominant producers being Japan 41%, Chile 40%, USA 10% and the former Soviet Union 9%. Crude iodine is packed in double polythene-lined fibre drums of 10-50-kg capacity. Resublimed iodine is transported in lined fibre drums (11.3 kg) or in bottles containing 0.11, 0.45 or 2.26 kg. The price of I2 has traditionally fluctuated wildly. Thus, because of acute over-supply in 1990 the price for I2 peaked at 22/kg in 1988, falling to 12/kg in 1990 and 9.50/kg in 1992. Unlike CI2 and Br2, iodine has no predominant commercial outlet. About 50% is incorporated into a wide variety of organic compounds and about 15% each is accounted for as resublimed iodine, KI, and other inorganics. The end uses include catalysts for synthetic rubber manufacture, animal- and fowl-feed supplements. 

When polymerizing dienes for synthetic rubber production, coordination catalysts are used to direct the reaction to yield predominantly 1,4-addition polymers. Chapter 11 discusses addition polymerization. The following reviews some of the physical and chemical properties of butadiene and isoprene. 

Polystyrene (PS) is the fourth big-volume thermoplastic. Styrene can be polymerized alone or copolymerized with other monomers. It can be polymerized by free radical initiators or using coordination catalysts. Recent work using group 4 metallocene combined with methylalumi-noxane produce stereoregular polymer. When homogeneous titanium catalyst is used, the polymer was predominantly syndiotactic. The heterogeneous titanium catalyst gave predominantly the isotactic. Copolymers with butadiene in a ratio of approximately 1 3 produces SBR, the most important synthetic rubber. 

Polychloroprene is the oldest synthetic rubber. It is produced by the polymerization of 2-chloro-1,3-butadiene in a water emulsion with potassium sulfate as a catalyst ... 

The polybutadienes prepared with these barium t-butoxide-hydroxide/BuLi catalysts are sufficiently stereoregular to undergo crystallization, as measured by DTA ( 8). Since these polymers have a low vinyl content (7%), they also have a low gl ass transition temperature. At a trans-1,4 content of 79%, the Tg is -91°C and multiple endothermic transitions occur at 4°, 20°, and 35°C. However, in copolymers of butadiene (equivalent trans content) and styrene (9 wt.7. styrene), the endothermic transitions are decreased to -4° and 25°C. Relative to the polybutadiene, the glass transition temperature for the copolymer is increased to -82°C. The strain induced crystallization behavior for a SBR of similar structure will be discussed after the introduction of the following new and advanced synthetic rubber. 

Polybutadiene and polyisoprene are produced and used mainly as synthetic rubber on an industrial scale by using transition metal catalysts, especially titanium- and nickel-based ones. By contrast, only minor attention has been paid to the palladium-catalyzed polymerization of butadiene. A mixture of 1,2-polybutadiene and trans- and c/s-l, 4-polybutadiene was obtained by using PdCl2 as a catalyst (7, 2). 

Alfin An obsolete process for making synthetic rubber by polymerizing butadiene in pentane solution. The catalyst was an insoluble aggregate of sodium chloride, sodium iso-propoxide, and allyl sodium. The name is actually the name of the catalyst, derived from alcohol, used to make the sodium Aopropoxide, and olefin, referring to the propylene used to make the allyl sodium. 

Buna [Butadien natrium] The name has been used for the product, the process, and the company VEB Chemische Werke Buna. A process for making a range of synthetic rubbers from butadiene, developed by IG Farbenindustrie in Leverkusen, Germany, in the late 1920s. Sodium was used initially as the polymerization catalyst, hence the name. Buna S was a copolymer of butadiene with styrene Buna N a copolymer with acrylonitrile. The product was first introduced to the pubhc at the Berlin Motor Show in 1936. Today, the trade name Buna CB is used for a polybutadiene rubber made by Bunawerke Hiils using a Ziegler-Natta type process. German Patent 570, 980. 

In another Reppe process, acetylene is reacted with formaldehyde to yield butyndiol, which can be converted to butadiene for the manufacture of the synthetic rubber Buna the catalyst is nickel cyanide ... 

The first synthetic rubbers to be commercially available in United States were Thiokol (1930) and Neoprene (1931). Both of these are still being produced commercially because they have special properties that are not matched by natural rubber. Various types of synthetic rubbers were introduced during (1939-43) World War II. After world war, stereo rubbers have been made using stereo specific catalysts. 

Anionic polymerisation was known for many years before the nature of the polymerisation was predicted. The production of buna type synthetic rubbers in Germany and Russia by the polymerisation of butadiene with the sodium or potassium as the catalyst was known. 

During World War II, isopropyl benzene, more commonly and commercially known as cumene, was manufactured in large volumes for use in aviation gasoline. The combination of a benzene ring and an iso-paraffin structure made for a very high octane number at a relatively cheap cost. After the war, the primary interest in cumene was to manufacture cumene hydroperoxide. This compound was used in small amounts as a catalyst in an early process of polymerizing butadiene with styrene to make synthetic rubber. Only by accident did someone discover that mild treating of cumene hydroperoxide with phosphoric acid resulted in the formation of... 

The Government Rubber Reserve Company in the 1940s pioneered the development of styrene-butadiene copolymers, by far the largest volume of synthetic rubber used today. Now usually known as SBR, it has also been called Buna-S, Rzrtadiene with a sodium (Na) catalyst and copolymerized... 

Poly(l,3-butadiene)s with high 1,4-ds contents are valuable materials that have a wide range of applications as synthetic rubbers. A variety of transition metal-based catalysts have been investigated so far for the polymerization of... 

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