Development of Synthetic Rubber

Until the 1930s natural rubber from Hevea brasiliensis was the only available elastomer. The United States had to, and still does, import every pound. Although research on synthetic substitutes began before 1940 in this country. World War II influenced speedy development of substitutes when our supply of natural rubber from the Far East was cut off. Gasoline had to be rationed not because of its shortage, but because of the automobile tire shortage. 

In 1910 scientists concluded that natural rubber was cw-l,4-polyisoprene. 

In 1931 Du Pont introduced the first synthetic elastomer, polychloroprene (Neoprene , Duprene ), and Thiokol Corporation introduced a polysulfide rubber called Thiokol . Polychloroprene, although veiy expensive compared to polyisoprene, has superior age resistance and chemical inertness. It is also nonflammable. 

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 

Hypalon chlorosulfonated polyethylene was introduced by Du Pont in 1952. Although not a high volume rubber it has found use in coatings and hoses. 

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The serious development of synthetic rubbers commenced in the late 1930s and early 194(ls. accelerated by a cutoff of supplies of natural rubber because of political turmoil and war. Synlhetic rubbers fall into two major classifications (1) general-purpose rubbers, the major volume of which is nevertheless used for tire production and (2) specialty rubbers that essentially find little use in (ires, hut that are important for a number of other categories. Synthetic rubbers have not replaced natural rubber for numerous uses. For large, heavy-duty truck and bus tires, natural rubber tends to mn considerably cooler and wears better than a blend of natural and synthetic rubbers. On the other hand, a tire (read made of a blend of styrene-butadiene (SBR) and butadiene rubber (polybutadiene) wears longer than natural rubber in conventional automobile, usage, where lower temperatures can be maintained. 

Until modern techniques allowed better purification, toluene and xylene contained significant amounts of benzene. Gasoline still contains significant quantities of benzene (Gosselin et al. 1984). Little commercial interest existed for styrene until World War II, when the development of synthetic rubber required styrene in the production process (Miller et al. 1994). Outside of applications in the plastics and rubber industries, few other uses of styrene exist. 

As indicated in Chapter 1, the polymerization of organic compounds was first reported about the mid-19th century. However, it was not until about 1910 that the simultaneous polymerization of two or more monomers (or copolymerization) was investigated when it was discovered that copolymers of olefins and dienes produced better elastomers than either polyolefins or polydienes alone. The pioneering work of Staudinger in the 1930s and the development of synthetic rubber to meet wartime needs opened the field of copolymerization. 

The development of synthetic rubber played a special role in the history of polymerization chemistry. This was due primarily to the fact that attempts to synthesize rubber were made long before there was even the faintest idea of the nature of polymerization reactions. Such attempts began very soon after the elegant analytical work of Williams [1] in 1860, which clearly demonstrated that Hevea rubber was composed of isoprene. Thus, Bouchardat [2] in 1879 was actually able to prepare a rubberlike substance from isoprene (which he obtained from rubber pyrolysis), using heat and hydrogen chloride. Tilden [3] repeated this process in 1884 but used isoprene obtained from pyrolysis of turpentine to demonstrate that it was not necessary to use the mother substance of rubber itself. These explorations were soon followed by the work of Kondakow (1900) [4] with 2,3-dimethylbutadiene, that of Thiele (1901) [5]... 

The amine antioxidants discussed above have the problem that they discolor the rubber products. They are not suitable for products intended to be light colored. With the development of synthetic rubber in the 1930s and 1940s, which was initially white from its polymerization reactors, it became even more desirable to develop non-staining antioxidants [ 1 ]. Substances such as hydroquinone, resorcinol, 1-naphtol, and 2-naphthol had been claimed as antioxidants early in the century [6, 7]. By the 1940s tris(nonyl phenyl)phosphite (Polygard )... 

It is difficult, indeed almost impossible, to visualize a modern society without rubber products. The development of synthetic rubber began out of the need for countries to establish independence from natural products that grew only in tropical climates. In times of conflict the natural product might not be available, and its loss would seriously threaten national security. Synthetic rubber, then, became a strategic concern during World Wars I and II. Beyond the security issue, the need for materials with better performance also provided a strong impetus for the development of new rubbery materials. In particular, improvements in oil resistance, high temperature stability, and oxidation and ozone resistance were needed. Research today is driven to develop materials with even better performance in these areas. 

Rubber and Elastomers Rubber and elastomers are widely used as lining materials. To meet the demands of the chemical indus-tiy, rubber processors are continually improving their products. A number of synthetic rubbers have been developed, and while none has all the properties of natural rubber, they are superior in one or more ways. The isoprene and polybutadiene synthetic rubbers are duphcates of natural. 

Development of various rubber components based on NR and their derivatives to replace synthetic elastomers... 

Neoprene, Carothers first practical invention, was made reluctantly, as a kind of side issue to his scientific investigation of polymers. Synthetic rubber was of great commercial interest. The car-happy United States used half the world s natural rubber, and demand had outstripped the supply from wild rubber trees in the Amazon. Price fluctuations on British rubber plantations in Southeast Asia provided further incentive for the development of synthetic substitutes. Du Pont had been trying without success to... 

Since its recognition and systematic exploration by Otto Diels and Kurt Alder in the 1920s, the Diels-Alder reaction motif (5.84b) has provided one of the most powerful tools of organic synthesis. The Diels-Alder reaction led directly to the dramatic pre-World War II development of the chemical industry for production of synthetic rubber and other polymeric materials. Today, the commercial impact of Diels-Alder methods extends to virtually all areas of agricultural, pharmaceutical, and natural-products chemistry. 

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. 

Whereas, at the beginning of the thirties, polystyrene had been the driving force in the styrene monomer and polystyrene fields, this development was soon reversed. Under Germany s efforts to become self-sufficient there was a much bigger demand for styrene monomer for the manufacture of synthetic rubber than for polystyrene. As early as 1938 approximately 2500 t of styrene monomer was produced in Ludwigshafen for the newly commissioned rubber plants. When the Allies were cut off from their Asian rubber plantations in the Second World War, the U.S.A. followed suit with large styrene monomer capacities for the manufacture of rubber. Thus there were big capacities for styrene monomer available by 1945 for other uses. 

During World War II, the Japanese cut ofFU.S. access to sources of natural rubber, giving the Americans a strategic imperative to develop and expand the manufacture of synthetic rubber. The C4 streams in refineries were a direct source of butadiene, the primary synthetic rubber feedstock. As a coincidence, the availability of this stream was growing rapidly with the expansion of catalytic cracking to meet wartime gasoline needs. Additional butadiene was manufactured by dehydrogenation of butane and butylene also. 

Latex originally meant the sap of the rubber plant and is a dispersion of particulate rubber. Emulsion polymerization produces a similar dispersion of synthetic rubber or polymers and was rapidly developed to obtain a substitute for natural rubber during World War II. Therefore the product of emulsion polymerization was first called polymer latex, but is now known simply as latex. Sometimes the product of emulsion polymerization is called polymer emulsion. But this terminology is incorrect for latices of solid polymer particles, because emulsion indicates liquid-in-liquid dispersion (1). 

Of equal importance is the fact that synthetic rubber has been improved to such an extent that it is more than capable of meeting the competition of the natural product, and there is no longer any doubt that synthetic rubber is here to stay. New types of synthetic rubber now in the development stage are expected to enhance the competitive position of synthetic rubber still further. 

Phillips Petroleum in the United States [23] developed a propellant composed of ammonium nitrate as oxidant and rubber as a combustible and binding agent. The rubber consists of synthetic rubber and such typical rubber ingredients as carbon black (to improve the mechanical properties of rubber), an accelerator and an inhibitor (to prevent oxidation). To endow the rubber with sufficient plasticity... 

In the 1930s, more than 90 percent of the natural rubber used in the United States came from Malaysia. In the days after Pearl Harbor was attacked in December 1941 and the United States entered World War II, however, Japan captured Malaysia. As a result, the United States—the land with plenty of everything, except rubber—faced its first natural resource crisis. The military implications were devastating because without rubber for tires, military airplanes and jeeps were useless. Petroleum-based synthetic rubber had been developed in 1930 by DuPont chemist Wallace Carothers but was not widely used because it was much more expensive than natural rubber. With Malaysian rubber impossible to get and a war on, however, cost was no longer an issue. Synthetic rubber factories were constructed across the nation, and within a few years, the annual production of synthetic rubber rose from 2000 tons to about 800,000 tons. 

The emulsion SBR (styrene-butadiene rubber) developed in the 1940s, utilizing free-radical initiation, was of enormous benefit to tire technology. The improvement in performance and cost of SBR over natural rubber in tire treads firmly established the utility of synthetic rubber. The success of emulsion SBR led to further research. As a result, the percentage of natural rubber in rubber produced since that time has been steadily declining, and extensive research efforts have been carried along on a continuing basis to develop even better synthetic elastomers. 

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