Styrene Butadiene Rubbers

The precursors of SBR were first prepared in Germany in 1929 but, as mentioned in Chapter 1, they possessed no particular virtues over natural rubber and the synthetic polymer was not at that time exploited commercially. Shortly before World War II production of the rubber was started in Germany under the name of Buna S, details of the production of which were supplied to the American Standard Oil Company under a, very fortuitous, information exchange 

The comonomers for SBR production, styrene and butadiene, are today invariably produced from petroleum sources. The methods of preparation of butadiene were outlined in the previous chapter. 

Styrene is produced by a two-stage process via ethyl benzene. In a typical process ethylene and benzene are reacted at about 95 C in the presence of a Friedel-Crafts catalyst such as aluminium chloride. To improve the catalyst efficiency some ethyl chloride may be added to the reacting mixture, the former producing some hydrochloric acid at the reaction temperatures. 

Ethyl benzene may also be produced via catalytic reforming processes. The reforming process is one which converts aliphatic hydrocarbons into a mixture of aromatic hydrocarbons. This may subsequently be fractionated to give benzene, toluene and a xylene fraction from which the ethyl benzene may be obtained. 

Styrene is obtained from ethyl benzene by a variety of methods of which that of dehydrogenation is the most well-known. 

FIGURE 2.9 X-ray diffractogram (XRD) spectra of unmodified and modified nanoclays and styrene-butadiene rubber (SBR)-based nanocomposites with styrene content of (a) 15% and 40% and (b) 23%. (From Sadhu, S. and Bhowmick, A.K., J. Polym. Set, Part B Polym. Phys., 42, 1573, 2(304. Courtesy of Wiley InterScience.) 

The most successful method developed for the production of a general-purpose synthetic rubber was the emulsion copolymerization of butadiene and styrene (SBR), which still represents the main process in use today (Blackley, 1975 Hofmann, 1989 Blow, 1971 Brydson, 1981 Bauer, 1979 Sun and Wusters, 2004 Demirors, 2003). The general principles of copolymerization will be discussed in a later section, but it is instructive at this point to examine the other main features of this system. The types of recipes used are seen in Table 2.5 (Bauer, 1979). The recipes shown are to be considered only as typical, as they are subject to many variations. It should be noted that the initiator in the 50°C recipe (hot rubber) is the persulfate, whereas in the 5°C recipe (cold mbber) the initiator consists of a redox system comprising the hydroperoxide-iron(II)-sulfoxylate-EDTA. In the latter case, the initiating radicals are formed by the reaction of the hydroperoxide with the ferrous iron, whose concentration is 

Trisodium phosphate (Na3P04 IOH2O) Ferrous sulfate (FeS04 7H2O) 

Sodium formaldehyde sulfoxylate Tetrasodium salt of ethylenediamine tetraacetic acid (EDTA) 

Viscosity average Weight average Number average 

In both recipes, the thiol acts as a chain transfer agent to prevent the molecular weight from attaining the excessively high values possible in emulsion polymerization systems (see Table 2.6). It acts in an analogous fashion to the solvent 

Attempts to produce synthetic mbber have been carried out since the 1800s. The introduction of automobiles in the early 1900s gave added impetus to find a substitute for natural mbber, the price of which tripled from 2.16/kg in 1900 to 6.73/kg in 1910 (1). The advent of World War I gave Germany incentive to start a crash program on an alternative to natural mbber. From this work, products based on dimethylbutadiene were used, but these were not found to be good substitutes. 

In the late 1920s Bayer Company began reevaluating the emulsion polymerisation process of polybutadiene as an improvement over their Buna technology, which was based on sodium as a catalyst. Incorporation of styrene (qv) as a comonomer produced a superior polymer compared to polybutadiene. The product Buna S was the precursor of the single largest-volume polymer produced in the 1990s, emulsion styrene—butadiene mbber 

In the mid-1950s, the Nobel Prize-winning work of K. Ziegler and G. Natta introduced anionic initiators which allowed the stereospecific polymerization of isoprene to yield high cis-1,4 stmcture (3,4). At almost the same time, another route to stereospecific polymer architecture by organometaHic compounds was aimounced (5). 

Desirable properties of elastomers include elasticity, abrasion resistance, tensile strength, elongation, modulus, and processibiUty. These properties are related to and dependent on the average molecular weight and mol wt distribution, polymer macro- and microstmcture, branching, gel (cross-linking), and 

Unlike SSBR, the microstmcture of which can be modified to change the polymer s T, the T of ESBR can only be changed by a change in ratio of the monomers. Glass-transition temperature is that temperature where a polymer experiences the onset of segmental motion (7). 

Major polymer applications tires, flooring, conveyor belts, shoe products, sheet, tubing, tank and caterpillar tracks, sporting goods, toys, coated fabrics, automotive mechanical goods 

Important processing methods mixing, compression molding, calendering, vulcanization, coating 

Typical fillers carbon black, silica, lead oxide (y-radiation shields), sodium aluminum silicate, clay, mica, kaolin, carbon fiber crosslinked PS beads 

Typical concentration range carbon black - 20-50 wt%, precipitated sihca - 25-60 wt%, calcium carbonate - 40-70 wt%, lead oxide - 88 wt%, zinc oxide - 1-2 wt%, clay - 20-80 wt%, mica - 20-30 wt%, kaolin - 20-35 wt%, carbon fiber - 15-30 wt% 

Auxiliary agents silane modification of silica, process oils, lubricants 

Silicone sealant with improved high temperature adhesion Polydimethylsiloxane having a viscosity of 50,000 cps 55 parts 

Calcium carbonate treated with stearic acid 15 

Ftrmed silica reinforcing filler treated with cyclic polydimethylsiloxane 15 Ethyltriacetoxysilane crosslinking component 5.2 

Styrene-butadiene rabber, SBR, is compatible with the majority of mineral oils but has a limited compatibility with paraffinic oils.  

Dihydroquinoline derivative p-phenylene-diamine derivative Sulfonamide accelerator Zinc oxide Sulfur 

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SBP spirits Special boiling point spirits. SBR Styrene butadiene rubber. 

Styrene is manufactured by alkylating benzene with ethene followed by dehydrogenation, or from petroleum reformate coproduction with propylene oxide. Styrene is used almost exclusively for the manufacture of polymers, of which the most important are polystyrene, ABS plastics and styrene-butadiene rubber. U.S. production 1980 3 megatonnes. 

The elastomer produced in greatest amount is styrene-butadiene rubber (SBR) Annually just under 10 lb of SBR IS produced in the United States and al most all of it IS used in automobile tires As its name suggests SBR is prepared from styrene and 1 3 buta diene It is an example of a copolymer a polymer as sembled from two or more different monomers Free radical polymerization of a mixture of styrene and 1 3 butadiene gives SBR... 

Styrene-butadiene rubber is prepared from the free-radical copolymerization of one part by weight of styrene and three parts by weight of 1,3-butadiene. The butadiene is incorporated by both 1,4-addition (80%) and 1,2-addition (20%). The configuration around the double bond of the 1,4-adduct is about 80% trans. The product is a random copolymer with these general features ... 

Styrene-butadiene rubber (SBR) is also known as government rubber styrene (GRS) and Buna S. 

Styrene-butadiene rubber (SBR) (also known as Buna S) 0.94 40-100 400-600 1600-3700 -60 107... 

Polymers of chloroprene (structure [XII]) are called neoprene and copolymers of butadiene and styrene are called SBR, an acronym for styrene-butadiene rubber. Both are used for many of the same applications as natural rubber. Chloroprene displays the same assortment of possible isomers as isoprene the extra combinations afforded by copolymer composition and structure in SBR offsets the fact that structures [XIIll and [XIV] are identical for butadiene. 

COLORANTS FORFOOD,DRUGS,COSTffiTICS AND TffiDICALDEVICES] (Vol 6) ESBR See Emulsion styrene-butadiene rubber. 

SAN copolymers [ACRYLONITRILE POLYTffiRS - SURVEY AND SAN (STYRENE-ACRYLONITRILECO-POLYTffiRS)] (Vol 1) -SBRfrom [STYRENE-BUTADIENE RUBBER] (Vol 22)... 

Styrene—Butadiene Rubber (SBR). This elastomer is used primarily in tires, vehicle parts, and electrical components. 

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