Isoprene-butadiene rubber

Natural rubber, synthetic cw-1,4-poly(isoprene), butadiene rubbers, and styrene-butadiene rubbers are all sensitive to oxidation because of their high carbon-carbon double bond fractions. Attempts to reduce sensitivity to oxidation with maintenance of the vulcanizability have lead to the development of what are known as the butyl rubbers, IIR, which are copolymers of isobutylene with a little isoprene. But butyl rubbers only have a small rebound elasticity. However, since they also have poor gas permeability, they are mostly used for tire inner tubes. 

FIGURE 11.36 Gas chromatogram showing pyrolysis of isoprene-butadiene rubber [1 = butadiene, 2 = isoprene, 3 = butadiene dimmer, 4 = Umonene (isoprene dimmer)]. Conditions pyrolyzer—CDS Analytical Model 2500, 750°C, 20 s interface oven 300°C, GC—6890 (Agilent), colunrn HP-5, 30 m x 0.25 nun. Carrier gas helium, 5.9 psi, split ratio 75-1, temperature program 40°C, 2 min, 6°C/min to 295°C. Detector mass selective detector. [Reprinted with permission from T. P. Wampler, J. Chromatogr. A 842, 207-220 (1999), Figure 7.]. 

Styrene-isoprene butadiene rubbers are manufactured with varying combinations of styrene, butadiene, and isoprene contents here, different isomers can be present in the isoprene. Degradation in these double bonds begins with cis-1,4 units, followed by trans-1,4 units, whereas 3,4 and 1,2 units degrade only slightly. Thus, more aging-resistant elastomers can be manufactured by the targeted use of poly-isoprene with 3,4 and 1,2 units. The styrene units are not subject to attack [797]. 

Figure 3 (A) Under the same reaction conditions, the hydrogenation reactivity of PIP is much slower than that of PBD for steric reasons. (B) Complete hydrogenation of PIP is achieved but with significant reduction in molecular weight MJ. (C) Complete hydrogenation of styrene-isoprene-butadiene rubber (SIBR) achieved under mild conditions and no change in molecular weight was observed.

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. 

Thermoplastic block copolymers were used for pressure-sensitive and hot-melt rubber adhesives as from the middle sixties. These adhesives found application in packaging, disposable diapers, labels and tapes, among other industrial markets. The formulation of these adhesives generally includes an elastomer (generally containing styrene endblocks and either isoprene, butadiene or ethylene-butylene midblocks) and a tackifier (mainly a rosin derivative or hydrocarbon resin). 

In 1994, the worldwide consumption of rubber was approximately 14.5 million tons a year, of which about 40% consisted of natural rubber. Natural rubber is produced as latex by tropical rubber trees (Hevea brasiliensis). It is processed locally and therefore the quality of natural rubber fluctuates remarkably [ 140]. Due to increasing demand for rubbers, combined with a decreasing production capacity in Asia and a vast increase in labor costs, the price of natural rubber is still rising sharply. In 1990-1994, the average price of natural rubber was about 0.38 /lb, while in 1996 it was already over 0.80 /lb. The remaining 60% of the articles were manufactured from synthetic petroleum-based rubbers such as isoprene rubber, styrene-butadiene rubber, chloroprene rubber and polyurethanes. The quality of synthetic rubbers is constant, and their price varies between 2 and 5 US per kilogram [137-140]. 

Diene polymers refer to polymers synthesized from monomers that contain two carbon-carbon double bonds (i.e., diene monomers). Butadiene and isoprene are typical diene monomers (see Scheme 19.1). Butadiene monomers can link to each other in three ways to produce ds-1,4-polybutadiene, trans-l,4-polybutadi-ene and 1,2-polybutadiene, while isoprene monomers can link to each other in four ways. These dienes are the fundamental monomers which are used to synthesize most synthetic rubbers. Typical diene polymers include polyisoprene, polybutadiene and polychloroprene. Diene-based polymers usually refer to diene polymers as well as to those copolymers of which at least one monomer is a diene. They include various copolymers of diene monomers with other monomers, such as poly(butadiene-styrene) and nitrile butadiene rubbers. Except for natural polyisoprene, which is derived from the sap of the rubber tree, Hevea brasiliensis, all other diene-based polymers are prepared synthetically by polymerization methods. 

An estimation of ZnCFO efficiency as vulcanization active component was carried out in modelling unfilled elastomeric compositions on the basis of isoprene, butadiene-nitrile, chloroprene and butyl rubbers of sulphur, thiuram, peroxide, metaloxide and resin vulcanization systems. 

Several polymers based on 1,3-dienes are used as elastomers. These include styrene-1,3-butadiene (SBR), styrene-1,3-butadiene terpolymer with an unsaturated carboxylic acid (carboxylated SBR), acrylonitrile-1,3-butadiene (NBR or nitrile rubber) (Secs. 6-8a, 6-8e), isobutylene-isoprene (butyl rubber) (Sec. 5-2i-l), and block copolymers of isoprene or... 

Other commercial copolymers which are typically random are those of vinyl chloride and vinyl acetate (Vinylite), isobutylene and isoprene (butyl rubber), styrene and butadiene (SBR), and acrylonitrile and butadiene (NBR). The accepted nomenclature is illustrated by EP, which is designated poly-ethylene-co-propylene the co designating that the polymer is a copolymer. When the copolymers are arranged in a regular sequence in the chains, i.e., ABAB, the copolymer is called an alternating copolymer. A copolymer consisting of styrene and maleic anhydride (SMA) is a typical alternating copolymer. 

Another large use of normal butenes in the petrochemical industry is in the production of 1,3-butadiene (CH2 = CH = CH = CH2). In the process, a mixture of n-butenes, air, and steam is passed over a catalyst at a temperature of 500°C to 600°C. Butadiene is used extensively to produce synthetic rubbers (see Isoprene) in polymerization reactions. The greatest use of butadiene is for styrene-butadiene rubber, which contains about a 3 1 ratio of butadiene to styrene. Butadiene is also used as a chemical intermediate to produce other synthetic organics such as chloroprene, for adhesives, resins, and a variety of polymers. 

The most important hydrocarbon copolymers are styrene-butadiene rubbers (SBR) produced by free-radical emulsion or anionic polymerization. Anionic polymerization allows the manufacture of styrene-butadiene and styrene-isoprene three-block copolymers. 

The products are elastomers (recall that the starting material for natural rubber is isoprene). Butadiene can give almost complete 1,2- or 1,4-polyme depending primarily upon the coordination catalyst and the polymerization conditions ... 

The major general purpose rubbers are natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, and ethylene-propylene rubber. These rubbers are used in tires, mechanical goods, and similar applications. Specialty elastomers provide unique properties such as oil resistance or extreme heat stability. Although this differentiation is rather arbitrary, it tends also to classify the polymers according to volumes used. Styrene-butadiene rubber, butadiene rubber, and ethylene-propylene rubber account for 78 percent of all synthetic rubber consumed. 

These are the most important. The two double bonds mutually activate each other conjugation is essentially not destroyed by addition to the growing chain end. Therefore the conjugated dienes are difunctional monomers. They are polymerized by a relatively simple mechanism. Of all the polymers generated in living tissues, we have so far been able to imitate most closely natural rubber, poIy-cis-l,4-isoprene. Butadiene, isoprene and chloroprene are the dienes most often employed in macro-molecular chemistry. 

Rubber has a structure intermediate between thermosets and thermoplastics, with molecular chains linked by sulphur bridges during vulcanization. In pyrolysis, the main material is tyre rubber, a compound of styrene- butadiene- and isoprene-based rubber (SBR), of carbon black, sulphur, vulcanization aids, and zinc oxide. 

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