Butyl rubber development

W. D. Gunter, Butyl and halogenated butyl rubbers, Developments in Rubber Technology-2 (A. Whelan and K. S. Lee, eds.), Applied Science Publishers, London 1981, Chap. 6, p. 155. 

Butyl Rubber. Butyl mbber was the first low unsaturation elastomer, and was developed ia the United States before World War II by the Standard Oil Co. (now Exxon Chemical). It is a copolymer of isobutylene and isoprene, with just enough of the latter to provide cross-linking sites for sulfur vulcanization. Its molecular stmcture is depicted ia Table 1. 

In the early stages of development of polypropylene rubbers, particularly butyl rubber, were used to reduce the brittleness of polypropylene. Their use declined for some years with the development of the polypropylene copolymers but interest was greatly renewed in the 1970s. This interest has been centred largely around the ethylene-propylene rubbers which are reasonably compatible in all proportions with polypropylene. At first the main interest was with blends in which the rubber content exceeded 50% of the blend and such materials have been designated as thermoplastic polyolefin elastomers (discussed in Section 11.9.1). There is also increasing interest in compounds with less than 50% rubber, often referred to as elastomer-modified thermoplastics. It is of interest to note... 

Whilst polyisobutene is a non-rubbery polymer exhibiting high cold flow (see Section 11.3), the copolymer containing about 2% isoprene can be vulcanised with a powerful accelerated sulphur system to give moderately rubbery polymers. The copolymers were first developed in 1940 by Esso and are known as butyl rubbers and designated as HR. As they are almost saturated they have many properties broadly similar to the EPDM terpolymers. They do, however, have two properties that should be particularly noted ... 

The demand for isoprene for Butyl rubber led to the development of a recovery process for this Cj diolefin. Extractive distillation with acetone was the first process used but it has been replaced with acetonitrile (ACN ). The first step in the process is the fractionation of steam cracker debutanizer bottoms in a conventional two tower system to produce a C5 cut containing 30% isoprene. The first tower rejects C and heavier while the second rejects C4 and lighter materials. 

Recent trends in protective coatings used on buried pipelines have been away from reinforced hot applied coal tar and asphalt enamels and butyl rubber laminate tapes, particularly where applied over-the-ditch . The more recently developed coatings based on fusion bonded epoxies, extruded poly-ethylenes, liquid-applied epoxies and polyurethanes, require factory application where superior levels of pipe preparation and quality control of the application process can be achieved. 

Generally, systems developed in the USA favour a combination of polyethylene with either butyl-rubber or hot-applied mastic adhesives, the latter consisting of a blend of rubber, asphalt and high molecular weight resins. In European and Far East coating plants, epoxy type primers and hard ethylene copolymer adhesives have been successfully employed. 

Brominated butyl rubber, 4 436 development of, 4 434 manufacture, 4 400, 442—444 Brominated carbonate oligomers,... 

Chlorinated additive flame retardants, 11 468-470, 471-473t Chlorinated aromatics, 6 242 decomposition using microwaves, 16 555 Chlorinated butyl rubber, 4 436 development of, 4 434 manufacture, 4 400, 442-444 Chlorinated ethanes... 

DPE suits, and butyl rubber (NRC, 2001b). The levels were 0.0002 to 0.0008 ng/m3, three orders of magnitude below the EPA criterion of 0.2 ng/m3 for dioxin emissions from incinerators. In the test with neat GB, the product gas contained 0.01 to 0.06 percent phosphine. As noted previously in the section on methods development testing, phosphine can interfere with the measurement of GB. Based on results from the EPA s toxicity characteristic leachate procedure, stabilization would be necessary only for solid wastes derived from DPE suit material, because the cadmium and lead criteria were not met by the treated dunnage in some tests (NRC, 2001b). 

Butyl rubber was discovered by R.M. Thomas and W.J. Sparks in 1937, and was developed by the Standard Oil Company (New Jersey) and was part of an exchange of information between the German chemical giant LG. Farbenindustrie AG and Standard Oil. 

Butyl rubber is one product formed when isobutylene is copolymerized with a few percents of isoprene. In the Exxon process an isobutylene-methyl chloride mixture containing a small amount of isoprene is mixed at — 100°C with a solution of AICI3 in methyl chloride. An almost instantaneous reaction yields the product, which is insoluble in methyl chloride and forms a fine slurry. Molecular weight can be controlled by adding diisobutylene as a chain-transfer agent. Increased catalyst concentration and temperature also result in lowering molecular weight. The product can be vulcanized and is superior to natural rubber. A solution process carried out in C5-C7 hydrocarbons was developed in the former Soviet Union.471,472... 

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous liquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see OLEFIN POLYMERS ELASTOMERS, SYNTHETIC-BUTYL rubber). 

McNiell has developed a useful technique for the determination of unsaturation using chlorine-36. It is not suggested that the technique should replace existing methods but that it is highly suitable for micro analyses when only small samples are available or for estimation of very low unsaturation values where other methods are not sufficiently sensitive. The superiority of the method for the analysis of butyl rubbers has been demonstrated (61) and it has also been used to measure unsaturation of 0.1—0.01 mole-% of polyisobutene (62). 

Berkowitz JB, Young GS, Anderson RC, et al. 1981. Research and development for health and environmental hazard assessment, Task Order 5. Occupational and environmental hazards associated with the formulation and use of white phosphorus-felt and red phosphorus-butyl rubber screening smokes. Cambridge, MA Arthur D. Little, Inc. DAMD17-79-C-9139. AD-A116956. 

Adhesives on the basis of a rubber are applied as watery dispersions, as solvents, or as solvent-free fluids. Sometimes the rubber is vulcanised after the gluing process, sometimes it remains uncured. Polymers often used are butyl rubber, polyisobutylene, and polychloroprene. A more recent development is the use of... 

A significant portion, as high as 70% with new tools, of research time is dedicated to purely methods development. Methods development is necessary, as polymer chemistries, properties, and applications are extremely diverse. A portion of this methods development is focused on how to handle different materials, such as butyl rubber versus low-density polyethylene. However, the largest portion of methods development is dedicated to data correlation. 

Butyl rubber is one of the older synthetic rubbers, having been developed in 1937. Because of the saturated nature of a polyolefin elastomer, the commercial polymer is actually a copolymer of isobutylene and isoprene. The isoprene is added to provide cure sites. In addition, halogenated (bromo or chloro) derivatives are available. 

Cationic polymerizations are not only important commercial processes, but, in some cases, are attractive laboratory techniques for preparing well-defined polymers and copolymers. Polyacetal, poly(tetramethyl-ene glycol), poly(e-caprolactam), polyaziridine, polysiloxanes, as well as butyl rubber, poly(N-vinyl carbazol), polyindenes, and poly(vinyl ether)s are synthesized commercially by cationic polymerizations. Some of these important polymers can only be prepared cationically. Living cationic polymerizations recently have been developed in which polymers with controlled molecular weights and narrow polydispersity can be prepared. 

Large-scale manufacture of butyl rubber started during World War II, in the scope of the U.S. Government rubber-procurement program, and the actual process is essentially similar to the historical one [9]. Bromi-nated butyl (BIIR) was introduced in the 1950s by Goodrich Chemical Co. [54-56] but substantial commercial development occurred only in 1971 when the Polysar Ltd continuous and economic manufacturing process based on elemental bromine came onstream [57]. Production of chlorinated butyl (CIIR) was introduced on a commercial scale by Exxon Chemical in 1961. 

The latexes upon which this industry developed were natural rubber and polychloroprene for solvent resistance. However, technology is advancing to permit penetration of carboxylated nitrile latex for optimized solvent resistance and tougher abrasion resistance. Among the competition to latexes in this field are poly(vinyl chloride) plastisols. As technology develops in producing small particle size latexes from polymers whose synthesis is loo water-sensitive for emulsion polymerization, the dipped goods industry will quickly convert to their utilization from the solvent-based cements of these polymers now employed Prime candidates include butyl rubber, EPDM, hypalon, and vlton. 

Significant developments in synthetic rubber began at this time. Outstanding were the introduction of polychloroprene (neoprene) by Carothers, and of the oil-resistant polysulfide rubber Thiokol by Patrick. These were soon followed by styrene-butadiene copolymers, nitrile rubber, butyl rubber, and various other types, some of which were rushed into production for the war effort in the early 1940s. The stereospecific catalysts researched by Ziegler and Natta aided this development, including synthesis of true rubber hydrocarbon (polyisoprene). Since 1935 synthetic rubbers have been referred to as elastomers. 

Research with anaerobic cultures can be in batch or continuous culture. Fed-batch anaerobic reactors are not known to us but may very well be feasible. A reliable technique for batch cultures uses serum bottles sealed with butyl rubber stoppers and crimp sealed with an aluminum cap. Anaerobic microorganisms in batch flasks are mainly cultured by Hungate s methods [7] that are widely accepted in the research community. We will not describe these techniques but will focus on the different continuous culture apparatuses that have been developed over the years. 

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