Isobutylene and isoprene, butyl rubbers

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. 

To this category belong homopolymers of polyisobutylene, copolymers of isobutylene and isoprene (butyl rubber), chlorobutyl, and bromobutyl. All these have been produced commercially for decades. 

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. 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

Buna-S Elastomeric copolymer of butadiene and styrene, butyl rubber Elastomeric copolymer of isobutylene and isoprene. 

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... 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

Butyl rubber - A copolymer of isobutylene and isoprene rubber ASTM designation HR butyl rubber is the common name for such materials. 

Known as MR. butyl rubber is a copolymer of isobutylene and isoprene. The elastomers contain only (1.5 2.5 mole 9r of isoprene. This is introduced to effect sufficient unsaturatinn to make the rubber vulcanizublc. Polymerizations are usually earned out at low temperature (-80 to -1(KJ C) with methyl chloride as solvent. Anhydrous aluminum chloride and a trace of water serve as catalyst. 

RUBBER (Synthetic). Any of a group of manufactured elastomers that approximate one or more of the properties of natural rubber. Some of these aie sodium polysulfide ( Thiokol ). polychloiopiene (neoprene), butadiene-styrene copolymers (SBR), acrylonitrilebutadiene copolymers (nitril rubber), ethvlenepropylene-diene (EPDM) rubbers, synthetic poly-isoprene ( Coral, Natsyn ), butyl rubber (copolymer of isobutylene and isoprene), polyacrylonitrile ( Hycar ). silicone (polysiloranei. epichlorohy-drin, polyurethane ( Vulkollan ). 

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. 

The importance of isobutylene in the petrochemical industry is well recognized. Isobutylene is used on a large scale for the production of (i) methacrolein by direct oxidation, (ii) polyisobutylene by polymerization, (iii) synthetic rubber (a copolymer of isobutylene and isoprene), and (iv) methyl tert-butyl ether (MTBE, a gasoline octane-number enhancer) by reaction with methanol. 

The most important of the commercial cationic copolymers is butyl rubber prepared from isobutylene and isoprene. Because of its very low air permeability, butyl rubber finds extensive use in tire inner tubes and protective clothing. It is manufactured by low-temperature (— 100°C) copolymerization of about 97% isobutylene and 3% isoprene in chlorocarbon solvents with AICI3 coinitiator (see Table 8.5). More recently, an ozone-resistant copolymer of isobutylene and cyclopentadiene has been marketed. 

Depending on the grade of polymer, polychloroprene can be vulcanized by zinc oxide or magnesium oxide. Tetramethylthiuram disulfide can serve as a retarder. Polychloroprene is inferior to NBR for oil resistance but is still significantly better than natural rubber, SBR, or BR. Like NBR it also finds extensive use in such products as oil seals, gaskets, hose linings, and automotive engine transmission belts where resistance to oil absorption is important. Butyl rubbers are a copolymer of isobutylene and isoprene ... 

Isobutylene and isoprene are in a ratio of approximately 50 1. Chlorobutyl rubber and bromobutyl rubber are produced by the halogenation of butyl rubber. Butyl rubber and halobutyl rubber are highly impermeable to air and show very low water absorption, and good heat, oxygen and ozone resistance. As noted earlier, they therefore find extensive use in liners of radial tires, covers and insulation of high-voltage electric cables, and automobile engine and radiator hoses. 

Synonyms 1,3-Butadiene-2-methyl polymer with 2-methyl-l-propene Butyl rubber HR Isobutylene/isoprene copolymers 3-Methyl-1,3-butadiene polymer with 2-methyl-1 -propene Poly (isobutylene-co-isoprene) Definition Copolymer of isobutylene and isoprene monomers Formuia (CsHs C4H8),... 

High molecular weight polyisobutylene has fair tensile strength, but suffers from the disadvantage of considerable cold flow. A copolymer of butylene with some isoprene for crosslinking is therefore used as a commercial elastomer and called butyl rubber. The isoprene is present in the copolymer in only minor proportions (1.4-4.5%). The uncrosslinked material is very similar to polyisobutylene. Copolymers of isobutylene with other dienes are also called butyl rubbers. They can also be terpolymers, where the third component may be cyclopentadiene for improved ozone resistance. 

Isobutylene and isoprene copolymerize to give butyl rubber. Draw the structure of the repeating unit in butyl rubber, assuming that the two monomers alternate. 

The physical aspects of ozone cracking are clearly seen in the case of the predominantly saturated butyl rubber (HR), a copolymer of isobutylene and isoprene containing - 1-3% isoprene. Although the chemistry is the same as for its diene rubber counterpart, IR, butyl rubber is much more resistant to ozone cracking. Unsaturated elastomers must be stretched for ozone cracking to occur. 

Butyl rubber is an elastomeric polymer used widely in adhesives and sealants, both as primary binders and as tackifiers and modifiers. Butyl rubber is a copolymer of isobutylene with a small amount of isoprene. These materials have relatively low strength and tend to exhibit creep under load. They are useful in packaging apphcations where their low permeability to gases, vapors, and moisture can be exploited. Butyl rubber is also used as an adhesive sealant. It is generally applied from a solvent-based solution. Table 5.1 summarizes some of the important properties of butyl rubber adhesives. 

Butyl rubber (HR) is an isobutylene-based rubber which includes copolymers of isobutylene and isoprene, halogenated butyl rubbers, and isobutylene/p-methylstyrene/bromo-p-methylstyrene terpoly-mers. HR can be slurry polymerized from isobutylene copolymerized with small amounts of isoprene in methyl chloride diluent at -130 to - 148°F (-90 to - 100°C). Halogenated butyl is produced by dissolving butyl rubber in a hydrocarbon solvent and introducing elemental halogen in gas or liquid state.Cross-linked terpolymers are formed with isobutylene + isoprene + divinylbenzene. 

Most of the butyl poljuners made commercially are produced by copolsrmerizing isobutylene and isoprene in precipitation processes that use methyl chloride as the diluent and a catalyst system comprising a Lewis Acid and an alkyl halide. The Lewis acid used in many of the commercial butyl rubber plants is aluminum chloride, which is low cost, a solid, and soluble in methyl chloride. Aluminum alkyls are now becoming popular because they simplify catalyst preparation and have been shown to increase monomer conversion. 

Method of synthesis the manufacture of the bromobutyl rubber is a two step process the polymerization of isobutylene and isoprene to produce butyl rubber, followed by bromination to form bromobutyl rubber a slurry of fine particles of butyl rubber dispersed in methyl chloride is formed in the reactor after Lewis acid initiation bromine is added to the butyl solution in highly agitated reaction vessels ... 

---