Butyl rubber chemical structure

Oyama H and Nakaishi E (2003) Thermoplastic elastomer compositions, moldings and automobile interior parts therefrom with high wear resistance and good sliding property, Jpn Kokai Tokkyo Koho JP 2003,277,519, to Sumitomo Chem Co, Ltd. Ikeda Y, Kodama K, Kajiwara K and Kohjiya S (1995) Chemical modification of butyl rubber. II. Structure and properties of poly(ethyleneoxide)-grafted butyl rubber, J Polym Sci Part B Polym Phys Ed 33 387-394. 

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

Within the database there may be many chemicals for which butyl rubber gloves provide good protection and we could reasonably anticipate that at least some structural similarities would exist among these chemicals that would help us rationalize the choice of butyl rubber. 

Chemical reactions are used to modify existing polymers, often for specialty applications. Although of considerable importance for plastics, very few polymer reactions (aside from crosslinking) are important for elastomers. Chlorination and bromination of Butyl rubber to the extent of about one halogen atom per isoprene unit yields elastomers which are more easily crosslinked than Butyl rubber. Substitution occurs with rearrangement to yield an allylic halide structure... 

At first glance, ASA possesses a similar chemical structure to ABS, since both consist of a SAN matrix containing a graft rubber. However, while the core of the graft rubber of ABS consists of polybutadiene, that of ASA consists of poly(n-butyl acrylate) (Figure 16.8), and this accounts for important differences in the properties of the two plastics. 

Butyl rubber consists mostly of isobutylene (95-98%) and about 2-5% isoprene units. 1 The isoprene unit is halogenated by either chlorine or bromine to obtain the corresponding halobutyl rubbers. Despite the superior elastomeric properties of halobutyl, the elastomer can easily undergo dehydrohalogenation leading to crosslinfang, and the isoprene unsaturation is subject to ozone cracking. To remedy these problems and to improve the halobutyl properties, a new class of elastomer poly(isobutylene-co-p-methylstyrene) [poly (IB-PMS)] was developed. Unlike butyl rubber, it contains no double bonds and therefore cannot be crosslinked unless otherwise functionalized. The chemical structures of butyl rubber and poly (IB-PMS) copolymers are shown below. 

Apart from the rather expensive and inferior methyl rubber produced in Germany during World War I, the first industrial production of synthetic rubbers took place in 1932, with polybutadiene being produced in the USSR, from alcohol derived from the fermentation of potatoes, and neoprene (polychloroprene) being produced in the USA from acetylene derived from coal. In 1934 the first American car tyre produced from a synthetic rubber was made from neoprene. In 1937 butyl rubber, based on polyisobutylene, was discovered in the USA. This material has a lower resilience than that of natural rubber but far surpasses it in chemical resistance and in having a low permeability to gases. The chemical structures of these materials are shown in fig. 6.10. 

The chains must be crosslinked to form a network (cf. Fig 7.16). In most elastomers containing double bonds, covalent bonds are introduced between chains. This can be done either with sulfur or polysulfide bonds (the well known sulfur vulcanisation of natural rubber is an example), or else by direct reactions between double bonds, initiated via decomposition of a peroxide additive into radicals. Double bonds already exist in the chemical structure of polyisoprene, polybutadiene and its copolymers. When this is not the case, as for silicones, ethylene-propylene copolymers and polyisobutylene, units are introduced by copolymerisation which have the property of conserving a double bond after incorporation into the chain. These double bonds can then be used for crosslinking. This is how Butyl rubber is made from polyisobutylene, by adding 2% isoprene. Butyl is a rubber with the remarkable property of being impermeable to air. It is used to line the interior of tyres with no inner tube. 

Summarising the mechanical characteristics of halogen butyl rubbers are not optimal (stronger deformation, less elastic than natural rubber), but the saturated structure leads to excellent chemical characteristics (see Table 24.5). 

V. P. Roshchupkin, I. S. Kochneva, and B. V. Ozerkovsky, A Structural Kinetic Method of the Formation of Crosslinked Polymeric Compositions, Vysokomol. Soedin. A20(10), 2252 (1978). Kinetics of chemical and microsyneresis processes in nonylacrylate/butyl rubber undergoing simultaneous vulcanization. 

The more serious cause of deterioration in rubbers is its reaction with atmospheric oxygen. This is possible because rubber is a diene polymer and some, such as natural rubber, EPDM, SBR, nitrile rubber, and butyl rubber, have olefinic double bonds in their structure. Much research work is being done on the oxidative degradation of unvulcanized rubbers, but this is not relevant to the resistance of vulcanized rubbers in storage or in service as their aging behaviors differ widely. Unvulcanized rubber compound has to be vulcanized in order to produce usable products. The nature of the cross-link produced varies considerably, and this can affect the balance of chemical and particularly of physical properties of the vulcanizates. 

Butyl rubber, because of its chemical structure, imparts high damping properties in dynamic applications where energy absorption is needed in automotive and other applications. In addition, certain grades of butyl are used in medical applications. 

Polyisobutene and Butyl Rubber. Pol5dsobutene, referred to sometimes as pol5dsobutylene, is considered the precursor of butyl rubber and is processed by low temperature cationic polymerization of isobutylene. The chemical structure can be represented as P ... 

Give the chemical structure and unique characteristics of each of the following synthetic rubbers styrene-butadiene rubber, polybutadiene, neoprene, butyl rubber, nitrile rubber, and silicone rubber. 

Moore and Trego described the use of triphenyl phosphine and di-A/-butyl phosphate as chemical probes to establish a cross-link network structure in rubber vulcanizates. " Triphenyl phosphine and trialkyl phosphates cleave di- and polysulfide, as illustrated in Fig. 4. 

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