Bromobutyl elastomer

Fig. 32 Kinetic characteristics for thermal oxidation of some rubbers assessed at three temperatures. The data were taken from [96J1]. (white) butyl elastomer, (dark grey) chlorobutyl elastomers, (pale grey) bromobutyl elastomer, (a) induction time of oxidation, (b) oxidation rate, (c) maximum oxidation time.

Exxon Mobil in brochures argues that butyl elastomer (HR) apparently is miscible with chlorobutyl elastomer (CIIR) and bromobutyl elastomer (BUR). This occurs because they have the same backbone structure of polyisobutylene and polyisoprene with an occasional different functional group of chlorine and bromine, respectively [33,34]. 

Butyl rubber is not compatible with natural rubber, SBR, nitrile rubber or with any other elastomer having an appreciable degree of unsaturation modified butyls (chlorobutyl and bromobutyl) are compatible with such elastomers and used as liners in tubeless tyres to improve air retention. 

In the above experiment, we note that a relatively smaller fraction (40-60%) of the total moisture associated with bromobutyl stoppers was extractable while about 75% of the total moisture was extracted from the stopper containing a blend of natural and synthetic rubbers. We postulate that stoppers made from synthetic elastomers have a higher amount of bound water than those made from a blend of natural and synthetic rubbers. The natural rubber component in the blend presumably imbibes more moisture that is relatively free and consequently more easily extractable upon drying. Moreover, bound water is less likely to effuse into the lyophilized product than free water. 

The elastomer determines most of the physical and chemical characteristics of a rubber compound. Typical elastomers are natural elastomers such as natural rubber (NR), sometimes called crepe, and synthetic elastomers such as butyl (including chlorobutyl and bromobutyl), ethylene propylene diene monomer (EPDM), and styrene butadiene rubber (SBR). A list of commonly used elastomers is shown in Table 2. 

The choice of elastomer has the greatest effect on a formulation. The most common elastomers that can be used for closures for injectable products are given in Table 12.5. Of these elastomers, natural rubber, synthetic polyisoprene, butyl, chlorobutyl and bromobutyl rubber are typically used for the manufacture of rubber closures and stoppers used in the packaging and administration of parenterals. 

The above criteria were employed to select several commercially supplied Class PS elastomers for laboratory screening by employing selected tests taken from National Bureau of Standards NBSIR 77-1437(j4) and ANSI/ASTM D-3667-78 specifications for "Rubber Seals Used in Flat-Plate Solar Collectors". Four silicone, three EPDM, two fluorocarbon, three epichlorohydrin, one ethylene-acrylic, one polyacrylic, one chlorosulfonated polyethylene, one bromobutyl and two butyl rubbers were studied in these screening tests. These materials are identified in Table I and those compositions which were revealed by their manufacturers are shown in Table II. Undoubtedly some materials which should have been included were omitted however, we hope that this sampling will provide an indication of the applicability of a wide range of materials for use as sealants in thermal solar collectors. 

Novel process on the base of compact tubular reactors is principally fitted for production of bromobutyl rubber and also others chlorinated elastomers. Process is accepted at OAO "Nizhne-kamskneftekhim". In 2001-2002 pilot plant worked at which chlorobutyl rubber of required quality was received without any problems. Technical schedule was made. At present experimental-industrial plant is projected. 

Synonyms BIIR Brominated butyl rubber Brominated isobutylene/isoprene copolymer Bromobutyl rubber 1,3-Butadiene, 2-methyl-, polymer with 2-methyl-1-propene, brominated Butyl rubber, brominated Isobutylene, isoprene polymer, brominated Definition Elastomer vulcanized by sulfur systems vulcanizate offers low gas permeability, good weather/ozone resist., better chem./heat resist, than butyl rubber... 

As seen from the results obtained (Table 3.3), the proposed method may also be used for bromobutyl rubber preparation. Moreover, other elastomers including copolymers of ethylene and propylene were halogenated in a turbulent mode. 

Accelerated-sulfur vulcanization is the most widely used method. For many applications, it is the only rapid crossUnking technique that can, in a practical manner, give the delayed action required for processing, shaping, and forming before the formation of the intractable vulcanized network. It is used to vulcanize natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (HR), chlorobutyl rubber (ClIR), bromobutyl rubber (BUR), and ethylene-propylene-diene-monomer rubber (EPDM). The reactive moiety for all of these elastomers can be represented by... 

With bromobutyl/butyl rubber blends, elastomer structures are essentially the same, but the different reactive functionalities provide different vulcanization chemistry. Since bromobutyl rubber has greater cure reactivity, accelerators that will over-cure the bromobutyl rubber phase should be avoided. Briefly... 

In bromobutyl/chlorobutyl rubber blends, both elastomers have the polyisobutylene backbone and halogen reactive functionality. These polymers, being molecularly miscible, constitute an ideal system for co-vulcanization. Bromobutyl and chloro-butyl can be used interchangeably without significant effect on state of cure as measured by extension modulus, tensile strength, and cure rheometer torque development. Bromobutyl will increase the cure rate of a blend with chlorobutyl. However, where bromobutyl is the major part of the blends, chlorobutyl does not reduce scorch tendencies because the more reactive halogen unit can dominate. 

Based on the same virtually saturated PIB backbone, bromobutyl and chlorobutyl rubbers possess the same low permeability toward air, gases and moisture vapor of regular butyl rubbers. Their vulcanizates exhibit similar elastic features and higher vibration dampening in comparison with general-purpose (dienic) elastomers. The vulcanizates of CIIR and BUR obtained with many curing systems... 

Bromobutyl rubber is a little more expensive to produce than chlorobutyl rubber however, it will sometimes give better adhesion than chlorobutyl rubber to other elastomer-based compounds. Also, bromobutyl rubber cures a little faster than chlorobutyl. However, bromobutyl rubber may also have a greater tendency than chlorobutyl rubber to impart scorch problems to a compound during processing. 

Brominated copolymer of isobutylene and para-methylstyrene (DIMS) is the latest new class of synthetic rubber that has been developed for the rubber industry. The sole producer of this new class of elastomer is ExxonMobil, which commercialized it successfully under the trade name Exxpro in the first decade of this new century. The advantage of this new polymer class vs. bromobutyl rubber is that this new elastomer possesses a completely saturated backbone and possesses more reactive benzylic bromine functionality than the bromine sites on the conventional bromobutyl backbone. This means that DIMS reportedly gives superior performance in service vs. BUR. This superiority is shown as better high-temperature resistance, better aging stability than either BUR or EPDM, better weathering resistance, and better ozone resistance. Also, BIMS provides the potential of imparting superior air permeability resistance. 

The properties required of a liner to perform this function include the ability to adhere permanently to the tyre carcass, heat resistance, flexibility and flex crack resistance over the full operating temperature range and a low level of permeability to air and moisture. Regular butyl rubber cannot be used in this application except, in the form of butyl reclaim, as a flexible, highly impermeable filler for other elastomers, because it cannot be made to adhere strongly enough to the tyre carcass. Bromobutyl rubber possesses all the properties, in ample measure, required for premium quality inner liners, but a few parts of natural rubber are normally included in chlorobutyl liner stocks to ensure that they have adequate cured bond strength (see Tables 16 and 17). 

The combination of elastomers used in the formulation shown in Table 23 provides an essential balance of adhesion, low heat build-up, and excellent resistance to ozone, weathering and flex cracking. Ultra-white grades of talc and clay were used. Bromobutyl would scorch if substituted directly for the chlorobutyl in this formulation. 

---