Halogenation diene rubbers

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

Chlorobutyl (CIIR) and bromobutyl (BIIR) are modified types containing 1.2% wt of chlorine or bromine, the isoprene unit being the site of halogenation. Introduction of the halogen gives greater cure flexibility, and enhanced cure compatibility in blends with other diene rubbers. It also confers increased adhesion to other rubbers and metals. 

These two rubbers are prepared by halogenation of the butyl. Halogenation gives increased cure reactivity. As a result, improvement occurs in vulcanization rates resulting in improved properties over butyl. The state of cure and reversion resistance and covulcanization with other diene rubbers can also be suitably monitored. CIIR and BIIR vulcanizates have lower gas permeability,... 

In addition to titanium-based Ziegler-Natta catalysts, vanadium-based systems have also been developed for PE and ethylene-based co-polymers, particularly ethylene-propylene-diene rubbers (EPDM). Homogeneous (soluble) vanadium catalysts produce relatively narrow molecular mass distribution PE, whereas supported V catalysts give broad molecular mass distribution.422 Polymerization activity is strongly enhanced by the use of a halogenated hydrocarbon as promoter in combination with a vanadium catalyst and aluminum alkyl co-catalyst.422,423... 

Diene rubbers such as natural rubber, SBR, and BR can be vulcanized by the action of phenolic compounds [65-68], which are (usually di-)substituted by -CH2-X groups where X is an -OH group or a halogen atom substituent. A high-diene rubber can also be vulcanized by the action of a dinitrosoben-zene that forms in situ by the oxidation of a quinonedioxime [69-73] that had been incorporated into the rubber along with the oxidizing agent, lead peroxide. 

Like the very important diene rubbers (polyisoprene, polybutadiene and SBR) the ethylene-propylene rubbers are hydrocarbons. They are therefore resistant to polar solvents but dissolve (when unvulcanized) or swell (when vulcanized) in hydrocarbons. Being saturated they are somewhat inert chemically and therefore have good resistance to oxygen, ozone, acids and alkalies. Besides being attacked by peroxide radicals they may also be halogenated. 

Morrissey, R. T. Halogenation of Ethulene Propylene Diene Rubbers. Rubber Chem. Technol. 1911,44(4), 1025-1042. 

Common solvent is used for polymerization and bromination in production of bro-mobutyl rubber. Solvent is aliphatic hydrocarbon. Liquid, solventless ethylene propylene diene rubber can be produced according to invention." It is possible to produce water and solvent-free synthetic rubber products such as non-halogenated and halogenated butyl rubber products. ... 

In some cases, diene polymers (for instance polychloroprene rubbers) can add to the growing polymer chain by 1,2 addition (also called vinyl addition). This creates labile hydrogen or reactive halogen on tertiary carbon atoms. A few percent of this type of structure in the rubber will assist cross-linking reactions. 

The introduction of conjugated diene functions in polyisobutene chains has been recently accomplished through an indirect approach which utilizes the dehydro-halogenation of chlorinated butyl rubber, i. e. randomly chlorinated poly(isobutene-co-isoprene), by means of basic agents8. ... 

Alkali and acid treatments have also been used to modify surface properties of polymers sulfonated polyethylene films treated first with ethylenediamine and then with a terpolymer of vinyhdene chloride, acrylonitrile, and acrylic acid exhibited better clarity and scuff resistance and reduced permeabihty. Permanently amber-colored polyethylene containers suitable for storing light-sensitive compoimds have been produced by treating fluorosulfonated polyethylene with alkali. Poly(ethylene terephthalate) dipped into trichloroacetic/chromic acid mixture has improved adhesion to polyethylene and nylons. Antifogging lenses have been prepared by exposing polystyrene films to sulfonating conditions. Acid and alkali surface treatments have also been used to produce desired properties in polymethylmethacrylates, polyacrylonitrile, styrene-butadiene resins, polyisobutylene, and natural rubber. Surface halogenation of the diene polymers natural rubber and polyisobutylene resulted in increased adhesion to polar surfaces. 

Halogenation and hydrohalogenation of elastomers have been reported extensively in the literature [26]. The main problems with these reactions are the cyclization and chain scission that occur parallel to the halogenation reaction. These introduce difficult problems in the characterization of the resulting products. Despite these problems, several products have been prepared and commercialized. Chlorination of poly(l, 4-butadiene) to prepare a product similar to poly(vinyl chloride) has been reported by several workers [27]. This process had extensive side reactions and chain degradation. The chlorination of butyl rubber and conjugated diene-butyl rubbers gives end products that are used in the tire industry as inner liners for air retention. 

Ethylene-propylene copolymers (EPDM) are, by their random copolymerization, amorphous in structure and therefore easily halogenated. EPDM has been chlorinated to improve its properties and cocurability with other rubbers. The chlorination was directed toward the termonomer dicyclopenta-diene to form the allylic chloride [28], In this manner, EPDM was chlorinated, and the resulting products had improved properties. 

As in the case of hydrohalogenation the bulk of the theoretical studies on the halogenation of diene polymers has been made on natural rubber with chlorine as the halogen. As with natural rubber hydrochloride the derivative has some commercial value. 

Butyl rubbers are copolymers of isobutylene with minor amounts of a diene that enable chemical cross-linking via unsaturated sites. The My is in the range of (3-4)xl0 . To improve the possibilities for cross-linking, it can be mixed with halobutyl rubber, which contains the halogen in the a-position to the double bond. 

Representative diene-based polymers include natural rubber (NR), polyisoprene (PIP), PBD, styrene—butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR), which together compose a key class of polymers widely used in the rubber industry. These unsaturated polyolefins are ideal polymers for chemical modifications owing to the availability of parent materials with a diverse range of molecular weights and suitable catalytic transformations of the double bonds in the polymer chain. The chemical modifications of diene-based polymers can be catalytic or noncatalytic. The C=C bonds of diene-based polymers can be transformed to saturated C—C and C—H bonds (hydrogenation), carbonyls (hydrofbrmylation and hydrocarboxylation), epoxides (epoxidation), C—Si bonds (hydrosilylation), C—Ar bonds (hydroarylation), C—B bonds (hydroboration), and C—halogen bonds (hydrohalogenation). ... 

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