Halogenated butyl rubbers mixing

The standard polymers used for rubber linings consist of materials that are cross-linkable macromolecules which, on mixing with suitable reactants that form strong chemical bonds, change from a soft deformable substance into an elastic material. These polymers include natural rubber and its corresponding synthetic, c/s-polyisoprene, styrene-butadiene rubber, polychloroprene, butyl rubber, halogenated butyl rubbers, acrylonitrile-... 

The mixing of halogenated butyl rubbers differs from that of regular butyls in that the halo butyls are too reactive to be heat t eated (they gel) zinc oxide and other curatives should not be added until late in the mixing cycle stock temperatures should be kept below 135°C for bromobutyl, and 145 °C for chlorobutyl, compounds and residues of unsaturated... 

Typical halogenation processes for making halobutyl rubbers involves the injection of chlorine or bromine into a solution of butyl rubber. The reactants are mixed vigorously in the halogenation reactor with a rather short resident time, typically less than 1 min, followed by the neutralization of the HC1 or HBr and removal of the unreacted halogen (13). The procedures of halogenation have been described in detail elsewhere (41,42). 

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. 

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 halogenated products improve the mixing and cure compatibility with the more common unsaturated rubbers such as natural or styrene-butadiene rubber. 

Halogenation is the second major chemical reaction in the production of halobutyl pol5uners. It is usually carried out by adding bromine liquid or chlorine vapor to a solution of rubber in hydrocarbon solvent (hexane or pentane), which is often referred to as cement. The cement must be essentially free of monomers, or low molecular weight toxic species will be formed dining the chlorine or bromine reactions. The halogenation of the butyl backbone is an ionic-substitution reaction in which the halogen is added to the cement stream in a well-mixed reactor (eq. 1). This reaction is unusual for polymers where it s more typical for the bromine to add across the double bond. 

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