Halogenated butyl rubbers compounding

There has been Kttle research on the halogen atom-containing elastomer compounds because the volume of consumption of those materials is relatively small. Halogenated butyl rubber compounds generally involve the following components ... 

In the presence of light, halogens attack both vulcanised and unvulcanised butyl rubber. Whether vulcanised or unvulcanised the effect of the reaction is to produce rapid deterioration in molecular weight. A strip of butyl vulcanisate suspended in bromine gas degrades rapidly. In a few minutes the specimen becomes fluid enough to drip to the bottom of the vessel. Chlorosulfonated polyethylene is resistant to ozone being better than Neoprene and butyl rubber compounds [18]. 

Halogenated butyl rubbers can be vulcanized with various reagents, e.g., diamines, dihydroxy aromatic compounds and zinc oxide. 

HR is not miscible with general-purpose rubbers because of its dissimilar structure and quite different cure rate, so that blends with these rubbers are not of practical interest. HR can be blended in any ratio with PIB and with halogenated butyl rubbers (having quite similar structure). Compounds of HR with polyolefins (LDPE), and particularly with PIB, are encountered in some appKcations (sheetings, corrosion resistant tank linings). EP(D)M can also be blended with HR blends of HR -I- EPDM are recommended in the production of inner tubes. 

Vulcanization rates are higher than for normal butyl rubber because the presence of allylic halide increases the reactivity of the unsaturated sites. Brominated butyl rubber shows higher vulcanization rates than chlorinated butyl rubber. Halogenated butyl rubbers can be vulcanized with various reagents, e.g. diamines, dihydroxy aromatic compounds and zinc oxide. 

As mentioned in Section 8.1.1, ethylene-propylene elastomers are currently used in compounds for tyre sidewalls. In this application also ternary blends have been used, including halogenated butyl rubber.With regard to EPDM and butyl rubber blends, there are no covulcanisation problems because both have a similar level of unsaturation. 

The differences in the cure reactivity of chlorobutyl and bromobutyl rubbers are sufficiently great so that one cannot usually be substituted directly into compounds designed specifically for the other. Bromobutyl substituted for chlorobutyl in a chlorobutyl compound would be likely to prove unacceptable for factory processing because of a greatly increased risk of scorch. Chlorobutyl substituted for bromobutyl in a bromobutyl compound would be unlikely to reach an adequate state of cure in a reasonable time. In other respects, however, the compounding principles and practices used for unmodified butyl rubbers apply also to the halogenated butyl rubbers. 

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... 

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. 

The chloride is used to manufacture silicones, tetramethyl lead and triptane (2,2,3 trimethylbutane). Lesser uses include the manufacture of butyl rubber, higher halogenated methanes, methyl cellulose, quaternary ammonium compounds, methyl mercaptan, methionine, fungicides and pesticides (primarily the Me-arsenate herbicides). Recently the chlorinated fluorocarbons have replaced CH3CI as high volume refrigerants and propellants (ref. 32) Tables 12 and 13 list the chemical and physical properties and potential numbers of workers exposed to the monohalomethanes. 

Phenolic resins are effective in conjunction with zinc oxide as cross-linking agents. Fast cures are possible with bromobutyl rubber without the need for adding halogen-containing compounds as in conventional butyl rubber. The products in this case have good dry heat resistance but inferior steam ageing resistance compared with the vulcanizates of unmodified butyl. 

A study was made of the ozonolysis of butyl rubber and its halogenated derivatives, as well as their model compounds in hexane. The effect of various additives, such as diphenylamine, triisopropyl phosphite, hexylamine and 2,6-di-tert-butyl cresol, on chain scission and rearrangement of bromobutyl rubber, was also evaluated. It was found while the ozonolysis of butyl and chlorobutyl mbbers involved normal cleavage of olefmic double bonds, the mechanism of ozonolysis of bromobutyl mbber was more complicated. 8 refs. 

Almost all polymer and oligomer syntheses by eationic polymerization, both in industry and in the laboratory, employ MX -type initiators, typically AICI3 and BF3 complexes. Non-MX initiators (0x0 acids and halogens) have been used much less frequently, only for basic studies on polymerizations of styrenes and vinyl ethers. In industry, most cationic polymerization processes [e.g., polyisobutene (butyl rubber) and petroleum resin production] utilize MX initiators perhaps the only one involving non-MX initiators is the synthesis of oligo(isobutene) with strong protonic acids. The very rare use of non-MX initiators may be due to a lack of information on the characteristics of these unique compounds. 

Vukov R (1984) Halogenation of butyl rubber — a model compound approach. Rubber Chem Technol... 

Resin cures utilise phenol-formaldehyde resins with reactive methylene groups and a small added amount of either a chlorinated rubber, e.g., polychloroprene, or stannous chloride. If halogenated phenolic resins are used the additional source of a halogen may not be required. Resin cures give butyl compounds excellent heat stability and are used to good effect where this is required, e.g., in tyre curing bags which have to resist service at 150 °C in a steam atmosphere. 

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