Halogenated butyl rubbers curing systems

Modified butyl rubbers—the crosslinked butyl and halogenated butyl rubbers—all possess the shock absorbency, stability and gas barrier properties that are characteristic of standard butyl rubbers. However, they differ from each other, and from standard butyl rubbers, in terms of the variables that distinguish standard butyl rubbers from each other, and in respects related to the types, amounts and functions of their modifiers. The crosslinked butyl rubbers resist flow, which is an important requirement in uncured sealant tape, their primary application. The halogenated butyl rubbers cure much faster than standard or crosslinked butyl rubbers, use less complicated curing systems and can be covulcanised with highly unsaturated elastomers. 

Butyl rubber(s), 4 433-458 9 561 14 265. See also Halogenated butyl rubber annual capacity, 4 451t carbon monoxide compatibility with, 5 4t chemical reactions, 4 448 copolymers, 4 444-446 cure systems for, 21 802-803 economic aspects, 4 451, 452t elastomeric vulcanizates, 4 448-450 formulation for reclaiming, 21 475t health and safety factors, 4 452-453 isobutylene polymerization mechanism, 4 434-436... 

Peroxide cross-linked terpolymers have a lower compression set than conventional butyl rubber vulcanizates and better ozone resistance than butyl rubbers of comparable unsaturation. Suitably stabilized, these systems have a heat resistance comparable to phenolic resin cured conventional butyl rubbers but with faster cure rates and higher compatibility with other types of rubber (Walker et ai, 1974). Some of these latter properties may also be shared with halogenated butyl rubber vulcanizates. 

The halogenated butyl rubbers may be cross-linked via either allylic hydrogen or the halogen group. As a broad generalization it may thus be considered that the materials may not only be cured by the methods used with butyl rubber but also those employed with polychloroprenes. The main systems to consider are ... 

It has already been reported that halogenated butyl rubbers are moisture-curable with The details of the cure system,... 

Despite the obvious merits of quinoid curing systems they have been used less extensively in recent years, partly because some of them are reported to be health hazards under some conditions, but also because of inroads made by the fastcuring halogenated butyl rubbers. 

Halogenated Butyl. Butyl elastomers have a low density of unsaturation, which results in a low cure rate when conventional vulcanization systems are used. Butyl copolymers containing a small amount of combined chlorine or bromine are vulcanized more quickly than normal butyl rubber because the halogen atoms provide additional sites for the cross-linking process. Butyl rubber has poor adhesive properties to metals and other rubbers because of the lack of polar groups. This is the reason for using halogenation. 

Exceptional heat resistance and low compression set can be obtained by curing butyl rubbers with dimethylol phenol resins. The curing reaction is very slow even at high temperatures and when activated by halogens. Stannous chloride, and combinations of a halogenated polymer (such as neoprene, halobutyl or brominated resin) with zinc oxide, are the most commonly used halogen-bearing activators. The systems shown in Table 5 are typical. 

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. 

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