Polymer bromobutyl/chlorobutyl rubber

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. 

The choice of materials available for long-term drug contact is very limited—borosilicate glass, bromobutyl or chlorobutyl rubber closures, certain inert polymers such as polytetrafluoroethylene (PTFE), tetrafluor-oethylene (TFE), and derivatives thereof, and stainless steels. Since the Code of Federal Regulations mandates that it be possible to inspect the drug product after filling, steel cannot be used as the primary drug container. In addition, polycarbonates, which would be ideal materials from durability, scratch-resistance, and cost perspectives, have very poor moisture vapor and extractables profiles. 

Grafting from, exploits the active sites, which exist or can easily be generated on a polymer. Halogenated polymers are most frequently used for this purpose poly(vinyl) chloride), polychloroprene, chlorinated EPDM, chlorobutyl rubber, bromobutyl rubber, chlorinated polybutadiene, chlorinated butadiene-styrene copolymers etc.145). 

Chlorobutyl Rubber and Bromobutyl Rubbers (CIIR and BUR). The addition of chlorine or bromine to HR in an inert solvent (e.g., hexane) gives the facile attachment of one halogen atom per isoprene unit in the allylic position. Compared with HR, the halogenated butyl rubbers have certain advantages. The cure reactivity is increased to give faster vulcanization rates, greater extents of vulcanization, and reduced reversion. Also, the halo-genation improves the compatibility of the isoprene polymer with other types of rubber (e.g., NR) to make useful rubber-blend compositions possible. 

The manufacture of halobutyl rubbers such as Bromobutyl, Chlorobutyl, and Exxpro [bromopoly(isobutylene-co-/j-methylstyrene)] requires a second chemical reaction the halogenation of the polymer backbone. This can be achieved in two ways, the finished polymer produced in the butyl plant can be dissolved in a hydrocarbon solvent such as hexane or pentane, or a solvent replacement process can be used to dissolve the polymer from the slurry leaving the reactor. A schematic flow diagram of the halogenation process is shown by Figure 2. 

Suitable polymers bromobutyl rubber, chlorobutyl rubber, ionomers, natural rubber, EPDM, NBR, PA12, PP, PS, SBR ... 

Unless the reaction with bromobutyl was carried out at high dilution (0.75%) compared to chlorobutyl rubber (2.35%), it was not possible to isolate the AgBr because the polymer gelled and trapped the salt. We... 

General. The cure reactivity associated with the presence of halogen in the polymer molecule is inversely related to the strength of the bond by which the halogen is attached. Consequently, chlorobutyl and bromobutyl rubbers have quite different cure reactivities. The difference is such that at one extreme organic peroxides, or even sulphur alone, will cure bromobutyl rubber but will not affect the less reactive chlorobutyl rubber, and at the other extreme, certain amines provide safe, practical cure systems for chlorobutyl rubber, but immediately scorch bromobutyl rubber. 

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