Bromobutyl compound

Polychloroprene (PC) rubbers should not be stored for more than three months and when compounded are best used within three weeks. This is due to a slow crosslinking action that produces unacceptable levels of scorch in PC as well as in chlorobutyl and bromobutyl compounds. 

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. 

Bromobutyl Rubber Compounding and Applications, Exxon Chemical Co. 

In a particular application involving a typical O type mount, the nitrile rubber (NR) compound causes a resonance frequency of 28 Hz, whereas resonance was previously tolerable only well below 20 Hz. In this case, a blend of NR and bromobutyl rubber is more suitable. A comparison is shown in Table 3. 

Physical Properties from Vulcanized Bromobutyl Inner Liner Compound (Unaged)... 

Table 8.7B Physical Properties from Vulcanized Bromobutyl Inner Liner Compound (Aged 240 h at 125°C). ..193...

Two synthetic routes for 3-[4-[4-(2-methoxyphenyl)piperazin-l-yl]butyl]-thieno[3,4-d]pyrimidine-2,4-dione 316 were described by Russell et al. (90JHC1761). Carbamate 310a, prepared by treating a mixture of amine hydrochloride 309 and ethyl chloroformate with dilute sodium hydroxide, was reacted with 4-[(2-methoxyphenyl)piperazin-l-yl]butanamine 313 in the presence of trimethylaluminum/toluene. The yield of 316 was a modest 20%. However, when bromobutyl urea 314 was heated with l-(2-methoxyphenyl)piperazine hydrochloride 315 in the presence of sodium bicarbonate and sodium iodide in propan-2-ol, compound 316 was obtained in 84% yield. The first route was also used to synthesize thieno[3,4-d]py-rimidine-2,4-dione 312 in 36% yield from 310a and 4-(2-methoxyphenyl)-1-piperazinethanamine 311. 

The halogenation reaction proceeds in darkness and is reasonably considered as ionic. It has been shown that if chlorine gives primarily free radical addition on mono- and di-substituted alkenes, it gives ionic substitution products with tri- and tetra-substituted alkenes [73], A model compound study, together with NMR analysis of commercial chloro and bromobutyl samples, confirmed that the reaction on isoprenyl unit leads predominantly to the exomethylene-substituted structure A, and this is explained by steric hindrance due to the tetra-substituted carbon in f3-position which favors proton elimination rather than the nucleophilic attack of halide counter ion in the second phase of addition (Fig. 11, Table 1) [74,75]. 

The elastomer determines most of the physical and chemical characteristics of a rubber compound. Typical elastomers are natural elastomers such as natural rubber (NR), sometimes called crepe, and synthetic elastomers such as butyl (including chlorobutyl and bromobutyl), ethylene propylene diene monomer (EPDM), and styrene butadiene rubber (SBR). A list of commonly used elastomers is shown in Table 2. 

Such compounds have been prepared by reacting (3-bromopropyl)triphenylphosphonium bromide and (3-bromobutyl)triphenylphosphonium bromide with 2 equivalents of a strong base under anhydrous and inert conditions.However, the products obtained, (cyclo-propylidene)triphenyl-2 -phosphane and (2-methylcyclopropylidene)triphenyl-A -phosphane, respectively, are unstable like most phosphorus ylides and have only been prepared in situ to be utilized in Wittig reactions (see Section 5.2.1.2.16.2.). 

Nano-CaCOs is one of the many emerging applications of nanotechnology that is already finding successful commercial application. Reinforcing effect of nano-CaC03 in different compounds - NR and NR/NBR blend used in sports goods (laminated sheet for inflated balls), NR based cycle tube, bromobutyl-based pharmaceutical closures and CPE/CSM blend used for coated fabric was studied with one characteristic in mind that is to improve barrier properties as all these products have requirement of one common property - air retention. 

Low level blending of butyl rubber into bromobutyl rubber increases the scorch time and improves the heat resistance of the compound. 

Butyl rubber levels in excess of 20 phr sharply reduce adhesion to general purpose rubber compound substrates. Blending up to 30% butyl into bromobutyl rubber slows the cure rate and provides a small benefit in lower modulus increase and higher retained elongation after heat aging. 

Because butyl has the same permeability coefficient as bromobutyl mbber, blending it into a bromobutyl rubber compound does not alter the compound permeability as, for example, natural rubber would. 

Ethylene propylene diene terpolymers (EPDM) can be used to improve the ozone resistance of bromobutyl/natural rubber binary polymer blends, eliminating the need for chemical antiozonants. Addition of 10 phr of EPDM (with a high ethylidene norbornene, ENB, content of9%) to a 50/50 bromobutyl rubber/natural rubber blend results in a compound vdth good static and dynamic ozone resistance. EPDM with a 5.7% ENB level is another suggested grade of polymer. 

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