Exxon™ butyl and halobutyl rubber Model vulcanization systems for butyl rubber and halobutyl rubber manual Country name(s) 2 - Model vulcanization systems for butyl rubber and halobutyl rubber manual Model vulcanization systems for butyl rubber and halobutyl rubber manual - 3 Abstract The vulcanization of isobutylene-co-isoprene rubber (IIR), brominated isobutylene-co-isoprene rubber (BIIR), chlorinated isobutylene-co-isoprene rubber (CIIR), and brominated isobutylene-co-para-methylstyrene elastomer (BIMSM) differs from that of general-purpose rubbers (GPR). Butyl rubber has approximately 2% unsaturation in the backbone. Halobutyl rubber (BIIR and CIIR) incorporates the butyl backbone with either bromine or chlorine, which significantly increases the chemical reactivity of the isoprenyl units located in the butyl backbone. Similarly, in BIMSM the bromine atom is bonded to the para-methylstyrene (PMS) group, thus affording the completely saturated polymer backbone a site of chemical reactivity. Utilization of the unique attributes of butyl rubber and halobutyl rubbers with their minimal backbone unsaturation and of BIMSM elastomers with no backbone unsaturation is found in many areas of industry. These properties are excellent vapor impermeation, resistance to heat degradation, and improved chemical resistance as compared to general-purpose rubbers. However, this low amount of reactivity requires special consideration to vulcanize these isobutylene-based polymers. The type of vulcanization system selected is a function of the composite structure in which it is used, and the cured product performance requirements. Therefore, vulcanization systems vary and may include an accelerator package along with resins, zinc oxide, zinc oxide and sulfur, and quinoid systems. This review will discuss the types and selection of appropriate vulcanization systems for isobutylene-based elastomers. Model vulcanization systems for butyl rubber and halobutyl rubber manual - 3 1. Introduction ........................................................................................................................................................................................................................................................ 4 2. Composition of isobutylene polymers ................................................................................................................................................................................. 5 3. General trends in vulcanization chemistry ......................................................................................................................................................................7 4. Overview of the vulcanization of isobutylene-based elastomers ................................................................................................... 10 5. Vulcanization of butyl rubber ..................................................................................................................................................................................................... 11 6. Halobutyl rubber ....................................................................................................................................................................................................................................... 14 7. Vulcanization of brominated isobutylene-co-para-methylstyrene (BIMSM) ..................................................................... 18 8. Model cure system formulary .................................................................................................................................................................................................... 20 9. Summary ............................................................................................................................................................................................................................................................ 24 Appendix 1 ..............................................................................................................................................................................................................................................................25 10. References ........................................................................................................................................................................................................................................................ 26 4 - Model vulcanization systems for butyl rubber and halobutyl rubber manual Model vulcanization systems for butyl rubber and halobutyl rubber manual - 5 1. Introduction Isobutylene-based elastomers include butyl rubber, halogenated butyl rubber, star-branched versions of these polymers and brominated isobutylene-co-para-methylstyrene (BIMSM). Due to their impermeability and resistance to heat and oxidation, these polymers find application in tire innerliners, innertubes, curing bladders and envelopes, and other specialty applications where air retention and resistance to heat and oxidation are desired. Butyl rubbers are produced via a cationic polymerization in a methyl chloride diluent at temperatures less than -90°C. These unique attributes and difficult manufacturing requirements place butyl rubbers in the special purpose elastomers category distinct from general- purpose rubbers (GPR) such as polybutadiene rubber (BR), natural rubber (NR), and styrene-butadiene rubbers (SBR) 1. Model vulcanization systems for butyl rubber and halobutyl rubber manual - 5 2. Composition of isobutylene polymers Butyl rubber (IIR) is the copolymer of isobutylene and a small Copolymers of isobutylene and para-methylstyrene have a amount of isoprene, typically in the order of 2%. Figure 1 is a random structure, again due to the monomer reactivity ratios schematic of butyl rubber. being nearly equivalent. After polymerization and subsequent bromination some of the para-methylstyrene Figure 1 groups are converted to reactive bromomethylstyryl groups. Structure of butyl rubber These saturated backbone polymers contain isobutylene, 1 to 5 mole-% of para-methylstyrene, and 0.5 to 1.3 mole-% of 2 brominated para-methylstyrene (Figure 3) . 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