Isobutylene based polymers

The elastomers and elastomer blends used in tire compounds, and particularly tread compounds, are thus equally important to the structural design parameters of the tire (Table 4.7). A properly designed tread compound will ensure the tire can meet its performance targets. Tread compounding materials fall into one of five general categories polymers, fillers, protectants, vulcanization system, and various special purpose additives. Elastomers for tread compounds are typically natural rubber (NR), styrene-butadiene rubber (SBR), polybutadiene (BR), and in some instances isobutylene based polymers for winter and special performance tires. 

Structure, Properties, and Product Applications of Isobutylene-Based Polymers... 

Isobutylene-based polymers exhibit high damping and have imiquely broad damping and shock absorption ranges in both temperature and frequency. Molded rubber parts from butyl and halobutyl find wide applications in automobile suspension bumpers, exhaust hangers, and body moimts. 

Isobutylene-based elastomers include HR, the copolymer of isobutylene and isoprene, halogenated HR, star-branched versions of these polymers, and the terpolymer isobutylene-p-methylene styrene-bromo-p-methyl styrene (BIMS). A number of recent reviews on isobutylene-based elastomers are available [33-35]. 

Jacob, S, and Kenned /. Synthesis, Characterization and Properties of OCTA-ARM Poly-isobutylene-Based Star Polymers. Vol 146, pp. 1-38. 

Ambkoz, L., and Z. Zlamal Donor-acceptor interactions in cationic polymerization XI. Influence of some bases on polymerization of isobutylene. J. Polymer Sci. 30, 381 (1958). 

Bulyk. Butyl-based materials are sold in the form of preformed tapes, thermoplastic hot melts, and one-part solvent-releasing sealants. Butyl polymers are made by the copolymerization of 97-98 mol % isobutylene with 2-3% isoprene. Another butyl-based polymer, polyisobutylene, is produced by the polymerization of isobutylene. Formulations of butyl-based sealants also include plasticizer, filler, and lackifier resins. Poly butenes are common plasticizers for butyl sealants. Solvents, such as mineral spirits, are used for the one-part solvent-releasing formulations. As the solvent leaves the typical one-part butyl, the sealant hardens and loses its elastomeric ability. This limits the use of solvents to low movement applications where durability is not of high concern. 

Tread compounds can be based on either a single polymer or a blend of polymers. Natural rubber, emulsion SBR, solution SBR, BR, and isobutylene-based elastomers are used in such blends. The following tables illustrate tread formulations designed for specific applications ... 

Most butyl rubber is used in the tire industry. Isobutylene-based rubbers are used in underhood hose for the polymer s low permeability and temperature resistance, and high damping, resilient butyl rubbers are used for NVH (noise, vibration, harshness) applications such as automotive moinits for engine and vehicle/road NVH attenuation. ... 

M.F. Tse, H.C. Wang, R. Krishnamoorti, and A.H. Tsou, Polymer blend compatibilization using isobutylene-based block copolymers ii, US Patent 7119146, assigned to ExxonMobil Qiemical Patents Inc. (Houston, TX), October 10,2006. 

Grades of polyisobutylene, butyl mbber, halogenated butyl mbber, and partially cross-linked isobutylene—isopiene—divinylbenzene terpolymer have been developed to meet specific processing and property needs. Recently, two new polyisobutylene-based elastomers have been developed. One is now available commercially as Exxon SB Butyl Polymers (32) and the other is under market development as Exxon bromo XP-50. 

New copolymers based on a copolymerization of isobutylene and p-methyl-styrene with improved heat resistance have been reported [64]. Once copolymerization was accomplished, the polymer was selectively brominated in the p-methyl position to yield a terpolymer called EXXPO. In contrast to butyl and halobutyl, the new terpolymer has no unsaturation in the backbone and therefore shows enhanced thermal stability and resistance to oxidation. Useful solvent-based adhesives can be formulated using the new terpolymer in combination with block copolymers [65]. The hydrocarbon nature of the new terpolymer results in excellent compatibility with hydrocarbon resins and oils. 

Using the f-BuX/Me3Al/MeX system, a preferred reagent addition sequence has been found to be /-C4Hg/MeX/Me3 Al/t-BuX. This sequence has been used in these investigations. Based on polymerization rates at —40 °C, overall polymer yields, floor temperature and initiator efficiencies at —40 °C, overall initiator reactivity is found to decrease as f-BuCl > f-BuBr > t-BuI = 0 and initiator reactivity is dependent on solvent as MeCl > MeBr > Mel = 0. Similarity of reactivity sequences in isobutylene polymerization and in cationic model initiation and termination studies13) suggest that initiator reactivities are determined by the rate of initiation, Rj. 

Several polymers based on 1,3-dienes are used as elastomers. These include styrene-1,3-butadiene (SBR), styrene-1,3-butadiene terpolymer with an unsaturated carboxylic acid (carboxylated SBR), acrylonitrile-1,3-butadiene (NBR or nitrile rubber) (Secs. 6-8a, 6-8e), isobutylene-isoprene (butyl rubber) (Sec. 5-2i-l), and block copolymers of isoprene or... 

---