Butyl rubbers chemistry

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

A significant portion, as high as 70% with new tools, of research time is dedicated to purely methods development. Methods development is necessary, as polymer chemistries, properties, and applications are extremely diverse. A portion of this methods development is focused on how to handle different materials, such as butyl rubber versus low-density polyethylene. However, the largest portion of methods development is dedicated to data correlation. 

J. Duffy and G. J. Wilson, Synthesis of butyl rubber by cationic polymerization, Vol. A23, pp. 288-294 Halobutyl rubber, Vol. A23, 314-318, Ull-mann s Encyclopedia of Industrial Chemistry, 5th Ed., VCH Publishers, Weinheim, 1993. 

Butyl rubber is a copolymer of isobutylene and I -2% isoprene. As a result the polymer chains contain internal double bonds which are expected to participate in cross-linking reactions. However, the overall molecular mass is expected to fall on irradiation due to the predominance of main-chain scission through the isobutylene units. Thus the radiation chemistry of the isoprene units within butyl rubber is accessible to study via solution NMR. In a comprehensive study Hill identified the primary free radical species by electron spin resonance spectroscopy at low temperatures, and the products of their subsequent reaction by C solution-state NMR. A number of new cross-link structures were identified and the mechanisms of cross-linking determined. Initial reaction involves addition of radicals either directly to the isoprene double bonds or to allyl radicals. Further addition of hydrogen atoms results in a mixture of fully-saturated and unsaturated cross-link structures. Cross-links of both H- and Y-type were identified and the yields of products agreed closely with the yields determined from measurement of changes in molecular weight on irradiation. 

Chemical-resistant suits — Protection is frequently needed in chemistry incidents for protection against corrosive liquids and vapors. In standardized situations, materials for protective suits can be custom selected for maximum protection for the specific chemicals of concern. Where a variety of chemicals such as acids, bases, and frequently used solvents are involved, a butyl rubber suit is often a reasonable choice. Combination units of chemical and fire resistant entry suits are available. 

The physical aspects of ozone cracking are clearly seen in the case of the predominantly saturated butyl rubber (HR), a copolymer of isobutylene and isoprene containing - 1-3% isoprene. Although the chemistry is the same as for its diene rubber counterpart, IR, butyl rubber is much more resistant to ozone cracking. Unsaturated elastomers must be stretched for ozone cracking to occur. 

With bromobutyl/butyl rubber blends, elastomer structures are essentially the same, but the different reactive functionalities provide different vulcanization chemistry. Since bromobutyl rubber has greater cure reactivity, accelerators that will over-cure the bromobutyl rubber phase should be avoided. Briefly... 

Bob was recognized as a fifty year member of the American Chemical Society. He received the Charles Goodyear medal in 1969 and his talk on "Early History of Butyl Rubber" was published in Rubber Chemistry and Technology. 42 (4) G90 (1969). He was named a Pioneer in Polymer Science by Polymer News just prior to his death in 1986. 

F. P. Baldwin and I. J. Gardner, in Chemistry and Properties of Crosslinked Polymers, S. S. Labana, ed.. Academic, New York (1977). Graft Curing with Modified Butyl Rubber and AB Crosslinked Copolymers of Butyl Rubber with Polystyrene. Crosslinking of the polystyrene. Physical and mechanical Properties. Swelling and extraction. 

J. Duffy and J. E. Puskas, Synthesis of Butyl Rubber by Cationic Polymerization, in Ullmann s Encyclopedia of Industrial Chemistry, Vol. A23, 6th ed., Wiley-VCH, Weinheim, 1998, p. 51. 

W. H. Waddell, in M. B. Rodgers, Butyl Rubbers, In, Rubber Compounding, Chemistry Applications, Marcel Dekker, Inc., New York, in press. 

Polyisobutene (PIB) and butyl rubber are unusual in that they are polymerized commercially by the process of cationic polymerization. As in the case of free radical and other polymerizations involving a double bond the process involves a chain reaction but in this case the active species is a carbonium ion. The chemistry of cationic polymerization is complex and outside the scope of this book but has been the subject of a number of reviews (Tsukamoto and Vogl, 1971 Plesch, 1963). There are however a number of salient features which should be noted. 

On the basis of our grafting studies with halo-genated butyl rubbers we must conclude that although the bromide is more easily displaced to form AgX, as expected from organic chemistry, the chloride is more suitable for making grafts. 

Amine salts as butyl rubber modifier U.S.S.R. 730,734 PAPER MODIFIER 1980 Institute of Physical Chemistry... 

McKenna, G.B. and Zapas, L.J. (1981) Response of carbon black filled butyl rubber to cyclic loading. Rubber Chemistry and Technology, 54,718. 

Plasticizers are used in butyl rubber, polyureAane, polysulfide, solvent aerylies, polyvinyl acetate, and silicone rubber adhesives and sealants. The compatibility of the plasticizer depends on base polymer chemistry. Plastieizers for silicone systems are low molecular weight... 

There are several factors to consider when choosing a solvent for a given polymer system. These include solubility of the polymer, viscosity stability, cost, drying time, flammability, toxicity and environmental factors. The solubility of a polymer in an organic solvent is dependent on the chemistry of the two materials. Generally, nonpolar polymers dissolve easily in nonpolar solvents and vice-versa. For example, nonpolar butyl rubber dissolves well in hydrocarbons such as hexane, whereas polar acrylic polymers are usually compounded with xylene or toluene. Solvents can be selected based on their Hildebrand Solubility Parameters and that of the polymer. If their solubility parameters are similar, within 2 imits, the polymer will dissolve readily in the solvent. 

The development of systems that operate in non-halogenated solvents at temperatures closer to ambient has been a long-standing goal in the cationic polymerization field. This is especially true in regards to the copolymerization of isobutene with isoprene to make butyl rubber industrial production is conducted as a slurry in MeCl using AlClj at low temperatures ( -100°C) [55-61]. The majority of improvements that have been made in terms of reduced energy consumption, omission of chlorinated solvents, and elimination of waste have come from developments in the chemistry of initiator systems. The bulk of these stems from research conducted in the area of IB polymerization and have been previously covered... 

The above compound (Perkalink 900) was shown to be an effective antireversion agent for sulphur-cured diene elastomers. The performance advantages of using Perkalink 900 in butyl rubber (inner tubes, bladders), halobutyl rubber (iimer liners) and nitrile rubber were demonstrated, the aim being to improve the heat resistance of the compounds. A mechanistic interpretation of the chemistry underlying the crosslinking in butyl rubber and halobutyl rubber was provided. 15 refs. 

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing... 

World War II represents the accelerated adolescence of the rubber industiy, the preparation for its great postwar maturation and growth. Developments in organic and polymer chemistry provided insight into the properties of natural rubber, which led to neoprene, SBR, nitrile and butyl... 

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