1.3- Butadiene, ozone

Fluoroethylene ozonide, 0752 /rMaleic anhydride ozonide, 1406 f 2-Methyl-1,3-butadiene, Ozone, 1893 3-Methyl-l,2,4-trioxolane, 1235 trans-2-Pentene ozonide, 1982... 

See Dienes, above, also 2-Methyl-l,3-butadiene Ozone Nitrogen... 

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances. 

Nitrile mbber finds broad application in industry because of its excellent resistance to oil and chemicals, its good flexibility at low temperatures, high abrasion and heat resistance (up to 120°C), and good mechanical properties. Nitrile mbber consists of butadiene—acrylonitrile copolymers with an acrylonitrile content ranging from 15 to 45% (see Elastomers, SYNTHETIC, NITRILE RUBBER). In addition to the traditional applications of nitrile mbber for hoses, gaskets, seals, and oil well equipment, new applications have emerged with the development of nitrile mbber blends with poly(vinyl chloride) (PVC). These blends combine the chemical resistance and low temperature flexibility characteristics of nitrile mbber with the stability and ozone resistance of PVC. This has greatly expanded the use of nitrile mbber in outdoor applications for hoses, belts, and cable jackets, where ozone resistance is necessary. 

Ozone cracking is a physicochemical phenomenon. Ozone attack on olefinic double bonds causes chain scission and the formation of decomposition products. The first step in the reaction is the formation of a relatively unstable primary ozonide, which cleaves to an aldehyde or ketone and a carbonyl. Subsequent recombination of the aldehyde and the carbonyl groups produces a second ozonide [58]. Cross-linking products may also be formed, especially with rubbers containing disubstituted carbon-carbon double bonds (e.g. butyl rubber, styrene-butadiene rubber), due to the attack of the carbonyl groups (produced by cleavage of primary ozonides) on the rubber carbon-carbon double bonds. 

Rubbers differ in their resistance to ozone. All the highly unsaturated rubbers (natural rubber, styrene-butadiene rubber, butyl rubber, nitrile rubber) are readily cracked while the deactivated double carbon-carbon bonds rubber (such as polychloroprene rubber) shows moderate ozone resistance. 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

Ozone and carbon dioxide demonstrate that p orbitals can overlap side by side with more than one neighbor. This feature can lead to a system of 7r bonds that can extend over many atoms. Extended systems can be long chains, or they can be more compact clusters or rings. We begin by describing two examples of four-atom tt systems, butadiene and the carbonate anion. 

At least 90 percent of free-radical-polymerized 2,3-dimethylbutadiene consists of 1,4 units according to ozone degradation experiments. Successive substitution of the methyl groups on carbons 2 and 3 of butadiene is seen to increase the proportion of 1,4 units formed. In polychloroprene no less than 97 percent of the structure consists of 1,4 Cl... 

Antiozonant additives are employed with unsaturated rubbers such as natural rubber, nitrile rubber, styrene-butadiene rubber, etc., to minimise the atmospheric ozone degradation reaction. Common antiozonant types include the parapheny-lene diamines such as N-(l,3-dimethylbutyl)-AT-phenyl-p-phenylene diamine (6PPD) and N-isopropyl-N7 phenyl-p-phenylene diamine (IPPD). Both these antioxidants can be identified and quantified using GC- or LC-based techniques. 

The enolethers give ozone protection but not ageing protection with natural rubber (NR) and polyisoprene (IR), styrene-butadiene rubber (SBR) and butadiene rubbers (BR), but are less... 

Photolytic. The following rate constants were reported for the reaction of 1,3-butadiene and OH radicals in the atmosphere 6.9 x 10 " cmVmolecule-sec (Atkinson et al., 1979) and 6.7 x lO " cmVmolecule-sec (Sabljic and Glisten, 1990). Atkinson and Carter (1984) reported a rate constant of 6.7-8.4 X 10 " cmVmolecule-sec for the reaction of 1,3-butadiene and ozone in the atmosphere. Photooxidation reaction rate constants of 2.13 x 10 and 7.50 x 10cm /molecule-sec were reported for the reaction of 1,3-butadiene and NO3 (Renter and Schindler, 1988 Sabljic and Glisten, 1990). The half-life in air for the reaction of 1,3-butadiene and NO3 radicals is 15 h (Atkinson et al., 1984a). 

The estimated atmospheric lifetimes for the reaction of 2-methyl-1,3-butadiene with ozone, OH, and NO3 radicals are 28.3, 2.9, and 0.083 h, respectively (Atkinson and Carter, 1984). Chemical/Physical. Slowly oxidizes and polymerizes in air (Huntress and Mulliken, 1941). 

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

More than 800 million pounds of EPM and EPDM polymers were produced in the United States in 2001. Their volume ranks these materials fourth behind styrene-1,3-butadiene copolymers, poly( 1,4-butadiene), and butyl rubber as synthetic rubbers. EPM and EPDM polymers have good chemical resistance, especially toward ozone. They are very cost-effective products since physical properties are retained when blended with large amounts of fillers and oil. Applications include automobile radiator hose, weather stripping, and roofing membrane. 

As discussed in detail in Chapters 6 and 16, organic compounds play a key role in the formation of ozone, particles, and other species of interest. While some of the individual species are of concern from the point of view of health effects (e.g., the carcinogens benzene and 1,3-butadiene), for most VOC it is because of their... 

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