divinyl-nitrile rubbers, synthetic rubbers that are the products of the copolymerization of butadiene (I) and acrylonitrile (II) having the general formula
These rubbers are obtained by copolymerizing the monomers in an aqueous emulsion at ~ 5° C or ~ 30° C. The content of bound acrylonitrile is 17-45 percent. Butadieneacrylonitrile rubbers vary in color from light yellow to light brown and have a density of 940-1, 020 kg/m3 (0.94-1.02 g/cm3); they are soluble in ketones and chlorinated hydrocarbons. Owing to the presence of the polar nitrile groups (—CN), the rubbers are resistant to the action of industrial oils, gasoline, and aliphatic hydrocarbons. They resist heat aging; their low resistance to the action of ozone can be increased by modifying them with polyvinyl chloride.
Sulfur, and also organic disulfides and peroxides, are used in vulcanizing butadiene-acrylonitrile rubbers. The fillers used are mainly active and semiactive carbon blacks and finely-divided silicon dioxide (“white carbon black”). As the content of bound acrylonitrile in the rubbers is increased, the strength properties and the resistance to wear, oil, and gasoline are improved, but the elastic properties and the frost resistance of the cured rubbers derived from these polymers are reduced (see Table 1).
Cured butadiene-acrylonitrile rubbers are also characterized by comparatively high water absorption (2.1 mg/cm2 of rubber surface when a specimen is immersed in water for
|Table 1. Properties of black-filled cured rubber made with domestic brands of butadiene-acrylonitrile rubbers|
|SKN-18 (17-20)1||SKN-26 (27-30)1||SKN-40 (36-40)1|
|1 Content of bound acrylonitrile, percent|
|Tensile strength [meganewtons per sq m (kg-force/cm2)]...............||35 (250)||28 (280)||30 (300)|
|Brittleness temperature (°C)...............||—62||—54||—35|
|Wear resistance [cm3/(kW-hr)]...............||330||250||200|
|Swelling in a 3:1 gasoline-benzene mixture [percent (by mass)]...............||70||38||20|
two months at 25° C) and low dielectric properties: the specific volume electric resistance is 100 megohm-m (1010 ohm cm), and the dielectric constant is 10-11.
The rubbers are produced in the form of strips, briquettes, and chips. The most common brands of foreign butadiene-acrylonitrile rubbers are Chemigum, Butaprene, Hycar, and Paracril (USA), Polysar and Krynac (Canada), Perbunan N (Federal Republic of Germany), Buna N (German Democratic Republic), and Nipol N (Japan).
Butadiene-acrylonitrile rubbers are among the most im-portant special rubbers that are used in the fabrication of various oil- and gasoline-resistant items. They are also used as plasticizers for plastics that are the basis for making shock-resistant materials. In 1971 the production capacity for butadiene-acrylonitrile rubbers in the capitalist countries was about 250, 000 tons.