synthetic rubber whose mac-romolecule contains a small number of —COOH carboxyl groups. The carboxylate rubbers that have been studied most thoroughly are copolymers of butadiene (or a mixture of butadiene with styrene or acrylonitrile) and 1–5 percent methacrylic acid. The main method of preparing carboxylate rubbers is emulsion polymerization.
A feature of carboxylate rubbers is the ability to be vulcanized by the oxides and hydroxides of divalent metals, particularly ZnO, MgO, and Ca(OH)2 because of the presence of carboxyl groups. The partial reaction of carboxyl groups with these vulcanizing agents during the preparation of rubber mixes or at other stages of the production process preceding vulcanization hinders the processing of carboxylate rubber in apparatus and limits its potential for practical use.
Vulcanized rubber specially prepared from raw carboxylate rubbers using systems composed of metal oxides and sulfur-containing vulcanizing agents, such as thiuram, are characterized by good mechanical properties and high thermal stability. For example, the tensile strength of black-filled vulcanized rubber prepared from butadiene-styrene carboxylate rubber (type SKS-30–1) is about 40 meganewtons per sq m (about 400 kilograms-force per sq cm), its relative elongation is about 800 percent, and its wearability is about 140 cu cm per kilowatt-hr. After aging for 480 hr at 100°C, the vulcanized rubber retains about 90 percent of its original tensile strength and relative elongation.
Aqueous dispersions (latexes) of carboxylate rubbers are usedfor the impregnation of tire cord to increase the strength of itsbond with vulcanized rubber, as well as for dressing leather andfinishing paper. Carboxylate rubbers are used in the manufactureof some industrial products and of glues for joining rubber andmetal.