Vulcanized Unsaturated polyhydrocarbons

Vulcanization is an industrial process applied to various polymers from the class of unsaturated polyhydrocarbons. The major practical use of vulcanized elastomers is the tire industry. Tires are made from various polymer blends, including natural rubber, typically between 20 and 50%. The other polymers used in various blends that can be vulcanized include copolymers such as poly(styrene-co-1,3-butadiene) or SBR, poly(acrylonitrile-co-1,3-butadiene-co-styrene) or ABS, poly(isobutylene-co-isoprene), poly(ethylene-co-propylene-co-1,4-hexadiene, etc. 

The common vulcanization process (not for chloroprene) consists of a chemical reaction of sulfur (0.5-5% wt.) with the polymer containing double bonds in the backbone. The reaction takes place at 130-145° C and may require mechanical mixing. The reaction for polyisoprene can be written schematically as follows  

The final product may contain a single sulfur atom bridge, sulfur in cyclic or pendant groups, or may contain polysulfide bridges between the polymer chains. The vulcanization introducing sulfur in the polymer also can be done at room temperature with S2CI2. 

Besides sulfur, during the vulcanization process other chemical compounds are commonly added. One group of such compounds consists of vulcanization accelerators. Substances such as diphenylguanidine, mercaptobenzothiazole, tetramethythiuram disulfide, N-oxydiethylene-2-benzothiazolylsulfenamide, N-oxydiethylenethiocarbamoyl-N -oxidiethylenesulfenamide, cyclohexylbenzothiazolyl-sulfenamide, etc. are utilized for this purpose. The structures of two sulfenamide accelerators are shown below  

Besides accelerators, other additives are used, including antioxidants, activators, solubilizers, plasticizers, and fillers. Among the antioxidants more frequently used are N-phenyl-(3-naphthylamine, 2,6-di-fert-butyl-4-methyl-1-hydroxybenzene (BHT), N- 

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