There are four types of rubbers under general purpose rubbers. They are:
Styrene-Butadiene Rubber – Styrene-Butadiene Rubber (SBR) constitutes more than half of the world production of synthetic rubber and exceeds natural rubber supply. In fact, tyre industry depends more on SBR than a natural rubber because it is available in plenty and serves the purpose better after the incorporation of fillers.
Butyl Rubber – Butyl rubber is produced by copolymerising small amount of isoprene (1-3%) with isobutylene catalysed by aluminium chloride (AlCl3) dissolved in methyl chloride. The extremely rapid reaction is complete in less than a second. Methyl chloride diluent and monomer should be carefully dried. They possess unique age-resistant properties. This type of rubber is used for inner tubes of tyres. Other uses are in the field of mechanical goods.
Synthetic Polyisoprene Rubber – Isoprene is derived from petroleum. It is mixed with hydrocarbon solvent. Two types of catalysts can be used. One is based on coordination catalyst of titanium chloride and an aluminium alkyl such as tri-isobutyl aluminium while the other anionic catalyst is butyl lithium. It is virtually colourless due to high purity and freedom from contamination and is used for medicinal purposes. It has high elongation break which leads to its use in rubber threads for golf balls.
Polybutadiene Rubber – Formerly butadiene was made from alcohol. However now it is derived exclusively from petroleum. It is manufactured similar to Polyisoprene employing solution polymerisation using pure dry monomer and hydrocarbon solvents. This type of rubber exhibits excellent dynamic properties, low hysteresis and good abrasion resistant.