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Isoprene was first isolated from the pyrolysis products of natural rubber. The first preparation of polyisoprene was reported in 1879. In 1950, the goal of preparing synthetic cis 1,4‐polyisoprene as a counter part to natural rubber was achieved. Attention was then focused on commercial preparation of isoprene for polymerization use. Shortly after the discovery of stereospecific catalysts, the first commercial polyisoprene plant came on stream in 1959–1960 using a lithium catalyst. Isoprene is a reactive diene that undergoes cycloaddition, electrophilic, nucleophilic, free‐radical, and coordinated catalytic addition, and thermal dimerization. Information on the production of isoprene by naphtha cracking as well as the synthetic processes is detailed. Depending on the catalyst and conditions, isoprene may undergo 1,2,3,4, or 1,4 addition leading to several isomeric structures. Coordination catalysts, alkali metal catalysts, and Alfin catalysts are important for polymerization and are discussed. Chemical modification of polymers is a convenient way of altering physical and mechanical properties. Highly unsaturated polymers such as polyisoprene are easily modified because the olefinic bond is readily available. Their high reactivity with a variety of chemical substances offers advantages in chemical modification and vulcanization. However, reaction with oxygen and ozone causes degradation and loss of physical and mechanical properties. Synthetic polyisoprene is processed on conventional rubber machinery. Compounding technology is similar to that used for natural rubber. Typical formulations are given. A brief discussion of isoprene copolymers and 1,4‐ trans ‐polyisoprene is included. Isoprene is classified as a flammable liquid. It is a moderate irritant to the skin, eyes, and mucous membranes. The primary use for cis ‐1,4‐polyisoprene is in tires and tire products. It is also used, eg, in molded and mechanical goods, adhesives, belts, foam rubber, and elastic threads.. Automotive molded products and medical applications are typical. Trans ‐1,4‐Poyisoprene can be extracted, calendered, injection molded, and compression molded. It can be used in blends with other polymers. Its main use is in golf ball covers.

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Ozone resistance and high flex life are some of the important features of elastomers needed in the rubber industry. EPDM, a terpolymer of ethylene, propylene, and small amounts of a nonconjugated diene, has a saturated carbon‐carbon backbone and therefore shows excellent resistance to ozone and aging, and good flex properties. However, butyl rubber (1IR) has a small amount of unsaturation in its carbon‐carbon backbone and consequently does not exhibit as good ozone resistance and aging characteristics as EPDM. We discovered a family of new rubbers named HexsynTM, which were synthesized by copolymerizing higher α‐olefins (C4‐C10) with a mixture of 4‐methyl‐ and 5‐methyl‐1,4‐hexadienes. One outstanding Hexsyn™ rubber is a copolymer of 4‐hexene and the 5‐methyl‐1,4‐hexadiene. This copolymer uniquely combines the useful properties of EPDM and butyl. Outstanding features are excellent flex life, excellent ozone resistance, good compression set resistance, and high damping. Due to its excellent flex life, HexsynTM( (hexene copolymer) has been found useful in fabricating experimental pumping diaphragms of air‐driven artificial hearts of calves and also for left ventricle assist devices. This rubber has found application as a flexing element in artificial finger joints for damaged or diseased human fingers.