Isoprene

Isoprene is a branched, conjugated diolefin: a methyl-substituted butadiene skeleton with two conjugated double bonds. That conjugation gives it the same dual reactivity toward addition polymerisation and Diels-Alder cycloaddition as 1,3-butadiene, while the methyl branch places it in a category of its own — isoprene's repeat unit is the exact structural unit found in natural rubber (cis-1,4-polyisoprene), which is why synthetic polyisoprene made from this monomer can be engineered to closely reproduce the properties of natural rubber.

Unlike the C4 olefins and diolefins, isoprene's boiling point of 34°C puts it just above room temperature, so at ambient conditions it is a highly volatile, colourless liquid rather than a gas, with a characteristic mild, somewhat pungent odour. Because its conjugated double bonds are prone to spontaneous radical polymerisation, commercial material is always stabilised with a polymerisation inhibitor, typically tert-butylcatechol (TBC), and is best kept refrigerated given its very low flash point.

Where it fits in the value chain

Isoprene's single largest end use is stereospecific polymerisation to synthetic polyisoprene (cis-1,4 configuration), used as a direct substitute for natural rubber in tyres and rubber goods where consistent, contaminant-free supply is valued over the natural product. A significant second use is as the minor comonomer (typically 1–2% by weight) copolymerised with isobutylene to give butyl rubber, where the isoprene units provide the residual unsaturation needed for sulphur vulcanisation. Isoprene is also the building block for styrene-isoprene-styrene (SIS) thermoplastic elastomer block copolymers used in pressure-sensitive adhesives, and for a range of fragrance and fine-chemical intermediates built from its characteristic branched diene structure.

Grade we supply

Chelora Chemicals offers Isoprene in polymer grade (99%+ purity), inhibited with TBC, suited to synthetic polyisoprene and butyl rubber polymerisation and SIS block-copolymer manufacture. The grade is supplied with a batch-wise certificate of analysis.

Isoprene is recovered, like butadiene, as a co-product of steam cracking: the C5 fraction of the cracked gas from naphtha or gas oil cracking contains isoprene alongside cyclopentadiene, piperylenes and saturated C5 hydrocarbons. Because these components have closely spaced boiling points, isoprene is separated by extractive distillation using a selective solvent, in a process directly analogous to butadiene recovery from the C4 stream, followed by further fractionation to reach polymer-grade purity.

Where steam-cracker C5 supply is insufficient for isoprene demand, dedicated on-purpose routes are also used, most notably catalytic dehydrogenation of isopentane or the isoamylenes (methylbutenes), and the Prins reaction, which builds the isoprene skeleton in two steps from isobutylene and formaldehyde. These on-purpose routes have been particularly important in regions where tyre-rubber demand for isoprene outstrips what naphtha cracking alone can supply.