Coumarone-indene plastics along with cellulose nitrate were the first synthetic resins developed commercially in the middle of the nineteenth century. Industrially, they are produced from coal-tar light oils by-produced either during coking or petroleum cracking operations. By treating the fraction distilling between 150 and 200°C that contains mainly indene and coumarone, with concentrated sulfuric or phosphoric acid, polymerization occurs readily. The synthetic resins obtained are mixtures of polyindene and polycoumarone, that are called cumar gum and commercialized under the trade name Nevindene with properties varying from a soft gum melting at 4°C to a hard brown solid with a melting point of ca. 150°C depending of the ratio of the two monomers. In all cases, the density is usually close to 1080 kg.m–3. These resins are resistant towards alkalis but are easily soluble in organic solvents and hence are used as lacquers, varnishes, or waterproofing compounds.
