GB814676A - Essentially cis rubbery polyisoprene and method of producing same - Google Patents

Abstract

Isoprene is polymerized to an essentially cis-1,4-polyisoprene in the presence of metallic lithium and in the substantial absence of elemental oxygen or oxygen-containing organic compounds. Elemental nitrogen and water should also preferably be absent. Liquid or vapour phase polymerization may be used at temperatures from 100 DEG to 0 DEG C. or lower; it is convenient to initiate the polymerization at 30-70 DEG C. and then reduce the temperature and conduct the major proportion of polymerization at the lower temperature which may be from below the initiation temperature to -20 DEG C. Lower temperatures give products of higher molecular weight and better polymer properties. The monomer is preferably at least 95 mol. per cent pure, other unsaturated compounds particularly being kept at a minimum and any inhibitor should be removed. The catalyst is prepared by melting the metal under petroleum jelly, mineral oil or paraffin and agitating. The dispersion may contain 35 per cent lithium of mean diameter 20 m . The surface of the metal may be kept clean during reactions by burnishing by mechanical abrasion with spheres of inert material moved by stirring or rotating means. Polymerization may be effected in glass bottles; the monomer is added in 10 per cent excess which excess is boiled off to drive out air and the bottle is sealed, it may be static or rotated on a wheel during the reaction. When polymerization is complete the polymer is removed and washed to destroy catalyst. Antioxidant, e.g. 3 per cent phenyl-beta-naphthylamine, is added, the polymer water washed again, sheeted out and dried in vacuo at 50 DEG C. The products are very similar to Hevea rubber and contain at least 80 per cent cis 1,4-structure, no more than 7 to 10 percent trans 1,4-structure, no more than 10 per cent 3,4-structure and no or very little 1,2-structure. Examples give chemical and physical data of products obtained by polymerizations employing between 0.025 and 0.2 parts by weight lithium per 100 parts monomer and of tyres prepared from the product. Specification 603,630, [Group XIII], is referred to.