GB813198A - Improvements in polymerization of isoprene - Google Patents

Abstract

Isoprene is polymerized in the presence of a hydrocarbon lithium or polylithium to give a rubbery essentially cis 1,4-polyisoprene. Specified catalysts are methyl-, ethyl-, butyl-, amyl-, hexyl-, 2-ethyl hexyl-, n-dodecyl- and n-hexadecyl-lithium; allyl- and methallyl-lithium; phenyl-, tolyl- and xylyl-lithium; alpha- and beta-naphthyl lithium; methylene-, ethylene-, trimethylene-, pentamethylene-, hexamethylene-, decamethylene-, octadecamethylene-dilithium; 1,2-dilithium propane; 1,4-dilithium benzene, 1,5-dilithium naphthalene, and 1,2-dilithium-1,3-diphenyl propane; 1,3,5-trilithium pentane, 1,3,5-trilithium benzene and the compound of the formula <FORM:0813198/IV (a)/1> Mixtures of such compounds may be used and the mixture obtained by treating 1 mol. of an alkyl lithium with 2/3 mol. of an alcohol and thereafter with an olefine for a period of two hours, e.g. treating amyl lithium with isopropanol and propylene. The polymerization is preferably carried out in bulk, solvents particularly hydrocarbons such as pentane, hexane, heptane, petroleum ether, benzene or cyclopentane may be used. The monomer should be at least 90 mol. per cent pure and may be submitted to a final purification by passing through silica gel into the reaction vessel. Oxygen and water should be excluded and final traces of air are removed by venting a portion of the monomer before sealing the reaction vessel; inert gases may be used during and before charging. The amount of catalyst may be 0.005-0.5 gram of carbon-linked lithium per 100 grams of isoprene. Temperatures of 0 DEG to 100 DEG C. for small-scale and 150 DEG C. for large-scale operations may be used for reaction times of 3 to 60 hours. Polymerization may be stopped by adding an alcohol. The polymer should be washed to remove catalyst and an antioxidant added. Numerous examples are given.