GB826990A - Improvements in polymerization of diolefins - Google Patents

Abstract

A catalyst for use in polymerizing diolefines (see Group IV (a)) comprises (a) lithium or a lithium compound capable of displacing hydrogen from water; and (b) a salt of a complex anion containing boron, silicon, arsenic, aluminium or a heavy metal other than Ti, Zr, Ce, V, Nb, Ta, Cr, Mo or W. The component (a) if lithium metal is used as a finely divided suspension in petroleum jelly or a hydrocarbon solvent boiling above 200 DEG C. Compounds of lithium which may be used include lithium hydride, hydrocarbon lithiums and polylithiums of which numerous examples are given, the hydrocarbon derivatives of lithium amide and the adducts obtained by reacting polynuclear aromatic hydrocarbons with lithium metal. In the component (b), typical heavy metals in the anion are manganese, iron, cobalt, nickel, zinc, lanthanum, platinum, mercury and uranium, and they are complexed with negative groups such as halogen, oxygen, hydroxyl and hydrocarbon groups, and may also have neutral components such as carbonyl or water. The anions will generally be of salts of light metals such as the alkali metals, calcium and magnesium. Specified anions are [AlCl6]-; [AlF6]-; [AlBr6]-; [AlI6]-; [AlOCl4]-; [Al(CH3)Cl5]-; [ZnBr4]-; [ZnBr5]-; [PdCl6]-; [SbCl6]-; [VO2Br4]-; [AlCl5(H2O)]-; [AlCl4(H2O)2]-; [PtCl6]-; [SiF6]-; [BF4]-; [ZnF6]-; [AlO3]-; FeO3]-. The complex may be formed in situ by reacting a suitable heavy metal, boron, silicon or arsenic compound such as an oxide or halide with lithium or a lithium compound which may be supplied in excess to serve also as the component (a) of the catalyst. In some cases an oxide coating on the surface of a metal. If a lithium hydrocarbon is employed as the lithium compound, the hydrocarbon radical may appear in the anion as part of the complex. In the examples, lithium metal is reacted with aluminium trichloride, aluminium powder and silicon carbide, aluminium powder, zinc powder, iron powder, aluminium trichloride and water, boron trifluoride, aluminium trifluoride monohydrate or ferric chloride, and lithium ethyl is reacted with aluminium chloride, in each case the lithium or its compound being used in excess first to form a complex to form component (b) the remainder forming component (a); in one case the catalyst is formed on a silica support. Mixtures of lithium naphthalamide with lithium aluminium chloride are also used. Specifications 813,198 and 826,918, [both in Group IV (a)], are referred to.ALSO:Lithium naphthalenide, an addition product of lithium and naphthalene, for use as a component of a polymerization catalyst (see Groups III and IV (a)) is prepared by agitating naphthalene with a dispersion of lithium in petrolatum in diethyl ether for 20 hours. The ether was then replaced by n-heptane by continuously adding heptane while distilling off the ether. The lithium content of the resultant dispersion was found, by titration with HCl, to be 0.67 molar. Other aromatic hydrocarbons mentioned as forming addition compounds with lithium are anthracene, chrysene, stilbene, diphenylmethane, fluorene, naphthacene, 1 - methylnaphthalene, phenanthrene, acenaphthene, diphenyl, pyrene, triphenylene and dibenz(a, h)-anthracene. Specifications 813,198 and 826,918, [both in Group IV (a)], are referred to.ALSO:A conjugated diolefin is polymerized or copolymerized with ethylenically unsaturated monomers free of highly negative groups in the presence of a catalyst comprising (a) lithium or a lithium compound capable of displacing hydrogen from water, and (b) a salt of a complex anion containing boron, silicon, arsenic, aluminium, or a heavy metal other than Ti, Zr, Ce, V, Nb, Ta, Cr, Mo or W (see Group III). The preferred diolefin is isoprene, other diolefins are butadiene; 2-methyl-1,3-pentadiene; 2,3-dimethyl butadiene and cyclopentadiene; they should be of at least 90 mol. per cent purity. Comonomers if present preferably constitute not more than 25 weight per cent of the total weight of monomers and may be styrene or alphamethyl styrene. Oxygen, other components of air, water, ethers, esters, amines, nitriles and nitro-compounds should be excluded from the system. Bulk or solution technique may be used, suitable solvents being propane, pentane, hexane, heptane, dodecane, petroleum ether, cyclopentane, cyclohexane and methyl cyclohexane, and should be pure. Solvent and monomers are preferably given a final purification before charging to the reaction zone by passing through a silica gel, alumina or calcium chloride column. Inert gases such as helium or argon may be used during charging. The catalyst is generally introduced last and polymerization is carried out at 0-150 DEG C. for 3-60 hours. The product may be immersed in methanol or isopropanol, containing an anti-oxidant, to destroy the catalyst and precipitate the polymer. The polyisoprenes produced by this method generally contain at least 93% cis-1,4 addition. Specifications 813,198 and 826,918 are referred to.