Catalysts for the polymerization of acetylene and monosubstituted acetylenes comprise mixtures of (1) a complex of formula [M(R3Y)p]mXn where m and n are 1 to 4 or when M is osmium 1 to 6; p is 1 to 6 or when M is osmium 1 to 8; M is nickel, cobalt, palladium, platinum, rhodium, iridium, ruthenium or osmium; R represents hydrogen or alkyl, aryl, alkaryl, aralkyl, alkanoyloxy, alkoxy, aryloxy or cyanoalkyl radicals; Y represents phosphorus, arsenic, nitrogen, antimony or bismuth; and X is an anion; and (2) a compound of an element of Group I, II, III or IV of the Periodic System having at least one hydridic hydrogen bond. Many suitable catalyst components are specified and examples describe the use of (1) complexes of tributyl phosphine with nickel chloride, nickel nitrate, cobalt bromide, cobalt thiocyanate, palladium chloride, palladium nitrate and rhodium chloride; tricyanoethyl phosphine with nickel chloride, nickel bromide, nickel sulphate, nickel phosphate, nickel ferrocyanide and cobalt chloride; triphenyl phosphine with nickel chloride and nickel thiocyanate; triethyl phosphine with platinum chloride and ruthenium chloride; dibutyl phosphine with nickel chloride; butyl phosphine with nickel nitrate; triethyl arsine with nickel chloride, cobalt nitrate, palladium sulphate and rhodium phosphate; triphenyl arsine with platinum sulphate; triethyl stibine with cobalt phosphate; tributylamine with nickel chloride and iridium chloride; ammonia with cobalt chloride; diethyl arsine and ethyl stibine with palladium bromide; and triethyl arsine and triethyl phosphine with osmium chloride; and (2) lithium hydride, calcium hydride, diborane, monosilane, lithium, sodium, potassium calcium and aluminium borohydrides, ethyl sodium borohydride and dimethyl aluminium hydride. U.S.A. Specification 2,880,058 is referred to.ALSO:Acetylene and monosubstituted acetylenes are polymerized by contacting under polymerizing conditions with a catalyst comprising a mixture of (1) a complex of formula [M(R3Y)p]mXn wher m and n are 1 to 4 or when M is osmium 1 to 6; p is 1 to 6 or when M is osmium 1 to 8; M is nickel, cobalt, palladium, platinum, rhodium, iridium, ruthenium or osmium; R represents hydrogen, alkyl, aryl, alkaryl, aralkyl, alkanoyloxy, alkoxy, aryloxy or cyanoalkyl radicals; Y represents phosphorus, arsenic, nitrogen, antimony or bismuth; and X is an anion; and (2) a compound of an element of Group I, II, III or IV of the Periodic System having at least one hydridic hydrogen bond. Many groups by which acetylene may be substituted are listed and examples describe the polymerization of acetylene, propyne, pentyne-1, heptyne-1, heptadiyne-1,6, octadiyne-1,7, phenyl acetylene, propargyl alcohol, propargyl chloride, 3-diethylaminopropyne-1 and ethyl propiolate; and the copolymerization of heptyne-1 and pentyne, and propyne and acetylene. Many suitable catalyst components are specified and examples describe the use of (1) complexes of tributyl phosphine with nickel chloride, nickel nitrate, cobalt bromide, cobalt thiocyanate, palladium chloride, palladium nitrate and rhodium chloride; tricyanoethyl phosphine with nickel chloride, nickel bromide, nickel sulphate, nickel phosphate, nickel ferrocyanide and cobalt chloride; triphenyl phosphine with nickel chloride and nickel thiocyanate; triethyl phosphine with platinum chloride and ruthenium chloride; dibutyl phosphine with nickel chloride; butyl phosphine with nickel nitrate; triethyl arsine with nickel chloride, cobalt nitrate, palladium sulphate and rhodium phosphate; triphenyl arsine with platinum sulphate; triethyl stibine with cobalt phosphate; tributylamine with nickel chloride and iridium chloride; ammonia with cobalt chloride; diethyl arsine and ethyl stibine with palladium bromide; and triethyl arsine and triethyl phosphine with osmium chloride; and (2) lithium hydride, calcium hydride, diborane, monosilane, lithium, sodium, potassium, calcium and aluminium borohydrides, ethyl sodium borohydride and dimethyl aluminium hydride. Polymerization may be effected in liquid media, e.g. water, ethanol, dibetamethoxyethyl ether, acetonitrile, benzene and tetrahydrofuran. The products may be extracted with benzene petroleum ether, acetone and water, and comprise liquid polymers which may be used as drying oils in coating compositions, and solid, high molecular weight, linear polymers. The polymerization of butadiene and acrylonitrile is also referred to. U.S.A. Specification 2,880,058 is referred to.ALSO:Acetylene and monosubstituted acetylenes are polymerized by contacting under polymerizing conditions with a catalyst comprising a mixture of (1) a complex of formula [M(R3Y)p]mXn where m and n are 1 to 4 or when M is osmium 1 to 6; p is 1 to 6 or when M is osmium 1 to 8; M is nickel, cobalt, palladium, platinum, rhodium, iridium, ruthenium or osmium; R represents hydrogen or an alkyl, aryl, alkaryl, aralkyl, alkanoyloxy, alkoxy, aryloxy or cyanoalkyl radical; Y represents phosphorus, arsenic, nitrogen, antimony or bismuth; and X is an anion; and (2) a compound of an element of Group I, II, III or IV of the Periodic System having at least one hydridic hydrogen bond. Many groups by which acetylene may be substituted are listed and examples describe the polymerization of acetylene, propyne, pentyne-1, heptyne-1, heptadiyne-1,6, octadiyne-1,7, phenyl acetylene, propargyl alcohol, propargyl chloride, 3-diethylamino-propyne-1 and ethyl propiolate; and the copolymerization of heptyne-1 and pentyne, and propyne and acetylene. The polymers may be linear or aromatic, those described being linear except for those prepared from propargyl alcohol and phenyl acetylene which yield a mixture of aromatic and linear polymers. Many suitable catalyst components are specified and examples describe the use of (1) complexes of tributyl phosphine with nickel chloride, nickel nitrate, cobalt bromide, cobalt thiocyanate, palladium chloride, palladium nitrate and rhodium chloride; tricyanoethyl phosphine with nickel chloride, nickel bromide, nickel sulphate, nickel phosphate, nickel ferrocyanide and cobalt chloride; triphenyl phosphine with nickel chloride and nickel thiocyanate; triethyl phosphine with platinum chloride and ruthenium chloride; dibutyl phosphine with nickel chloride and butyl phosphine with nickel nitrate; triethyl arsine with nickel chloride, cobalt nitrate, palladium sulphate and rhodium phosphate; triphenyl arsine with platinum sulphate; triethyl stibine with cobalt phosphate; tributylamine with nickel chloride and iridium chloride; ammonia with cobalt chloride; diethyl arsine and ethyl stibine with palladium bromide; and triethyl arsine and triethyl phosphine with osmium chloride; and (2) lithium hydride, calcium hydride, diborane, monosilane, lithium, sodium, potassium, calcium and aluminium borohydrides, ethyl sodium borohydride and dimethyl aluminium hydride. Polymerization may be effected in liquid media, e.g. water, ethanol, dibetamethoxyethyl ether, acetonitrile, benzene and tetrahydrofuran. Phosphorus-containing complexes of the above formula may be prepared by mixing phosphines with metal salts in polar solvents such as ketones and alcohols from which the complexes crystallise on standing. In examples (1) tricyanoethyl phosphine is mixed with nickel bromide in acetone to give [P(CH2CH2CN)3]2NiBr2 (2) tricyanoethyl phosphine is mixed with nickel chloride in acetone to give [P(CH2CH2CN)3]2NiCl2; (3) triphenylphosphine is mixed with nickel chloride in acetic acid to give (#F3P)2NiCl2; (4 tributyl phosphine is mixed with nickel chloride in ethanol to give [(nC4H9)3P]2NiCl2 and (5) tributyl phosphine is mixed with palladium chloride in air-free water to give [(nC4H9)3P]2PdCl2.