An adhesive composition comprises a polymer of a branched chain 1.3-hexadiene containing a straight chain of five carbon atoms or a copolymer of such a hexadiene with one or two other such hexadienes and/or one or more other conjugated double bond diolefines, the polymer or copolymer being dissolved or suspended in a volatile organic liquid. Specified hexadienes are 2 - methyl - 1,3 - pentadiene, 3 - methyl - 1,3 - pentadiene and 4-methyl-1,3-pentadiene; and suitable diolefines are 1,3-butadiene, 2-chloro-1,3-butadiene, piperylene, isoprene, myrcene, 2,3-dimethyl-1,3-butadiene and higher 1,3-dienes. The polymerization may be effected in aqueous emulsion, in bulk or solution, with persulphate, perborate or peroxide catalysts, but preferably with diazoaminoaryl compounds, e.g. diazoaminobenzene, at temperatures above 70 DEG C. Suitable solvents for the polymeric methylpentadienes include aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, alcohols, ethers, esters, ketones, dioxane, dioxolane and methyl dioxolane. Plasticizers, antioxidants, fillers, pigments, vulcanization agents and accelerators, stabilizers, tackifiers, lubricants, dyes and modifiers may be added. Plasticizers: wood rosin, gum rosin, ester gum, shellac, dibutyl sebacate, dibutyl, dicapryl and dioctyl phthalates, coal and pine tar, cumarone resins, tricresyl phosphate, chlorinated tricresyl phosphate, alkoxy alkyl phosphates, dibenzyl ether, triacetin, stearic acid, lauric acid and petroleum compounds. Antioxidants: phenyl beta-naphthylamine, p-amino phenol, p-hydroxy diphenyl, hydroquinone, p,p1-diamino-diphenyl-methane, 2,4-toluylene diamine, diphenylamine, o-dioctylamine, p-ditolylamine, phenyl-alpha-naphthylamine, phenyl beta-naphthyl nitrosoamine, sym - di - beta - naphthyl p - phenylene diamine, diphenyl diamino ethane and 2,4-diaminodiphenylamine. Fillers and pigments: carbon black, clay, calcium silicate, iron, chromium, zinc and titanium oxides. Vulcanizing agents: sulphur, sulphur-containing compounds, e.g. sulphur dioxide, hydrogen sulphide and sulphur thiocyanate; oxygen and oxygen yielding compounds, e.g. ozone, organic and inorganic peroxides; selenium, halogens and halogen-containing compounds; and nitrogen-containing compounds such as the nitrobenzenes. Accelerators: tetramethyl thiuram di- and mono-sulphides, zinc dibutyl dithiocarbamate, dipentamethylene thiuram tetrasulphide, mercapto benzo thiazole, hexamethylene-tetramine, aldehyde - ammonia, diphenylguanidine, diphenylthiourea, benzo thiazyl disulphide, piperidinium pentamethylene-dithiocarbamate, di-o-tolyl-guanidine, triphenylguanidine and lead dimethyl-dithiocarbamate. Modifiers: phenol-aldehyde, urea-aldehyde and alkyd resins, polymers and copolymers of unsaturated compounds, protein plastics and cellulose derivatives. These may sometimes be produced in situ in the presence of the polymethylpentadienes and may be present during the polymerization reaction. The polymethylpentadienes may be blended with natural rubber or synthetic rubbers such as polymers of butadiene, isoprene, piperylene, 2,3 - dimethyl - 1,3 - butadiene, chloroprene, olefines such as isobutylene, copolymers of 1,3-dienes with styrene or acrylonitrile, copolymers of isobutylene with butadiene, high molecular polyesters and polyvinyl halides. Specification 606,807 is referred to.ALSO:An adhesive composition comprises a polymer of a branched chain 1, 3-hexadiene containing a straight chain of five carbon atoms or a copolymer of such a hexadiene with one or more other such hexadienes and/or one or more other conjugated double bond diolefines, the polymer or copolymer being dissolved or suspended in a volatile organic liquid. Specified hexadienes are 2-methyl-1, 3-pentadiene, 3-methyl-1, 3-pentadiene and 4-methyl-1, 3-pentadiene; and suitable diolefines are 1, 3-butadienes, 2-chloro-1, 3-butadiene, piperylene, isoprene, myrcene, 2, 3-dimethyl-1, 3-butadiene and higher 1, 3-dienes. Suitable solvents include aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, alcohols, esters, ethers, ketones, dioxane, dioxolane and methy dioxolane. Plasticisers, antioxidants fillers, pigments, vulcanization agents, and accelerators, stabilizers, tackifiers, lubricants, dyes and plastic modifiers may be added. Plasticers: wood rosin, gum rosin, ester gum, shellac, dibutyl sebacate, dibutyl phthalate, dicapryl phthalate, dioctyl phthalate, coal and pine tar, coumarone resins, tricresyl phosphate, chlorinated tricresyl phosphate, alkoxy alkyl phosphates, dibenzyl ether, triacetin, stearic acid, lau ic acid and petroleum compounds. Antioxidants: phenyl beta- or alpha-naphthylamine, p-amino phenol, p-hydroxy diphenyl, hydroquinone, p and p1-diamino diphenyl-methane, 2, 4-toluylene diamine, diphenylamine, or -dioctylamine, p-ditolylamine, phenyl alpha-naphthylamine, phenyl betanaphthyl nitrosoamine, symdi-beta-naphthyl p-phenylene diamine, diphenyl diamino ethane and 2, 4-draminodiphenylamine. Fillers and pigments: carbon black, clay, calcium silicate, iron, p chromium, zinc and titanium oxides. Vulcanizing agents: sulphur and sulphur-containing compounds, oxygen and oxygenyielding compounds, selenium, halogens and halogen-containing compounds, and nitrogen-containing compounds such as the nitrobenzenes. Accelerators: tetramethyl thiuram diand mono-sulphides, zinc dibutyl dithiocarbamate, dipentamethylene thiuram tetrasulphide, mercapto benzo thiazole, hexamethylene-tetramine, aldehyde-ammonia, diphenylguanidine, diphenylthiourea, benzo thiazyl disulphide, piperidium pentamethylene-dithiocarbamate, di-o-tolyl-guanidine, triphenylguanidine and lead dimethyl-dithiocarbamate. Plastic modifiers: phenol-aldehyde, urea-aldehyde and alkyd resins, polymers and copolymers of unsaturated compounds, protein plastics and cellulose derivatives. The polymethyl-pentadienes may also be blended with natural rubber and synthetic rubbers such as polymers of butadiene, isoprene, piperylene, 2, 3-dimethyl-1, 3-butadiene, chloroprene, olefines such as isobutylene, copolymers of 1, 3-dienes with styrene or acrylonitrile, copolymers of isobutylene with butadiene, high molecular polyesters and polyvinyl halides. The adhesives are useful in the manufacture of tyres and other articles comprising fabric and natural, synthetic or reclaimed rubber and in pressure-sensitive adhesive sheets (see Group VIII). Specification 606,807 is referred to.