Plastic masses are prepared by incorporating wholly or partially polymerized methacrylic acid methyl ester or ethyl ester with one another or with one or more additional substance at any stage in the polymerization which may be effected if desired in solution or in aqueous emulsion and with the aid of catalysts. The term additional substance includes softeners such as phthalic, tartaric, phosphoric and stearic acid esters, acetin, drying and non-drying oils, camphor and naphthalene, hardeners such as paraformaldehyde, plastifiers, products of methacrylic acid or its derivatives differing from those which form the basic constituents of the mass such as methacrylic acid nitrile, polyvinyl alcohols, organic and inorganic vinyl esters such as vinyl acetate and chloride, vinyl ethers, vinyl ketones, olefines and diolefines such as styrene or butadiene, cellulose derivatives such as cellulose acetates, nitrocellulose, methyl, ethyl and benzyl cellulose, natural resins, such as copal, dammar, colophonium and shellac, artificial resins such as condensation product of formaldehyde and phenol or urea, p-toluene sulphonamide resins, and fillers such as zinc oxide, ferric oxide, kaolin, talc, lampblack, organic and inorganic colouring matters. Suitable catalysts for polymerization are oxygen or substances developing oxygen such as the peroxides of sodium, barium or hydrogen, benzoyl peroxide and uranyl acetate. Solvents include hydrocarbons of the benzine and benzene series, ethylene chloride, chloroform, trichlorethylene, chlorobenzene, alcohol, ether, dioxane, acetone, cyclohexanone, ethyl acetate and amyl acetate. The products may be used for the manufacture of films, lacquers, varnishes, glass substitutes and in the production of knife handles, umbrella handles, billiard balls, penholders, tiles, electric insulating materials, artificial silk, leather and guttapercha, bandaging materials, lacquers for leather and bases for pasty colours. In examples: (1) polymerized methacrylic acid and ethyl ester, which may be polymerized by heat, light or with benzoyl superoxide, is mixed with dibutyl tartrate and dissolved in ethyl acetate. By evaporation of the solvent from the solution on bands, films or plates are obtained suitable for use as boiler linings, protective coatings and gas-tight materials. (2) Powdered polymerized methacrylic acid ethyl esters is mixed with dibutyl phthalate and pressed to a transparent mass from which plates or sheets may be obtained by slicing. (3) Methacrylic acid and ethyl esters and blown linseed oil are polymerized in presence of a solvent such as ethy acetate by means of benzoyl peroxide to yield a leather substitute. (4) Polymethacrylic ethyl ester is blended with linoxyn with or without the addition of a phenol-formaldehyde condensation product and the diphthalic acid ester of ethylene glycol monoethylether. (6) Films suitable as photographic films or foli are prepared by evaporating a solution of polymethacrylic acid ethyl ester and nitrocellulose in acetic ester. (7) A product suitable for the manufacture of oilcloth is prepared by evaporating a solution of acetone of polymethacrylic acid ethyl ester, colophonium or other natural or synthetic resins, and softeners. (8) Methacrylic acid ethyl ester, linoxyn, kaolin, and the diphthalic acid ester of ethylene glycol monomethyl ether are heated together to yield a film which may be applied to fabrics to produce oilcloth or gas-tight materials. (9) A mixture of methacrylic acid ethyl ester and nitrile is polymerized by means of benzoylperoxide, mixed with lampblack and used, in the manufacture of gramophone records. (10) A mixture of methacrylic acid methyl ester, methyl cellulose, a phenolformaldehyde condensation product and ferric oxide is polymerized in the presence of a solvent for the product such as acetone. (11) A solution of methacrylic acid methyl ester and nitrile and vinyl acetate in acetic esters is polymerized by means of sodium peroxide and mixed, after removal of the solvent, with sulphur and kaolin. (12) A mixture of a solution of cellulose acetate in acetone and polymerized methacrylic acid methyl ester in benzene is used for the production of artificial silk. (13) Lacquers are prepared from polymethacrylic acid methyl esters, dibutyl phthalate and benzene or polymethacrylic acid ethyl esters, methyl glycol phthalate, ethyl acetate and titanium dioxide. Specifications 355,712, [Group IV], 358,534, and 371,812, [Group V], are referred to. Reference has been directed by the Comptroller to Specification 395,687, [Group IV].ALSO:Plastic masses are prepared by incorporating wholly or partially polymerised methacrylic acid methyl ester or ethyl ester with one another and/or with one or more additional substance at any stage in the polymerisation which may be effected if desired in solution or in aqueous emulsion and with the aid of catalysts. The term additional substance includes softeners such as phthalic, tartaric, phosphoric and stearic acid esters, acetin, drying and non-drying oils, camphor and naphthalene, hardeners such as paraformaldehyde, plastifiers, products of methacrylic acid or its derivatives differing from those which form the basic constituents of the mass such as methacrylic acid nitrile, polyvinyl alcohols, organic and inorganic vinyl esters such as vinyl acetate and chloride, vinyl ethers, vinyl ketones, olefines and diolefines such as styrene or butadiene, cellulose derivatives such as cellulose acetates, nitrocellulose, methyl, ethyl and benzyl cellulose, natural resins, such as copal, dammar, colophonium and shellac, artificial resins such as condensation product of formaldehyde and phenol or urea, p-toluene sulphonamide resins, and fillers such as zinc oxide, ferric oxide, kaolin, talc, lampblack, organic and inorganic colouring matters. Suitable catalysts for polymerisation are oxygen or substances developing oxygen such as the peroxides of sodium, barium or hydrogen, benzoyl peroxide and uranyl acetate. Solvents include hydrocarbons of the benzine and benzene series, ethylene chloride, chloroform, trichloroethylene, chlorobenzene, alcohol, ether, dioxane, acetone, cyclohexanone, ethyl acetate and amyl acetate. The products may be used for the manufacture of films, lacquers, varnishes, glass substitutes and in the production of knife handles, umbrella handles, billiard balls, penholders, tiles, electric insulating materials, artificial silk, leather and guttapercha, bandaging materials, lacquers for leather and bases for pasty colours. In examples (1) polymerised methacrylic acid ethyl ester, which may be polymerised by heat, light or with benzoyl superoxide, is mixed with dibutyl tartrate and dissolved in ethyl acetate. By evaporation of the solvent from the solution on bands films or plates are obtained suitable for use as boiler linings, protective coatings and gas tight materials. (2) Powdered polymerised methacrylic acid ethyl ester is mixed with dibutyl phthalate and pressed to a transparent mass from which plates or sheets may be obtained by slicing. (3) Methacrylic acid ethyl ester and blown linseed oil are polymerised in presence of a solvent such as ethyl acetate by means of benzoyl peroxide to yield a leather substitute. (4) Polymethacrylic acid ethyl ester is blended with linoxyne with or without the addition of a phenol-formaldehyde condensation product and the diphthalic acid ester of ethylene glycol monoethyl ether. (6) Films suitable as photographic films or foliae are prepared by evaporating a solution of polymethacrylic acid ethyl ester and nitro cellulose in acetic ester. (7) A product suitable for the manufacture of oil cloth is prepared by evaporating a solution in acetone of polymethacrylic acid ethyl ester, colophonium or other natural or synthetic resins, and softeners. (8) Methacrylic acid ethyl ester, linoxyne, kaolin and the diphthalic acid ester of ethylene glycol monomethyl ether are heated together to yield a film which may be applied to fabrics to produce oil cloth or gas tight materials. (9) A mixture of methacrylic acid ethyl ester and nitrile is polymerised by means of benzoyl peroxide, mixed with lampblack and used, if desired, in the manufacture of gramophone records. (10) A mixture of methacrylic acid methyl ester, methyl cellulose, a phenol-formaldehyde condensation product and ferric oxide is polymerised in the presence of a solvent for the product such as acetone. (11) A solution of methacrylic acid methyl ester and nitrile and vinyl acetate in acetic esters is polymerised by means of sodium peroxide and mixed, after removal of the solvent, with sulphur and kaolin. (12) A mixture of a solution of cellulose acetate in acetone and polymerised methacrylic acid methyl ester in benzene is used for the production of artificial silk. (13) Lacquers are prepared from polymethacrylic acid methyl esters, dibutyl phthalate and benzene or polymethacrylic acid ethyl esters, methyl glycol phthalate, ethyl acetate and titanium dioxide. Specifications 355,712, 358,534, and 371,812, [Group V], are referred to. Reference has been directed by the Comptroller to Specification 395,687.ALSO:Plastic masses are prepared by incorporating wholly or partially polymerised methacrylic acid methyl ester or ethyl ester with one another and/or with one or more additional substance at any stage in the polymerisation which may be effected if desired in solution or in aqueous emulsion and with the aid of catalysts. The term additional substance includes softeners such as phthalic, tartaric, phosphoric and stearic acid esters, acetin, drying and non-drying oils, camphor and naphthalene, hardeners such as paraformaldehyde, plastifiers, products of methacrylic acid or its derivatives differing from those which form the basic constituents of the mass such as methacrylic acid nitrile, polyvinyl alcohols, or