Polymerizable esters are obtained by reacting acrylic, methacrylic, or alpha-haloacrylic acid or an ester-forming derivative thereof with a dihydric polyester formed from a dihydric alcohol, the hydroxyl groups of which are separated by a chain of x atoms, and a dicarboxylic acid, the carboxyl groups of which are separated by a chain of y atoms, x + y being 3 or more, or ester-forming derivatives thereof, a mixture of such esters, or a mixture of one or more of such esters and one or more dihydric alcohols, said ester or mixtures having between 2.5 per cent and 25 per cent by weight hydroxyl groups. In making the dihydric polyesters, the dihydric alcohol is employed in molecular excess. Dicarboxylic acids specified are maleic, adipic, sebacic, phthalic, terephthalic and diglycollic, and dihydric alcohols are ethylene, trimethylene, pentamethylene and diethylene glycols. In the preparation of the dihydric polyesters, and in their reaction with the acrylic acid or derivative, water or alcohols produced may be removed by azeotropic distillation, using, e.g. benzene or trichlorethylene. An esterification or ester - interchange catalyst, such as hydrochloric, sulphuric, or toluene sulphonic acids, or sodium methoxide may be employed, or combined catalysts and polymerization inhibitors such as hydroquinone disulphonic acid (see Specification 606,685, [Group IV (b)], may be used, together with a stream of air. A polymerization inhibitor such as hydroquinone may be present when solvent is distilled off from the reaction product. The reactions are preferably carried out in glass or enamel-lined vessels. The products may be polymerized in presence of a polymerization catalyst, and for this purpose they may be mixed with other unsaturated substances which copolymerize or polymerize simultaneously, e.g. di(allyl glycollyl) succinate, glycol dimethacrylate, methyl methacrylate, butyl methacrylate, vinyl chloride, vinyl acetate or styrene, maleic anhydride, or polyesters of maleic or fumaric acid and dihydric alcohols. Dyes, pigments, fillers, reinforcing materials and thermoplastic polymers may also be incorporated when the products are polymerized. The products may be used to bond fibrous materials by polymerization, e.g. in producing laminated products. In examples, methacrylic acid is reacted with the product obtained from ethylene glycol and (1) phthalic anhydride; (2) adipic acid; (3) sebacic acid; (4) maleic anhydride. Also in examples, methacrylic acid is reacted with (5) the ester from diethylene glycol and maleic anhydride, and (6) the ester from pentane diol and maleic anhydride; the ester from ethylene glycol and phthalic anhydride is reacted with (7) methyl chloracrylate, and (8) methyl methacrylate. Also in examples, the product of (1) above is (9) mixed with benzoyl peroxide and butyl methacrylate and the mixture used to produce laminated products from glass fibre cloth or from canvas, or (10) is mixed with benzoyl peroxide and polymerized in a glass cell. Specifications 423,790 and 595,881 also are referred to.ALSO:Polymerisable esters are obtained by reacting acrylic, methacrylic, or alpha-haloacrylic acid or an ester-forming derivative thereof with a dihydric polyester formed from a dihydric alcohol, the hydroxyl groups of which are separated by a chain of x atoms, and a dicarboxylic acid, the carboxyl groups of which are separated by a chain of y atoms, x+y being 3 or more, or ester-forming derivatives thereof, a mixture of such esters, or a mixture of one or more of such esters and one or more dihydric alcohols, said ester or mixtures having between 2.5 per cent and 25 per cent by weight hydroxyl groups. In making the dihydric polyesters, the dihydric alcohol is employed in molecular excess. Dicarboxylic acids specified are maleic, adipic, sebacic, phthalic, terephthalic, and diglycollic, and dihydric alcohols are ethylene, trimethylene, pentamethylene, and diethylene glycols. In the preparation of the dihydric polyesters, and in their reaction with the acrylic acid or derivative, water or alcohols produced may be removed by azeotropic distillation, using, e.g. benzene or trichlorethylene, an esterification or ester-interchange catalyst, such as hydrochloric, sulphuric, or toluene sulphonic acids, or sodium methoxide may be employed, or combined catalysts and polymerisation inhibitors such as hydroquinone disulphonic acid (see Specification 606,685) may be used, together with a stream of air. A polymerisation inhibitor such as hydroquinone may be present when solvent is distilled off from the reaction product. The reactions are preferably carried out in glass or enamel-lined vessels. The products may be polymerised in presence of a polymerisation catalyst, and for this purpose they may be mixed with other unsaturated substances which co-polymerise or polymerise simultaneously, e.g. di-(allyl glycollyl)succinate, glycol dimethacrylate, methyl methacrylate, butyl methacrylate, vinyl chloride, vinyl acetate, or styrene, maleic anhydride, or polyesters of maleic or fumaric acid and dihydric alcohols. Dyes, pigments, fillers, reinforcing materials, and thermoplastic polymers may also be incorporated when the products are polymerised. The products may be used to bond fibrous materials by polmerisation, e.g. in producing laminated products. In examples, methacrylic acid is reacted with the product obtained from ethylene glycol and (1) phthalic anhydride; (2) adipic acid; (3) sebacic acid; (4) maleic anhydride. Also in examples, methacrylic acid is reacted with (5) p the ester from diethylene glycol and maleic anhydride, and (6) the ester from pentane diol and maleic anhydride; the ester from ethylene glycol and phthalic anhydride is reacted with (7) methyl-a -chloracrylate, and (8) methyl methacrylate. Also in examples, the product of (1) above is (9) mixed with benzoyl peroxide and butyl methacrylate and the mixture used to produce laminated products from glass fibre cloth or from canvas, or (10), is mixed with benzoyl peroxide and polymerised in a glass cell. Specifications 423,790 and 595,881 also are referred to.