Epoxy-compounds obtained by epoxidizing diene-dicarboxylic acids having at least one non-terminal ethylenic group and one carboxylic group connected by a chain of carbon atoms, which may form part of a cycloaliphatic ring, and which does not exceed six in number (excluding the carbon atoms of the carboxy and ethylenic group), or functional derivatives of such acids, such as esters and amides, are polymerized, either alone or with other epoxy compounds at temperatures between 50 DEG and 100 DEG C., preferably between 20 DEG and 60 DEG C., in the presence of catalysts such as aluminium chloride, boron trifluoride, triethylamine, melamine, ethylene diamine and 2,4,6-tri-(dimethylaminomethyl) phenol, preferably in solvents such as petroleum ether, chloroform, benzene and isopropyl ether. The preferred epoxy compounds are derived from acids of the formula <FORM:0770481/IV(a)/1> wherein each A represents a divalent hydrocarbon radical having a chain of not more than 5 carbon atoms, and each R represents a hydrogen or chlorine atom or an alkyl radical having up to and including six carbon atoms, or a functional derivative of such an acid. The epoxy compounds which also have an ethylenic double bond in the molecule may be copolymerized with unsaturated monomers, e.g. vinyl monomers, such as vinyl chloride, vinyl acetate, vinyl pyridine, acrylonitrile, methyl methacrylate and styrene, using free radicalyielding catalysts, such as benzoyl peroxide. The resulting products may be cured with an epoxy-curing catalyst such as the previously described amines. In examples: (1) epoxidized octadecadiene - 7,11 - dicarboxylic acid - 1,18 is heated with a boron trifluoridephenol complex to form a solid polymer; the same epoxy compound is also heated with diglycidyl ether and 2,4,6-(trimethylaminomethyl) phenol giving a tough resin; (2) the epoxidized dimethyl ester of octadecadiene-7,11-dicarboxylic acid1,18 when heated with 2,4,6-(trimethylaminomethyl) phenol gives a tough resin; the same epoxy ester is heated with methylmethacrylate and benzoyl peroxide to give a viscous liquid which is then cured through the epoxy group by heating with the above amino phenol; (3) the epoxidized dimethyl ester of hexadecadiene6,10 - dicarboxylic acid - 1,16 when heated with the above amino-phenol gives a tough resin; [For preparation of the monomeric epoxy compounds see Group IV (b)]. Monomeric epoxidized amides and esters of dicarboxylic acids of the above type are suitable as additives for synthetic resins and cellulose derivatives. In examples: (2) a solution of vinyl chloride and vinyl acetate copolymers, in methyl ethyl ketone as solvent is mixed with a solution of the epoxidized dimethyl ester of octadecadiene-7,11-dicarboxylic acid-1,18 in the same solvent to form a lacquer. Nitrocellulose dissolved in methyl ethyl ketone is also mixed with a similar solution of the epoxy ester to form a lacquer; (3) the epoxidized dimethyl ester of hexadecadiene-6,10-dicarboxylic acid-1,16 is found to be miscible with cellulose esters or others and with vinyl chloride polymers.ALSO:The invention comprises an epoxy-compound derived from a diene-dicarboxylic acid having at least one non-terminal ethylenic group and one carboxylic group connected by a chain of carbon atoms, which chain may form part of a cycloaliphatic ring, and which does not exceed six in number (excluding the carbon atoms of the carboxyl and ethylenic groups) or a functional derivative of such an acid, by converting at least one such non-terminal ethylenic group into an epoxy group. Preferred epoxy compounds are derived from dicarboxylic acids with the formula <FORM:0770481/IV(b)/1> in which A represents a divalent hydrocarbon radical having a chain length of not more than 5 carbon atoms and each R represents a hydrogen or chlorine atom or an alkyl group having up to and including six carbon atoms, or a functional derivative of such an acid. Such acids are described in Specification 762,340. It is preferred to effect epoxidation with a peracid such as peracetic, perbenzoic or monoperphthalic acid, which may, if desired, be formed in situ by reacting an organic acid with hydrogen peroxide. A solvent such as chloroform, diethyl ether, dichloromethane, benzene or ethylacetate may be used. Up to 25 per cent of water may be tolerated in the solvent. Reaction temperatures vary between - 20 DEG and 60 DEG C., preferably between 10 DEG and 40 DEG C. The products may be used as additives to plastics, synthetic resins, lacquers or varnishes. They may be polymerized per se, copolymerized with other epoxy compounds or the mono-epoxy products may be co-polymerized with vinyl monomers. Examples are given of the preparation of unsaturated dicarboxylic acid starting materials by reacting cyclohexane or cyclopentane with hydrogen peroxide to form the corresponding dihydroxy-dicycloalkylperoxide which is then reacted with butadiene in the presence of ferrous sulphate and sulphuric acid to give octadecadienedicarboxylic or hexadecadienedicarboxylic acid together with isomeric acids, e.g. vinylhexadecene dicarboxylic acid and divinyltetradecene dicarboxylic acid, vinyltetradecene dicarboxylic acid and divinyldodecanedicarboxylic acid. The dimethyl esters may be formed by reacting the crude products with methanol and p-toluenesulphonic acid. Examples also describe the treatment with peracedic, acid in chloroform of (1) octadecadiene-7,11-dicarboxylic acid-1,18, (2) dimethyl ester of (1), (3) hexadecadiene-6,10-dicarboxylic acid-1,16, and its dimethyl ester, (4) the di-acid chloride and the diamide of the acid of (1), and (5) 4 - methylcyclohexadiene - 1,4 - dicarboxylic acid-1,2, giving the corresponding epoxidized compounds.