DETAILED DESCRIPTION I claim: 1. An ester as a composition of matter, which is soluble in an aqueous solution of a base before exposure to actinic radiation, but which polymerizes on exposure to actinic radiation and becomes insoluble in said aqueous solution, which comprises the condensation product of (A) the reaction product of (1) a phenol of the formula ##STR17## where each R represents a halogen atom, an alkyl, cycloalkyl, alkenyl or alkoxy group of 1 to 9 carbon atoms or a nitro group, each a represents zero or an integer of 1 to 4, each b represents zero or an integer of 1 to 3, each c represents zero or an integer of 1 to 5, R. sup. 2 and R. sup. 3 individually are each a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, or a phenyl group, or conjointly denote a polymethylene chain of 2 to 4 methylene groups, d and e are each zero, 1, or 2, with proviso that they are not both zero, and (2) a glycidyl ester selected from the group consisting of the polyglycidyl esters of alkanedioic acids of 5 to 10 carbon atoms, of dimerised linoleic acid, of trimerised linoleic acid, of tetrahydrophthalic acid, of 4-methyltetrahydrophthalic acid, of hexahydrophthalic acid, of 4-methylhexanydrophthalic acid, of phthalic acid, or isophthalic acid, of terephtnalic acid, of polyacrylic acid and of polymethacrylic acid; the copolymer of styrene with glycidyl acrylate, the copolymer of styrene with glycidyl methacrylate, the copolymer of methyl methacrylate with glycidyl acrylate, the copolymer of methyl methacrylate with glycidyl methacrylate, glycidyl acrylate, glycidyl methacrylate, glycidyl 3-(styryl)-acrylate, glycidyl 3-(2-furyl)acrylate, glycidyl 3-(2-pyridyl)acrylate, glycidyl 3-(3-pyridyl)acrylate, glycidyl cinnamate and glycidyl sorbate, said phenol (1) and glycidyl ester (2) being reacted at a temperature of 80. degree. to 150. degree. C. in the presence of an inert solvent. a free-radical polymerization inhibitor and a ring opening catalyst selected from the group consisting of a tertiary amine and a quaternary ammonium compound, and in a ratio of from 0
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