Abstract: A substantially NCO-free radiation-curable prepolymer which is the reaction product of (A) an organic diisocyanate with (B) a hydroxyl-containing unsaturated monomer and (C) a polyester polyol containing 2 to 8 hydroxyl groups per molecule, the polyester polyol (C) having a number average molecular weight of 400 to 6,000 and a hydroxyl equivalent weight of 200 to 3,000 and containing a dimer acid residue derived from 9 to 70%, based on the weight of the total weight of the starting materials, of dimer acid and an alcohol residue derived from 20 to 75%, based on the total weight of the starting materials, of an ethylene oxide or propylene oxide adduct of bisphenol A with the proportion of the oxide added being 2 to 4 moles.