Abstract: In the first stage a mixture of a crude diene adduct of 2-naphthol with maleic anhydride is polycondensed at a temperature within the range from 180.degree. to 200.degree. C. with excess glycol or with a dihydric aromatic alcohol, from 0.1 to 3 moles of the alcohol being used per 1 mole of the adduct. In the second stage, the thus obtained product is condensed at a temperature within the range from 160.degree. to 210.degree. C. with an unsaturated acid or the anhydride thereof and with the addition of an equimolar quantity (with respect to the acid or its anhydride) of glycol and/or a dihydric aromatic alcohol. The resulting product is then dissolved in styrene and copolymerized to obtain a cured polyester resin. Propylene glycol, diethylene glycol, dipropylene glycol or butylene glycol may be used as the glycol. The C.sub.2 or C.sub.