Terephthalic acid, ethylene glycol and 2-hydroxyethyl ethyl(3-hydroxy-propyl)phosphinate (produced as in Example 11) are polymerized in a weight ratio of 1000:650:70 in the presence of zinc acetate and antimony(III) oxide under the usual conditions. To 19.6 g of 2-hydroxyethyl ethyl(3-hydroxypropyl)phosphinate are added 290 g of terephthalic acid, 188 g of ethylene glycol and 0.34 g of zinc acetate, and the mixture is heated to 200° C. for 2 h. Then, 0.29 g of trisodium phosphate anhydrate and 0.14 g of antimony(III) oxide are added, followed by heating to 280° C. and subsequent evacuation. The melt obtained (351 g, phosphorus content 0.9%) is used to injection mold test specimens 1.6 mm in thickness for measurement of the limiting oxygen index (LOI) to ISO 4589-2 and also for the UL 94 (Underwriter Laboratories) flammability test. The test specimens thus produced gave an LOI of 40% O2 and were UL 94 classified as flammability class V-0. Corresponding test specimens without 2-hydroxyethyl ethyl(3-hydroxypropyl)phosphinate gave an LOI of just 31% O2 and were UL 94 classified as flammability class V-2 only. The polyester molded article containing 2-hydroxyethyl ethyl(3-hydroxypropyl)phosphinate hence clearly has flame-retardant properties.
