31 litres of methylene chloride are added to a solution, rendered inert with nitrogen, of 3903.9 g (17.1 mol.) of bisphenol A, 182 g (0.9 mol.) of 4,4′-dihydroxydiphenyl ether and 1584 g (39.6 mol.) of sodium hydroxide in 31 litres of water. In a one-step procedure, 108.14 g (0.72 mol. or 4 mol. % relative to bisphenol A) of p-tert.-butylphenol (BUP) are added as chain terminator. At a pH value of 13.4 and at 21° C., 3560 g (36 mol.) of phosgene are added in the course of 1 hour and 20 minutes. In order to prevent the pH value from falling below 12.6, 25% sodium hydroxide solution was added during the phosgenation. When the phosgenation is complete, and after rinsing with nitrogen, 24.7 ml (0.18 mol., 1 mol. % relative to bisphenol A) of n-ethylpiperidine are added as catalyst, and stirring is then carried out for one hour. The aqueous phase is separated off, and the organic phase is acidified with phosphoric acid and washed with distilled water until neutral and free of salt. After replacing the solvent with chlorobenzene, the product is extruded at 290° C. using an evaporating extruder.
