Acid impurities, such as carboxylic acid-terminated polymers, are removed from macrocyclic oligoesters with ion exchange resins, resulting in macrocyclic oligoesters that are substantially free of acid impurities. The ion exchange resins can be regenerated anew and reused by washing the resins with various wash solutions. Macrocyclic oligoesters substantially free of acid impurities polymerize to much higher molecular weight polyesters than macrocyclic oligoesters containing acid impurities.