Process for the continuous preparation of linear thermoplastic polyesters

Process for the continuous production of linear thermoplastic polyesters, whereina) a transesterification or esterification of aliphatic and / or aromatic dicarboxylic acids having a molecular weight <300 or their ester-forming derivatives with aliphatic and / or cycloaliphatic diols having a molecular weight <250 which additionally contain poly (alkylene oxide) glycols having a molecular weight of 400 to 4000 may be passed at a temperature above 240 ° C and under reduced pressure from top to bottom through a substantially vertical tubular precondensation zone to form a precondensate and vapor diols having a molecular weight <250,b) separating the precondensate and vaporous diols andc) discharges the precondensate from the sump, characterized in that in the step a) a temperature of 250 to 360 ° C, a pressure of 0.5 to 20 Torr and a residence time of 3 to 10 minutes and the tubular precondensation zone is provided with internals having a free surface of 0.3 to 1.5 m² / l and in the step c) the precondensate is further condensed at a temperature of 240 to 290 ° C under a pressure of 0.5 to 20 Torr and a residence time of 10 to 40 minutes and receives granulierfähigen polyester.