| abstract |
The present invention relates to polytetrahydrofuran and aromatic dicarboxylic acids and / or their multistage operations at different pressure levels (one or more reaction stages at normal pressure and one or more reaction stages in vacuum) in the presence of a transesterification catalyst. A method of condensing anhydrides and / or esters thereof, preferably isophthalic acid, phthalic acid and terephthalic acid, particularly preferably isophthalic acid, to produce a polyester alcohol, and relates to a method in which a distillate is discharged from the reaction system. The process is characterized by introducing phosphoric acid in a molar ratio of catalyst to phosphoric acid of 1: 1 to 1: 3.5 after polycondensation to deactivate the catalyst. |