Method for producing an alcoholic solutions of polyetrahydrofurane that comprises terminal oh groups

In a process for preparing polytetrahydrofuran having terminal OH groups (PTHF) from the corresponding polytetramethylene ether having acyloxy end groups by transesterification with alcohols in the presence of a sodium-containing catalyst followed by passing the alcoholic PTHF solution in the presence of a catalytic amount of water directly through at least one ion exchanger to remove the sodium ions, the removal of the sodium ions is carried out in a fully continuous ion exchange unit which comprises: a plurality of ion exchange cells (Z) which are arranged on a rotary platform and are each provided with a distribution element and a collection element and a central valve (V) having a stator disk (S) and a rotor disk (R) via which the introduction and discharge of all liquid streams into or out of the ion exchange unit occurs, and feed and discharge lines from each ion exchange cell (Z) to the central valve (V).