Adjustment of the average molecular weight of polyoxyalkylene glycols and polyoxyalkylene derivatives in the heteropolyacid-catalyzed polymerization of cyclic ethers and/or acetals with ring cleavage

In a process for the heteropolyacid-catalyzed polymerization of a monomeric reactant selected from the group consisting of cyclic ethers, acetals and mixtures thereof, with ring cleavage in the presence of a proton donor to produce a polymer which is a polyoxyalkylene glycol or a derivative thereof, the improvement for adjusting and maintaining the average molecular weight of said polymer to a substantially constant value, which comprises:

• setting up a calibration curve, or its equivalent mathematical equation or algorithm, for the particular polymerization system containing a specific monomeric reactant, a specific proton donor and a specific heteropolyacid, to establish the correlation between the measured electrical conductivity in said polymerization system, based upon the content of said proton donor in the catalyst phase of the reaction mixture, and the average molecular weight of the resulting polymer at a particular polymerization reaction temperature;
• and
• then carrying out said polymerization for this particular polymerization system and reaction temperature by continuously measuring the conductivity of said system during the reaction and, as determined by the calibration curve established for said system, and continuously metering an amount of said proton donor into the polymerization mixture to keep the conductivity substantially constant over the entire course of the polymerization reaction.