A process for preparing polymers containing polyortho ester groups and optionally NCO groups by reacting A) and B) where A) is a polyortho ester containing at least one isocyanate-reactive group prepared by reacting at least one or more acyclic ortho esters with low molecular weight polyols having a functionality of 4-8 and a number-average molecular weight of 80-500 g/mol and B) is least one polyisocyanate. The polymers obtained from the process can be used to produce coatings, adhesive bonds and/or seals. The coating compositions can include one or more of the above-described polymers, optionally polyisocyanates, catalysts, and optionally auxiliaries and additives and can be used to coat substrates.