Ring‐opening polymerization of cyclic urethanes and ring‐closing depolymerization of the respective polyurethanes

The cationic ring‐opening polymerization of trimethylene urethane (tetrahydro‐2 H ‐1,3‐oxazin‐2‐one) in the melt with methyl trifluoromethanesulfonate as initiator results in poly(trimethylene urethane) in yields of ≈70%. Under the same reaction conditions 2,2‐dimethyltrimethylene urethane (5,5‐dimethyltetrahydro‐2 H ‐1,3‐oxazin‐2‐one) cannot be polymerized. Poly(2,2‐dimethyltrimethylene urethane), however, was obtained via polycondensation polymerization. Both polymers exhibit a uniform microstructure as deduced from NMR spectroscopic analysis. Ring‐closing depolymerization in the melt with dibutyltin dimethoxide or titanium tetraisopropoxide at 140°C results the respective monomers in yields of ≈90%.