Cyclo-depolymerisations of polyurethanes to give macrocyclic oligomers: entropically driven ring-opening polymerisations of the macrocyclic oligomers produced

Abstract

We report the cyclo-depolymerisations of two polyurethanes by heating suspensions in 1,2-dichlorobenzene at ≈180 °C in the presence of 2 mol% of either tetrabutylammonium tetraphenylborate, titanium tetraisopropoxide, a dioxastannane, sodium hydride or boron trifluoride ethererate as the catalyst. Each reaction gave an homologous series of macrocyclic oligomers: one with 20 ring atoms per repeat unit and one with 26 ring atoms per repeat unit. The mixtures of cyclics were characterized by matrix assisted laser desorption ionisation time of flight mass spectrometry and by gel permeation chromatography. In each case the cyclic monomer was isolated and characterized by infrared and 1H NMR spectroscopy, matrix assisted laser desorption ionisation time of flight mass spectrometry and elemental analysis. Some entropically driven ring-opening polymerisations of the pure macrocyclic monomers and of the series of macrocyclic oligomers were investigated.