We report the cyclo-depolymerisations of two polyurethanes by heating suspensions in 1,2-dichlorobenzene at approximate to 180 degreesC 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 H-1 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. (C) 2004 Elsevier B.V. All rights reserved.