Cyclobis(hexamethylene carbonate), (HMC)(2), was prepared from 1,6-hexane diol and diethylcarbonate by a combined polycondensation-depolymerization procedure. The recrystallized monomer was characterized by standard methods and subjected to polymerization in bulk at 140 degrees C. Either BuSnCl(3) or SnOct(2) were used at initiator. When the reaction time was varied at constant monomer/initiator (M/I) ratio both initiators yielded the highest molecular weights at 20 h. Variation of the M/I ratio proved that the molecular weights do not parallel the M/I ratios. The best results were obtained with BuSnCl(3) as initiator : yields up to 89% and weight average molecular weights (M(w)) around 200 000 were found. In all cases the M(w)/M(n) ratio was of the order of 2. Differential scanning calorimetry measurements showing that polyHMC is a rapidly crystallizing polymer, which crystallizes even at a cooling rate of -40 degrees C min(-1) Thermogravimetrical analyses were conducted at a heating rate of 3 degrees C min(-1) under nitrogen, and under oxygen. The degradation begins around 250 degrees C and reaches its maximum around 350 degrees C. Under nitrogen, CO2, H2O and tetrahydropyran were found as low molar mass degradation products, whereas formaldehyde and the monomeric cyclocarbonate were not formed. Under an O-2 atmosphere oxidation is the main degradation process above 300 degrees C.