Polymers of carbonic acid 18: polymerizations of cyclobis(hexamethylene carbonate) by means of BuSnCl3 or Sn(II)2-ethylhexanoate

Abstract

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°C. Either BuSnCl3 or SnOct2 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 BuSnCl3 as initiator: yields up to 89% and weight average molecular weights (Mw) around 200 000 were found. In all cases the Mw/Mn 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°C min−1. Thermogravimetrical analyses were conducted at a heating rate of 3°C min−1 under nitrogen, and under oxygen. The degradation begins around 250°C and reaches its maximum around 350°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 O2 atmosphere oxidation is the main degradation process above 300°C.