Polymers of carbonic acid, 21. Ring‐opening polymerization of cyclobis(diethylene glycol carbonate) by means of BuSnCl3, SnOct2 or Bu2SnO as catalysts

Cyclobis(diethylene glycol carbonate), (DEGC)2, was synthesized by polycondensation of diethylene glycol with diethyl carbonate followed by thermal depolymerization of the crude polycarbonate in vacuo. BuSnCl3‐initiated polymerizations of (DEGC)2 in chlorobenzene at 100°C gave poor results. Therefore, all further polymerizations were conducted at 145°C in bulk. Two series of polymerizations were performed with BuSnCl3 as catalyst, so that either the time was varied at constant monomer/initiator (M/I) ratio, or the M/I ratio at constant time. Two analogous series were conducted with SnOct2 With both catalysts high yields but only moderate molecular weights were obtained. SnOct2 yielded polycarbonates having octoate end‐groups, which were detected by 1H NMR spectroscopy. (DEGC)2 was also polymerized with Bu2SnO at M/I = 200 or 500 with variation of time. The highest yields and molecular weights were obtained at the shortest time, whereas longer times caused rapid depolymerization. Therefore, Bu2SnO appeared to be the most reactive catalyst. Both 1H and 13C NMR spectra proved that all poly(diethylene glycol carbonates) prepared in this work possess an alternating sequence of ether and carbonate groups.