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. BuSnCl 3 -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 BuSnCl 3 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 SnOct 2 . With both catalysts high yields but only moderate molecular weights were obtained. SnOct 2 yielded polycarbonates having octoate end-groups, which were detected by 1 H NMR spectroscopy. (DEGC) 2 was also polymerized with Bu 2 SnO 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, Bu 2 SnO appeared to be the most reactive catalyst. Both 1 H and 13 C NMR spectra proved that all poly(diethylene glycol carbonates) prepared in this work possess an alternating sequence of ether and carbonate groups.