Polymers of carbonic acid, 6. Polymerization of trimethylene carbonate (1,3-dioxan-2-one) with complexation catalysts

Numerous bulk polymerizations of trimethylene carbonate (1,3-dioxan-2-one, 2 ) were conducted at 90, 120 and 150°C. Tributyltin methoxide, tributyltin acetate, dibutyltin dibromide, tin(II) 2-ethylhexanotate, bismuth(III) 2-ethylhexanoate and zinc stearate were used as initiators. On the basis of GPC measurements with universal calibration, weight-average molecular weights up to approx. 22000 were found. The chemical structure of the resulting polycarbonates was examined by elemental analyses and ¹H NMR spectroscopy. In contrast to similar polymerizations of ethylene carbonate, either groups were never found. However, all polycarbonates contain a CH₂OH end-group. Furthermore, methylcarbonate, acetate, 2-ethylhexanoate or stearate end-groups were found. Cyclic oligomers were not detectable in the gel-permeation chromatograms of reaction mixtures. IR spectra indicate complexation of the carbonyl group by the initiators. The reaction mechanism is discussed.