Poly(ethylene ether carbonate) polyols have been prepared from ethylene carbonate and monoethylene glycol (MEG) or diethylene glycol (DEG) using sodium stannate trihydrate as catalyst. When these polyols (catalyst removed) are heated to elevated temperatures (< 180°C) at reduced Pressures, volatile impurities are removed, as distillate, molecular weight builds in a controllable manner. This is thought to be a transesterification process in which [BOND]OC(O)CH2CH2OCH2CH2OH end groups on one molecule react with carbonate moieties on a second molecule with loss of DEG. These advanced polyols form rapidly with high CO2 retention and relatively low polydispersity. This process has been characterized by size exclusion chromatography, quantitative capillary gas chromatography of the distillates, 13C-NMR of the products, and alkaline hydrolysis of the products followed by quantification of the resultant glycols. The advanced polyols are largely alternating copolymers of DEG and CO2. They are valuable polyols for polyurethane fabrication.