A method of preparing a poly(glycolic acid) (PGA) from the C1 feedstocks carbon monoxide and formaldehyde or its equivalent. By controlling the comonomer feed ratios and the polymerization temperatures, high quality PGA can be prepared. The method is extended to copolymers of PGA where alkylene oxides or cyclic ether comonomers are included into the polymerization mixture with the C1 monomers to yield polyester-ether thermoplastics.