Abstract :  The desire for sustainability drives interest in the production of chemicals from carbon dioxide. The synthesis of poly(trimethylene carbonate), PTMC, by copolymerization of carbon dioxide and oxetane using organocatalysis affords a green route to this important polymer but has proven to be a very challenging process. Herein we report that the application of iodine, in combination with organic superbases provides a highly active system for the direct synthesis of PTMC from CO2 with very high levels of carbonate linkage (95 % in selectivity). Mechanistic studies reveal the in-situ formation of trimethylene carbonate which eventually polymerizes through an active chain-end process from an I2-oxetane adduct.