RING-OPENING POLYMERIZATION OF L-LACTIDE BY MEANS OF DIFFERENT IRON COMPOUNDS

L-lactide was bulk-polymerized in the presence of various commercially available iron compounds. The polymerization temperature was in the r ange of 140 and 230 degrees C, the monomer to initiator/catalyst ratio varied between 100 and 10 000, and the polymerization time between 30 minutes and 24 hours. Iron oxides, iron chlorides and sulfuric iron c ompounds were low efficient and are not suitable for melt polymerizati on of lactide. The oxidation state was noticed not to affect the effic iency. Ferrocene required long polymerization times and a high concent ration of the compound before a high molar mass polymer was received. Organic iron salts were also found to be efficient initiators/catalyst s, except for the hydrated iron(III)citrate. Especially iron(II)acetat e caused a rapid polymerization with a high conversion and molar mass.