Stannous octoate is the most commonly used initiator, since it is approved by the FDA as a food stabilizer. Usage of other catalysts has been disclosed as well, among these are aluminium isopropoxide, calcium acetylacetonate, and several lanthanide alkoxides (e.g. yttrium isopropoxide).[1][5][6] The procedure followed for ring-opening polymerization is briefly outlined: a catalytic amount of initiator is added to glycolide under a nitrogen atmosphere at a temperature of 195 °C. The reaction is allowed to proceed for about two hours, then temperature is raised to 230 °C for about half an hour.