Poly(lactic acid) Polymerized by Aluminum Triflate

The ring-opening polymerization of L -lactide (LA) has been initiated by aluminum triflate (trifluoromethanesulfonate) in air using a simple glass tube at 100 °C without desiccation steps and stirring. It was found that the molecular weight of poly(lactic acid) (PLA) was increased by the addition of an alcohol as an initiator to the reaction mixture. The highest number averaged molecular weight, molecular weight distribution, and recovery of the obtained PLA at 100 °C for 6 h were 18,200, 1.20, and 73%, respectively. With the addition of a small percentage of alcohol and a long reaction time of the polymerization method with the re-addition of LA, PLA (ca. 80 wt%) with a higher molecular weight (ca. 30,000) initiated by the added alcohol was produced with PLA (ca. 20 wt%) with a lower molecular weight (ca. 2,000) initiated by impurities such as water, which exist in a monomer, initiator, or catalyst.