Synthesis of Poly(L-lactic acid) from Lactic Acid

Lactic acid (700 g) was added into a 2 L reaction flask equipped with a mechanical stirrer and nitrogen inlet. The flask was sequentially degassed by a vacuum pump and purged with high purity Ar 3 times to ensure an Ar atmosphere during the reaction. The system was first heated to 110 °C for approximately 1 h under 400 mbr, then to 150 °C for approximately 2 h under 130 mbr, and then degassed to 40 mbr for 4 h; reduced pressure ensured the removal of water monomers. The products were finally poured out of the flask, resulting in the production of oligo (L-lactic acid) (OLLA).
The synthetic catalyst (SnCl₂·2H₂O/TSA, 0.5 wt% of gross weight) was added to the OLLA, warmed to 180 °C, and reacted under vacuum for 12 h. After the reaction was stopped, the product was removed from the reactor and cooled to room temperature naturally. The product is the PLLA sample.