Controlling Oligomer Chain Length via Ultrasonic Pretreatment in Lactic Acid Polycondensation for Enhanced Poly(lactic acid) ROP

Controlling oligomer chain length in lactic acid (LA) polycondensation is crucial for producing good properties of poly(lactic acid) (PLA). This study explores the use of ultrasonic pretreatment to reduce the water content of LA, aiming to optimize the polycondensation process and enhance the quality of PLA through ring-opening polymerization (ROP). The methodology involved varying ultrasonic treatment time and power during LA pretreatment, followed by polycondensation at the optimized temperature. The study results indicate that ultrasonic pretreatment effectively reduces the water content in LA, with optimal conditions found at 90 min and 75 W, yielding the lowest water content. The polycondensation process, conducted at a gradual temperature of 150 °C followed by 180 °C, resulted in the highest yield of 92.75% and a molecular weight of 25,126 g/mol for the oligomers. Ultrasonic pretreatment enhances water removal efficiency, reduces byproduct formation, and increases oligomer reactivity, resulting in higher-purity oligomers and improved chain length control. During the ROP stage, oligomers prepared through ultrasonic pretreatment produced PLA with a higher molecular weight and crystallinity.