Relationship between the branching architecture and hydrolysis behavior of poly(lactic acid) with precisely controlled molecular structures

Abstract Poly(lactic acid) (PLA), a biomass-derived biodegradable polymer, has garnered considerable attention as a sustainable material and is potentially useful for membranes. However, few studies have reported the synthesis of PLA with a high weight-average molecular weight ( M w ) and narrow molecular weight distribution, and the relationship between molecular structure and hydrolytic behavior remains unclear. Herein, linear and star-branched PLAs (four- or eight-arm) with a M w of ~100,000 and a narrow molecular weight distribution ( ≤ 1.2) were synthesized by ring-opening polymerization using an organocatalyst. Films were prepared with these PLAs, and accelerated hydrolysis tests were conducted. The weight loss of the nonporous films under surface erosion conditions (pH 11 and 35 °C) for 215 h followed the order of four-arm, eight-arm, and linear PLA (1.5, 1.4, and 1.3 μg/mm², respectively). Similarly, under bulk erosion conditions (pH 9, 65 °C), the rates of decrease in molecular weights of the nonporous films after 125 h were 90% for four-arm, 80% for eight-arm, and 75% for linear PLA. Gel permeation chromatography analysis suggested that chain ends degrade faster, whereas dense regions near branching points degrade more slowly. These results indicate that four-arm PLA provides an optimal balance of these structures, promoting hydrolytic degradation under surface and bulk erosion conditions.