Cyclic Oligolactic Acid in Direct Polycondensation PLLA and Its Extraction with Organic Solvent

Abstract

The contents of poly( L -lactic acid) (PLLA) prepared by direct condensation polymerization without using a catalyst were studied. 1 H NMR and mass spectrometry analyses suggested that PLLA contained cyclic oligo( L -lactic acid) (c-OLLA) with 3–20 repeat units. Notably, only c-OLLA was extracted and isolated using hexane or cyclohexane at 4°C; thus the hydrophobicity, topology, and temperature dependence of the solubility of the obtained PLLA enabled the selective extraction of c-OLLA. The effect of cyclic compounds on direct polycondensation and the potential for c-OLLA to form molecular inclusion complexes were also discussed.