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.

Interactions between cyclic oligo(l-lactic acid) and alkali metal ions in organic solvent

“…As we reported previously, c-OLLA has the capability of forming inclusion complexes in solvent [19]. To analyze the behavior of c-OLLA in solution, ESI-MS was conducted in the presence of various ions including sodium, potassium, rubidium, and cesium with c-OLLA in acetonitrile and aqueous solutions through the addition of chloride salts of alkali metals (Fig.…”

“…In an earlier work, we reported the extraction of cyclic oligo(L-lactic acid) (c-OLLA) using specific organic solvents [19], in which we succeeded in extracting only cyclic compounds from a mixture of linear and cyclic compounds, using specific organic solvents. In addition, c-OLLA was assumed to interact with guest molecules and form inclusion complexes.…”