Purpose: The amount of residual monomers present in biodegradable poly-lactides, poly-glycolides, and copolymers thereof is often important for the behavior of a polymer in its intended application. Historically, levels of residual L-lactide, DL-lactide, and glycolide have been determined by 1H NMR and gas chromatographic (GC) methods.
Methods: Recently, we have developed a GC method that confirms the presence of additional monomers—namely meso-lactide and methyl glycolide—within copolymers of lactide and glycolide. Polymers of varying L:G ratios, molecular weights, end groups, and branching structures have been analyzed and compared by the new method.
Results: Methyl glycolide and meso-lactide were confirmed and quantified in all the tested copolymers, and the relative reactivities of each were examined.
Conclusion: We believe that meso-lactide and methyl glycolide are formed as a result of transesterification and depolymerization processes that occur during the course of the normal polymerization reaction, and that they represent underreported reactive impurities that can affect the stability of materials produced from these polymers.
John Tipton– Scientist, DURECT Corporation / Lactel Absorbable Polymers, Birmingham, Alabama
Keith Branham– Associate Director of Polymer R&D, DURECT Corporation / Lactel Absorbable Polymers, Birmingham, Alabama
John Gibson– Vice President of Birmingham Operations, DURECT Corporation / Lactel Absorbable Polymers, Birmingham, Alabama