Compositional Analysis of Biodegradable Polyphosphoester Copolymers Using NMR Spectroscopic Methods

Abstract

The chemical composition and quantitative molar ratios among all components of biodegradable polyphosphoester copolymers of DL-lactide and ethylphosphate were determined by a comprehensive set of NMR spectroscopic methods. The polyphosphoester copolymers studied were synthesized using condensation polymerization of oligomeric DL-lactide prepolymers and ethyl dichlorophosphate. Conclusive identification of the chemical shift patterns of all functional groups in the copolymers required additional NMR methods such as 31P-NMR and two-dimensional 1H-1H COSY NMR, in addition to the synthesis and comparative NMR analysis of model compounds possessing identical phosphoester linkages in the polyphosphoester co-polymers. For the polymers synthesized using the bulk polycondensation process, 1H-1H COSY NMR analysis revealed the presence of a small amount of side products that were undetected by 1H-NMR alone. These side reactions most likely occurred between the pendant ethoxy group of the phosphoesters and the hydrogen chloride gas generated in the bulk polycondensation process. 31P-NMR spectra of the copolymers revealed a consistent triple-peak pattern characteristic of phosphoesters linked to a racemic mixture of D,L-lactides. These results offered new insight into the side reactions occurring in bulk polymerization of polyphosphoesters and provided a powerful tool of characterizing complex biodegradable polymers. © 2003 Wiley Periodicals, Inc.