Characterization of co-polymers of lactic and glycolic acid for supercritical fluid processing

Polymers of lactic and glycolic acid are often used for the production of injectible microparticles with controlled drug release. In the variety of processes used for the microparticle formulation, the Aerosol Solvent Extraction System (ASES) is rather special. Microparticle formation and drying take place in one step by precipitating a methylene chloride solution of the polymer in supercritical CO2. This process sets special requirements to the polymers in crystallinity, solubility, and thermal behavior that are best fulfilled by blocked copolymers. This study investigates a number of lactide-co-glycolide polymers with blocked distribution of the co-monomers by NMR spectroscopy and powder diffraction. The molar ratios are determined by 1H-NMR spectroscopy to verify the manufacturer's declarations of the purchased specimens. Additionally, the block length is determined by application of 13C-NMR. Therefore, a method reported in the literature was modified and evaluated in order to calculate the length of lactide and glycolide sequences in the polymer. Furthermore, this study looks at the impact of synthesis conditions on block length and crystallinity, and the impact of the blocking on both, crystallinity and solubility of the polymers.