Synthesis and characterization of a new biodegradable semi-solid poly(ortho ester) for drug delivery systems

Since the late 1970s, three families of poly(ortho esters) (POE) were synthesized to provide bioerodible carriers for drug delivery devices. The most recent POE is a semi-solid polymer with a viscous behavior at room temperature. Polymer synthesis by a transesterification reaction between a triol and a trialkyl ortho ester is described. The structure of the polymer was confirmed by conventional methods such as 1H-NMR, 13C-NMR and FT-IR. Information concerning average molecular weight and intrinsic viscosity was obtained respectively by GPC and viscosimetry. Residual solvents in the polymer were determined using gas chromatography. The chromatographic conditions were optimized to enable the quantification of the solvents in concentrations of a few percent. The mechanical behavior of the semi-solid POE was determined by rheometric measurements. Hydrolysis of the polymer leads to the formation of the original triol and the carboxylic acid derived from the trialkyl ortho ester used in the transesterification step. No toxicological problems associated with these compounds are anticipated.