(197o) Synthesis and Degradation of Biodegradable Copolymers

Kalaga, E. A., South Dakota School of Mines and Technology
Brenza, T., South Dakota School of Mines & Technology

Over the last few decades, synthetic biodegradable polymers captured the attention of drug delivery scientists with their prominent features-biocompatibility and in vivo degradation into benign materials. Different classes of synthetic biodegradable polymers (polyesters, polyanhydrides and polyethers) have different properties (degradation method and rate, hydrophobicity, and thermal stability) which can be tailored for specific applications. The aim of this project is the optimization of polymer synthesis procedures to tailor biodegradation rate and thermal stability of innovative biodegradable polymers.

The optimization was performed by synthesizing homopolymers of poly(lactic acid) and poly(sebacic acid) by melt polycondensation. The operating parameters investigated were reaction time, temperature, pressure and the effect of acetylation of monomers on degree of polymerization. The resulting polymers were characterized by H-NMR for purity and to determine the average molecular weights of the homopolymers synthesized. Other properties such as Morphology, thermal properties, molecular structure will be studied using Scanning Electron Microscopy (SEM), Dynamic Scanning Calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Lactic acid and sebacic acid were copolymerized to obtain random copolymers. In this study, we are also studying the effect of acetylation on degree of polymerization for lactic acid and sebacic acid. Moreover, we are looking at different conjugating options for coupling blocks of homopolymers of lactic acid and sebacic acid.

To study the influence of monomer composition on biodegradation we are developing a COMSOL Multiphysics model which considers: 1) time dependent variables - number average molecular weight of long chains, number of chain scissions per unit volume, total number of hydrolysable units of all the long chain per unit volume, average degree of polymerization of all the short chains, total number of hydrolysable units of all the short chains formed; and 2) kinematic parameters - diffusion coefficient of short chains in a degrading polymer, porosity of the polymer caused by loss of short chains.

Future work will look at expanding design space of biodegradation rate and thermal stability by introducing additional monomers in the synthesis process.