Synthesis of pendent carbonate ester groups onto aliphatic polycarbonates

The reactions of mono-α-bromo ethyl carbonate with carboxylic acids, amines, and alcohols were investigated as a model tool for the preparation of novel aliphatic polycarbonate esters. The formation of the corresponding carbonate ester, carbamate, and carbonate derivatives, showed that of the three types of groups chosen to react with α-bromo ethyl carbonate, only the carboxylate anions displaced the bromo group to form the corresponding α-carbonate ester bond (R-COO-CH(CH₃)-O-CO-CH ₂-CH₃). This approach was applied to the synthesis of pendent carbonate ester groups onto aliphatic polycarbonates. The synthetic pathway involved partial bromination of polytrimethylene carbonate (PTMC) to Br-PTMC, which was then reacted with benzoic acid or acetic acid to form the corresponding benzoate and acetate pendent polycarbonate, respectively. The hydrolysis of Br-PTMC and its derivatives as possible biodegradable polymers were investigated. The benzoate group was more susceptible to hydrolysis than the carbonate group hence degradation of the ester catalyzed the hydrolysis of the polymer and improved its biodegradability. The decrease in molecular weight, the release profile for benzoic acid from the grafted polymer and the degradation of Br-PTMC, AC-PTMC and PTMC, in terms of the change in pH, were evaluated.