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Synthesis and characterization of biodegradable hyperbranched poly(ester-amide)s based on natural material.

A series of novel AB3-type monomers were prepared from nontoxic natural gallic acid and amino acids. These monomers were then melt-polycondensed in the presence of MgO as a catalyst via a transesterification process at 170-190 degrees C to yield the hyperbranched poly(ester-amide)s bearing terminal acetyl groups. FTIR and NMR spectra confirmed the structures of all the monomers and polymers. The degrees of branching, estimated from 1H NMR and quantitative 13C NMR spectra, were 0.50-0.68. These hyperbranched polymers displayed moderately high molecular weights. Hydrolytic and enzymatic degradation studies were carried out in vitro at 37.5 degrees C in NaOH hydrotropic solution and in Tris-HCl buffer (pH = 8.6) containing proteinase K, respectively. The results indicate that the hyperbranched poly(ester-amide)s are degradable hydrolytically as well as enzymatically, and the rate of hydrolytic degradation increases with the pH value of the solution.