Synthesis and Properties of Polyanhydrides Containing Urethane Bonds in the Main Chain†

Polyanhydrides containing urethane linkages in the main chain have been synthesized from bis(4-carboxyphenyl-amino-carbonyloxy) alkanes and oxyalkanes by melt polycondensation of the corresponding acetic mixed anhydrides. Weight-average molecular weights up to 27,000 were obtained. All polymers have been characterized by 1H-NMR and IR spectroscopy as well as by TG analysis. The dicarboxylic acid monomers were prepared by reaction of 4-aminobenzoic acid with suitable bis(chloroformate)s. Hydrolysis of the synthesized polyanhydrides (pH 7.4; 37°C) proceeds with cleavage of anhydride bonds and maintenance of urethane linkages to give nearly constant degradation rates. Comparative hydrolysis studies including poly(amide-anhydride)s and poly(esteranhydride)s having analogous structures are described. The release of 4-nitroanisole as a drug model from a polyanhydride matrix followed the polymer degradation to a large extent.