Ar and R are preferably selected so that the hydrolysis products of the polyanhydrides have a chemical structure resembling pharmaceutically-active materials, particularly salicyclates such as aspirin, non-steroidal anti-inflammatory naphthyl or phenyl propionates such as ibuprofen, ketoprofen, naproxen, and the like, or other aromatic anti-inflammatory compounds such as indomethacin, indoprofen,