Synthesis of Polyanhydride. I. Mixed Anhydride of Aromatic and Aliphatic Dibasic Acids

Copolymerization reactions of mixed anhydrides of aliphatic and aromatic dibasic acids have been investigated. It has been shown that a polyanhydride of regular structure was obtained from diacid chlorides and dibasic acids in organic medium, and that polyanhydrides of random structure were obtained from the mixed aromatic and aliphatic dibasic acids. A polyanhydride having its melting point at 225°C was prepared for terephthalic acid and adipic acid copolymer of regularly linked structure and that having its melting point at 215°C for terephthalic acid and sebacic acid copolymer. It was found that the stability of copolymer towards hydrolytic and thermal degradations was greater for those with regularly linked structure than for a polyanhydride of random structure. The mixed polyanhydrides of random structure were prepared and the diagram of composition versus melting point was obtained. The mole fractions of the two acid components were found to be 35∼40 mol. % of terephthalic acid and 60∼65 mol. % of aliphatic dibasic acid for copolymers melting at 220 to 240°C. It has further been shown that aliphatic and aromatic dibasic acids furnish a series of copolymers in which the solubility decreases and the melting point and the degree of crystallinity increase as the proportion of aromatic dibasic acid is increased.