Preparation and properties of poly(aspartic acid)-based hydrogel

High molecular weight polysuccinimide (PSI), as a precursor of poly(aspartic acid), was prepared by thermal polycondensation of L-aspartic acid. The molecular weight was high when phosphoric acid was used as a catalyst, and the ratio to monomer was 0.75:1 (phosphoric acid : L-aspartic acid). Attempted solution polymerization in various sulfolane/mesitylene mixtures gave only low molecular weight polymers. By the post polymerization of PSI using DCC as a condensing reagent, the molecular weight of PSI could be increased to some extent. Hydrogels was prepared by crosslinking reaction of PSI with diamine, followed by hydrolysis with NaOH either in water or in DMF solution. As high as 104 g water/g-polymer absorption could be obtained from the hydrogel prepared with 3mol% of hexamethylenediamine.