Abstract: It is an object of the present invention to provide a cross-linked poly(aspartic acid) product that can retain the gel shape, water absorbency, water retentivity, and other performance because it does not undergo hydrolysis over time owing to the absence of an ester bond, and a method for producing the cross-linked poly(aspartic acid) product. The cross-linked poly(aspartic acid) product according to an embodiment of the present invention is a reaction product of a polysuccinimide (PSI), a compound (A: a1-A1-a2) containing a first functional group (a1) and a second functional group (a2), and a polyfunctional epoxy compound (B). The cross-linked poly(aspartic acid) product contains a cross-linked structure (PABAP) represented by PSI-a1-A1-a2-B-a2-A1-a1-PSI, the cross-linked structure (PABAP) is partially hydrolyzed, and the second functional group of the compound (A) does not react with the polysuccinimide (PSI) or is less reactive with the polysuccinimide (PSI) than the first functional group.

Abstract: Provided is a method for producing a polysuccinimide that can simply produce a high molecular weight polysuccinimide. The method for producing a polysuccinimide is a method for producing a polysuccinimide in which a second polysuccinimide is produced using a polysuccinimide composition containing a first polysuccinimide. The method includes: performing a chain elongation reaction of the first polysuccinimide to obtain the second polysuccinimide. The first polysuccinimide has a weight average molecular weight (Mw) falling within a range of 25,000 to 50,000. The polysuccinimide composition contains dicarboxylic acid at a ratio of 1.5 mol % to 4 mol %.