To obtain a polysuccinimide of high quality within a short time in high purity by thermally polymerizing aspartic acid in the presence of a hydrochloric acid aqueous solution and/or a hydrogen chloride gas.
This high-molecular-weight polysuccinimide is obtained by adding, to aspartic acid, a hydrochloric acid aqueous solution having a concentration of 35% and/or a hydrogen chloride gas used an acid catalyst in an amount of 0.1 to 0.95 equivalents relative to the aspartic acid, and heating for polycondensation reaction at a normal pressure or under a reduced pressure of 600 to 1 mmHg in a stream of nitrogen at 120 to 220°C for 5 to 20 hours. Where the hydrochloric acid aqueous solution is used for the polycondensation reaction, aspartic acid is introduced into the hydrochloric acid aqueous solution and reacted. On the other hand, where a hydrogen chloride gas is used, aspartic acid is introduced into an organic solvent and/or water, after which a predetermined amount of a hydrogen chloride gas is absorbed therein for the reaction. Examples of the solvent employed for the absorption upon use of the hydrogen chloride gas include alcohols such as methanol and the like, aromatic hydrocarbons such as toluene and the like, aromatic halogenated hydrocarbons such as dichlorobenzene and the like, acetic esters such as ethyl acetate and the like, and the like.
SUKEGAWA MAKOTO
IRISATO YOSHIHIRO
TAMAYA HIROAKI
