To obtain a new compound having three functional groups such as a tertiary amine in a molecule and useful as a polymerization catalyst for an anionic polycondensed compound.

This derivative is a compound expressed by the formula [X is an alkyl-substituted tertiary amino, morpholyl, etc.; (CH2)n is a lower alkylene], e.g. N-(2-dimethylaminoethyl)trimellitimide. The compound of the formula is obtained by reacting a diamime compound of the formula: H2 N-(CH2)n-X with trimellitic anhydride in an aprotic organic polar solvent by heating at a room temperature-a boiling point of the solvent.