Abstract: The present invention relates to trimellitic anhydride imide ester, a method of making it, and polyesters or polyamides that can be modified with trimellitic anhydride (TMA) to provide better heat resistance and mechanical properties. With the present invention, there are two processes for making TMA-ester. The first process is by charging into a reactor equimolar amounts of trimellitic anhydride and primary hydroxyalkylamine, primary carboxylalkylamine or primary carboxylarylamine, with an excess of alcohol or diol. The second process for producing the imide ester is to react two moles of TMA with one mole of a diamine of the formula H2N—X—NH2 with an excess of alcohol or diol; where X is an aliphatic, alicyclic, or aromatic group. Generally the reactor contains water as a dispersant for the reactants. The reaction time is from about 1-8 hours. The reaction temperature is from about 160° C. to about 220° C.