| abstract |
A method of preparing a purified dianhydride is provided comprising the steps of preparing a first mixture comprising water, at least one inorganic acid, and at least one dianhydride, said dianhydride comprising at least one impurity which is soluble in aqueous acid; heating said first mixture until substantially all of said dianhydride is converted to a tetraacid comprised in a second mixture; filtering at least a portion of said second mixture to provide a solid tetraacid and a filtrate, said filtrate comprising at least a portion of said impurity; and heating the tetraacid provided in a solvent with concurrent distillation of water to provide a third mixture comprising a purified dianhydride and a solvent. |