Purification procedure dianhydrides and polyetherimides dianhydrides formed and formed from the same

摘要

Process for purifying a oxydiphthalic anhydride having the structure I, the process comprising the steps (a) to (f): ** ** Formula (a) providing a first mixture comprising at least one oxydiphthalic anhydride, at least one solvent, at least one catalyst and at least one inorganic salt selected from the group consisting of halide salts of alkali metal salts, alkaline earth metal halides and mixtures thereof, the oxydiphthalic anhydride being present in the first mixture in an amount of 10 to 30 weight percent based on the total weight of the first mixture; (B) diluting the first mixture with at least one solvent to provide a second mixture having a solids content of 10 to 30 percent based on the total weight of the second mixture; (C) filtering the second mixture at a temperature below the crystallization point of oxydiphthalic anhydride temperature and wash the solid with solvent to provide a mother liquor, a wash liquor and a third mixture of oxydiphthalic anhydride and salts; (D) hydrolyzing by adding (1) a water-soluble acid having a pKa less than or equal to the pKa of oxydiphthalic tetraacid and (2) water to the third mixture, forming a fourth mixture and heating the fourth mixture; wherein the fourth mixture is cooled to provide a solid-liquid mixture; filtering the solid-liquid mixture to provide a mother liquor and a solid component; and washing the solid component with water to provide wash liquor and a fifth mixture of oxydiphthalic tetraacid and water; and (e) closing the oxydiphthalic tetraacid ring heating the fifth mixture at a temperature and pressure sufficient to convert the oxydiphthalic tetraacid in the oxydiphthalic anhydride, forming a sixth mixture; and (f) filtering the sixth mixture to obtain substantially pure oxydiphthalic anhydride wherein said at least one solvent of step (b) is the mother liquor or wash liquor or mixtures thereof recycled from step (c) and obtained from a previous batch of first mixture.