Patent attributes
A method for purifying dianhydrides is provided. In one aspect, purified oxybisphthalic anhydrides, intermediates useful in the preparation of polyetherimides are provided. In one embodiment, a first solution containing a dianhydride compound, a solvent, and a phase transfer catalyst is contacted with a solid inorganic adsorbent material having a total pore volume of about 0.5 milliliters/gram or greater and a cumulative pore volume distribution of about 20 percent or greater of particles having a pore diameter in a range between about 3 nanometers and about 20 nanometers. The solution containing the dianhydride compound is then separated from the solid inorganic adsorbent material to provide a purified dianhydride compound which is substantially free of the phase transfer catalyst. The purification technique is especially valuable for preparing high purity oxybisphthalic anhydrides, such as 4,4′-oxybisphthalic anhydride (4,4′-ODPA), which are substantially free of residual phase transfer catalyst.
