Experimental

disorder in main residue; R factor = 0.054; wR factor = 0.132; data-to-parameter ratio = 14.3. The title compound, C22H28N2O6, crystallizes with four half-molecules in the asymmetric unit: each molecule is located about a crystallographic inversion centre. The central methyl-ene groups of two molecules are disordered over two sets of equally occupied sites. The crystal packing is characterized by sheets of molecules parallel to (114). Related literature For background to thermally-stable polyimides, see: Hsiao &amp