Aromatic polyimide is a thermal- and chemical-resistant polymer with high mechanical strength, which is widely used for electrical insulation materials and aerospace materials. One of the major polyimides is made from tetramethyl biphenyltetracarboxylate, which is prepared by dehydrogenative coupling of dimethyl phthalate catalyzed by conventional [Pd(OAc)2]/[Cu(OAc)2]/1,10-phenanthroline (phen) system. However, the product yield is normally less than 10 percent. Nevertheless, this process is used for industrial production. The mechanism was largely unknown because the process needed harsh conditions (over 200 degrees Celsius), cross-linked catalyses using Pd and Cu complexes, and very diluted catalyst conditions.