| Abstract: | Based on nuclear magnetic resonance (NMR) studies, a probable reaction mechanism was proposed for the condensation polymerization of pyromellitic dianhydride with aromatic diamines in aprotic solvent, N,N-dimethylacetamide (DMAc), to yield aromatic polyimides. The mechanism shows the essential role played by the solvent during polymerization reaction and in imidization. It explains the formation of polyamic acid and that of its high molecular weight buildup under the conditions in which solid dianhydride was added to the solution of diamine in DMAc. A prepolymer complex formation was observed, along with the main polyamic acid, when solid diamine was added to the solution of dianhydride in DMAc. The structure of the prepolymer was derived on the basis of NMR and its formation explained in the mechanism. The nature of the prepolymer was such that on treatment with anhydride it goes to polyamic acid. |
