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The synthesis of polyamides from short‐chain aliphatic diacids, such as oxalic and fumaric acids, is difficult because of the thermal instability and volatility of the intermediates and side reactions with the polymerization media. A variety of synthetic routes to these polymers has been explored. Several aromatic polyoxamides with high molecular weight were obtained in high yield by an acid chloride vapor‐solvent‐water interfacial process. Polyoxamides of intermediate molecular weight also were obtained by preparation of oligomers from diamines and oxalic diesters and condensing these oligomers further in a thermal polymerization step. Aromatic polyfumaramides and terephthalamidefumaramides were prepared by modified solution procedures in amide solvents. Another route to polyfumaramides was the synthesis of N,N′‐bis(4‐aminophenyl) fumaramide and its use as a diamine with diacid chloride. The 1,4‐phenylene and benzidine polyfumaramides and oxamides have extended‐chain structures in solution in sulfuric, chlorosulfonic, and fluorosulfonic acids. Some of the polymers were soluble enough to yield liquid crystalline solutions. High‐tenacity high‐modulus fibers from poly(1,4‐phenylene fumaramide/terephthalamide)s are described.

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