AbstractBis(2‐carb‐n‐butoxyethyl)methylphosphine oxide was prepared and condensed with 1,2‐diaminoethane, 1,6‐diaminohexane, 1,8‐diaminooctane, 1,10‐diaminodecane, and 1,12‐diaminododecane to form polyamides with an increasing number of methylene groups between the amide moieties. Polyamides made from the 1,10‐ and 1,12‐diaminoalkanes were shown by x‐ray and DSC to be semicrystalline, while those based on the 1,6‐ and 1,8‐diaminoalkanes were amorphous to x‐ray and revealed no first‐order transitions. The repeat distances of the crystalline polymers were determined, and an extended planar zigzag conformation was excluded as a possible conformation for these polymers. The thermal stability of the phosphorus‐containing polyamides, in both oxygen and nitrogen, was studied by TGA and the results were correla