Nylon 65 has a unique structure with two directions of hydrogen bonds

A new type of polyamide structure has been found for nylon 65 and it is reported here. The structure and morphology of nylon 65 lamellar crystals have been investigated using transmission electron microscopy, selected-area electron diffraction, and X-ray diffraction. Additional data have been obtained from uniaxially oriented fibers. The deduced unit cell parameters (a = 4.60 Angstrom, b = 30.95 Angstrom, c = 8.62 Angstrom, alpha = beta = 90 degrees, and gamma = 114 degrees) and the space group symmetry indicate a different structure for nylon 65 than the conventional alpha and gamma-forms of nylons. Each molecule is linked to its four neighbors by a network of hydrogen bonds made by amide groups in two different orientations. Structural modeling has been carried out using the linked-atom least-squares (LALS) methodology. The results obtained point to a particular conformation for the glutaryl units which play a decisive role in establishing such a unique structure. The temperature-induced structural changes have also been studied. A pseudohexagonal packing is found at 190 degrees C. Modifications are believed to occur without changes in the hydrogen bond system, in a way that is similar to that found in nylon 66. Fiber diffraction patterns of nylon 66 at 220 degrees C are also presented in order to confirm such conclusion.