Polymorphic forms of nylon 3

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Abstract
The crystal structure of nylon 3 was studied, and four crystalline modifications were observed. Modification I, as determined from the x‐ray diffraction pattern of drawn fibers, is similar to the α crystal structure of nylon 6. The unit cell is monoclinic; a = 9.33 Å, b = 4.78 Å, (fiber identity period), c = 8.73 Å, and β = 60°. The theoretical density for nylon 3 with four monomeric units in the unit cell is 1.39 g/cm3, and the observed density is 1.33 g/cm3. The space group is P21. The nylon 3 chains are in the extended planar zigzag conformation. Although other odd‐numbered nylon form triclinic or pseudohexagonal crystals when oriented, drawn nylon 3 crystals are monoclinic. In addition to modification I, modifications II, III, and IV were studied. Lattice spacings of modifications II and III are equal to those of modification I. However x‐ray diffraction intensities are different. Infrared spectra of those forms indicate an extended planar zigzag conformation of the chains. Modification IV is thought to correspond to the so‐called smectic hexagonal form. No γ crystals were found, and it appears that polyamide chains with short sequences of methylene groups cannot form crystals of this type.

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