Abstract
The crystal structure of nylon 3 was studied, and four crystalline modifications were observed. Modification I, as determined from the xโray diffraction pattern of drawn fibers, is similar to the ฮฑ crystal structure of nylon 6. The unit cell is monoclinic; a = 9.33 ร
, b = 4.78 ร
, (fiber identity period), c = 8.73 ร
, and ฮฒ = 60ยฐ. The theoretical density for nylon 3 with four monomeric units in the unit cell is 1.39 g/cm^3^, and the observed density is 1.33 g/cm^3^. The space group is __P__2~1~. The nylon 3 chains are in the extended planar zigzag conformation. Although other oddโnumbered 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 xโray 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 soโcalled smectic hexagonal form. No ฮณ crystals were found, and it appears that polyamide chains with short sequences of methylene groups cannot form crystals of this type.