RE-EXAMINATION OF THE CRYSTAL-STRUCTURE AND MOLECULAR PACKING OF ALPHA-NYLON-6

During studies of polymorphism of polyamides with an even number of carbon atoms, it was thought worthwhile to re-examine the crystal structure and molecular packing of the α-form of nylon 6 by more advanced instrumentation and computing facilities. X-ray diffraction measurements on mono-oriented fibres confirm that nylon 6 crystallizes in the monoclinic system, with crystallographic parameters: a = 9.71 A ̊, b = 8.19 A ̊, c = 17.40 A ̊ (fibre axis), γ = 115°, 8 monomeric units in the unit cell and space group P22. The crystal packing can be represented by parallel sheets of hydrogen-bonded antiparallel chains; the sheets are all oriented in the same sense and alternately displaced 3.73 Å along the c axis. The hydrogen bond distance is 2.98 Å. Although the structure was substantially similar to that previously found, some differences were observed; they are discussed on the basis of theoretical calculations. © 1979.