Crystallographic studies of nylon 4. I. Determination of the crystal structure of the α polymorph of nylon 4

The crystal structure of the α polymorph of nylon 4 has been determined from the x‐ray diffraction patterns of uniaxially oriented monofilaments. In general the crystal structure of α nylon 4 is similar to that of α nylon 6. The unit cell is monoclinic with the following dimensions: a = 9.29 ± 0.05 A., b = 12.24 ± 0.05 A., c = 7.97 ± 0.05 A., and β = 114.5 ± 1.0°. There are eight monomeric units in the unit cell. The theoretical density is 1.37 g./cc. and the observed density 1.25 g./cc. The space group is P2 1 . The nylon 4 chains are of the extended planar zigzag type, with the plane of the zigzag approximately parallel to the a axis of the unit cell. Along the a axis, every other chain is inverted—an antiparallel arrangement of chains—thus permitting complete hydrogen bonding and the formation of sheets of nylon 4 chains. Along the c axis of the unit cell, the second sheet is displaced by3/10 of the b axis, thus leading to a staggered arrangement of sheets. The sheets are held in place by van der Waals forces.