Survey of the long spacing of polyamides crystallized from solution

A series of linear, aliphatic polyamides in which the number of carbon atoms in the repeat unit ranged from three to twenty‐four was crystallized from solution. All gave lath‐shaped crystallization products (usually aggregated in the form of sheaves) that were unmistakable lamellar. Sedimented mats of the crystals were examined by lowangle and wide‐angle x‐ray diffraction. Each polyamide had a characteristic layer thickness (fold length) which was determined by the length of the repeat unit and the number of hydrogen bonds in the lamella. The thickness was independent of other variables examined including crystallization conditions. The polyamides studied cover a wide range: they border on polypeptides at the one extreme and approach polyethylene at the other. For all these materials there emerged a unifying pattern which relates chemical structure directly to chain folding.