Crystal structures in polyamides made from ω‐amino acids

Abstract The crystal structures of several polyamides made from ω‐aminocarboxylic acids have been studied at room temperature by x‐ray diffraction. Previous workers have reported structures for only two members of the series, polycaproamide (nylon 6) and polyundecamide (nylon 11). It is found that the amino acid polymers fall into two main groups. Those which are made from monomers containing an odd number of carbon atoms are reminiscent of the triclinic structures found with the even‐even diamine‐dioic acid polyamides. Those which are made from amino acids having an even number of carbon atoms recall the hexagonal structures of the odd‐odd diamine‐dioic acid polymers. Evidently the preference for one crystal form over the other depends largely upon details of the coupling between amide groups on neighboring chains. The molecular arrays found in crystallites apparently occur to an important degree in the melt. Models for the molecular arrangements are discussed. Polycaproamide, hitherto the most widely studied member of the series, appears to be anomalous in its crystal structure.