Change with Temperature in Crystal Structures of Nylons 6, 66 and 610

It is verified from the results of infrared absorption and X-ray analyses that the hydrogen bonds between the adjacent amide groups in crystalline regions of nylons 6, 66 and 610 are not broken but the motion of amide groups in a molecule is rather restricted in the whole temperature range below respective melting points. All lattice parameters of three polyamides are determined at about 20, 80, 120, 160, 200 and 240°C. It is deduced that the length of a-axis or hydrogen bond varies little, but the large thermal expansion along b-axis causes inversion of (100) and (010) spacings for nylons 66 and 610. The difference in the melting point and in the behavior of the structure change between even polyamide and even-even one is attributed to the degree of ease with which the CH2-segment is rotated.