Structural transitions of nylons 8 9 and 12 9 heating and cooling processes were investigated using calorimetric, spectroscopic during and real time X‐ray diffraction data. These even‐odd nylons had three polymorphic forms related to structures where hydrogen bonds were established in two planar directions. Heating processes showed a first structural transition at low temperature where the two strong reflections related to the packing mode of the low temperature structure (form I) disappeared instead of moving together and merging into a single reflection, as observed for conventional even‐even nylons. The high temperature structure corresponded to a typical pseudohexagonal packing (form III) attained after the named Brill transition temperature. Structural transitions were not completely reversible since an intermediate structure (form II) became clearly predominant at room temperature in subsequent cooling processes.
A single spherulitic morphology with negative birefringence and a flat‐on edge‐on lamellar disposition was obtained when the two studied polyamides crystallized from the melt state. Kinetic analyses indicated that both nylons crystallized according to a single regime and a thermal nucleation. Results also pointed out a secondary nucleation constant for nylon 12 9 higher than that for nylon 8 9, suggesting greater difficulty in crystallizing when the amide content decreased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016
Aliphatic polyamides also called nylons are important industrial materials, valued for their good physical properties and processability. The aim of the present work is to gain insight into the structural transitions induced by temperature observed in even‐odd nylons. This kind of polyamides revealed a peculiar arrangement characterized by the establishment of intermolecular hydrogen bonds along two different directions, which contrasts with the single direction characteristic of the room temperature structure of conventional nylons. Thermal induced transitions of the studied even‐odd nylons are complex but well supported considering calorimetric, spectroscopic and real time X‐ray diffraction experiments.