Ferroelectric properties in polyamides consisted of hepta- and nonamethylenediamines

Ferroelectric properties were investigated for aliphatic polyamides, nylon 77, nylon 79, nylon 97, and nylon 99, that were prepared by polycondensation of heptamethylenediamine and nonamethylenediamine with heptan-1,7-dioic acid and nonan-1,9-dioic acid. Polyamides obtained were melt-pressed into films, followed by thermal or mechanical treatments such as quenching, slow-cooling, or uniaxial drawing. The differential thermal analysis of specimen films subjected to different treatments showed distinct thermograms in the fusion process near 480 K, indicating polymorphs in the polyamides studied. X-ray diffraction patterns also displayed differences in the diffraction peak, depending in thermal and mechanical treatments. The conspicuous dielectric hysteresis was observed for uniaxially drawn films of these polyamides. In a typical example of electric displacement-electric field hysteresis for nylon 99 as observed by the Sawyer-Tower method the remanent polarization and the coercive field were 85 mC m^-2 and 65 MV m^-1 respectively, at 30 mHz, triangular wave field with the maximum magnitude of 160 MVm^-1 , while a much smaller value of the remanent polarization was observed for quenched amorphous specimens. Poled films of these nylons exhibited the reversible pyroelectric activity and the pyroelectric coefficient was about 15 μC m^-2 K^-1 at room temperature. The piezoelectric stress constant of about 3 mC m^-2 was noted for poled drawn films near room temperature. The ferroelectric behavior in nylons 77, 79, 97, and 99 were ascribed to the parallel alignment of amide dipoles in crystalline regions in the same manner as in odd nylons consisting of ω-aminocarboxylic acid with the odd number of carbon atoms