Ferroelectric properties of polyamides consisting of hepta- and nonamethylenediamines

Ferroelectric behavior was investigated for aliphatic odd 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 treatment such as quenching, slow-cooling, or uniaxial drawing. Different treatments caused distinct thermograms over the temperature range of 300 to 500 K, indicating polymorphs in the polyamides studied. Dielectric hysteresis was observed for uniaxially drawn films of these polyamides, electric field hysteresis for nylon 99 as observed by the Sawyer-Tower method, gave a remanent polarization and coercive field of 85 mCm^-2 and 65 MVm^--1, respectively, at 30 mHz triangular wave field with peak 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 with a pyroelectric coefficient of ~15 μCm^-2 K^-1 at room temperature. The piezoelectric stress and strain constants observed for drawn-poled films of nylon 99 were 4.8 mCm^-2 and 2.2 pCN ^-1, respectively, at 300 K. Polarized IR spectra of poled nylon 11 revealed that the polar amide groups preferably are oriented with the poling direction in poled specimens and that the orientation of amide dipoles contribute to the remanent polarization. The ferroelectric behavior in nylons 77, 79, 97, and 99 was ascribed to the parallel array of amide dipoles in the crystalline regions, in the same manner as in nylon consisting of ω-aminocarboxylic acid with an odd number of carbon atoms