Dielectric relaxation in alicyclic and aromatic polyamides

We have investigated dielectric behavior of alicyclic and aromatic polyamides such as nylons BAC n, MXD n, and PXD n, obtainable by polycondensation of 1,3-bis(aminomethyl)cyclohexane (BAC), m-xylylene diamine (MXD), and p-xylylenediamine (PXD), respectively, with dicarboxylic acid of n carbon atoms and nylon mI from polymethylenediamines with n carbon atoms and isophthalic acid (I) in a frequency range of 25 Hz to 1 MHz over a wide range of temperature. Two dipole relaxation processes were observed: one of them (α relaxation) appeared at high temperatures above the glass transition; the other (β relaxation) occurred in the glassy state. The α relaxation was related with the large scale configurational rearrangement of molecular chains and featured with a large value of the relaxation strength that led to a large effective dipole moment per repeating units of polyamide chain. The large relaxation strength arose from intermolecular hydrogen bonding. Relaxation in the glassy state below the glass transition was small in size, shifting to lower temperature by absorption of moisture and was attributed to the local motion of the amide group molecules. These polyamides studied except for amorphous nylon mI showed a decrease in the permittivity due to crystallization on heating. At higher temperatures both the real and imaginary parts of the permittivity increased due to the space charge polarization caused by ionic charge carriers