Ferroelectric behavior and hydrogen bonding in polyamides

We have presented that dielectric hysteresis was observed for amorphous polyamides consisting of m-xylylenediamine (MXD) and 1,3-bis(aminomethyl)-cyclohexane (BAC) with aliphatic dicarboxylic acid with the number of carbon atoms n (nylons MXDn and BACn) and of hexamethylenediammine with six carbon atoms and isophthalic (I) acid (nylon 61) and an amorphous copolyamide of hexamethylenediamine with isophthalic and terephthalic (T) acids (nylon 61/6T). Polarized infrared spectra of poled polyamides displayed that the polar NH and C=O groups are oriented to the poling direction and revealed that the ferroelectric polarization is retained in the glassy state below the glass transition. In the present work details of the relation between the ferroelectric polarization and the infrared spectra were examined for nylon 11. The spectral intensity of the NH and C=O bands oriented to the poling direction was dependent on the remanent polarization in poled polyamides. The NH band near 3300 cm^-1 indicated strong intermolecular hydrogen bonding between the NH and C=O groups that played a major role in retaining the ferroelectric polarization in amorphous polyamides. Poled samples of amorphous polyamides exhibited piezoelectric activity. Typical value of the piezoelectric strain constant was 1.1 pCN^-1 for nylons MXD6 and 61/6T at room temperature