FERROELECTRIC BEHAVIOR IN THIN-FILMS OF POLYUREA-5

Thin polyurea-5 films were prepared by vapor-deposition polymerization of 1,5-diaminopentane and 1,5-diisocyanatepentane. In order to invest igate the ferroelectric properties of polyurea-5, we used dielectric h ysteresis measurements. Ferroelectric hysteresis loops were observed f or the polymer thin him at room temperature. The dielectric hysteresis curve shows large polarization values above 70 degrees C, which are m uch larger than the calculated value of the spontaneous polarization i n the single crystal of polyurea-5. To evaluate the residual polarizat ion, sinusoidal electric fields with varying frequency were applied at various temperatures and the time variation of the electric displacem ent was detected by a charge amplifier. As a result, we obtained a res idual polarization of about 25 mC/m(2) at temperatures in the range of 20-70 degrees C. This value is consistent with a polyurea-5 film crys tallinity of 50%.