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%.