Xs. Wang et al., DEPENDENCE OF PIEZOELECTRIC AND PYROELECTRIC ACTIVITIES OF AROMATIC POLYUREA THIN-FILMS ON MONOMER COMPOSITION RATIO, JPN J A P 1, 32(6A), 1993, pp. 2768-2773
Thin films of aromatic polyurea were prepared by simultaneous depositi
on of 4,4'-diamino diphenylmethane (MDA) and 4,4'-diphenylmethane diis
ocyanate (MDI) on a polyimide film substrate. By changing the evaporat
ion temperature of the monomers, the monomer molar ratio of MDA to MDI
of the deposited film was varied to yield MDA-rich, balanced, and MDI
-rich films. After poling, the balanced films exhibited the maximum va
lues of pyroelectric and piezoelectric constants, which were stable up
to 200-degrees-C. Elemental analysis confirmed that oligomers consist
ing of about five monomers were present in as-deposited films. In the
balanced films, an exothermic peak appeared at about 110-degrees-C in
the first run of DSC measurements and the IR absorption peak due to is
ocyanate groups disappeared after heat treatment. These results sugges
t that during the poling process polymerization of oligomers, which fo
rms polar urea bonds, takes place at about 110-degrees-C under a high
electric field. The large residual polarization thus produced leads to
high pyroelectric and piezoelectric activities.