PIEZOELECTRIC AND DIELECTRIC-PROPERTIES OF AROMATIC POLYUREAS SYNTHESIZED BY VAPOR-DEPOSITION POLYMERIZATION

Four different kinds of aromatic polyurea were synthesized by vapor de position of monomers. As a diisocyanate, [4,4'-diphenyl methane diisoc yanate] (MDI) was used. As a diamine: [4,4'-diamino diphenyl methane] (MDA), [4,4'-diamino-3,3'-dimethyl diphenyl methane] (MeMDA), [4,4'-di amino diphenyl ether] (ODA), and [4, 4'-diamino diphenyl sulfide] (SDA ) were used. Poled thin films of P(MDA/MDI), P(MeMDA/MDI), P(ODA/MDI), and P(SDA/MDI) exhibited piezoelectric activity which remained up to almost 200 degrees C. The stable value of the piezoelectric constant f or P(ODA/MDI) was 26 mC/m(2). The piezoelectric constant plotted again st the evaporation temperature of MDI showed a maximum. where the stoi chiometrically balanced composition of MDI and diamine monomer was obt ained. The curve was sharp for P(MDA/MDI), but broad for P(ODA/MDI) an d other polyureas. It was suggested that the high probability of produ ction of balanced oligomers might be due to the longer time of residen ce of ODA molecules on the substrate.