Synthesis of Aliphatic Polyurea Films by Vapor Deposition Polymerization and Their Piezoelectric Properties

Aliphatic polyurea 9 films were prepared by vapor deposition polymerization of the monomers 1,9-diisocyanatononane and 1,9-diaminononane on a glass substrate cooled to various temperatures below 0° C. When the temperature of the substrate was low, the residence time of deposited monomers was sufficiently long to allow addition polymerization. The piezoelectric constant of poled films depended on the poling electric field and the poling temperature. Three relaxation processes were observed at -150° C (γ), -50° C (β) and 100–140° C (α) in the measurement of the temperature dependence of the elastic and dielectric constants. The thermal molecular motins at these three relaxations influenced the crystallization, poling process and thermal stability of piezoelectric activity.