Low-temperature piezoelectric and dielectric properties of aromatic polyureas prepared by vapour deposition polymerization

Abstract

Thin films of aromatic polyurea were prepared by vapour deposition of a diisocyanate tmonomer and a diamine monomer. Three kinds of aromatic polyurea were synthesized by combining 4,4'-dipheny Lnethane diisocyanate (MDI) with 4,4'-diamino-3,3'-dimethyldiphenylmethane (MeMDA), 4,4'-diaminodiphenylether (ODA), and 4,4'-diamino-diphenylmethane (MDA). After poling, for example applying a field of 120 MV m -I at 210C for 10 min, these films acquired piezoelectric activity. The piezoelectric constant (13-26 x 10 3 C m' 2) and dielectric constant (3-4) were almost constant over a temperature range between -150C and 50 C. Infrared spectra observed for as-deposited, poled and annealed films indicated that CO and NH dipoles were oriented along the poling field and that hydrogen bonds were formed between adjacent molecular chains.