NEW PIEZOELECTRIC POLYMERS

Four kinds of piezoelectric polymers are introduced. Submicron thin fi lms of polyurea are prepared by vapor deposition polymerization. Poled films of aromatic polyurea exhibit the piezoelectric constant d(31) = 20 pC/N, which is almost independent of temperature in the range of 1 00 to 200 degrees C. Aliphatic polyureas show a ferroelectric hysteres is with a coercive field of about 100 MV/m. Single crystalline films o f a copolymer of vinylidene fluoride and trifluoroethylene were prepar ed by annealing elongated films at a paraelectric temperature range av oiding the side surface contacts. No lamella structures were present a nd the crystallinity was near 100%. The large electromechanical coupli ng factors k(33) = 0.3 and k(31) = 0.1 were observed. A large electros trictive constant R = 2.6 x 10(-17) m(2)/V-2 was observed for polyuret hane. With a de bias field of 15 MV/m, a piezoelectric constant of d(3 3) = 600 pC/N was obtained, which was larger than that of PZT. A shear piezoelectric constant d(14) = -10 pC/N was obtained for oriented fil ms of poly-L-lactic acid, which were optically active and biodegradabl e. After poling, this polymer showed the tensile piezoelectricity and pyroelectricity.