Synthesis And Properties Of Novel Piezoelectric Polyimide Composites

Polymer matrix piezocomposites possess high electromechanical coupling coefficient, low acoustic impedance, and an intermediate dielectric constant. Moreover, composites are flexible to develop design flexibility in a given transducer. Thus there has been a growing interest in developing novel piezoelectric ceramic/polymer composites which combine the reseasonable properties with excellent thermal stability.Polyimide is chose as the polymer matrix because of its outstanding thermal stability, chemical resistance and mechanical strength. They have been widely used in aerospace and electric industries. In our study, polyimide hybrid films containing bimetalic compounds were prepared by codoping poly(amic acid) with a bariumand titanium precursor (BTL) prepared from Ba(CH₃COO)₂, Ti(OBu)₄, and acetic acid followed by casting and thermal curing. FTIR, WAXD reults indicated that barium and titanium precursor could be completely transformed to BaTiO₃ at a temperature above 650℃.Four kinds of high-temperature polyimide/BTL composites were successfully prepared through two steps. All of related procedures were optimized. The composites showed good solubility in some common organic solvents, such as N-methylpyrrolidinone (NMP) and chloroform (CHCl₃) etc., and had excellent thermoxidative stability (5% weight loss temperature above 420℃) and high glass-transition temperatures (above 250℃), which can be attributed to the introduction of twisted and non-coplanar phthalazinone structure into the backbone of polyimides. The piezoelectric constant of these hybrid films incorporating of 15 wt % BTL were bigger than that of the pure polyimide and increased from 5.3 to 12.5 pc/N.