Synthesis and characterization of novel piezoelectric nitrile copolyimide films for high temperature sensor applications

Abstract

A series of amorphous polyimides and copolyimides containing nitrile were obtained by a two-step procedure. The first step consists on a polycondensation reaction of the 4,4’-oxydiphtalic anhydride (ODPA) with one or two aromatic diamines, namely 1,3-Bis-2-cyano-3-(3-aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-Bis(3-aminophenoxy)benzene (diamine 0CN). In the second step a thermal cyclodehydration converts each poly(amic acid) or copoly(amic acid) into their corresponding polyimide films. The piezoelectric response was improved after corona poling of the films. A maximum d33 modulus value of 16 pC·N-1 was obtained for the polymide with two cyano groups (poly 2CN) Polarization also showed time and thermal stability up to 160°C. Additionally, the thermal stability of the amorphous polyimides, (β-CN)APB/ODPA, was studied by determining the glass transition temperature (Tg) and thermal decomposition, through Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TG), respectively. The high piezoelectric response (1-16 pC·N-1), Tg (160-180ºC) and degradation temperature (315-450ºC) make such polyamides excellent candidates for their use as high temperature sensors.