Synthesis and Properties of High Performance Functional Polyimides Containing Rigid Nonplanar Conjugated Fluorene Moieties

A diamine (WuFDA) containing vertical rigid non-planar conjugated fluorene moiety and low polarizability group (C―F) was designed and synthesized through three steps of reactions (halogenated reaction, Suzuki coupling reaction, and reduction reaction). Four kinds of high performance functional polyimides (WuFPI-6F, WuFPI-BP, WuFPI-BT, and WuFPI-PM) were thus prepared by the condensation polymerization of WuFDA with four commercial dianhydride 6FDA, BPDA, BTDA, and PMDA, respectively. The polyimides exhibited low dielectric constant, excellent thermal stability, outstanding solubility, good film-forming property, and mechanical properties. The dielectric constants of the polyimides were in the range of 2.28−2.88 (f = 104 Hz). The 5% weight-loss temperatures (Td5%) in nitrogen were in the range of 555−584 °C, and the glass transition temperatures (Tg) were in the range of 408−448 °C. The weight loss of WuFPI-BP maintaining at 450 and 500 °C for half an hour was only 0.33% and 1.26%, respectively. All the WuFPIs could be dissolved in almost all organic solvents, even chloroform. The tensile strength and tensile modulus of these films were in the ranges of 78.6−85.7 MPa and 3.1−3.2 GPa, respectively. In addition, the polyimides displayed light color with special fluorescent and resistive switching (ON-OFF) characteristics; the maximum fluorescence emission was observed at 422−424 nm in NMP solution and at 470−548 nm in film state. The memory devices with the configuration of indium tin oxide/WuFPIs/aluminum (ITO/WuFPIs/Al) exhibited distinct volatile memory characteristics of static random access memory (SRAM), with an ON/OFF current ratio of 105−106. These functional polyimides showed attractive potential applications in the field of high performance flexible polymer photoelectronic devices or polymer memory devices.