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-6 F, WuFPI-BP, WuFPI-BT, and WuFPI-PM） were thus prepared by the condensation polymerization of WuFDA with four commercial dianhydride 6 FDA, 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 = 10～4 Hz）. The 5% weight-loss temperatures（Td 5%）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 10～5-10～6. These functional polyimides showed attractive potential applications in the field of high performance flexible polymer photoelectronic devices or polymer memory devices.