Research on the Synthesis and Characterization of Colorless Polyimide Based on a Novel Asymmetric Dianhydride Monomer

As is known, colorless polyimide (CPI) is usually regarded as a substrate material for transparent flexible printed circuit boards (FPCB) as a high-performance optical-grade polymer film. The problem of CPI films being nonwetting with the metal interface in the preparation of transparent FPCB urgently needs to be solved. The 6FDA and 3FPODA monomers containing flexible structures were selected to prepare CPI films with TFDB by the copolymerization reaction for improving the optical properties. Two series of copolymerized CPI films (3F6FP/C-PI-<i>x</i> and 3F6FP/H-PI-<i>x</i>) with different ratios of dianhydride were prepared by using chemical imidization and thermal imidization methods. The solubility, optical properties, thermal properties, and mechanical properties of the two series of CPI films were characterized to explore the introduction of the 3FPODA monomer on the optical, thermal, and mechanical properties of CPI films. According to the research on the two series of copolymerized CPI films, it was found that the introduction of 3FPODA and 6FDA with a copolymerization method could improve the thermal and mechanical properties of optical-grade CPI films significantly. The optical, thermal, and mechanical properties of the CPI films prepared by the chemical imidization method are superior to those of the CPI films prepared by the thermal imidization method, which indicates that the chemical imidization method is more suitable for preparing such optical-grade CPI films. Based on the most excellent comprehensive performance, the optical indicators and other key properties of the 3F6F/C-PI-4 CPI film could meet the requirements for preparing transparent FPCB.