Ultra-low dielectric constant and high thermal stability of low-crosslinked polyimide with zinc tetraamino phthalocyanine

A series of novel tetraamino phthalocyanine zinc (TAPcZn) micro-crosslinked polyimide films were successfully synthesized by the copolymerization of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 4,4′-oxydianiline. The UV–Vis, FTIR, NMR, MALDI-TOF-MS, and SEM–EDS technologies were used to demonstrate the synthesis of TAPcZn. The copolyimide films were mainly characterized via their morphologies, thermal stability, and mechanical properties. As expected, the copolyimide films inherited the optical properties of phthalocyanine compounds and showed good mechanical properties, excellent thermal stability, and flame retardancy with low content of TAPcZn (< 5.0 wt%), regularly. Smooth, uniform, and defect-free copolyimide films all showed good mechanical properties, and the tensile strength of PI with 1.52 wt% of TAPcZn reached 116.9 MPa, which is 19.7% higher than that of pure PI. In addition, as the amount of TAPcZn increases, both the residue char and the initial decomposition temperature of the copolymer film improved significantly, and the fire resistance of PI showed the same rules according to the limiting oxygen index and UL-94 tests. Amazingly, the obtained copolyimides are π-conjugate macrocycle homogeneous copolymers with excellent low dielectric properties. In particular, the 4.49 wt% TAPcZn/PI film showed an ultra-low dielectric constant of 2.326 (at 1 MHz) and a dielectric loss of less than 0.007. Therefore, the copolyimide films containing TAPcZn are highly prospective candidates as high-performance flexible substrates and dielectrics for electronics devices. Graphical Abstract: [Figure not available: see fulltext.]