Design, synthesis, and application of polyimide with highly intrinsic black color and low thermal expansion derived from a novel diamine containing TDPP moiety

With the rapid expansion of microelectronics, there is a surging demand for black polyimide (BPI). However, the current BPIs have shortcomings of reduced thermal and electrical capabilities, low dimension stability, and poor masking ability. Hence, the development of BPIs with outstanding overall properties is urgent. To obtain highperformance BPIs, this study introduces a chromophore called 3,6-bis(thiophen-2-yl)diketopyrrolopyrroles (TDPP), which is known for its exceptional molar extinction coefficient. A new diamine (DPPTPyDA) incorporating TDPP grafted with pyrimidine groups was synthesized. DPPTPyDA was then polymerized with pyromellitic dianhydride (PMDA) to yield black polyimide (DPPTPyPI). TDPP grafted with pyrimidine acted as a chromophore system that red-shifted and broadened the light absorption of PI. The resulting DPPTPyPI exhibited total absorption in the visible region and showed a deep black appearance. Its cut-off wavelength (lambda cut) reached 695 nm, and CIE-Lab coordinate L* was low to 1.25. DPPTPyPI also displayed a low coefficient of thermal expansion (CTE) and outstanding thermal and electrical characteristics. Density functional theory calculations demonstrated that the exceptional light absorption of DPPTPyPI primarily stemmed from the transitions from HOMO to LUMO+1 within the chromophore framework. The flexible copper-clad laminate (FCCL) fabricated from DPPTPyPI showed exceptional peeling strength and resistance to high soldering temperature. This intrinsic BPI with excellent overall properties has important applications in the field of microelectronics.