A Design Strategy for Next-Generation Low-Dielectric Polyimide Materials: Regulating Aggregated Structures via Flexible Biphenyl Side Chains

Abstract The advancement of 5G and 6G communication technologies has introduced stringent requirements for the dielectric properties of the base materials employed in communication devices. Materials exhibiting a low dielectric constant (Dk) and low dielectric loss (Df) are particularly beneficial for signal transmission, as they reduce signal loss and latency. Modulating the molecular structure represents an effective approach to tailoring the dielectric characteristics of polymers. In this study, to concurrently decrease the Dk and Df values of polyimide (PI), we incorporate side chains comprising flexibly linked biphenyl liquid crystal (LC) units. These side chains increase the interchain spacing, thereby enhancing the free volume and reducing PI density, which contribute to lowering Dk. Concurrently, the flexible biphenyl LC moieties spontaneously organize into ordered stacks, promoting the ordered packing of the main polymer chains and effectively diminishing the Df. A series of PI films were synthesized to investigate the influence of side chains on the dielectric behavior. At a frequency of 17.4 GHz, the BPDA/6MPD film demonstrated a Dk value of 2.73 and a Df value of 0.0040, in contrast to values of 3.36 and 0.0318, respectively, for the BPDA/PDA film lacking side chains. This simultaneous reduction in dielectric parameters was further corroborated in the homopolymers. TAHQ/6MPD exhibited a Dk value of 2.79 and a Df value of 0.0029, while 6FDA/6MPD achieved values of 2.42 and 0.0036, respectively. The presented molecular design strategy thus offers a promising pathway for the development of high-performance, low-dielectric materials suitable for high-frequency-communication applications.