Computation-Guided Screening and Thermal Stretching for Synergistic Thermal and Dielectric Regulation in Filler-Free Polyimide Films

Abstract Compared with conventional approaches to enhance thermal conductivity with inorganic fillers, intrinsic structural regulation of polymers can circumvent interfacial phonon scattering and dielectric deterioration introduced by filler addition. In this work, a two-step strategy integrating computation-assisted molecular screening and orientation-induced aggregate-state reconstruction was developed to simultaneously regulate the thermal and dielectric properties of polyimide (PI) films. By combining density functional theory (DFT), molecular dynamics (MD) simulations, and experimental characterization, six representative PI systems were comparatively evaluated, and BPDA-BAPB was identified as the optimal candidate with a balanced combination of thermal transport and dielectric performance. This film exhibited an in-plane thermal conductivity (λ∥) of 1.45 W m–1 K–1, a through-plane dielectric constant (Dk) of 2.64 at 1 MHz, and a dielectric loss (Df) of 5.37 × 10–3. The selected system was then subjected to uniaxial thermal stretching at a strain of 150%. Two-dimensional and one-dimensional wide-angle X-ray diffraction analyses revealed that stretching promoted chain extension and orientation along the stretching direction, improved in-plane packing order, and slightly increased the average out-of-plane interchain correlation distance. Owing to this aggregate-state reconstruction, λ∥ increased to 1.89 W m–1 K–1, while the through-plane Dk at 1 MHz decreased to 2.51, accompanied by a low Df of 4.63 × 10–3, a tensile strength of 307.60 MPa, and excellent thermal stability (Td5% > 550 °C). These results suggest that integrating molecular structure screening with orientation regulation provides a viable filler-free route for simultaneously improving in-plane heat transport and through-plane dielectric response in PI films.