Enhanced mechanical and thermal performance of Crosslinked Polyimides: Insights from molecular dynamics simulations and experimental characterization for motor insulation applications

Abstract

This study evaluated the impact of various cross-linking methodologies on the properties of polyimide (PI) to gain insights into how molecular structure influences the thermal stability and mechanical characteristics of PI, thereby fulfilling the performance criteria for motor insulation applications. The investigation utilized crosslinking agents such as TAB, 4-PEPA, and NA. The relationships among different cross-linkers, molecular structures, and properties were explored using molecular dynamics simulations and further refined through experimental characterization. The results indicate that a high degree of crosslinking can significantly counteract the negative influence of Si-O-Si structures and alkyl chains on PI's thermal stability, while preserving excellent mechanical properties. The introduction of 4-PEPA and NA to form crosslinked networks significantly improved the glass transition temperature (T_g), tensile strength, and modulus of PI. Additionally, BPDA and ODA effectively compensated for the disordered crosslinking caused by NA, further enhancing the mechanical properties of NPI. Notably, the T_g of PIs with phenylacetylidene crosslinking increased significantly to 408 °C, while maintaining a tensile strength of 122 MPa, and the swelling rate in high-temperature oil solutions was reduced to 28 %. Additionally, this study introduced a novel concept of polymerization propensity(POP) and, uniquely, integrated the selection of cross-linking processes with the capacity of different monomers to bind long-chain molecules to analyze the effects of crosslinking on the polymerization process and final performances. These findings provide valuable insights into optimizing the properties of PI materials, with both theoretical and practical implications for materials science.