Highly Heat-Resistant and Compression Strength Strong Co-cross-linked Acetylene-Based End-Capped Polyimide Foams Using a Norbornene-Based Blowing Agent

High-performance polyimide foams combining exceptional heat resistance with robust mechanical properties are increasingly in demand in lightweight applications requiring thermal stability, insulation, and flame retardancy. Herein, we present a scalable fabrication strategy for thermally stable and compression strength robust co-cross-linked acetylene-terminated polyimide rigid foams (PIRFs) through the foaming of acetylene-end-capped precursor powders using a norbornene-terminated cross-linking blowing agent (NE-CBA). A series of acetylene-terminated polyimide oligomers (AE-PIO) with controlled molecular weights were synthesized and subsequently melt-copolymerized with an m-phenylenediamine-derived cross-linking blowing agent (NE-CBA-MPD) to establish high-density co-cross-linked networks. The polyimide rigid foams (PIRFs) synthesized from acetylene-terminated precursor powders (Mn = 2264 g/mol) demonstrate exceptional multifunctional characteristics. Specifically, these materials exhibit remarkable thermal stability evidenced by a glass transition temperature (T_g) of 415.1 °C and 10% weight loss temperature (T_10%) at 572.0 °C. The mechanical performance remains robust across temperature regimes, with compressive strengths of 2.72 MPa at ambient conditions and 2.58 MPa under thermal stress at 200 °C, achieved at a low density of 140 kg/m³. Furthermore, the foams display superior insulation capabilities, maintaining ultralow thermal conductivity values (λ < 0.035 W/m·K) throughout the 25-200 °C range. Notably, the material achieves Class A fire resistance standards with a limiting oxygen index (LOI) exceeding 45%, demonstrating exceptional flame retardancy. These co-cross-linked PIRFs achieved an optimal balance between structural integrity and foam expansion, showing significant potential as advanced structural materials for extreme environments in aerospace engineering, naval architecture, rail transportation, and other specialized high-temperature applications.