Copolymerization-designed polyimide backbones enable processable high-performance engineering plastics with strength-toughness synergy

The inherent trade-off between mechanical performance and processability in polyimides (PIs), compounded by the processing difficulties arising from their high crystallinity, limits their wider application as advanced engineering plastics. This limitation is further exacerbated by a lack of systematic investigation into the dynamic crystallization behavior of polyimide chains during the molding process, which ultimately restricts the mechanical performance of unfilled PI engineering plastics. In this work, a copolymerized polyimide backbone was designed and synthesized for fabricating high-performance bulk engineering plastics via solid-state compression molding (SCM). By integrating crystallizable rigid segments (BPDA-PPD) and flexible amorphous units (BPDA-MPD) through precisely controlled random copolymerization, we successfully address this inherent trade-off by creating a thermally persistent amorphous architecture that simultaneously enhances mechanical properties and processability. The optimized amorphous copolymer PI-PM-37 demonstrates exceptional strength-toughness synergy, achieving a tensile strength of 171.1 MPa (2.4 × ), elongation at break of 10.4 % (1.4 × ) and flexural strength of 270.2 MPa (3.3 × ) compared to the DuPont's VESPEL® SP-1. Furthermore, dynamic crystallization behavior of polyimide material during SCM was elucidated: amorphous copolymers exhibited superior melt flowability (viscosity ∼ 6558 Pa s at 380 °C) and reduced anisotropic thermal expansion (CTE anisotropy ratio ∼ 1.6), outperforming their crystalline counterparts. Multi-scale characterization revealed that balanced chain entanglement and phase homogeneity enabled simultaneous enhancement of processability and mechanical robustness. This work establishes a molecular design paradigm that concurrently addresses processability constraints and mechanical performance limitations in engineering thermoplastics. • Random copolymerization integrates crystallizable and flexible polyimide segments. • Thermally persistent amorphous structures enable superior melt flowability. • Optimized PI-PM-37 shows strength-toughness synergy (171 MPa, 10.4 %, 117.8 kJ/m 2 ). • Suppressed crystallization during SCM processing minimizes anisotropy.