Design of high-performance bio-based polyamide 512/6 with exceptional toughness and dimensional stability

Bio-based polyamides are attractive candidates for sustainable engineering plastics. However, the high crystallinity of long-chain bio-based polyamides often leads to brittleness and limited impact resistance. In this study, a series of bio-based PA512/6 were synthesized via melt polycondensation by copolymerizing bio-based 1,5-pentanediamine, dodecanedioic acid, caprolactam, and 6-aminohexanoic acid. Adjusting the copolymer composition effectively regulated crystallization behavior, hydrogen-bonding density and molecular chain entanglement. FT-IR, 1 H NMR, and WAXD analyses confirmed the formation of PA512/6 dominated by the γ-crystalline phase with reduced crystal perfection. Thermal analysis revealed lower melting and crystallization temperatures than the corresponding homopolymers. Mechanical testing revealed a clear brittle-to-ductile transition as the PA6 content increased. Notably, PA512/6 0.7 exhibited an exceptional combination of tensile strength (57.9 MPa), ultra-high impact toughness (100 kJ/m 2 ) and high elongation at break (732%). Meanwhile, low water absorption was preserved, with 24-h uptake below 0.7%, together with good dimensional stability. This study provides valuable insights into the structure–property relationships of copolymerization and offers a viable strategy for developing high-performance, sustainable, bio-based polyamides.