Castor oil-derived sulfur-containing copolyamides as functional materials for sustainable polymer engineering

The design of sustainable polymers that combine high strength, ductility, and compatibility with existing bioplastics remains a critical challenge. Here we report a castor-oil-derived sulfur-containing copolyamide (PAS-X) synthesized via thiol-ene click reaction followed by melt polycondensation, providing a scalable route for high-performance bio-based materials. The incorporation of flexible thioether linkages and strongly hydrogen-bonding amide motifs enables precise control over chain mobility, crystallinity, and mechanical response. The optimized copolymer, PAS-50, exhibits a tensile strength of ≈39.8 ± 2.4 MPa and a work-to-fracture of ≈120.7 ± 8.0 MJ m −3 . When blended with polylactic acid (PLA) at low loadings (≤5 wt%), PAS-50 forms robust hydrogen-bond-mediated interfaces that induce a brittle-to-ductile transition, increasing fracture toughness from 9.2 MJ m −3 to 60.7 MJ m −3 without sacrificing yield stress. This work establishes a chemically simple and industrially viable approach to transform renewable plant-oil derivatives into multifunctional polyamides, offering a general framework for hydrogen-bond-assisted design of strong and tough bio-based polymers.