Preparation and Properties of High-Strength and High-Toughness Furan-Based Copolyamides PA(XFX) _<i>m</i> Y via a Facile Sequential Copolymerization Strategy

Biobased 2,5-furandicarboxylic acid (FDCA) is an attractive surrogate for petroleum-derived terephthalic/isophthalic acids, yet its utilization in high-performance polyamides is hindered by monomer instability, end-group deactivation, and the absence of a green synthesis strategy. Herein, a facile controllable sequential copolymerization approach is developed to synthesize furan-based polyamides with balanced mechanical and thermal properties. Specifically, XFX diamine-terminated oligomers were first prepared via an ester–amine exchange reaction in a methanol solution at room temperature (30 °C), using dimethyl 2,5-furandicarboxylate (F) and aliphatic diamine (X) as monomers, and 1-butyl-3-methylimidazolium dihydrogen phosphate ([Bmim][H2PO4]) as the metal-free catalyst. Subsequent melt polycondensation of these oligomers with aliphatic dicarboxylates (Y) afforded a series of furan-based copolyamides (PA(XFX)mY) featuring tailorable sequence structures and tunable balance of strength and toughness. By systematically regulating the alkyl chain lengths of diamines and dicarboxylates, the hydrogen-bond density and segmental rigidity of the copolyamides were precisely tuned, affording copolyamides whose initial decomposition temperature ranges from 329.8 to 386.7 °C and glass-transition temperature ranges from 42.5 to 91.9 °C. At the same time, the copolyamides exhibit a yield strength of 25.80–100.21 MPa and an elongation at break of 56.29–684.61%, performances outperform the corresponding commercial aliphatic polyamides. Molecular dynamics (MD) simulations corroborate that rigid furan rings and robust hydrogen-bond networks cooperate to enhance their thermal and mechanical properties. Overall, this work establishes a viable and sustainable route to high-performance biobased polyamides with tunable functionalities, highlighting their great potential as next-generation engineering plastics and fibers for sustainable materials engineering.