Tough and Photothermally Weldable Poly(Ethylene Brassylate) Nanocomposites via Reactive Chain Extension with Reduced Graphene Oxide

Abstract Developing sustainable semicrystalline polymers from biobased macrolactones remains challenging because entropy-driven ring-opening polymerization generally produces low-molecular-weight polyesters with limited mechanical performance. Herein, ethylene brassylate (EB) was polymerized via solvent-free bulk ring-opening polymerization to afford dihydroxyl-terminated poly(ethylene brassylate), followed by an isophorone diisocyanate-mediated chain-extension strategy using reduced graphene oxide (rGO) as a reactive multifunctional chain extender. Covalent incorporation of rGO into the polymer backbone through urethane linkages effectively extended the polymer chains while strengthening the polymer–filler interface and improving filler dispersion, yielding a biobased polyester hybrid with a tensile strength of ≈39 MPa and an elongation at break of ≈1100%. Notably, the optimum rGO loading required for mechanical reinforcement decreased with increasing PEB molecular weight, whereas the highest photothermal performance was achieved at higher rGO loading. Upon near-infrared irradiation, the covalently integrated rGO rapidly increased the temperature to ≈180 °C within 10 s, enabling fast welding through interfacial melting and recrystallization without relying on dynamic covalent chemistry. This work demonstrates that reactive nanofillers can simultaneously function as chain extenders and photothermal agents, providing a versatile solvent-free strategy for overcoming the molecular-weight limitation of biobased macrolactone polyesters while imparting outstanding mechanical performance and reweldability.