Chemically recyclable and room-temperature self-healable siloxane-imine benzoxazine vitrimers for soft magnetic actuation

Abstract

Designing multifunctional vitrimers that combine ambient self-healing, magnetic responsiveness, reprocessability and high thermal stability is gaining importance for sustainable soft materials. Herein, we report a siloxane-imine-bridged benzoxazine-crosslinked vitrimer prepared from a bio-based vanillin-furfurylamine benzoxazine (Vfa) and amine-functional polysiloxane, yielding a low-viscosity imine-functional prepolymer with intact benzoxazine rings. Thermal ring-opening polymerization (ROP) affords a soft vitrimer network with high thermal robustness (T_max ∼ 550–560 °C). Stress-relaxation measurements reveal rapid exchange with an E_a of 23 kJ mol⁻¹ and an extrapolated topology-freezing temperature (T_v) well below T_g, consistent with fast network rearrangement. Incorporation of MNPs (20 wt%) reduces the E_a to 11.4 kJ mol⁻¹ and introduces field-addressable magneto-responsive behaviour, including reversible storage-modulus switching and shear-thinning magnetorheology. The networks show hydrophobic surfaces (water contact angle 116–130°), high creep recovery (∼93%), hydrolytic stability (≥8 days), and solvent-selective dissolution enabling recasting and reshaping. Macroscopic scratch healing occurs at room temperature within 8 h for the magnetic vitrimer while it required 24 h for the neat vitrimer, with tensile testing confirming repeatable self-healing over three cycles with average healing efficiency of 92% and 88%, respectively. Finally, reinforcement with recycled carbon-fibre felt enhances mechanical strength while preserving vitrimer-based reprocessability, enabling a sustainable circular route for soft magnetic actuators and chemically recyclable composites.