Visible light-driven benign synthesis of benzoxazine-sulfur copolymers: high-performance materials for...

Inverse vulcanization is an effective strategy for transforming abundant elemental sulfur into functional polymeric materials with tunable physicochemical properties for advanced applications. However, conventional methods typically require elevated processing temperatures, which are often accompanied by the evolution of toxic H₂S, and frequently yield highly crosslinked, poorly soluble networks that restrict material processability. Herein, we report a visible-light-mediated room-temperature inverse vulcanization approach for the bulk copolymerization of the benzoxazine monomer with elemental sulfur in the absence of catalysts or solvents under ambient conditions. Irradiation in the 400-500 nm range enables controlled photochemical activation of S₈, initiating radical ring-opening copolymerization (rROP). Compared with thermal and catalyst-assisted routes, the light-driven process suppresses H₂S evolution, improves solubility, and affords copolymers with distinct structural features and ∼3-fold lower thiol content. Comprehensive spectroscopic, thermal, and GPC analyses verify efficient sulfur incorporation (∼50 wt%) in the photo-triggered copolymerization, resulting in organo-sulfur networks with comparatively lower branching density, consistent with enhanced spatial and temporal regulation of polymer growth. Spin-trapping experiments in conjunction with EPR spectroscopy reveal the generation of sulfur-centered radicals under irradiation, while thiol quantification supports a controlled reaction pathway. Comparative evaluation of copolymers synthesized via different routes demonstrates that the light-mediated material exhibits superior electrochemical performance, delivering a specific capacitance of 551 ± 9 F g^-1 at 0.5 A g^-1 and retaining 97% capacitance after 2000 cycles. This visible-light-mediated inverse vulcanization strategy offers a sustainable and energy-efficient route to sulfur-rich, solution-processable copolymers with reasonable potential for fabrication on heat-sensitive substrates for advanced energy storage applications.