Photodegradable Biobased Polybenzoxazines: Toward Circular Thermosets

Biobased polybenzoxazine (PBz) thermosets are emerging as a promising class of high-performance resins due to their exceptional thermal, mechanical, and chemical resistance. While coumarin-based depolymerization strategies have been successfully established in various polymers, their potential in PBz photodegradation remains unexplored. To advance their sustainability, this study introduces a novel strategy for developing chemically deconstructable PBzs that retain the performance of their conventional counterparts. We report the synthesis of a coumarin-functionalized monofunctional benzoxazine monomer (Co-fa), followed by its [2 + 2] photocycloaddition to yield a cyclobutane-bridged bifunctional monomer, (Co-fa)_di. This dimeric monomer exhibited significantly enhanced polymerizability compared with both Co-fa and traditional bisphenol A-based benzoxazines. The resulting poly(Co-fa)_di thermoset demonstrated superior thermal stability, mechanical strength, and solvent resistance. Crucially, it underwent efficient photodegradation under 254 nm UV irradiation, enabling light-triggered depolymerization into soluble fragments and subsequent recross-linking. This validates its recyclability and reusability, establishing a dynamic and responsive material platform. This work presents a scalable and versatile approach for fabricating melt-processable photodegradable PBz thermosets. The integration of coumarin-based photochemistry not only enables end-of-life management but also paves the way for the development of photopatternable materials suitable for microfabrication, electronics, data encryption, and other advanced applications.