Sustainable Benzoxazine-Sulfur Copolymer with Dynamic Linkages: Recycling, Reprocessing, Self-Healing, and Shape Recovery (R2S2)

Improving the sustainability of thermosets is a crucial challenge in polymer science due to the overdependence on petrochemical-based feedstocks and their infusible cross-linked networks, which limit their reprocessing after use. Implementing renewable feedstocks and recyclability in the production of polymer networks paves the way for the development of next-generation sustainable materials. Polybenzoxazines (PBzs) provide a superior alternative to the traditional phenolic resin, with opportunities for incorporation of dynamic linkages owing to their high molecular design flexibility, endowing recyclability and reprocessability. Incorporating dynamic sulfide bonds in PBz can produce smart polymer functionalities with a reversible bond exchange mechanism, may provide a unique solution to address the issue of polymer end-of-life by enabling processability. The present work employs biobased cardanol-cystamine and industrial byproduct sulfur to construct a sustainable reusable thermoset poly(benzoxazine-random-sulfur) with intrinsic sulfide bonds undergoing dual exchange (associative and dissociative) mechanisms. The copolymer showed recycling (R), reshaping (R), self-healing (S), and shape recovery (S) and was explored as a load-bearing flexible film with debondable adhesive features showcasing appreciable mechanical strength. The flexibility and reprocessability of the synthesized copolymers will benefit the quest for benign by design polymers serving a wide arena of applications.