Dual-Functional Benzoxazines With Isopropenyl and Disulfide Linkages for Ambient-Temperature Polymerization

We report a sustainable, catalyst-free route for the synthesis of organo-soluble, sulfur-containing biobased polybenzoxazines, employing dithiothreitol (DTT) as a mild reducing agent At ambient temperature, the reaction between an alkenyl-disulfide-functionalized benzoxazine monomer and an in situ generated thiol proceeds through concurrent thia-Michael addition and oxazine ring-opening polymerization (ROP). The synergistic influence of disulfide bond reduction and π-conjugation effectively lowers the ROP activation barrier to room temperature, promoting efficient network formation without the need for external heat or catalysts. Among the studied monomers, the isoeugenol-derived monomer bearing an isopropenyl side chain exhibited higher reactivity, with ∼75% monomer conversion, compared to its eugenol analogue, which achieved only ∼35% conversion, attributed to improved electron delocalization and enhanced Michael acceptor characteristics. GPC and DOSY data confirmed oligomer formation, while time-dependent NMR and HRMS confirmed a thia-Michael-assisted ring-opening mechanism via thiazolidine intermediate. The presence of disulfide and isopropenyl chain provides a dual-activation approach that represents a low-energy alternative to traditional thermosets, offering room-temperature, solution-processable polymers suitable for applications in coatings, adhesives, biomedical devices, electronics, and reprocessable materials.