We report on the preparation of hexa-functional cardanol (renewable phenolic compound) benzoxazine with a phosphazene core (C PN ) for use as a greener eco-friendly halogen-free flame retardant reactive additive for the formation of sustainable polyphosphazene polybenzoxazine networks for flame resistant applications. The structure and purity of the monomer was confirmed by Fourier transform infrared (FTIR), nuclear magnetic resonance ( 1 H-, 13 C-, 31 P NMR) and gel permeation chromatography studies. The C PN monomer showed good compatibility with benzoxazine monomer (C PN 0) as suggested by the cocuring studies. The thermal properties of the copolymer can be directly tuned by altering the composition of the monomer blend. The occurrence of phosphazene−phosphazane thermal rearrangement is also suggested for the thermal behavior (thermogravimetry analysis) at higher loading of C PN in the monomer feed ratio. An improvement in mechanical properties of the copolymer with increase in glass transition temperature was confirmed by enhancement in cross-link density as compared to neat polybenzoxazine. The reactive nature and presence of phosphazene core improved both the smoke density rating, vertical burning rating and led to higher limiting oxygen index. The FTIR and scanning electron microscopy studies of residual char supported the formation of functionalities and morphologies favorable to support the flame resistance behavior of polymer by incorporation of reactive benzoxazine with phosphazene core. Finally, we demonstrate that incorporation of cardanol phosphazene network has good compatibility with the polybenzoxazine phenolic thermosets with improvement in flame retardancy. The higher cardanol (65.7%) and phosphorus content (3.4%) and reactive nature of synthesized compound is attractive as a sustainable additive with the scope of their utilization with other polymeric resins.

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Olefin bonds participate in co-reaction with the benzoxazine functionality of the monomer and are one of the strategies used to affect the crosslink density of a polybenzoxazine network. In general, the double bond incorporation in starting material is usually catalyzed by expensive, rare earth metals affecting the sustainability of the reaction. The natural abundance of feedstocks with inherent double bonds may be a powerful platform for the development of novel greener structures, with potential applications in polymers. Here, we report the design, synthesis, and characterization of a biobased non-halogen flame retardant, consisting of naturally occurring phenols, eugenol (E), and cardanol (C). The presence of a covalently linked phosphazene (P) core allowed the synthesis of hexa-functional flame retardant molecules, abbreviated as EP and CP. The chemical structures of the synthesized EP and CP were confirmed by Fourier transform infrared (FTIR), nuclear magnetic resonance (1 H, 13 C, 31 P NMR), and single crystal XRD (only in the case of EP). Their polymerization with cardanol sourced trioxazine benzoxazine monomer, C-trisapm, was followed by FTIR, NMR, and DSC studies. The thermal stability and flame retardant properties of the hybrid phosphazenebenzoxazine copolymers was determined by thermogravimetry analysis (TGA), limiting oxygen index (LOI), vertical burning, and smoke density analyses. SEM images of the char residues of the polymers with or without the addition of reactive phosphazene molecules confirmed the intumescent flame retarding mechanism. Current work highlights the utility of sustainable origin non-halogen flame retardant (FR) molecules and their utility in polybenzoxazine chemistry.

Stimulus-responsive polymers have been used in improving the efficacy of medical diagnostics through different approaches including enhancing the contrast in imaging techniques and promoting the molecular recognition in diagnostic assays.