Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

Despite recent advances in polybenzoxazines (PBzs), especially of sustainable origin, the lowering of the curing temperature still remains a challenge in addressing their exploration in low-temperature processing applications. Innovative iron-based catalysts which are naturally abundant, cost-effective, and with larger surface area could demonstrate a practical, economic and facile approach for the development of iron NPs–polybenzoxazine composites. Here we propose an approach to develop a composite based on smartly-capped iron nanoparticles (NPs) and agro-waste phenolic-sourced cardanol benzoxazine monomer as a one-step solution with the benefits of lowering the curing temperature and providing superparamagnetism. NPs are smartly designed with a variation in the nature of the functionality in the capping agent and are characterized by thermogravimetry analysis (TGA), Fourier transform infrared (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The NPs showed a spherical shape of ∼10 nm in size with appreciable magnetic characteristics. Both iron ions and available functionalities in the capping agent endow benefits in lowering the curing temperature of cardanol benzoxazine (64 °C), and enhancing its maximum thermal stability (34 °C), as determined by differential scanning calorimetry (DSC) and TGA, respectively. In addition, the nature of the chemical linkages in the polybenzoxazine network and the initial growth in the molecular weight of the polymer were found to be influenced by iron NPs, as supported by FTIR, nuclear magnetic resonance (¹H-NMR), UV-visible (UV-vis) spectroscopy, and gel permeation chromatography (GPC). The capping-agent-facilitated NPs distribution in the polybenzoxazine matrix was determined by atomic force microscopy (AFM). Polymer nanocomposites even with a 5 wt% loading of NPs showed good magnetic saturation and superparamagnetic behavior. The present work demonstrated a one-step solution with the incorporation of NPs in a benzoxazine monomer accounting for modification in the properties of polybenzoxazine composites with the benefits of magnetism.

Graphene, a two-dimensional material, has garnered significant interest among researchers globally due to its exceptional characteristics, including a substantial surface area, remarkable chemical stability, elevated electron mobility, and electrical conductivity. The present study explored the synthesis of reduced graphene oxide (rGO), a derivative of graphene materials, by the utilization of gallic acid as a green reducing agent. The successful reduction of graphene oxide (GO) was assessed by X-ray diffraction, UV-vis spectroscopy, Raman, Transmission Electron Microscopy (TEM), and X-ray photoelectron spectroscopy. Cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) investigations were employed to analyze the electrochemical and capacitive performance of reduced graphene oxide (rGO). The specific capacitance of rGO was determined to be 301.7 F g⁻¹ at a current density of 1 A g⁻¹. The electrode exhibits an energy density of 121.1 W h kg⁻¹ at a power density of 853.2 W kg⁻¹, and has an exceptional cycle stability of 91% after undergoing 2000 cycles. This green reduction technique is environmentally friendly and shows promising reduction of graphene oxide (GO) into reduced graphene oxide (rGO). Additionally, the prepared rGO exhibited improved electrochemical and capacitive properties showcasing its potential use in supercapacitor applications.