Phenolic compounds sourced from agro-based feedstock, viz. cashew nut shell liquid, lignin, tannin, palm oil, and coconut shell tar, have come up as sustainable alternatives to petro-based feedstock. This review explores their utility as green polymer feedstock with citation of ~ 600 references.

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.

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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.

Isomerization of double bonds from an allylic to propenyl position is generally mediated by expensive metal catalysts, demanding an additional synthetic step, thereby reducing sustainability of the reaction. However, such functionalities are inherent in naturally occurring compounds, enabling a versatile protocol for their industrial utility. Herein, we report the synthesis of benzoxazine monomers based on biosourced isomeric phenols, eugenol (E) and isoeugenol (IE), and biobased amine, furfurylamine (fa) to form E-fa and IE-fa monomer, respectively. The structural variation in the phenols revealed a differential chemical reactivity, during both the synthesis of the monomer and the polymerization reaction, confirming a significant influence of isomerism. The monomers only differ in the position of the double bond in the para-substituted propylene unit forming nonconjugated vs conjugated alkylene chain with the benzene ring containing benzoxazine in E-fa and IE-fa, respectively. The structure of the monomers was confirmed by 1 H NMR, 13 C NMR, FTIR, XRD, and mass spectrometry. The high purity of monomer was further affirmed by HPLC and DSC to demonstrate the effect of isomerization on the polymerization behavior. The extended conjugation of the double bond in IE-fa with the proximal benzoxazine ring showed a higher reactivity toward ring-opening polymerization, polymer conversion, and cross-linking reactions as supported by FTIR, NMR, and DSC-based kinetic studies. Thermal stability, mechanical properties, and adhesive analysis by TGA, DMTA, and lap shear strength measurements further supported the effect of structural isomerism of monomers with a higher potential of PIE-fa over the PE-fa network. Current work illustrates an economic, one-step, microwave-assisted, and VOC's-and catalyst-free synthesis with a simultaneous solventless processing of synthesized monomers using renewable materials as feedstocks for high-performance polymers.