Cardanol, a sustainable origin phenol, was utilized as a reactive diluent to mediate solventless Mannich-type condensation reaction with para-formaldehyde and primary aromatic amines to form a homologous series of benzoxazine (Bz) monomers namely C-a, C-ddm, C-trisapm and C-tetraapm which differ in their degree of oxazine functionality as mono-, di-, tri- and tetra-oxazine respectively. A strong correlation is reflected between the number of oxazine rings in the monomer and the polymerization behavior, thermo-mechanical transitions, and properties of the polybenzoxazine synthesized. The monomer structure was confirmed by FTIR, 1H-, 13C-NMR spectroscopy and mass spectrometry. The curing, rheological, thermo-mechanical and thermal properties were determined using DSC, FTIR, rheometer, DMTA, LSS and TGA studies. The curing characteristic due to ROP of Bz monomers was supported both by DSC and FTIR studies. The presence of neighboring oxazine group in monomers (C-a to C-tetraapm) strongly attenuates the curing temperature (Ti = 225-140°C), enhances Tg, thermal stability, and mechanical properties. Interestingly, DFT calculations also supported the lowest curing temperature for highest oxazine functionality monomer (C-tetraapm). The interplay between the degree of oxazine functionality in the monomer; extent of H-bonding and crosslink density values in sustainable origin synthesized polybenzoxazines is suggested. The thermoset showed an increasing trend (PC-a < PC-ddm < PC-trisapm < PC-tetraapm) in Tg (58-109°C), thermal stability (355-391°C), char yield (13-37\%), LOI (23-31) and storage modulus (3.6-66.5 MPa) values. The monomers are liquid to semi-viscous paste at room temperature and showed potential for solventless processing in adhesive applications. © 2015 Royal Society of Chemistry.

Bimlesh Lochab

Chemistry

(SoNS) School of Natural Sciences

Shukla S.

Mahata A.

Pathak B.

Fulltext

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Shiv Nadar University

RSC Advances

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 (1H, 13C, 31P NMR), and single crystal XRD (only in the case of EP). Their polymerization with cardanol sourced tri-oxazine benzoxazine monomer, C-trisapm, was followed by FTIR, NMR, and DSC studies. The thermal stability and flame retardant properties of the hybrid phosphazene-benzoxazine 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. © Copyright © 2020 Appavoo, Amarnath and Lochab.

Frontiers in Chemistry

Cardanol and Eugenol Sourced Sustainable Non-halogen Flame Retardants for Enhanced Stability of Renewable Polybenzoxazines

Polybenzoxazines are evolving as a new class of phenolic resins with a tremendous amount of applications. The ease of structural designing, synthetic procedure, and polymerization reactions are attractive to affect their properties ensuing as an effective substitute for many existing polymers. The nonrenewable origin, toxicity, and increasing cost of petro-based raw materials are alarming issues. Therefore, the emergence of sustainable benzoxazines, especially based on naturally abundant, agro-waste origin cardanol is encouraging as it allows both solventless synthesis of monomers and processing to form highly thermally stable thermoset resins. The inherent functionalities in cardanol benzoxazine provide a platform for further structural modifications to advance their applications as adhesives, composites, and energy storage devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Macromolecular Chemistry and Physics

Cardanol Benzoxazines: A Versatile Monomer with Advancing Applications

Biobased phenols and amines are attractive feedstock in rapid emerging polybenzoxazine thermosets. Renewable benzoxazines are mainly monofunctional due to structure limitation of raw materials, especially amines. Here, we report fully naturally sourced bifunctional benzoxazines by a simple one-step solventless microwave synthesis using cardanol/guaiacol- and carbohydrate-based isomannide diamine (ima). Chirality of ima led to complicated 1H NMR spectra of monomers. Heteronuclear single-quantum coherence (HSQC) and two-dimensional correlated spectroscopy (COSY) NMR and single-crystal X-ray diffraction confirmed the structure and formation of monomers. Polymerization and thermal stability of monomers and polymers were found to be either better than or comparable to widely studied fully and partly petro-based polybenzoxazines. Incorporation of rigid core ima in fully biobased polybenzoxazines showed a glass-transition temperature comparable to their petro-based aromatic diamine counterparts. Exploration of adhesive behavior revealed that the designed polybenzoxazine framework showed 2-fold higher lap shear strength than bisphenol-A (BPA) aniline polybenzoxazine. The current work highlights the utility of higher functionality renewable amines as promising candidates to design future high-performance fully biobased BPA-free polybenzoxazines. Copyright © 2019 American Chemical Society.

ACS Sustainable Chemistry and Engineering

Isomannide-Derived Chiral Rigid Fully Biobased Polybenzoxazines

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 1H NMR, 13C 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. © 2018 American Chemical Society.

Harvesting the Benefits of Inherent Reactive Functionalities in Fully Biosourced Isomeric Benzoxazines

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. © 2018 The Royal Society of Chemistry.

Journal of Materials Chemistry A

Sustainable one-step strategy towards low temperature curable superparamagnetic composite based on smartly designed iron nanoparticles and cardanol benzoxazine

Exploration of sustainable alternatives to chemicals derived from petro-based industries is the current challenge for maintaining the balance between the needs of a changing world while preserving nature. The major source for sustainable chemicals is either the natural existing plant sources or waste generated from agro-based industries. The utility of such resources will supplement new processed materials with different sets of properties and environmental friendliness due to their biodegradability and low toxicity during preparation, usage and disposal. Amongst other polymers used on a day-to-day basis, phenolic resins account for vast usage. Replacement of petro-based monomers such as phenol and its derivatives either partly or completely utilized for the synthesis of such resins is ongoing. Extraction of natural phenolic components from cashew nut shell liquid, lignin, tannin, palm oil, coconut shell tar or from agricultural and industrial waste, and their utilization as synthons for the preparation of bio-based polymers and properties obtained are reviewed in this paper. This review article is designed to acknowledge efforts of researchers towards the "3C" motto-not only trying to create but also adapting the principles to conserve and care for a sustainable environment. This review paper describes how extraction, separation and recovery of desired phenolic compounds have occurred recently; how substituted phenol compounds, unmodified and modified, act as monomers for polymerization; and how the presence of sustainable phenolic material affects the properties of polymers. There are about 600 references cited and still there is a lot to uncover in this research area. This journal is © the Partner Organisations 2014.

Naturally occurring phenolic sources: Monomers and polymers

Macromolecules

Benzoxazine-Based Thermosets with Autonomous Self-Healing Ability

New Journal of Chemistry

New benzoxazines containing polyhedral oligomeric silsesquioxane from eugenol, guaiacol and vanillin

Polymer Chemistry

Bifunctional polybenzoxazine nanocomposites containing photo-crosslinkable coumarin units and pyrene units capable of dispersing single-walled carbon nanotubes