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A sulfur-rich copolymer, poly(S-r-C-a) has been synthesized via a sustainable route, showing the utility of two major industrial wastes- elemental sulfur (petroleum waste) and cardanol (agro waste), to explore its potential as cathode material for Li-S batteries. The sulfur-rich copolymer exhibited a reduction in the active material dissolution into the electrolyte and a low self-discharge rate behavior during the rest time compared to an elemental sulfur cathode, indicating the chemical confinement of sulfur units. The presence of organosulfur moieties in copolymer suppress the irreversible deposition of end-discharge products on electrode surfaces and thus improve the electrochemical performances of Li-S batteries. This sulfur copolymer offered a reversible capacity of 892 mA h g-1 at 2nd cycle and maintained the capacity of 528 mA h g-1 after 50 cycles at 200 mA g-1. Reduced graphene oxide (rGO) prepared via a sustainable route was used as a conductive filler to extract the better electrochemical performances from this sulfur copolymer. Such sustainable origin batteries prepared via economically viable showed an improved specific capacity of ∼975 mA h g-1 after 100 cycles at 200 mA g-1 current rate with capacity fading of 0.15\% per cycle and maintained a stable performance over 500 cycles at 2000 mA g-1.

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Scientific Reports

Sustainable Sulfur-rich Copolymer/Graphene Composite as Lithium-Sulfur Battery Cathode with Excellent Electrochemical Performance

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.

RSC Advances

Cardanol benzoxazines-interplay of oxazine functionality (mono to tetra) and properties

Successful application of interfacial engineering for the preparation of cross-linked epoxy microspheres containing thermally polymerizable cardanol-based benzoxazine (Bz-C) monomer in the core is demonstrated. Bz-C is facilely synthesized by Mannich type condensation of cardanol (a by-product of cashew nut industry) and aniline with formaldehyde under solventless conditions. The encapsulation process relies on the preferential reaction of polydimethylsiloxane immiscible epoxy resin and amine-based hardener to form a cross-linked spherical shell at the interface. The microcapsule dimensions and core content could be tailored by modulating the operating parameters, particularly stirring speed and Bz-C: epoxy ratio. Spherical microcapsules with a core content of ∼37\% were obtained when the reaction was carried out at 600 rpm, while maintaining the reaction medium at 70°C with Bz-C: epoxy ratio of 2.3: 1. The simplicity and versatility of the present methodology are the forte of this technique, which widens the scope for large-scale application of benzoxazines in the field of temperature triggered healing. © 2015 Wiley Periodicals, Inc.

Journal of Applied Polymer Science

Interfacial encapsulation of bio-based benzoxazines in epoxy shells for temperature triggered healing

Benzoxazine (Bz) monomer was synthesized from renewable cardanol, a by-product from cashew-nut industry, using a solventless approach. The monomer was encapsulated in poly(styrene) (PS) shells by solvent evaporation technique to obtain spherical microcapsules. The microcapsule dimensions and core content could be tailored by optimizing the operating parameters, particularly stirring speed and PS concentration. Successful demonstration of this simple and versatile methodology widens the scope for large-scale application of benzoxazines in the field of self-healing. © 2014 Elsevier Ltd. All rights reserved.

Materials Letters

Microencapsulated cardanol derived benzoxazines for self-healing applications

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

This article describes synthesis, characterization and properties of blends of benzoxazine (Bz) monomers, i.e., m-alkylphenyl-3,4-dihydro-2H-benzoxazine (Bz-C), 6,6′-(propane-2,2-diyl)bis(3-phenyl-3,4-dihydro-2H-benzoxazine (Bz-A) and 3-phenyl-3,4-dihydro-2H-benzoxazine-p-carboxylic acid (Bz-pA). Binary blends of Bz-C with Bz-pA, and Bz-A with Bz-pA were prepared by first synthesizing Bz-C or Bz-A followed by the addition of all the ingredients of Bz-pA. In a similar manner, ternary blends of Bz-C, Bz-A and Bz-pA were prepared by first synthesizing Bz-C and subsequent addition of all the ingredients of Bz-A and Bz-pA in one pot. The Bz monomer blends were characterized by 1H-NMR, FTIR spectroscopy, and differential scanning calorimetry. The temperature of onset of curing (T o), due to ring-opening polymerization of Bz was found to decrease significantly by incorporation of carboxyl groups (Bz-pA) showing thereby the catalytic effect of acid functionality. Bz polymers showed good thermal stability and incorporation of Bz-pA in blends resulted in a highly cross-linked network. The interlaminar shear strength of glass fabric reinforced composites and the lap shear strength of metal-metal joints using these resin blends was also investigated. © 2012 Akadémiai Kiadó, Budapest, Hungary.

Journal of Thermal Analysis and Calorimetry

Blends of benzoxazine monomers: Effect of structure and composition on polymer properties

A new class of thermoset polymers was synthesized based on agrochemical renewable cardanol-A by-product of cashew nut industry. A solventless synthesis of bisbenzoxazine monomers based on bisphenol-A (b) and aniline (abbreviated as Bzb-A) and cardanol (c) with diamines namely bis-(4-(4-Aminophenoxy)phenyl)ether (HP), bis-(3-(4- aminophenoxy)phenyl)ether (HM), 4,40-diaminodiphenylsulphone (DDS) and 2,2-bis(4-(4-Aminophenoxy)phenyl)propane (BA) was carried out. The benzoxazine monomers (Bzc-HP, Bzc-HM, Bzc-DDS and Bzc-BA) were characterized by 1HNMR and FTIR spectroscopy. The curing exotherm depended on the structure of themonomers. The onset curing temperature (To) was lowest for Bzb-A (460 K) and highest in Bzc-HM (518 K). The decomposition temperature for 5% mass loss (T5%) of resins followed the order PBzb-A<PBzc-DDS< PBzc-BA<PBzc-HM & PBzc-HP. The materials showed their potential as adhesives. Lap shear strength on steel plates followed the trend PBzc-DDS<PBzc-HM<PBzc-BA< PBzc-HP. © Akademiai Kiado, Budapest, Hungary 2011.

Cardanol-based bisbenzoxazines: Effect of structure on thermal behaviour

A novel benzoxazine monomer (Bz-C) based on agrochemical renewable resource-cardanol (by-product of cashew nut tree, Anacardium occidentale) was synthesized. Bz-C, a liquid monomer, was used as reactive diluent for the solventless synthesis of bisphenol-A benzoxazine monomer (Bz-A). Benzoxazine monomer based on cardanol and bisphenol-A in 3:1, 1:1 and 1:3 blend ratio were prepared by this method. The resins had Brookfield viscosity at 316 K in the range of 145-81,533 mPa s. The resins were characterized by 1H-NMR, FTIR and elemental analysis. Curing characteristics were studied by DSC analysis. Thermal stability of cured resins was found to improve with increase in Bz-C content in the blends. © 2010 Akadémiai Kiadó, Budapest, Hungary.

Thermal behaviour of cardanol-based benzoxazines: Monomers and polymers

Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications

Design and Synthesis of Different Types of Poly(Lactic Acid)

We report a study of photoinduced charge separation in poly(1,4-phenylenevinylene) (PPV) derivatives with enhanced exciton dissociation using light-induced electron paramagnetic resonance (EPR). Four polymers were studied; all contained alkoxy and fluorenyl side chain units, and two of them also contained a nitro group on the 7-positon of the fluorenyl moieties. Pulsed EPR detected a light induced polaron for all the polymers with the intensity significantly higher for those with nitro groups. A second center was observed for these materials and spectra could be fitted assuming a radical anion was localized on the nitro groups. The fraction of radical anion and polaron centers was comparable, consistent with intramolecular exciton dissociation for the PPV derivatives containing the nitro groups. © 2008 Elsevier B.V. All rights reserved.

Organic Electronics

Photoinduced charge separation in poly(1,4-phenylenevinylene) derivatives studied by electron paramagnetic resonance

We report a study on the feasibility of using an intramolecular dipole to enhance charge separation for organic photovoltaic applications. We have developed a poly(1,4-phenylenevinylene) derivative, poly{2-[(9,9-di-n-propyl-9H-7-nitrofluoren-2-yl)]-5-(2-ethylhexyloxy)-1,4-phenylenevinylene} 12, which has electronically asymmetric chromophores as a result of the para attachment of alkoxy and nitrofluorenyl groups on the phenyl units of the polymer backbone. The luminescence of the polymer with the electronically asymmetric chromophores was found to be smaller by a factor of eight when compared to the equivalent polymer but without the nitro group attached to the fluorenyl unit. Light-induced electron spin resonance experiments showed that the polymer with the electronically asymmetric chromophores had more photo-induced spins, showing that the quenching of the luminescence was due to intramolecular charge separation. Single layer photovoltaic devices containing neat films of 12 showed efficiencies similar to other single layer devices and this was ascribed to poor transport of the separated charges. This was confirmed by a strong improvement in device power efficiency to 0.52% at AM1.5 by blending the polymer with an electron transporting material. © 2007 Elsevier B.V. All rights reserved.

Electronically asymmetric poly(1,4-phenylenevinylene)s for photovoltaic cells

The reaction of poly(allyl azide) (PAA; number-average molecular weight = 1800 g/mol) with N-phenyl maleimide, 4,4′-bis(maleimidodiphenyl) ether, 4,4′-(bismaleimidodiphenyl) sulfone, and 1,6-bismaleimido hexane is described in this article. As indicated by Fourier transform infrared studies, the azido group reacted with the highly electron-deficient olefinic bond of N-phenyl maleimide or bismaleimides in a 3 + 2 cycloaddition reaction under mild reaction conditions. The curing of PAA with bismaleimides (10-30 phr) was monitored with differential scanning calorimetry. In freshly prepared samples of PAA and bismaleimides, a broad exothermic transition was observed in the temperature range of 150-280°C and could be attributed to the loss of N 2 from PAA and the curing of bismaleimides. The heat of the exothermic reaction (ΔH) depended on the structure and composition and was in the range of 800-1413 J/g. Isothermal heating in an air oven at 40°C (2 days) followed by 60°C (5-6 days) resulted in the conversion of a sticky, viscous liquid into an elastic, nonsticky material. No significant difference in the ΔH values of uncured and cured samples was observed, and this indicated the reaction of fewer azido groups with the bismaleimides (dipolarophiles). In the thermogravimetry traces, a mass loss was indicated in the temperature range of 130-280°C due to the loss of nitrogen from the azido group. © 2006 Wiley Periodicals, Inc.

Curing and thermal behavior of poly(allyl azide) and bismaleimides

The synthesis, characterization and physical properties of energetic azido binders were discussed. The energetic composites of glycidyl azide polymer (GAP)/nitroplasticizers and polyethylene glycol with HMX in various particle sizes were studied and compared with hydroxy terminated polybutadiene (HTPB) composites. The particle size of the oxidizer played an important role in determining the performance of the propellants. It was found that the flame structure of the GAP propellants was altered by the nature of the oxidizers.

Journal of Macromolecular Science - Polymer Reviews

Azido Polymers - Energetic Binders for Solid Rocket Propellants

The paper describes the synthesis of low molecular mass poly(allyl chloride) (PAC) (Mn = 856-3834 g mol-1) using Lewis acid (AlCl3, FeCl3, TiCl4) and Al powder. Branching in PAC was indicated on the basis of elemental analysis and 1H-NMR spectroscopy. Azidation of PAC could be carried out at 100°C by using NaN3 and DMSO as solvent. Curing of poly(allyl azide) (PAA) by cyclic dipolar addition reaction with EGDMA (ethylene glycol dimethacrylate, 5-45 phr) was investigated by differential scanning calorimetry and structure of cured polymer was confirmed by FTIR. A two-step mass loss was exhibited by uncured and cured PAA in nitrogen atmosphere. A mass loss of 20-28% (155-274°C) and 50-61% (330-550°C) was observed.

Thermal behaviour of poly(allyl azide)

A dendritic polyester based on pentaerythritol and 1,2,4 - benzenetricarboxylic acid anhydride followed by modification with glycidyl methacrylate was synthesised by using a divergent approach. The dendrimer (D-2) thus obtained had approximately eight double bonds. Several blends of D-2 with varying proportions of bismethacryloxy derivative of diglycidyl ether of bisphenol-A having styrene as a reactive diluent (VE resin) were prepared. The Brookfield viscosity of VE resin increased with an increase in D-2 content in the blends. Curing behaviour of these resins in the presence of AIBN was investigated by DSC. No significant change in curing exotherm was observed by addition of D-2 to the VE resin. Isothermal curing of resin samples in the presence of AIBN was done at 60 °C for 5 h and then at 150 °C for 90 mins. A significant improvement in char yield at 600 °C in nitrogen atmosphere was observed in samples containing D-2. Mechanical properties of glass fiber reinforced laminates with 31 ± 3% of resin content (w/w) were also determined. Smoke density of laminates increased with decrease in D-2 content in the resin, whereas only a marginal effect on limiting oxygen index was observed.