Benzoxazine Moieties Research Articles

Convenient synthesis of phthalonitrile‐containing mono‐benzoxazines with exceptional thermal stability and improved curing activity

AbstractSimple synthesis and high performance are eternal pursuit for polymers. To lower the curing temperature, lower the melt viscosity and improve the processability of high performance phthalonitrile resins, a solvent‐free method was applied to synthesize three from different phenols. Their chemical structure was confirmed by FTIR and NMR spectra, the curing behavior was investigated by DSC and rheology. It was found that the polymerization of phthalonitrile groups could be effectively promoted by benzoxazine moieties and the curing temperature of phthalonitrile groups dropped to around 240°C. Consequently, owing to the high curing reactivity, polymers obtained at relatively low curing temperature possessed high crosslinking density and extremely high thermal stability. P‐apn‐200, which was cured at 200°C, showed 5 wt% weightloss temperature (Td5) of 472°C and char yield (Yc) of 75.77% at 800°C. Moreover, the polymers obtained after curing at 280°C showed superior dimensional stability, CN‐apn‐280 showed extremely low linear expansion coefficient (CTE) of 10.7 ppm/°C. And mP‐apn‐280 showed HR capacity of 3.99 J/g‧K, peak HRR of 4.0 W/K and total HR of 0.8 kJ/g.

Integrating Benzoxazine-PDMS 3D Networks with Carbon Nanotubes for flexible Pressure Sensors.

Shapeable and flexible pressure sensors with superior mechanical and electrical properties are of major interest as they can be employed in a wide range of applications. In this regard, elastomer-based composites incorporating carbon nanomaterials in the insulating matrix embody an appealing solution for designing flexible pressure sensors with specific properties. In this study, PDMS chains of different molecular weight were successfully functionalized with benzoxazine moieties in order to thermally cure them without adding a second component, nor a catalyst or an initiator. These precursors were then blended with 1 weight percent of multi-walled carbon nanotubes (CNTs) using an ultrasound probe, which induced a transition from a liquid-like to a gel-like behavior as CNTs generate an interconnected network within the matrix. After curing, the resulting nanocomposites exhibit mechanical and electrical properties making them highly promising materials for pressure-sensing applications.

Wettability Alteration to Reduce Water Blockage in Low-Permeability Sandstone Reservoirs

This study is a continuation of our previous work, which focused on a near-wellbore water blockage alleviation by applying a thermally cured silane-functionalized benzoxazine to modify rock wettability. In this new analysis, we have demonstrated that the resin can be applied in low-permeability sandstones (approximately 15 mD as opposed to 100 to 200 mD in the previous study) to change the rock surface wettability from water-wet to intermediate gas-wet. We have also demonstrated that curing temperatures as low as 125 °C (as opposed to 180 °C in our previous study) can significantly change wettability, indicating surface functionalization through the silane moiety and ring-opening polymerization of the benzoxazine moiety. In drainage core flooding experiments at 2.5 wt.% resin loading, compared to untreated samples, brine recovery increments of 6.3 to 6.9% were obtained for curing temperatures of 125 to 180 °C, respectively. A maximum 20% increment in the end-point relative gas permeability was achieved at a curing temperature of 180 °C. A coupled experimental and numerical study, conducted at core and wellbore scales, demonstrates the potential effectiveness of our chemical treatment in improving gas productivity at the field scale. Reservoir simulations indicate a 2.9 to 10.6% improvement in gas deliverability for a treatment radius of 4 to 16 m, respectively.

A cross-linkable phthalonitrile derivative as a precursor to synthesize nitrogen-doped carbon nanodots for Ni ion detection

A phthalonitrile derivative containing both melamine and benzoxazine moieties has been used as the precursor to prepare luminescent carbon nanodots for Ni ions detection.

Multiple catalytic polymerization of phthalonitrile resin bearing benzoxazine moiety: Greatly reduced curing temperature

Phthalonitrile resin is a high-performance thermosetting resin with excellent thermal stability, good mechanical properties, low water absorption and low dielectric constant, thus it shows great potential in aerospace, marine, and electronic packaging. However, the extremely high polymerization temperature and long curing cycle limit the practical application of phthalonitrile resin. It is revealed that the active species released by ring-opening of benzoxazine can promote the polymerization of phthalonitrile and the polymerization temperature of phthalonitrile resin containing benzoxazine (BAph) could be reduced to 240–280 ℃, but there is still difficultly in practical application. In this study, dicyandiamide (DCA), which contains reactive nitrile group and active amino groups, was selected as the curing agent to catalyze the curing reaction of BAph. The reaction activity, curing process and curing behavior of BAph-dca were investigated by differential scanning calorimetry (DSC), gelatin time (tgel) measurement and dynamic rheological analysis (DRA). The polymerization mechanism of BAph-dca was studied by Fourier transform infrared spectroscopy (FTIR) and DSC. It was shown that with 10 wt% of DCA, the initial exothermic temperature decreased from 222.9 ℃ (neat BAph) to 159.4 ℃, the peak temperature of ring-opening polymerization of benzoxazine (Tp1) decreased from 255.9 ℃ to 203.2 ℃, and the peak temperature of nitrile polymerization (Tp2) decreased from 288.5 ℃ to 271.6 ℃. Importantly, polymer films can be obtained at 200 ℃, which is substantially lower than the curing temperature of typical phthalonitrile resin. Moreover, the polymer films cured at 200 ℃ showed good thermal stability. The polymer film with 3 wt% of DCA showed initial decomposition temperature (Td5) of the 412 ℃ and the char yield (Yc) of 72.09 % at 800 ℃. This study is of great significance in reducing the polymerization temperature of phthalonitrile resin and promote its practical application.

Insightful characterization of sesamol-based polybenzoxazines: Effect of phenol and amine chain type on physical and nanomechanical properties

We report the synthesis of sesamol-based polyethyleneimine (PEI) polybenzoxazines. Their physico-chemical features have been compared with other aliphatic diamine chains and the influence on thermo-mechanical properties of the phenol substituent was investigated. Their molecular structures were checked through Fourier Transform Infrared Spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR and 13C NMR) spectrometry. Differential scanning calorimetry (DSC) revealed that the curing process takes place in two stages indicating the first polymerization exotherm <180 °C which is lower than for other similar PEI-based benzoxazines reported before. Thermogravimetric (TGA) and Dynamic mechanical analyses (DMA) showed good thermal stability, high glass transition (Tg) values (>120 °C) and elevated char yield suggesting that not only primary amines are involved in the benzoxazine rings formation, but also secondary or tertiary amines may participate influencing the crosslinking process. The limiting oxygen index (LOI) was determined by using van Krevelen equation showing that sesamol-based polybenzoxazines exhibit flame retardancy capability. Contact angle tests (CA) showed that sesamol-based thermosets display more hydrophilic character caused by the inherent hydrophilicity of the nitrogen enriched PEI oligomer. However, consistent differences between sesamol and phenol-PEI based polybenzoxazines were observed for the micromechanical properties, the latter showing overall increased micro-elastic and hardness modulus due to higher content of benzoxazine moieties.

Cover Image, Volume 139, Issue 21

This cover image by Takashi Doi and co-authors shows the development of a novel, non-reversible surface relief (SR) system using photoreactive bis- or tris-cinnamate derivatives containing thermally curable benzoxazine moieties. Not only does their photodimerization and thermal ring-opening polymerization contribute to this phenomenon, but also local mass transfer driven by concentration gradient of unreacted molecules. This image depicts that the thermally stable SR structure can be formed easily through a twostep development-free process of ultraviolet exposure under a photomask and subsequent heat treatment. This system is promising an alternative technology to photolithography. DOI: 10.1002/app.52173

Nonreversible surface relief formation in thin films of cinnamate derivatives containing benzoxazine structure

AbstractA novel, nonreversible surface relief (SR) system was developed using polymerizable low‐molecular‐weight compounds containing two or three [(E)‐3‐[4‐(6‐methyl‐2,4‐dihydro‐1,3‐benzoxazin‐3‐yl)phenyl]prop‐2‐enoyl]oxy units in which photoreactive cinnamate moieties and thermally curable benzoxazine moieties are included. The SR structure formation was conducted using thin films (thickness: 1.5 μm) on silicon wafers through a two‐step procedure including micropatterned ultraviolet irradiation at 23°C and then heating to induce the SR pattern formation. All of the four compounds synthesized in this study showed submicron‐height SR structure on their films. After being thermally treated at 200°C for 1 h, the thin films became insoluble, which ensured the formation of crosslinked network structures. The obtained nonreversible SR system is expected to be a candidate for microfluidic channel materials for cooling semiconductor chips as well as an alternative option for photolithography.

In-silico INVESTIGATION OF FERULIC ACID DERIVATES AGAINST MAIN PROTEASE SARS-COV

Ferulic acid is one of the natural compounds which is prevalent in various plants. This compound has known to possess extensive biological activity to get good health and well-being. In this study, we designed 23 derivates of ferulic acid and evaluate their potency in silico as potential SARS-CoV Mpro inhibitors. Furthermore, in silico ADME profiles of designed compounds were evaluated to verify whether the ferulic acid analogs possess an acceptable pharmacokinetic profile. The molecular docking result using AutoDock 4.2.6 showed that compound FA-24, which contained dihydro benzoxazine moiety, possesses a better docking score among the designed compound. Five top compounds based on docking score (FA-16, FA-17, FA-18, FA-23, and FA-24) were then evaluated using molecular dynamics for 10 ns, followed by free binding energy evaluation using the MM-PBSA approach. The result indicated that all compounds formed stable complexes with the enzyme for 100 ns. However, MM-PBSA result showed that compound FA-16, which contained phenyl benzoate moiety, possess higher free binding energy. It is argued that this difference was due to the nature of free binding energy evaluation, which was based on molecular dynamics results. Although, both the docking score and free binding energy of the designed compound are lower than the native ligand (AZP), it is believed that further structure modification could be performed to address this shortcoming. Ultimately, all designed ferulic acid analogs possess optimal absorption and drug-likeness characteristic, while several compounds were predicted to interact with isoforms of CYP450.

Bio-Based Bisbenzoxazines with Flame Retardant Linker.

This work explores the strategy of incorporating a highly substituted reactive flame retardant into a benzoxazine moiety. For this purpose, a DOPO-based flame retardant received a chain extension via reaction with ethylene carbonate. It was then reacted with phloretic acid to obtain a diphenol end-capped molecule, and further reacted with furfurylamine and paraformaldehyde to obtain a benzoxazine monomer via a Mannich-like ring closure reaction. This four-step synthesis yielded a partly bio-based halogen-free flame retardant benzoxazine monomer (DOPO-PA-fa). The successful synthesis was proven via NMR, IR and MS analysis. The polymerization behavior was monitored by DSC and rheological analysis both showing the polymerization starts at 200 °C to yield pDOPO-PA-fa. pDOPO-PA-fa has a significant thermal stability with a residual mass of 30% at 800 °C under ambient atmosphere. Furthermore, it reached a V-0 rating against small flames and an OI of 35%. Blended with other benzoxazines, it significantly improves their thermal stability and fire resistance. It emphasizes its potential as flame retardant agent.

Expanding the library of nitrogen enriched polybenzoxazine thermosets prepared from side-chain type benzoxazines functionalized with polyethylenimine

We present a simple methodology to develop nitrogen enriched polybenzoxazine thermosets by integrating polybenzoxazine network with polyethylenimine (PEI). Thermosets have been developed by polymerizing side-chain type resins, which have been prepared by introducing benzoxazine moieties on the amine terminated branches of nitrogen enriched PEI, using cardanol and eugenol as bio-based phenols. The aim of this study is to investigate the potential of benoxazines synthesized using different bio-based phenols and PEI, on the performance of nitrogen enriched thermosets, as well as to contribute in the array of side-chain type benzoxazine resins. The present work is a next leg of our previously reported article on the synthesis of side-chain type benzoxazine resins using guiacol and PEI (G-pei), where the reaction parameters such as reaction medium, time, and stoichiometry were optimized. It is to be noted that, due to relatively better performance of G-pei resins prepared at 8:1:16 and 10:1:20 (phenol: amine: paraformaldehyde) molar ratio, the same stoichiometry has been specifically adopted for the preparation of cardanol and eugenol-based analogous resins in the present work. The functionalization of PEI with benzoxazine as side-chains, has been confirmed using FTIR, 1H, 13C NMR spectroscopy techniques. Polar amine groups as well as alkyl chains of phenols, are expected to alter the polymerization behaviour of oxazine moieties and the same has been investigated using DSC studies, where the curing profiles display exotherms in the temperature range of 208–222 °C. Further, rheological studies suggest solvent-less processing for cardanol based resins. Polybenzoxazine network bonded with polyethyleneimine has been confirmed from FT-IR spectra of cured thermosets, and the nitrogen content has been evidenced from elemental analysis. Furthermore, the thermal stability of the crosslinked materials has been investigated using thermogravimetric analysis (TGA), while the glass transition temperature for the cured specimens has been obtained by dynamic mechanical analysis (DMA). Moreover, polarity associated with the polybenzoxazine network as well as nitrogen enriched amine, is expected to affect the surface property of the end materials, which has been investigated by performing contact angle measurements on the surface of cured thermosets. Lap shear adhesion experiments have been additionally performed using ASTM D1002 standard, and the results indicates relatively good wettability of cardanol based resins.

Recent Progress of High Performance Thermosets Based on Norbornene Functional Benzoxazine Resins

With the growing demand for high performance polymeric materials in industry, several types of thermosets such as bismaleimides, advanced epoxy resins, cyanate esters, and phenolic resins have been widely investigated to improve the performance of thermosetting products. Among them, benzoxazine resins have received wide attention due to their extraordinarily rich molecular design flexibility, which can customize our needs and adapt increasing requirements. To further improve the properties of polybenzoxiazines, researchers have found that the introduction of a norbornene functional group into the benzoxazine moiety can effectively improve the comprehensive performance of polybenzoxazine thermosets. This article focused on reviewing the recent development of high-performance thermosets based on norbornene functional benzoxazine thermosetting resins.

Wettability alteration using benzoxazine resin: A remedy for water blockage in sandstone gas reservoirs

As a low carbon fuel, natural gas is leading the transition to a cleaner energy system. However, water blockage is seen to reduce gas deliverability significantly in many gas producing wells. We have developed an environmentally friendly and cost-effective non-fluorinated chemical treatment using a new benzoxazine monomer as a wettability modifier to combat water blockage. This chemical would adhere to silicate surfaces through a silane moiety followed by the application of a thermally accelerated ring-opening polymerization of the benzoxazine moiety. The performance of the treatment has been evaluated using contact angle measurements, spontaneous imbibition tests, and core-flooding experiments at 60 °C and 10.35 MPa. After chemical treatment, the contact angle shifts from almost 0° to 90°, implying that the treatment alters the wettability from strongly water-wet to an intermediate gas-wetting state. Spontaneous imbibition measurements show about 65% reduction in the volume of water imbibed into the rock sample after chemical treatment, suggesting a substantial increase in hydrophobicity of rock pore surfaces. Core-flooding experiments indicate that the chemical treatment increases gas relative permeability (by up to 22%) whilst decreasing residual water saturation (by up to 10%). Taken together, we demonstrate that this novel non-fluorinated benzoxazine monomer can successfully shift wettability of sandstone rocks from a strongly water-wet to an intermediate-wet state and thus aid to mitigate water blockage at relatively low cost and in an environmentally friendly manner. Furthermore, this chemical can withstand extra high temperatures encountered in many deep low permeability gas reservoirs where water blockage may be highly pronounced.

Synthesis and study of new photochromic unsymmetrical bis-spiropyrans with nonequivalent heteroarene fragments conjugated through the common 2H,8H-pyrano[2,3-f]chromene moiety

Four novel bis-spiropyrans possessing two different photochromic units based on indoline and 1,3-benzoxazine heterocycles which are connected through the common 2H,8H-pyrano[2,3-f]chromene moiety and modified with electron donating substituents were obtained by multistep synthesis starting with 2,4-dihydroxy-iso-phthalic aldehyde. The structure of the compounds was confirmed by 1H and 13CNMR, FTIR and HRMS. All bis-spirocompounds exhibited photochromic activity at room temperature. Investigation of photochromic properties of bis-spiropyrans revealed that their once-opened merocyanine isomers were more stable than the double-opened ones under experimental conditions. It was also found that modification of the benzoxazine moiety of the molecule with electron donating substituents along with introduction of bulky benzyl group close to the oxazinespiro-center leads to an increase of the merocyanine lifetime up to 148 s.

A Cross-Linkable Electron-Transport Layer Based on a Fullerene-Benzoxazine Derivative for Inverted Polymer Solar Cells.

The synthesis, optoelectronic characterization and device properties of a cross-linkable fullerene derivative, [6,6]-phenyl-C61 -butyric benzoxazine ester (PCBB) is reported. PCBB shows all the basic photophysical and electrochemical properties of the parent compound [6,6]-phenyl-C61 -butyric methyl ester (PCBM). Thermal cross-linking of the benzoxazine moiety in PCBB resulted in the formation of cross-linked, solvent resistive adhesive films (C-PCBB). Atomic force microscopy (AFM) and optical microscopic studies showed dramatic reduction in the roughness and aggregation behaviour of P3HT-PCBM polymer blend film upon incorporation of C-PCBB interlayer. An inverted bulk heterojunction solar cell based on the configuration ITO/ZnO/C-PCBB/P3HT-PCBM/V2 O5 /Ag achieved 4.27 % power conversion efficiency (PCE) compared to the reference device ITO/ZnO/P3HT-PCBM/V2 O5 /Ag (PCE=3.28 %). This 25 % increase in the efficiency is due to the positive effects of C-PCBB on P3HT/C-PCBB and PCBM/C-PCBB heterojunctions.

Integration of silica with benzoxazine to improve particle dispersion and thermal performance of composites

The concentration gradient and non-uniform dispersion of the most commonly used filler (silica) in the polymer matrix is one of the main reason for the inferior performance of the polymer composite. The present work utilizes surface chemistry to integrate the surface of silica particles with benzoxazine moieties in order to improve the dispersion of silica particles in bio-based benzoxazine resin with a generic aim to develop polybenzoxazine composites with improved thermal performance. In view of the same, co-condensation of tetraethoxysilane (TEOS) and 3-aminopropylltriethoxysilane (APTES) at room temperature has been performed, resulting in amine functionalized silica (AFS) particles. The feed concentration of the reactants has been optimised to prepare least agglomerated particles. The organic functionalization on silica particles has been evidenced using Fourier transform infrared (FTIR), 13C solid state NMR, X-ray photoelectron (XPS) spectroscopies and thermogravimetric analysis (TGA). The free primary amine groups of amine functionalized silica (AFS) particles has been utilized as amine co-reactants which undergoes Mannich like condensation with various bio-based phenols to integrate oxazine functionality on the surface of silica particles. The presence of oxazine moieties on the surface of silica particles has been confirmed using various thermal techniques including differential scanning calorimetry (DSC) and TGA. The improved dispersion of benzoxazine functionalized silica (BFS) particles in a bio-based benzoxazine resin based on cardanol-aniline (C-a) as well as the polybenzoxazine thermoset has been demonstrated using digital and SEM images. Thermogravimetric results shows the influence of improved dispersion in terms of relatively higher thermal stability of the polybenzoxazine composite prepared using modified silica particles.

Synthesis and crosslinking reaction of a novel polymer containing benzoxazine and phenyleneethynylene moieties in the main chain

ABSTRACTA novel polymer, poly(1) containing benzoxazine and phenyleneethynylene moieties in the main chain with number‐average molecular weights ranging from 1400 to 9800 was obtained quantitatively by the Sonogashira–Hagihara coupling polymerization of the corresponding iodophenyl‐ and ethynylphenyl‐substituted monomer1. Poly(1) was heated at 200 °C under N2for 2 h to obtain the cured polymer, poly(1)′ via the ring‐opening polymerization of the benzoxazine moieties. The structures of the polymer before and after curing were confirmed by1H‐NMR, IR, and UV–vis absorption and reflectance spectroscopies. Poly(1)′ was thermally more stable than monomer1and poly(1). A specimen was prepared from a mixture of poly(1) and phenol‐diaminodiphenylmethane type benzoxazine2by heating at 200 °C for 2 h under N2. The poly(1)/2resin was thermally stable than bisphenol‐A type benzoxazine resin3. Poly(1) exhibited XRD peaks corresponding to thed‐spacings of 1.26–0.98 and 0.40 nm, assignable to the repeating monomer unit and alignment of polymer molecules, respectively. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019,57, 2581–2589

Synthesis and crosslinking reaction of polyacetylenes substituted with benzoxazine rings: Thermally highly stable benzoxazine resins

ABSTRACTNovel polyacetylenes, poly(1) and poly(2) substituted with benzoxazine rings were synthesized by the polymerization of the corresponding acetylene monomers 1 and 2 using Rh catalysts, [(nbd)RhCl]2, and (nbd)Rh+B–Ph4 (nbd = 2,5‐norbornadiene). The polymers were heated at 250 °C under N2 to obtain the corresponding polybenzoxazine resins, poly(1)′ and poly(2)′ possessing polyacetylene main chains via the ring‐opening polymerization of the benzoxazine moieties. The polyacetylene backbones were maintained after crosslinking reaction at 250 °C, which were confirmed by Raman spectroscopy. The benzoxazine resins were thermally highly stable as evidenced by differential scanning calorimetry and thermogravimetric analysis. The surface of poly(1)′ film became hydrophilic compared to that of poly(1), while the surfaces of poly(2) and poly(2)′ films showed almost the same hydrophilicity judging from the water contact angle measurement. Poly(1)′ and poly(2)′ exhibited refractive indices smaller than those of poly(1) and poly(2). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1884–1893

Synthesis and Thermal Properties of Difunctional Benzoxazines with Attached Oxazine Ring at the Para-, Meta-, and Ortho-Position

To investigate the role of position of oxazine ring in the benzoxazine backbone on their ring-opening polymerization (ROP) and thermal stability of resulting polybenzoxazine, we have synthesized difunctional monomers solely containing benzoxazine moieties (BZ2) with attached oxazine ring at the para-, meta-, and ortho-position. The ROP was examined by DSC analysis, which revealed a reduction in curing temperature in the order of meta (225 °C) < ortho (239 °C) < para (251 °C). The differences in structural and geometrical parameters were investigated by NMR (1H, 13C, 1H–1H NOESY) and X-ray crystallography analysis. The electronic effects and the intramolecular interaction between oxazine ring and aromatic hydrogen were higher when the attached oxazine ring was at the meta-position. The differences in their positioning also changed their ROP mechanism, an unusual intramolecular polymerization was observed in meta, while in ortho and para the polymerization proceeded in a regular manner. A curing mechanism r...

Microwave‐Assisted Sustainable Synthesis of Telechelic Poly(ethylene glycol)s with Benzoxazine End Groups

AbstractA microwave assisted synthetic route was explored as a sustainable tool for the preparation of cross‐linkable telechelic poly(ethylene glycol)s endcapped with benzoxazine functionality. In comparison to the conventional methodology, the reaction completion time could be significantly reduced using MAS technique and the sustainability of the procedure was improved. Microwave active bifunctional amines were prepared by the condensation reaction of p‐aminobenzoic acid and poly(ethylene glycol)s of different chain lengths to yield amine terminated poly(ethylene glycol)s (ATPEGs). Cardanol, an agro‐waste was chosen as the phenolic source, which was reacted with ATPEG to undergo Mannich like condensation resulting in reactive thermoplastic of telechelic nature. The structure of the resulting polymer was confirmed through FT‐IR and 1H‐NMR spectroscopy. Benzoxazine moieties present at the terminals undergo thermally accelerated ring opening polymerization to form cross‐linked networks which was studied using non‐isothermal differential scanning calorimetry (DSC). The rheological behavior of the resulting polymer suggests that the viscosity of the benzoxazine‐endcapped telechelic poly(ethylene glycol)s is sufficiently low to permit solventless processing which can be credited to the presence of flexible polyether linkages. The adhesive properties of the cross‐linked benzoxazine endcapped telechelic poly(ethylene glycol)s have also been studied.