Benzoxazine Research Articles

Solid-State Chemical Transformations to Enhance Gas Capture in Benzoxazine-Linked Conjugated Microporous Polymers

We describe the first examples of benzoxazine (BZ)-linked tetraphenylethylene (TPE)- and pyrene (Py)-containing conjugated microporous organic polymers (CMPs)—TPE-TPE-BZ and Py-TPE-BZ, respectively—having high surface areas and pore volumes, prepared through multistep syntheses (Schiff base, reduction, Mannich, and Sonogashira–Hagihara coupling), and their solid-state transformations through ring-opening polymerizations (ROPs) to give BZ linkages have never been reported previously. The chemical structures and, particularly, the presence of BZ units in the TPE-TPE-BZ and Py-TPE-BZ CMPs were confirmed through Fourier transform infrared and solid-state nuclear magnetic resonance spectroscopic analyses. The TEP-TPE-BZ CMP had a high BET specific surface area and a high total pore volume (325 m2 g–1 and 0.69 cm3 g–1, respectively). Because BZ units can undergo ROP through simple thermal treatment without the need for a curing agent or catalyst, the CMPs readily underwent one-step chemical transformations in the solid state to form new CMPs featuring phenolic OH and Mannich bridges as functional groups capable of forming strong intermolecular hydrogen bonds and/or acid/base interactions with molecules of CO2 gas to enhance the gas uptake ability.

Controlled Synthesis of Porous Hollow Fe–N/C Nanoshells as High‐Performance Oxygen Reduction Reaction Electrocatalysts for Zn–Air Battery

The development of high‐performance non‐noble oxygen reduction reaction (ORR) electrocatalysts is of significant importance for fuel cells and zinc–air batteries. Herein, a dual‐template‐assisted polymerization process is designed using both silica submicrospheres and ultrafine nanoparticles as hard templates, generating permeable hollow benzoxazine resin nanoshells with well‐controlled morphology and size; such resin nanoshells impregnated with urea and iron precursor salt are then calcined under different atmospheres and temperatures to produce a series of porous hollow Fe–N/C thin nanoshells with differentiated pore structures and various N compositions. The effects of the calcination atmosphere and temperature on the structure and composition of the Fe–N/C materials are also evaluated. Owing to its compositional and structural merits, the optimal porous Fe–N/C nanoshell with a specific surface area as high as 998.0 m2 g−1 exhibits a half‐wave potential E1/2 of 0.919 V (vs reversible hydrogen electrode (RHE)) in 0.1 m KOH, 37 mV more positive than that of the commercial Pt/C; when used as a cathode in a Zn–air battery, it displays a power density and specific energy density of 93.5 mW cm−2 and 779.7 mAh gZn−1, respectively. This work provides a straightforward method for the size‐ and shape‐controllable synthesis of Fe–N–C‐based ORR electrocatalysts.

An insight into thermal stability and decomposition kinetics of polybenzoxazine plasma treated graphene nanocomposites

This research was targeted to investigate the effect of oxygen plasma treated graphene nanosheets (tGNSs) on the thermal stability of benzoxazine resin and to have a further and deeper mechanistic understanding of thermal decomposition kinetics of such nanocomposites in 0.5, 1 and 3 wt% of tGNS. The samples were prepared as reported in our previous study. The quality of dispersion of tGNSs within benzoxazine was investigated by X-Ray diffraction (XRD) and scanning electron microscopy (SEM) technique. Also, to ensure the complete curing of samples the differential scanning calorimetry (DSC) analysis was performed. Using thermogravimetric analysis (TGA), it was found that the addition of tGNS improved the char yield and thermal stability parameter of benzoxazine nanocomposites and this improvement was more prominent at 1% and higher amount of nanoparticles. Moreover, the first stage of thermal degradation kinetic of benzoxazine was disappeared above 1 wt% of tGNS. The samples were kinetically analyzed through Kissinger, Flynn-Wall-Ozawa and Friedman and Coats-Redfern method. It was revealed that the overall activation energy was enhanced from 168 to 224 kJ mol−1 and 275 to 420 kJ mol−1 for the second and third stage of degradation using 1 and 3 wt% of tGNS.

A deep insight into polybenzoxazole formation in the heterocycle-containing polybenzoxazine: An enlightening thought for smarter precursor design

When artificially introducing an ortho-amide group into benzoxazine monomer, the conversion of polybenzoxazine (PBZ) into polybenzoxazole (PBO) could happen at higher temperature. However, the mechanism investigation for this reaction is far from enough, which is very significant for the PBO fabrication from PBZ. In this work, we designed three kinds of benzoxazines (PIC-abz, 4-MEP-abz and 6-MEP-abz) containing both pyridyl and amide group with similar structures. The existence of intramolecular N–H⋯N H-bonding involved with amide group and the N atom in pyridine ring, as well as the N–H⋯O H-bonding between the amide N–H and the O atom in oxazine ring, were confirmed by 1H–1H nuclear overhauled effect spectroscopy (NOESY) and concentration dependent 1H NMR spectra. In addition, the respective strength of these H-bonding in different precursors was calculated by non-covalent interaction (NCI) simulation. Results showed that besides the performance of resulted PBZ, the conversion temperature of PBZ into PBO was significantly influenced by the N–H⋯N hydrogen bonding involved with pyridyl and amide groups. Based on which, the mechanism of PBO formation was proposed and systematically investigated. The outcome of this work will help us to obtain PBO in a more efficient and reasonable manner starting from PBZ.

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.

Synthesis of Novel Benzoxazines Containing Sulfur and Their Application in Rubber Compounds.

This work reports the synthesis and successful use of novel benzoxazines as reinforcing resins in polyisoprene rubber compounds. For this purpose, three new dibenzoxazines containing one (4DTP-fa) or two heteroatoms of sulfur (3DPDS-fa and 4DPDS-fa) were synthesized following a Mannich condensation reaction. The structural features of each benzoxazine precursor were characterized by 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and Raman. The new precursors showed well suited reactivity as characterized by differential scanning calorimetry (DSC) and rheology and were incorporated in rubber compounds. After the mixing, the curing profiles, morphologies and mechanical properties of the materials were tested. These results show that the structural feature of each isomer was significantly affecting its behavior during the curing of the rubber compounds. Among the tested benzoxazines, 3DPDS-fa exhibited the best ability to reinforce the rubber compound even compared to common phenolic resin. These results prove the feasibility to reinforce rubber compounds with benzoxazine resins as a possible alternative to replace conventional phenolic resins. This paper provides the first guide to use benzoxazines as reinforcing resins for rubber applications, based on their curing kinetics.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers.

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.

Synthesis of a smart bisbenzoxazine with combined advantages of bismaleimide and benzoxazine resins and its unexpected formation of very high performance cross-linked polybenzoxazole

We report a bisbenzoxazine thermosetting system, oHPMI-ddm, which shows combined advantages of both bismaleimide and benzoxazine resins. The chemical structure of oHPMI-ddm has been identified by FT-IR and NMR spectroscopies, and its polymerization processes have been investigated using differential scanning calorimetry (DSC) and in situ FT-IR. The resulting polybenzoxazine derived from this thermosetting system exhibits significantly higher thermal stability than thermosets polymerized from the commercialized 4,4′-diaminodiphenylmethane based bisbenzoxazine (PH-ddm) and bismaleimide (DDM-BMI). This newly obtained benzoxazine also shows a unique structural thermal rearrangement in comparison to the cross-linked polybenzoxazole in a similar manner as other reported smart ortho-benzoxazines, although it has no obvious hydrogen bond forming group and cannot form 5- or 6-membered intramolecular interaction. Such conversion from polybenzoxazine to polybenzoxazole has been confirmed by both in situ FT-IR and solid state 13C NMR. Furthermore, the finally obtained cross-linked polybenzoxazole possesses outstanding properties of high thermal stability, excellent flame retardancy and low dielectric constant, indicating great potential for high performance material applications.

Effect of graphene oxide on photo- and thermal curing of chalcone–based benzoxazine resins

Benzoxazine monomer containing chalcone moiety was prepared through Mannich condensation reaction. The monomer and monomer mixed with different ratios of graphene oxide were exposed to UV irradiation followed by thermal curing to produce pristine thermoset and nanocomposites, respectively. The monomers, pristine thermoset and nanocomposites were characterized by analytical techniques such as 1H-NMR, 13C-NMR, FTIR, SEM and XRD. The peak characteristic to oxazine ring disappeared in the pristine thermosets and nanocomposites confirming successful ring-opening polymerization. The (001) plane in GO was not observed in the nanocomposites revealing the dispersion of graphene layers in the polymer matrix, and the dispersion was confirmed by SEM examination. The thermal properties using TGA and DSC indicate that the presence of graphene oxide catalyzes the ring-opening of oxazine and decreases the curing temperature up to 80 °C compared with pure benzoxazine monomer. In addition, the nanocomposites exhibit higher thermal stability and electrical conductivity compared with the pristine thermoset.

A novel thin-film image binarization method to detect nanofiller dispersibility for improving the mechanical performance of epoxy/polybenzoxazine laminate nanocomposites

Developing novel methods to detect and enhance the dispersibility of graphene nanofillers is critical for overcoming the limitations of polybenzoxazine (PBZ) resins, including difficulties in processing, the requirement of large amounts of solvents during sample preparation, and low fracture toughness. In this study, an epoxy resin was used to replace the solvents in PBZ preparation. Methylene-diphenyl-diisocyanate-grafted graphene nanosheets or multi-walled carbon nanotubes were incorporated to improve the mechanical strength and torsional fatigue life of carbon-fiber-reinforced polymer (CFRP) based on the PBZ resin. A novel thin-film image binarization method was developed to easily measure and assess the dispersibility of nanofillers in the nanocomposites at the macroscale. The effect of nanofiller dispersibility on the mechanical properties was systemically discussed. The results indicated that the dispersibility of the nanofillers and mechanical properties can be significantly improved by (1) taking advantage of the low viscosity and high toughness of Epoxy and (2) adjusting the sequence of sample preparation based on changes in the rheological behavior. These improvements ultimately extend the torsional fatigue life of CFRP and thus its applicability.

Effect of silane modified microcrystalline cellulose on the curing kinetics, thermo-mechanical properties and thermal degradation of benzoxazine resin

In the frame of developing sustainable, eco-friendly and high performance materials, microcrystalline cellulose modified through silane coupling agent (MCC Si) is used as a reinforcing agent of benzoxazine resin to manufacture composites at different loadings of 5, 10, 15, 20 wt%. The structural, morphological and crystallinity characterizations of the modified MCC were initially performed to scrutinize the changes and confirm the modification. Then, an investigation on the crosslinking process of the prepared composites was held through curing kinetic study employing isoconversional methods. The kinetic data revealed a decrease in the average values of activation energy and the pre-exponential factor, particularly for composite supplemented with 10% MCC Si, whereas all samples disclosed a tendency of an autocatalytic curing mechanism. Furthermore, the study of the dynamic mechanical properties and degradation features of the cured specimens, respectively, indicated a superior stiffness attributable to the good interaction between BA-a and MCC Si, and enhanced thermal stability for the composites compared to pristine resin.

Morphological, thermal and mechanical properties of benzoxazine resin reinforced with alkali treated alfa fibers

This paper explores a new class of composites based on bisphenol-A aniline benzoxazine (BA-a) and alfa fibers for which the aim is to enhance the properties of BA-a resin and investigate the ability of natural fillers to mitigate some of its outcomes. For this purpose, natural Alfa fibers (NAF) are firstly treated by an alkaline solution to obtain treated alfa fibers (TAF) then incorporated into BA-a at different loadings from 5 to 30 wt.% to form composites. The effect of the alkali treatment on the NAF was investigated through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). The results revealed a partial removal of hemicellulose and lignin with a better thermal stability and rougher surfaces. The influence of adding the TAF on the mechanical, morphological, thermal and thermomechanical features in addition to the curing behavior of the obtained composites was thoroughly investigated. The obtained results revealed significant improvements in micro-hardness, flexural and thermomechanical features compared to the unfilled resin. Moreover, the presence of numerous hydroxyl groups (OH) induced a strong fiber-matrix adhesion, a better stress-transfer with a consequence enhancement in the glass transition temperature.

Preparation and properties of Benzoxazine (BA) based BiFeO3-Poly(vinylidene fluoride) (PVDF) Composites: Enhanced Dielectric Constant and Suppressed Loss

ABSTRACT In this report, a simple solution-casting technique was employed to prepare benzoxazine (BA) encapsulated BiFeO3; BFO particles (BA@BFO) usable as fillers filled poly(vinylidene fluoride) (PVDF) composite films. The effects of encapsulated BA@BFO particle on the electrical and mechanical performance of the composites were carefully investigated. The results suggested that the introduction of BA@BFO particles enhanced dielectric constant (ԑr) (≈ 62) and negligible loss (tan δ) (< 0.5) at 100 Hz. This may be due to the improved polarization, which is induced by relatively high dielectric constant ceramic particles. In addition, compared to untreated BFO particles, BA@BFO particles can be dispersed homogeneously in the poly (vinylidene fluoride) (PVDF) matrix, this might be the reason for the suppression of loss which makes them interesting for possible applications in electronic devices. Moreover, the interfacial interaction between PVDF chains and the BA@BFO particles were revealed, this interaction leads to the increase of the dielectric constant, tensile strength and relatively suppressed dielectric loss. Consequently, this study opens up the avenue for developmental analysis with respect to the use of BA in addition with BFO-PVDF composites with low dielectric loss and high dielectric constant for the next generation of high-performance dielectric capacitors.

Synthesis and properties of a benzoxazine monomer containing maleimide and biphenyl groups

Benzoxazine resin exhibits excellent properties and is widely used in many fields. Herein, the synthesis of a novel compound, the bis(2,4-dihydro-2 H-3-(4- N-maleimido)phenyl-1,3-benzoxazinyl)biphenyl (BMIPBB), has been reported, which was synthesized by reacting N-(4-aminophenyl)maleimide (APMI), formaldehyde, and 4,4’-dihydroxybiphenyl. 1,3,5-three(4-(maleimido)phenyl)-1,3,5-triazine (TMIPT) was formed as an intermediate during the reaction. The proton nuclear magnetic resonance (1H-NMR) and Fourier transform-infrared (FTIR) spectroscopy experiments were conducted to determine the structure of BMIPBB. BMIPBB was obtained as a reddish-brown solid in 40.1% yield. The thermal properties of BMIPBB were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. Analysis of the DSC curves revealed that the broad peak representing the release of curing reaction heat appeared in the temperature range of 140–330°C. The peak temperature was 242.59°C and the heat of the reaction was 393.82 J/g, indicating that the rate of the curing reaction was low and the heat of the reaction was high. Analysis of the TGA results revealed that the weight loss rate was 5% at 110°C. The monomer exhibited a significant weight loss in the range of 320–500°C. The compound lost 50% of its weight at a temperature of 427°C.

A study of the effect of L-histidine on the polymerization of benzoxazines and properties of their thermosets

The cleavage of the oxazine ring of benzoxazine resins generally requires high energy during the ring-opening polymerization, which leads them to be processed at a much higher temperature than the traditional thermoplastics. In this paper, a bio-based substance, L-histidine, has been used as the catalyst to lower the ring-opening polymerization of the well-commercialized benzoxazine resin (BA-a) based on aniline and bisphenol-A. The catalytic effect of L-histidine on the polymerization behaviors of benzoxazine resin (BA-a) has been monitored by differential scanning calorimetry and in situ Fourier transform infrared spectroscopy. In addition, L-histidine has also been found to be a good property modifier for BA-a-derived thermosets. The thermal properties of resulting polybenzoxazines have been investigated by thermogravimetric analysis and dynamic thermomechanical analysis. Notably, the thermoset derived from BA-a with adding only 5 mol% L-histidine exhibits excellent thermal stability in consideration of high Tg (206 °C), high Td10 temperature (319 °C) and high chair yield value (40%), making this thermosetting resin a promising material for high-performance applications.

Enhanced thermal conductivity for polybenzoxazine matrix composites by constructing a hybrid conductive network and modification of fillers

Polyhedral oligomeric silsesquioxanes (POSS) and γ-glycidoxy propyl trimethoxy silane (KH560) were applied to modify boron nitride (BN) and boron nitride whisker (BNw), and modified BN (m-BN) and modified BNw (m-BNw) were added as thermally conductive fillers to polybenzoxazine (PBz) matrix to synthesize m-BN/m-BNw/PBz composite by hot press. The research results indicate that the modification of BN and BNw and the synergistic effect between m-BN and m-BNw can significantly improve the thermal conductivity of PBz composite. The thermal conductivity of PBz composite with 25 wt % m-BN and 25 wt % m-BNw reached to 1.27 W/mK, which is 35% higher than PBz composite with 50 wt % m-BN (0.94 W/mK), 76% higher than PBz composite with 50 wt % BN (0.72 W/mK), and also display excellent electrical insulation performance. The corresponding dielectric constant (ε) and dielectric loss (tan δ) were 3.83 and 0.0078, respectively. Besides, the Theat-resistance index (THRI) of PBz composite with 25 wt % m-BN and 25 wt % m-BNw is 242.26 °C, and the thermal degradation temperature at 30% weight loss (T30) is 557.72 °C, are higher than PBz matrix (224.46 and 498.88 °C). And the tensile strength of PBz composites with 25 wt % m-BN and 25 wt % m-BNw is 47.71 MPa.

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.

Behavior of Polybenzoxazine Composites Reinforced with Modified Carbon Nanotubes

The surface of conventional carbon nanotube (CNTs) were modified into 4-aminobenzoyl functionalized CNTs (ABCNT) and benzoxazine functionalized CNTs (BZCNT) to improve their surface interaction with bisphenol A based benzoxazine resins (BA-a). Polybenzoxazine (PBZ) composites using these materials were prepared to investigate the effect of different functional groups on the thermal and electrical properties of the composites. The surface modification of CNTs was characterized by Fourier Transform Infrared spectroscopy and thermogravimetric analysis. The PBZ composite with BZCNT showed the better conductivity and thermal properties than the composite with ABCNT due to the chemical bond between BZCNT/BA-a during the curing process which does not exist in the ABCNT/BA-a composite.

Effect on thermal stability of microstructure and morphology of thermally-modified electrospun fibers of polybenzoxazines (PBz) blended with sulfur copolymers (SDIB).

Simple modification by thermal treatment is the commonly used approach to enhance the performance of electrospun fibers. This was investigated in the thermal treatment of polybenzoxazine (PBz) fibers blended with sulfur copolymers (SDIB) to determine the effect of varying treatment conditions on the microstructure and morphology of PBz fibers with the effect of incorporating sulfur functional groups on resulting properties. Mechanical properties of PBz are greatly improved by thermally-induced ring-opening polymerization (ROP) of the oxazine ring. Blending with sulfur copolymers (SDIB) could have beneficial effects on endowed features on fibers but could also affect the resulting properties of SDIB-blended PBz fibers during crosslinking reactions. Fiber mats were fabricated by electrospinning of PBz (10 wt%) blended with SDIB (10 wt%). Physical modification with varying conditions of sequential thermal treatment were evaluated and compared to the conditions applied on pristine PBz fibers. Changes in morphology and microstructure of fibers after modification were analyzed through scanning electron microscopy (SEM) while elemental compositions were identified after varying the conditions of thermal treatment. Adjustment of treatment conditions using two-step temperature sequential thermal treatment with higher temperatures of 160 °C and 240 °C showed significant changes in microstructure and morphology of fibers. Lower temperatures of 120 °C and 160 °C exhibited microstructure and morphology of fibers which affected the fiber diameter and fiber networks. Cross-sectional SEM images also confirmed the adversed effect of high-temperature treatment conditions on fibrous structures while low-temperature treatment retained the fibrous structures with more compact and stiff fiber networks. SDIB-blended PBz fibers were also evaluated by TGA and DSC to correlate the changes in structure and morphology with the thermal stability and integrity of blended SDIB/PBz fibers as compared to pristine PBz with the effect of change in treatment conditions. Fiber strength indicated slower weight loss for blended fibers and higher onset temperature of degradation which resulted in more thermally stable fibers.

Propargylamine: an attractive amine source for designing high-performance benzoxazine resins with low polymerization temperatures

A series of benzoxazine resins using propargylamine as the amine source were synthesized to achieve highly thermally stable thermosets with low polymerization temperatures.