Polybenzoxazine Thermosets Research Articles

Weldable, Reprocessable, and Water-resistant Polybenzoxazine Vitrimer Crosslinked by Dynamic Imine Bonds.

Traditional polybenzoxazine thermosets cannot be reprocessed or recycled due to the permanent crosslinked networks. The dynamic exchangeable characteristics of imine bonds can impart the networks with reprocessabilities and recyclabilities. This study reported a weldable, reprocessable, and water-resistant polybenzoxazine vitrimer (C-ABZ) crosslinked by dynamic imine bonds. It was synthesized through a condensation reaction between an aldehyde-containing benzoxazine oligomer (O-ABZ) and 1,12-dodecanediamine. The resulting C-ABZ was able to be welded and reprocessed due to the dynamic exchange of imine bonds. The tensile strengths of the welded C-ABZ and the reprocessed C-ABZ after three cycles of hot-pressing were 76.7, 81.3, 70.8, and 58.1 Mpa, with corresponding tensile strength recovery ratios of 74.1 %, 78.6 %, 68.4 %, and 56.1 %, respectively. Furthermore, the polybenzoxazine backbone significantly improved the water resistance of the imine bonds. After immersing in water for 30 days at room temperature, the weight gain of C-ABZ was less than 1 % with corresponding tensile strength and tensile strength retention ratio of 59.5 Mpa and 57.5 %, respectively. Although the heat resistance of C-ABZ decreased slightly with increased hot-pressing cycles, a glass transition temperature (Tg, tanδ) of 150 °C was retained after the third hot-pressing. Overall, these findings demonstrate that the C-ABZ possesses excellent comprehensive performances.

Reaction-induced liquid crystalline polybenzoxazine thermosets using aryl ester bonds as cross-linkages

ABSTRACT The increasing tendency to develop integration in electronic devices lead to the demand for thermally conductive polymeric materials. We offered a simple synthetic route to thermally conductive polybenzoxazine thermosets bearing liquid crystalline structures without the addition of any filler. Benzoxazine monomer of BZ-COOH was synthesized via Mannich reaction of p-hydroxy benzoic acid, p-formaldehyde, and dodecyl amine. After ring-opening polymerization of BZ-COOH, the obtained benzoxazine oligomer of OBZ-COOH was converted into acetoxy-bearing benzoxazine oligomer of OBZ-AC. Through self-crosslinking reaction of acetoxy group and carboxyl group in OBZ-AC using Zn(CH3COO)2 as a catalyst, the polybenzoxazine thermosets of OBZ-PES were produced. The liquid crystalline behavior of OBZ-AC was studied by POM, SAXS, and DSC. The results show that OBZ-AC formed the LC mesophase during isothermal and non-isothermal curing. The LC mesophase displays a layered arrangement of the smectic C phase. The formation mechanism is esterification reaction-induced. Owing to the formation of liquid crystalline structure, the TC of OBZ-PES is found to be 0.284 W/m. K, which is 21% and 16% greater than those of OBZ-COOH and OBZ-AC, respectively. In addition, the OBZ-PES shows excellent thermal performance. Its Tg(G”) is up to 269°C. Its 5% weight loss temperature (Td5) and 10% weight loss temperature (Td10) are 383°C and 410°C, respectively.

Sustainable Upcycling of Nitrogen-Enriched Polybenzoxazine Thermosets into Nitrogen-Doped Carbon Materials for Contriving High-Performance Supercapacitors

Nitrogen-enriched polybenzoxazine thermosets derived from the ring-opening polymerization of side-chain-type benzoxazine-functionalized polyethylenimine resins (Bz-pei) have been previously reported by our group. In view of the appreciable nitrogen content and significant char yield, these thermosets have been envisioned as enticing carbon precursors and therefore have been sustainably upcycled to nitrogen-doped carbon materials. It is worth mentioning that the sustainable upcycling method should circumscribe energy as well as cost consumption, due to which carbon materials in the present work have been developed under moderate carbonization conditions, without chemical activation treatment. The developed nitrogen-doped carbon materials have been characterized by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, elemental analysis, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The pore topography has been analyzed using scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis has been performed, while the Brunauer–Emmett–Teller (BET) surface area has been determined using nitrogen adsorption–desorption experiments. A comparison of the results obtained from electrochemical investigations performed in a three-electrode setup shows that carbon material upcycled from the guaiacol-based polybenzoxazine thermoset, exhibiting 6.4% nitrogen doping in the carbon framework (labeled as C-GP81), exhibits an impressive capacitance of 700 F g–1 at 10 A g–1 current density, suggesting excellent efficiency and rate capability of the obtained N-doped carbon-material-based supercapacitor electrodes. Furthermore, the carbon material designated as C-GP81 could deliver a maximum energy density (Ed) of 48 Wh kg–1 at a power density (Pd) of 8400 W kg–1 in a three-electrode configuration. The performance of the crafted supercapacitor device for the present study has surpassed the performance reported for polybenzoxazine-derived carbons. Additionally, the performance of carbon material labeled as C-GP81 has been evaluated for its potential as an active component in the electrodes of a symmetric device.

A highly thermally stable benzoxazine resin derived from norbornene and natural renewable tyramine and furfurylamine

Highly thermally stable polymeric materials synthesized from renewable resources are highly desirable in many high-performance fields due to the sustainable development of human beings. Herein, a new norbornene-containing monobenzoxazine thermosetting resin (HPTM-fa) exhibiting very high thermal stability has been prepared using natural bio-resourced tyramine and furfurylamine as starting materials. The structural details of HPTM-fa were characterized by FT-IR, NMR as well as high-resolution mass spectroscopies. The polymerization behaviors of cross-linkable norbornene, oxazine ring, and furan groups in HPTM-fa were investigated by DSC and in situ FT-IR analyses. In addition, the polybenzoxazine thermoset derived from this newly obtained bio-based mono-benzoxazine resin showed very high thermal stability with a Td5 of 413 °C and a glass transition temperature of 290 °C. The outstanding performance of thermoset based on HPTM-fa evidences its potential applications in the design of highly thermally stable polymeric materials.

Synthesis of bio‐diamine derived main‐chain type benzoxazine resins with low surface free energy

AbstractA series of bio‐based fluorin‐free main‐chain type benzoxazine precursors were synthesized via bisphenol A/bisphenol F/diallyl bisphenol A, Priamine 1074 and paraformaldehyde by Mannich condensation reaction. Chemical structures of these obtained main‐chain type precursors were characterized by FT‐IR and NMR spectroscopies. The polymerization processes were studied by differential scanning calorimeter (DSC) and in situ FT‐IR analysis. Besides, the contact angle and surface free energy of polybenzoxazine coatings were measured by water contact angle instrument. Moreover, the thermal performance of the resulting polybenzoxazine thermosets were evaluated by dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA). Through the above various measurements, the newly developed bio‐based main‐chain type polybenzoxazine resins show good thermal stability and low surface free energy, suggesting great potential for applications as high‐performance resin matrix.

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages.

In order to obtain reprocessable polybenzoxazine thermosets with high heat resistance and mechanical strength retentions, network structures without irreversible parts were constructed via crosslinking benzoxazine oligomers using boronic ester cross-linkers. Firstly, the benzoxazine monomer containing carbon–carbon double bonds was synthesized via the Mannich reaction. After thermal ring-opening polymerization, the benzoxazine oligomer containing carbon–carbon double bonds (OBZ) was yielded. Through the thiol-ene click reaction of the OBZ and dithiol cross-linker bearing boronic ester bonds, the polybenzoxazine thermosets using boronic ester bonds as crosslinkages (OBZ-BDB) were successfully synthesized. The structures of OBZ and OBZ-BDB were characterized by SEC, 1H NMR, and FT-IR measurements. Reprocessing experiments showed that OBZ-BDB has remarkable reprocessability. The retention rates of the tensile strengths through three generations of reprocessing were 98%, 95%, and 84%, respectively. Meanwhile, OBZ-BDB cross-linked by boronic ester bonds had brilliant thermal properties. The Tg of the original OBZ-BDB was 224 °C. With the increase of the reprocessing generations, the Tgs basically remained unchanged.

Effects of hollow glass microspheres on the polybenzoxazine thermosets: Mechanical, thermal, heat insulation, and morphological properties

AbstractThe growing need for high thermal and mechanical resistant lightweight syntactic foams demands the designing of new materials. Herein, we report the successful fabrication of lightweight and high thermal resistance syntactic foams with excellent thermal and good mechanical properties. For this end, 10–50 wt% hollow glass microsphere (HGMS) containing polybenzoxazine based syntactic foams were prepared by using bisphenol‐A‐aniline (BA‐a) and phenol‐diaminodiphenylmethane (P‐ddm) benzoxazine via curing at 10 MPa compression molding. The curing behavior, tensile, flexural, compressive, and impact strength, thermal properties, and fracture morphology of the syntactic foams were studied by DSC, universal material testing machine, and drop hammer impact testing machine, TGA, and SEM, respectively. The curing temperatures of BA‐a and P‐ddm benzoxazine resins were slightly increased after blending the HGMS. The highest decline (59%) in the density and highest void contains (13.17%) was recorded for the poly(P‐ddm/HGMS50) sample. The excellent specific mechanical properties of the syntactic foams were observed on the 30 wt% HGMS loading. The thermal conductivity of the foams was gradually decreased and the lowest values of 0.106 and 0.0985 W/m.K were observed for poly(BA‐a/HMGS50) and poly(P‐ddm/HGMS50) sample, respectively. Furthermore, a gradual improvement in the thermal properties was observed as the loading of HGMS increased.

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.

Reprocessable polybenzoxazine thermosets crosslinked by mussel-inspired catechol-Fe3+ coordination bonds

The traditional thermosets cannot be reprocessed, which causes serious environmental pollution and resource waste. The catechol-Fe3+ coordination bonds existing in marine mussel byssal cuticle provide a reversible crosslinking structure for reprocessable thermosets. A reprocessable polybenzoxazine thermoset (PBOZ-dopa45-Fe3+) by catechol-Fe3+ coordination bonds was synthesized successfully based on mussel-inspired chemistry and benzoxazine chemistry. Firstly, benzoxazine monomers containing carboxyl groups were synthesized. Secondly, polybenzoxazine with carboxyl groups was obtained through thermal ring-opening polymerization. And then catechol groups were grafted onto the pendant groups of polybenzoxazine. Finally, the reprocessable polybenzoxazine was obtained by catechol groups coordinating with Fe3+. The structure of polybenzoxazine was characterized by NMR, FTIR and SEC measurements. The formation of reversible crosslinked network composed of catechol-Fe3+ coordination bonds is confirmed by UV–Vis absorbances, system color changes, and dissolution states in methanol solutions of different pH. Reprocessing experiments indicate that the reversible catechol-Fe3+ coordination bonds endow remarkable reprocessability of cured resin. Dynamic mechanical measurements and thermogravimetric measurements show that the PBOZ-dopa45-Fe3+ can still maintain excellent thermal properties. Cross-linking by catechol-Fe3+ coordination bonds provides a new way for the preparation of reprocessable thermosets.

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.

Isomannide-Derived Chiral Rigid Fully Biobased Polybenzoxazines

Biobased phenols and amines are attractive feedstock in rapid emerging polybenzoxazine thermosets. Renewable benzoxazines are mainly monofunctional due to structure limitation of raw materials, esp...

Synthesis of novel multi-functional fluorene-based benzoxazine resins: Polymerization behaviour, curing kinetics, and thermal properties

In this paper, a new series of novel aromatic multi-functional fluorene-based benzoxazine monomers (AMFB) were synthesized from the reaction of 9,9-bis(4-aminophenyl)-2,7-dihydroxy-fluorene, aniline, paraformaldehyde, and unsubstituted or substituted phenol including phenol, p-(tert-octyl)phenol, and nonylphenol, by two-stage Mannich condensation reactions. The structures of intermediates and the final benzoxazine monomers were identified via Fourier transform infrared (FTIR) and Hydrogen and Carbon nuclear magnetic resonance (1HNMR and 13CNMR) analyses. The rheology, polymerization behaviour, curing kinetics, and thermal stability of the obtained novel benzoxazines thermosets were measured by using rheometer, differential scanning calorimetry (DSC), FTIR, and thermogravimetric analysis (TGA), respectively. The o-nonyl phenol containing fluorene-based benzoxazine monomer (t-BF-a-n) showed the best processability with the lowest curing energy values. Moreover, the prepared polybenzoxazine thermosets showed excellent thermal stabilities and with higher glass transition temperature (258–333 °C) than the traditional difunctional fluorene-based benzoxazine resins.

Benzoxazine-Based Thermoset with Autonomous Self-Healing and Shape Recovery

A novel approach is reported for self-healing of polybenzoxazine thermosets based on both supramolecular attractions and metal–ligand interactions. The relating smart material was synthesized by using bis(3-aminopropyl)-terminated polydimethylsiloxane, formaldehyde, and bisphenol A. The films of the obtained main-chain polybenzoxazine precursor (Poly(Si-Bz)) containing 2% FeCl3 were prepared and cured at low temperatures (100–120 °C). The structures of the precursors and final products were characterized by spectral analysis. The curing and thermal stability of the related materials were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Self-healing efficiency was studied by stress–strain measurements. Potential shape recovery (SR) behavior was also demonstrated by preparing curled or spiral fixed shapes, and the transformation of temporary shapes to these fixed shapes was verified.

Reinforcement of economical and environment friendly Acacia catechu particles for the reduction of brittleness and curing temperature of polybenzoxazine thermosets

The brittleness always remained a major concern for the polybenzoxazine thermosets. Several attempts have been made to overcome the brittleness issue, but all find some kind of sacrificing in other properties. A new and economical approach is presented by the reinforcement of catechin-rich Acacia catechu (AC) particles. The micro size AC particles blended with bisphenol-A aniline-based benzoxazine (BA-a) resin and isothermally cured. The terminal OH groups of produced tannic acid participated in the curing process and helped in the ring opening of BA-a resin. The composites exhibited that the brittleness of polybenzoxazine has been improved by 35%, simultaneously its strength, Youngs’ modulus, stiffness, glass transition temperature, and thermal stabilities are also enhanced. The highest impact strength of the composite is observed on only 4 wt% loading of AC particles and read as 5.2 ± 0.16 kJ/m2, 307.1% higher than the value of neat poly(BA-a).

Reinforcement of waste hemp fibres in aromatic diamine-based benzoxazine thermosets for the enhancement of mechanical and thermomechanical properties

ABSTRACTNatural fibres (NFs) have been successfully reinforced in polymer matrices to strengthen the properties of the polymers. The polybenzoxazine thermosets are facing instable mechanical properties due to the high brittleness, herein, waste hemp fibres (WHF) reinforced polybenzoxazine composites are prepared. Effects of WHF volume % loading on curing, thermomechanical, mechanical, and thermal properties are studied. FTIR results confirmed that WHF rich in −OH groups increased the ring-opening of oxazines and reduced curing temperature. In addition, an increase of 223%, 111%, 64%, and 253% in impact, tensile strength, flexural and Young's modulus, respectively, were recorded after loading optimum concentration (30 vol. %) in composites. Considerable enhancements were also seen in the thermomechanical properties on optimum loading, double stiffness and 26°C increase was recorded in the glass transition temperature. Nonetheless, the decline was observed in thermal stabilities, T5% and Yc were 24°C and 1.4 % lower, respectively, than neat poly(P-ddm).

Modeling the formation and thermomechanical properties of polybenzoxazine thermosets

The nanostructural topology of polymer networks composed of elastic chains along with additional defects such as dangling chains and loops.

Polybenzoxazine nanocomposites containing 3,13‐Diglycidyl double‐decker silsesquioxane

3,13‐Diglycidyloxypropyloctaphenyl double‐decker silsesquioxane (3,13‐diglydidyl DDSQ) was synthesized via hydrosilylation between 3,13‐dihydrooctaphenyl double‐decker silsesquioxane (3,13‐dihydro DDSQ) and allyl glycidyl ether. This novel difunctional polyhedral oligomeric silsesquioxanes (POSS) macromer was incorporated into polybenzoxazine (PBZ) thermosets to obtain the organic–inorganic nanocomposites. Compared to control PBZ, the organic–inorganic nanocomposites displayed the enhanced glass transition temperatures (Tg's). Under the identical condition, the organic–inorganic nanocomposites exhibited the stable rubbery plateaus in the measurements by dynamic mechanical thermal analysis, which was in marked contrast to control PBZ thermoset. The enhanced Tg's and improved dynamic mechanical properties are attributable to the formation of the additional crosslinking between PBZ and the difunctional POSS macromer and the nanoreinforcement of POSS cages on PBZ networks. Thermogravimetric analysis indicates that the organic–inorganic nanocomposites displayed improved thermal stability. POLYM. COMPOS., 38:827–836, 2017. © 2015 Society of Plastics Engineers

Greatly enhanced thermo‐oxidative stability of polybenzoxazine thermoset by incorporation of m‐carborane

ABSTRACTNovel polybenzoxazine precursor containing m‐carborane unit in the main‐chain has been firstly synthesized through click reaction of diazidomethyl m‐carborane (DAMC) and diacetylene bisbenzoxazine (DABB). Meanwhlie, the traditional polybenzoxazine precursor was also prepared through click reaction of diazidomethyl p‐benzene (DAPB) and DABB as a control. 1H NMR was used to confirm the structures of the monomers and the resulting polymers. FT‐IR and differential scanning calorimetry (DSC) were used to study the curing behavior of carborane‐containing benzoxazine polymer (CCBP). Dynamic mechanical analysis (DMA) study demonstrated that the cured CCBP had high storage moduli and high Tg. Thermogravimetric analysis (TGA) and ablation test showed that the cured CCBP had outstanding thermo‐oxidative stability. During thermal ablation of cured CCBP, organic material was degraded, and a passivation layer with oxidized m‐carboranes was formed, which prevented the underlying polymer from further degradation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 973–980

Self-healing of poly(propylene oxide)-polybenzoxazine thermosets by photoinduced coumarine dimerization

In this work, a self-healing strategy for poly(propylene oxide)s bearing coumarine-benzoxazine units (PPO-CouBenz)s based on light induced coumarine dimerization reactions is described. Four different types of poly(propylene oxide) amines with molecular weights ranging from 440 to 5000 Da were reacted with formaldehyde and 4-methyl-7-hydroxycoumarin to yield desired (PPO-CouBenz)s. The crosslinked polymer films were prepared by solvent casting of various compositions of PPO-CouBenzs in chloroform followed by thermal ring opening reaction of benzoxazine groups at 210–240 °C. Thermal curing and thermal stability of the initial PPOs and final products were investigated. Using allyl benzoxazine in the formulation, it was demonstrated that the toughness of the films was improved. Photoinduced healing of coumarin-based cured PPO-CouBenz polymer films was investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2911–2918