Benzoxazine Research Articles

Investigating UV light and ziram catalyst as alternative activators for sulfur-promoted benzoxazine curing

High-temperature curing is a major limitation for the widespread use of benzoxazine resins. This study explores two strategies to reduce curing temperatures using minimal sulfur content (1–5 wt%): ziram catalysis and light activation. Both approaches effectively promoted curing at lower temperatures compared to traditional methods. The ziram-activated system achieved an activation energy as low as 83 kJ/mol, while the UV-activated system reached 63 kJ/mol. Furthermore, the UV-activated sulfur system exhibited improved thermal stability, particularly for cresol-based benzoxazines. The curing processes of monomers with catalysts were traced using various techniques, including nuclear magnetic resonance (NMR), Fourier-transform infrared (FT-IR), along with differential scanning calorimetry (DSC).

Characterization of Mechanical Properties and Surface Wettability of Epoxy Resin/Benzoxazine Composites in a Simulated Acid Rain Environment

Despite the robustness of thermosetting coatings in various applications, prolonged exposure to acidic environments can cause gradual deterioration, leading to structural or functional damage. This study investigates composite materials comprised of cycloaliphatic epoxy resin (CER) and benzoxazine (BZ) at three different weight ratios: 50:50, 25:75, and 0:100. These composites were exposed to nitric acid, simulating acid rain, for durations ranging from 1 to 5 h. The specimens were characterized for weight change, mechanical properties (flexural strength and short beam strength), and surface properties (contact angle and contact angle hysteresis). Although minimal changes in the physical and mechanical properties of both homopolymer and copolymer composites were detected after short acid exposure (up to 5 h), surface wettability analysis via static contact angle and contact angle hysteresis revealed more pronounced deterioration. The static contact angle decreased by 24.96% and 28.32% for homopolymer BZ and copolymer BZ-CER composites, respectively. Contact angle hysteresis increased by 19.39% and 27.80% for 5 h acid-exposed homopolymer BZ and copolymer CER, respectively. This study underscores the utility of surface wettability analysis as a valuable tool for monitoring deterioration from acidic aging in polymers, particularly in BZ-CER systems used in structural and high-performance applications.

A novel efficient flame-retardant curing agent for epoxy resin based on P-N synergistic effect: Bio-based benzoxazine phosphate ester

Most epoxy resins on the market have low thermal stability and flammable defects. As a potential curing agent for epoxy resin, polybenzoxazine (PBz) can effectively improve the thermal properties of the resin due to its low heat release capacity (HRC) and rigid aromatic ring support, and its raw materials can be derived from renewable resources. Here, we have successfully developed a molecular design strategy to obtain a trifunctional benzoxazine monomer with phosphate ester. Firstly, guaiacol-ethanolamine benzoxazine monomer (GE) was synthesized by Mannich condensation using guaiacol and ethanolamine as raw materials. Then trifunctional benzoxazine phosphate ester (TBP) was synthesized by the nucleophilic reaction of GE with phosphorus oxychloride. Finally, the epoxy resin DGEBA was cured by TBP to obtain a PBz modified epoxy resin (EP-TBP polymer) with Tg of 113.7 °C and char yield of 37.4 %. Due to the introduction of TBP rich in phosphorus and nitrogen, it releases phosphorus radicals and nitrogen-containing inert gases during combustion, which leads to quenching effect and dilution effect. In addition, TBP can also promote the dehydration and dehydrogenation of the polymer and accelerate the formation of the aromatic hybrid char layer. Therefore, the THR of TBP modified epoxy resin is 49.3 % lower than that of epoxy resin without TBP, and the char yield is 47 times higher. And when the phosphorus content is 1.76 %, the flame-retardant grade can reach V-0. In addition, the introduction of TBP also enhanced the mechanical properties, adhesion properties and hydrophobicity properties of the polymer. It is worth mentioning that under alkaline conditions, the phosphate ester in the structure of EP-TBP polymer will undergo ammonolysis reaction with ethanolamine, and the resulting oligomers will be dissolved in it, thereby achieving rapid degradation of EP-TBP polymer. This work is to develop a high-performance multifunctional epoxy resin flame retardant curing agent based on renewable raw materials, and provide important insights for the subsequent development of halogen-free bio-based PBz flame retardant materials.

Molecular dynamics simulations of hydrogen-bonded network structures of polybenzoxazines in the gas phase and aqueous solution

The crucial role of the amine functional group at the Mannich bridge of polybenzoxazines (PBZs) has been reported to be responsible for their hydrogen-bonded network structures. However, they have not been thoroughly studied in an aqueous solution and at the atomistic level. In this study, molecular dynamics simulations were applied to investigate the formation of hydrogen bond interactions of PBZs prepared from bisphenol A/methylamine (m-PBZ), bisphenol A/aniline-based (a-PBZ), and bisphenol A/2-(methylamino)ethylamine (e-PBZ). Based on the simulation results, the hydrogen-bonded network structures of the PBZs interfered with water molecules, leading to less compaction of the PBZ structure in the aqueous solution. The hydrogen bonding species of the m-PBZ and a-PBZ structures consisted of the –OH...N(Mannich) and –OH...O intramolecular interactions. However, for e-PBZ, the –OH...O species was not present, but the 2-(ethylamino)ethylamine substituent formed more hydrogen bonding species than those of m-PBZ and a-PBZ. Additionally, the intermolecular hydrogen bond interactions of the PBZs and water molecules were not detected in any of the aqueous solution simulations.

Efficient synthesis of main chain thermosetting polybenzoxazine resin containing tert-butylcyclohexanone and diphenylmethane units for supercapacitor energy storage

Ring-opening polymerization (ROP) can be utilized to synthesize polybenzoxazine (PBZ) precursors from their respective benzoxazine monomers, resulting in thermosetting phenolic resins. In this study, we synthesized DADCA-DADPM BZ using 4-(tert-butyl)-2,6-bis((E)-4-hydroxybenzalidene)cyclohexan-1-one (DADCA) and 4,4′-diamino-diphenylmethane (DADPM) with paraformaldehyde. The resulting DADCA-DADPM BZ and poly(DADCA-DADPM BZ)_X materials were obtained after thermal curing polymerization at temperatures ranging from 110 to 250 °C were employed as electroactive materials in electrode preparation for supercapacitors (SCs). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) revealed a thermal curing temperature of 230 °C, a char yield of 35 wt%, and a decomposition temperature (Td10) of 288 °C. The electroactive material DADCA-DADPM BZ and poly(DADCA-DADPM BZ)_X materials were evaluated for their suitability in SCs, showing a specific capacitance ranging from 84.6 to 166.6 F g−1, depending on the thermal curing temperature (110–250 °C). Notably, the poly(DADCA-DADPM BZ)_250 retained 84 % of its efficiency after 5000 consecutive cycles at 10 A g−1, highlighting its potential for recyclability.

Thermal insulating, flame retardant, and superhydrophobic polybenzoxazine/silica aerogels fabricated in water-ethanol solvent using eco-friendly method

Polybenzoxazine (PBz) aerogels have garnered considerable attention as an innovative and excellent thermal insulation material, celebrated for its lightweight, low thermal conductivity, and outstanding mechanical properties. However, the use of high boiling point toxic solvents in the preparation process requires a cumbersome solvent exchange procedure coupled with insufficient flame-retardant properties, which hinder the potential application of PBz aerogels. Herein, we employed tetraethyl orthosilicate (TEOS) into PBz using an easy, eco-friendly, and cost-less process to achieve hybrid structure polybenzoxazine/silica (PBz/SiO2) aerogels, by thermal catalysis (72 °C) ring-opening polymerization and polycondensation in water-ethanol solvent without any catalysts. The resulting PBz/SiO2 aerogels were characterized with low density (0.181 g/cm3), low thermal conductivity (0.0315 W/(m·K)), excellent flame-retardancy (PHRR value of 32.3 W/g and THR value of 6.3 kJ/g), and superhydrophobicity (the water contact angle up to 155°). Environment-friendly preparation strategy for the PBz/SiO2 aerogels with excellent comprehensive performance, poised to play a pivotal role in energy-saving buildings and fire-resistant applications.

Ambient drying to fabricate polybenzoxazine aerogels for thermal insulation in aerospace

Polybenzoxazine (PBz) aerogels are promising high-performance, halogen-free flame-retardant thermal insulation materials in aerospace applications. But their widespread use is hindered by high costs, significant drying shrinkage, and poor machinability. Herein, we successfully addressed these challenges by developing PBz aerogel composites using a cost-effective ambient pressure drying method that reduces energy consumption and shortening the preparation cycle. This approach expands the range of available monomers, reduces the inherent rigidity of the network structure, and enhances processability. The resulting PBz aerogels demonstrate low drying shrinkage (as low as 5.68 %), lightweight properties (lowest to 0.322 g cm−3), excellent fire-retardant (self-extinguishing in 1.8 s), and exceptional thermal insulation performance (as low as 0.0402 W m−1 K−1 at room temperature and normal pressure). Further studies under various pressures show that at an atmospheric pressure of 10 Pa, the thermal conductivity at room temperature can reach as low as 0.027 W m−1 K−1. Moreover, cryogenic treatment at −196 °C significantly enhances the compressive properties of PBz aerogels without inducing any noticeable shrinkage. Notably, PBz aerogels exhibit outstanding flame resistance, rated as nonflammable rating in vertical burning tests (UL-94, V-1 class), and showing a limiting oxygen index (LOI) as high as 33.7 %. Overall, these remarkable features underscore the exceptional potential of PBz aerogels as advanced thermal insulation materials in the aerospace industry.

Development of low temperature cure hybrid benzoxazine-epoxy resins for thermally stable and moisture resistant applications

New type of diallyl bisphenol-A (ABA) based benzoxazines and benzoxazine resins tailored with epoxy groups for low-temperature curing, have been developed using various curatives for high performance applications. The molecular structure of the synthesized compounds was analyzed using HRMS, 1H NMR, 13C NMR and ATR-FTIR analytical techniques. The cure behavior (Tp) of benzoxazine (Bz) and benz-epoxy (Bz-Ep) resin in the absence and presence of different nature of curatives were studied using DSC to evaluate their applicability for advanced composite applications. The values of Tp obtained are 279 °C, 190 °C and 247 °C for ABA-a, ABA-dmapa and ABA-ipa respectively. The cure behavior has been further lowered by converting ally group present in the benzoxazine has been transformed into epoxy groups by appropriate mechanism. The curing (Tp) temperature observed for hybrid ABA-a-Ep, ABA-dmapa-Ep and ABA-ipa-Ep benz-epoxy resins are 151 °C, 226 °C and 160 °C, 187 °C and 150 °C, 211 °C respectively. The Tp of different benz-epoxy resin systems studied in the presence of catalysts were found to be in the range of 101-155 °C. With a Tmax of 484 °C and a char yield of 43 %, poly(ABA-a) exhibits impressive thermal stability when compared to other synthesized polybenzoxazines. Further, incorporating various curatives into the benz-epoxy matrix enhances its thermal stability and char yield compared to the neat matrices. Additionally, the developed samples exhibit excellent moisture resistant (0.75 %) and hydrophobic nature with the highest contact angle value of 152o for poly(ABA-a). The findings from various studies indicate that the hybrid benz-epoxy resins demonstrate characteristics such as low-temperature curability, thermal stability, hydrophobicity. These results render them appropriate for a diverse array of high-performance industrial and engineering uses.

Lightweight, covalent-crosslinked, and ambient-dried polybenzoxazine aerogels for fire resistance and thermal insulation

The rapid advancement of modern industries has imposed demands on thermal insulators that possess not only low thermal conductivities but also multifunctional properties. Polybenzoxazine (PBz) aerogels with several advantages have garnered considerable research interest in recent years. Nevertheless, PBz aerogels acquired from ambient pressure drying still confront the challenge of exhibiting relatively high densities and thermal conductivities. In this study, to enrich the category and propose practical ideas for overcoming the above plight, hexamethylene diisocyanate (HDI) was selected as an additive to prepare lightweight and efficient thermal-insulating PBz aerogels through chemical modification. Compared with the pristine specimens (0.268 g·cm−3, 0.0387 W·m−1·K−1), the HDI-modified PBz aerogels exhibited lower densities (0.237–0.256 g·cm−3) and thermal conductivities (0.0354–0.0370 W·m−1·K−1). Moreover, the introduction of HDI has been demonstrated to not impact their superior intrinsic flame retardance, despite an observed reduction in the residual char yields in the HDI-modified groups. Given these excellent properties, PBz-HDI aerogels are expected to be promising candidates for thermal insulation and fire resistance applications.

Synergetic control of multi‐level interface structure of basalt fibers by plasma and chemical functionalization to enhance the mechanical, thermal and interfacial performances of PBZ composites

AbstractThe composites of polybenzoxazine (PBZ) containing functionalized plasma treatment basalt fibers (fP‐BFs) were fabricated through in‐situ polymerization‐mixing technique. fP‐BFs is an effective reinforcement material that can improve the mechanical, thermal, and interfacial properties of composites. Surface activation of fP‐BFs can be enhanced through plasma modification, which improves the interaction between fP‐BFs and 3‐aminopropyltriethoxysilane. A systematic study on fP‐BFs/PBZ composite showed that a processing power of 300 W, a processing time of 5 min, and a fiber content of 9% can achieve good comprehensive mechanical properties. Thermogravimetric analysis results showed that fP‐BFs‐7/PBZ has the highest thermal stability, and its carbon residue rate, decomposition temperature and thermal decomposition activation energy are 36.80%, 452.2 °C and 133.56 kJ/mol, respectively. The dynamic mechanical analysis experiment showed that the addition of fP‐BFs improved the Tg of the composites. Among them, fP‐BFs‐5/PBZ showed the highest Tg, reaching 233.2 °C.Highlights Plasma treatment produced multi‐level structure of basalt fibers (fP‐BFs). Polybenzoxazine (PBZ)/fP‐BFs composites showed excellent performance. Interfacial bonding mechanism between fP‐BFs and PBZ was elucidated. Interfacial interactions between BFs and PBZ contributed to property enhancement. This work provided a green fabrication strategy of PBZ composites.

A cellulose-based light-management film incorporated with benzoxazine resin/tannic acid exhibiting UV/blue light double blocking and enhanced mechanical property

Cellulose, as a biomass resource, has attracted increasingly attention and extensive research by virtue of its widely sources, ideal degradability, good mechanical properties and easy modification due to its rich hydroxyl groups. Nevertheless, it is still a challenge to attain high performance cellulose-based composite film materials with diverse functional combinations. In this work, we developed a multifunctional cellulose-based film via a facile impregnation-curing strategy. Here, benzoxazine resin (BR) is used as an optically functional component to endow the microfibrillated cellulose (MFC) film with powerful light management capabilities including UV and blue light double shielding, high transmittance, and high haze. Meanwhile, the introduction of tannic acid (TA) substantially enhanced the mechanical properties of the film, including tensile strength and toughness, by constructing energy-sacrificial bonds. An effective self-healing of the film was achieved by controlling the degree of BR curing. The final films exhibited 98.24 % UV shielding and 89.98 % blue light blocking, good mechanical properties including a tensile strength of 202.21 MPa and tensile strain of 7.1 %, as well as desirable thermal healing properties supported by incompletely cured BR. This work may provide new insights into the high-value utilization of biomass resources.

Biocompatibility, thermal and mechanical properties of glass fiber‐reinforced polybenzoxazine composites as a potential new endodontic post

AbstractA novel dental fiber post from glass fiber‐reinforced polybenzoxazine (PBZ) composites was developed in this work. The essential properties, that is, chemical characteristics, thermal and biological properties of the PBZ composites were investigated for various glass fiber loadings (10.5, 23.7, 41.2 and 65.1 vol%). Finite element analysis (FEA) was also utilized to observe mechanical behaviors of the tooth model repaired with PBZ composite posts compared to a natural tooth model. The findings reveal that for the fiber‐reinforced PBZ composites not only their thermal properties were significantly improved, but they also showed enhanced cytocompatibility; we found a coefficient of thermal expansion of 12.8 ppm/°C and cell viability of 91.55 for the 65.1 vol% glass fiber‐reinforced PBZ composite. Moreover, samples reinforced with higher glass fiber loadings effectively resulted in the reduction of stress distribution in dentin observed from FEA suggesting protection againt root fractures. Restoration using the PBZ composite post showed the same stress patterns in the dentin‐composite resin‐post interface of the repaired tooth as in the natural tooth model. The results revealed that the glass fiber‐reinforced PBZ composites possess good thermal properties and mechanical behaviors which renders them suitable candidates for biocompatible dental materials.Highlights The glass fiber/polybenzoxazine (GF/PBZ) composites had nontoxic properties as evidenced through cell viability, growth and morphology studies. The thermal expansion of the GF/PBZ composite was similar to that of dentin, promoting adaptation at the dentin‐post interface. Mechanical behaviors evaluated by FEA of tooth model restored with GF/PBZ composite post were similar to those restored with commercial glass fiber post. The biocompatible GF/PBZ composite with good thermal and mechanical properties is a promising new candidate material as dental fiber post.

Development of intrinsically flame-retardant bio-thermosets with further enhanced thermal stability through a photo-thermal dual polymerization strategy

In response to safety and environmental concerns, there has been a significant increase in research focused on developing high-performance thermoset materials from sustainable sources. In this study, a sophisticated chemical design approach integrates coumarin and furan moieties into a bio-based UV-dimerizable benzoxazine resin. The newly obtained bio-benzoxazine exhibits a reduced curing temperature along with improvements in both thermal stability and flame-retardant properties compared to conventional thermosetting counterparts. Extensive characterization of the chemical structure of the UV-dimerizable bio-based benzoxazine is conducted through nuclear magnetic resonance, Fourier transform infrared spectroscopy, elemental analysis, and high-resolution mass spectrometry. The photo-dimerization processes are monitored using UV–Vis and NMR techniques. Additionally, the thermally activated curing behavior is scrutinized via differential scanning calorimetry and in situ FT-IR techniques. Remarkably, the fully polymerized bio-thermoset demonstrates exceptional thermal stability, possessing a Td10 of 410 °C and a Tg of 283 °C. Moreover, the resulting thermosets also shows very low flammability, as evidenced by a heat release capacity of 14.6 J·g-1·K-1 and a total heat release of 2.97 kJ·g-1. This study not only outlines a method to enhance the overall performance of bio-polybenzoxazines but also provides a direct and sustainable synthesis route for bio-derived, intrinsically non-flammable thermosetting materials.

High-Performance Supercapacitors Using Compact Carbon Hydrogels Derived from Polybenzoxazine.

Polybenzoxazine (PBz) aerogels hold immense potential, but their conventional production methods raise environmental and safety concerns. This research addresses this gap by proposing an eco-friendly approach for synthesizing high-performance carbon derived from polybenzoxazine. The key innovation lies in using eugenol, ethylene diamine, and formaldehyde to create a polybenzoxazine precursor. This eliminates hazardous solvents by employing the safer dimethyl sulfoxide. An acidic catalyst plays a crucial role, not only in influencing the microstructure but also in strengthening the material's backbone by promoting inter-chain connections. Notably, this method allows for ambient pressure drying, further enhancing its sustainability. The polybenzoxazine acts as a precursor to produce two different carbon materials. The carbon material produced from the calcination of PBz is denoted as PBZC, and the carbon material produced from the gelation and calcination of PBz is denoted as PBZGC. The structural characterization of these carbon materials was analyzed through different techniques, such as XRD, Raman, XPS, and BET analyses. BET analysis showed increased surface of 843 m2 g-1 for the carbon derived from the gelation method (PBZGC). The electrochemical studies of PBZC and PBZGC imply that a well-defined morphology, along with suitable porosity, paves the way for increased conductivity of the materials when used as electrodes for supercapacitors. This research paves the way for utilizing heteroatom-doped, polybenzoxazine aerogel-derived carbon as a sustainable and high-performing alternative to traditional carbon materials in energy storage devices.

Novel polybenzoxazine-based arylidene moiety modified cellulose acetate for enhanced antifouling properties

Marine fouling is a widespread problem in the maritime industry, causing significant damage to equipment and vessels. Polybenzoxazine (PBz) is a resin that is both remarkable and captivating, and it has a wide range of sophisticated uses. Due to their distinctive characteristics, benzoxazines have sparked the interest of scholars globally. However, most benzoxazine resin production and processing depend on petroleum resources, particularly those based on bisphenol A. This study aimed to create new benzoxazine monomers using bio-based raw materials, primarily motivated by the environmental ramifications. The main goal of this study is to synthesize a benzoxazine molecule, specifically (2E,6E)-2,6-bis(3-(2-hydroxyethyl)-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methylene) cyclohexane-1-one, abbreviated as (CHPE), by employing an arylidene base. Later, the chemical was used as a modifier for the cellulose acetate (CA) matrix to create film samples. The primary objective is to evaluate the effectiveness of these film samples in preventing fouling. The CHPE molecule was produced using a bis(arylidene) cyclohexanone diol and analyzed using Fourier transform infrared (FTIR) and Nuclear magnetic resonance (NMR) spectroscopic techniques, respectively. The films were fabricated by blending various weight proportions. The composition of the (CHPE-CA) films was determined by FTIR analysis, while their morphology was examined using scanning electron microscopy (SEM). The thermal stability of the films was studied using Thermal Gravimetric Analysis (TGA). This study investigated the antifouling properties of polymer sheet compositions containing varying amounts of CA at two different processing temperatures, 180 °C and 200 °C and without curing. The results demonstrated the potential of incorporating CA into the polymer matrix to enhance antifouling performance. Among the polymer compositions tested, the 20% CA composition exhibited the highest percentage reduction in fouling at both processing temperatures, suggesting that a small amount of CA can contribute to effective antifouling properties.

Polybenzoxazine‐based PEMFC composite bipolar plates with three‐dimensional conductive skeleton

AbstractTo address the limitation of poor conductivity in composite bipolar plates (CBPs), a three‐dimensional (3D) conductive skeleton structure of graphite flakes (GF) is constructed using the sacrificial template method. This method prepares 3D polybenzoxazine/graphite flakes composite bipolar plates (3D‐PBA/GF CBPs) with high conductivity through vacuum impregnation of benzoxazine resin (BA). In this paper, the effect of the presence of a conductive network structure on the key properties of CBPs is analyzed, and the performance of GF randomly dispersed CBPs obtained through traditional solution dispersion is also compared. Thanks to the efficient conductive path within its 3D conductive skeleton structure, the 3D‐PBA/GF CBP achieves excellent conductivity meeting US Department of Energy (DOE) targets (in‐plane conductivity greater than 100 S/cm, area‐specific resistance less than 10 mΩ cm2) at a low filler content (50 wt%). In addition, CBPs with 3D conductive skeleton structures also exhibit qualified service performances to meet the requirements of proton exchange membrane fuel cells (PEMFCs). Compared with GF randomly dispersed CBPs, 3D‐PBA/GF CBPs exhibited higher power density in a single cell. This study demonstrates that constructing PBA/GF CBPs with a 3D conductive skeleton to achieve an accumulation distribution of conductive fillers is an efficient method for enhancing the conductivity of CBPs.

Vat photopolymerization 3D printing of biobased low viscosity photoactive benzoxazine thermosets

Preparing biobased benzoxazine resin through vat photopolymerization 3D printing is of great significance for its sustainable development and application in cutting-edge fields. In this work, biobased guaiacol and eugenol are used as phenol sources, while 2-(2-aminoethoxy) ethanol with flexible ether bonds is used as an amine source to create photoactive benzoxazine monomers, Eu-BzMA and Gu-BzMA. The viscosity of both monomers at room temperature is lower than 150 mPa·s, which can satisfy the requirements of digital light processing (DLP) 3D printing without adding diluents. The thermal and mechanical properties of the 3D printing benzoxazine resins are studied and the relationship between structure and properties is discussed by comparing the two molecules. Eu-BzMA resin has higher thermal decomposition temperature (T5 = 343 °C), higher hardness (0.70 GPa), higher flexural stress (43.5 MPa) and flexural moduli (2.71 GPa); while, Gu-BzMA resin has higher glass transition temperature (176 °C). This is because Eu-BzMA resin shows higher cross-linking density, but contains more flexible structures formed by allyl crosslinking. In this article, a preparation strategy of low viscosity biobased photoactive benzoxazine is proposed and successfully applied to vat photopolymerization 3D printing.

Improving comprehensive performance of norbornene‐furan functionalized benzoxazine resins by regulating the bridge length

AbstractIn this study, we designed and synthesized a series of norbornene‐furan functionalized benzoxazine monomers (HPAP‐fa, HPAMP‐fa, and HPTM‐fa) by regulating the bridge length in benzoxazine structure in order to improve the comprehensive performance of norbornene‐furan functionalized benzoxazine system. This research systematically examined the impact of flexible segments on the structural information, polymerization behaviors, thermal stability, and flame retardancy of resulting polybenzoxazines. Initially, the structural characteristics of benzoxazine were confirmed through nuclear magnetic resonance, Fourier‐transform infrared (FT‐IR), and HR‐MS. Subsequently, the polymerization mechanisms of each benzoxazine monomer were investigated utilizing differential scanning calorimeter and in situ FT‐IR analyses. Finally, the thermal stability and flame‐retardant properties were investigated by TGA and micro‐combustion calorimetry measurements. Consequently, HPAP‐fa exhibited the lowest polymerization temperature and the corresponding poly(HPAP‐fa) showed very high thermal stability (Td5 of 392°C and Td10 of 437°C) as well as excellent flame retardancy (HRC of 83.7 J g−1 K−1), which shows a significant improvement compared to poly(HPTM‐fa). As a result, the modulation of bridge segments within the monomer represents a viable approach towards enhancing the holistic efficacy of norbornene‐furan functionalized benzoxazine systems.

A New Polycyclic Naphthoxazine Resin: Facile Synthesis, Characterization, Polymerization, and Thermal Properties of Its Corresponding Thermosets.

A novel polycyclic naphthoxazine resin (NSA-thiq) is synthesized via N, O-acetal forming reaction between o-hydroxyl naphthaldehyde and 1,2,3,4-tetrahydroisoquinoline. The chemical structure of the monomer is investigated and confirmed by 1H and 13C NMR, Fourier-transform infrared (FT-IR) spectroscopy, and high-resolution mass spectrometry. Besides, the ring-opening polymerization behavior similar to ordinary benzoxazine resins is observed by differential scanning calorimetry (DSC) and in situ FT-IR analyses, leading to the formation of the phenolic cross-linked network. Notably, DSC thermograms indicate that the newly obtained polycyclic naphthoxazine resin exhibits much lower polymerization temperatures compared to many other reported benzoxazine or naphthoxazine resins. Moreover, the corresponding polybenzoxazine (poly(NSA-thiq)) shows comparable thermal stability in comparison with thermosets derived from monobenzoxazine resins. As a consequence of these unique performances, NSA-thiq is applied as a property modifier for a commercialized benzoxazine resin (BA-a). The glass transition temperature of copolymeric thermosets is enhanced without sacrificing too much thermal stability and heat resistance. Here, another series of naphthoxazine thermosetting resin is explored, which can provide more examples for constructing composites based on thermoset polymers.

Synthesis, Characterization, and Structure–Property Investigations of Benzoxazine Resins with Low Surface Free Energy

Synthesis, Characterization, and Structure–Property Investigations of Benzoxazine Resins with Low Surface Free Energy