Chemorheology and thermomechanical characteristics of benzoxazine‐urethane copolymers

In this research, processability and some important thermomechanical properties of polybenzoxazine (BA‐a) modified with a highly flexible urethane elastomer (PU) are discussed. This copolymer has been reported to show synergy in its glass transition temperature and some mechanical properties thus provides a fascinating group of high temperature polymers with enhanced flexibility. The results reveal that a processing window of the BA‐a/PU mixtures is widened with the increasing urethane prepolymer fraction, that is, the liquefying temperature is lowered and the gel point shifted to higher temperature with the amount of the PU. Synergism in glass transition temperature (T_g) of this copolymer was clearly confirmed, i.e., T_g's of the BA‐a/PU alloys were significantly greater than those of the parent resins, i.e., BA‐a (T_g = 166°C) and PU (T_g = ? 70°C). In addition, flexural modulus was found to systemically decrease from 5.4 GPa of the neat polybenzoxazine to 2.1 GPa at 40% by weight of the PU. Flexural strength of the alloys also shows a synergistic behavior at the BA‐a/PU ratio of 90/10. Coefficient of thermal expansion of the polymer alloys were also found to show a minimum value at BA‐a/PU = 90/10. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermomechanical characteristics of benzoxazine–urethane copolymers and their carbon fiber‐reinforced composites

Copolymers of polybenzoxazine (BA‐a) and urethane elastomer (PU) with three different structures of isocyanates [i.e., toluene diisocyanate (TDI), diphenylmethane diisocyanate, and isophorone diisocyanate], were examined. The experimental results reveal that the enhancement in glass transition temperature (T_g) of BA‐a/PU copolymers was clearly observed [i.e., T_g of the BA‐a/PU copolymers in 60 : 40 BA‐a : PU system for all isocyanate types (T_g beyond 230°C) was higher than those of the parent resins (165°C for BA‐a and ?70°C for PU)]. It was reported that the degradation temperature increased from 321°C to about 330°C with increasing urethane content. Furthermore, the flexural strength synergism was found at the BA‐a : PU ratio of 90 : 10 for all types of isocyanates. The effect of urethane prepolymer based on TDI rendered the highest T_g, flexural modulus, and flexural strength of the copolymers among the three isocyanates used. The preferable isocyanate of the binary systems for making high processable carbon fiber composites was based on TDI. The flexural strength of the carbon fiber‐reinforced BA‐a : PU based on TDI at 80 wt % of the fiber in cross‐ply orientation provided relatively high values of about 490 MPa. The flexural modulus slightly decreased from 51 GPa for polybenzoxazine to 48 GPa in the 60 : 40 BA‐a : PU system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of polyol molecular weight on properties of benzoxazine–urethane polymer alloys

Recently, a new thermoset resin namely benzoxazine (BA) resin has been developed. The polymer possesses several outstanding properties, such as, ease of synthesis, low viscosity, near‐zero shrinkage, lack of by‐product upon curing, high thermal stability, and high mechanical property. Moreover, the benzoxazine resins can be alloyed with various types of resins because of the various function groups in their structure. In this work, urethane elastomer (PU) is used to enhance toughness of the polybenzoxazine. The effects of polyol molecular weights on the properties of BA: PU polymer alloys are investigated. The experiment reveals that the similar curing peaks of the matrices at various polyol molecular weights, with the same urethane mass fraction, in the resin mixtures are obtained. The glass transition temperature increases from 160°C of polybenzoxazine to 240–245°C in the 70:30 BA:PU system. In addition, the char yield increases when the higher molecular weight of polyol is added. The flexural modulus of polybenzoxazine decreases from 6.2 GPa to be in the range of 2.2–2.8 GPa when 30 wt% of PU is presented in the alloys. Furthermore, the synergism with ultimate flexural strength is observed in the 90:10 BA:PU alloy for all molecular weights of the polyol used. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Enhanced film forming ability of benzoxazine–urethane hybrid polymer network by sequential cure method

Uniform copolymer films of benzoxazine resin (BA‐a) and urethane prepolymer (PU) were prepared at various BA‐a/PU mass ratios (100/0, 80/20, 60/40, 40/60, 20/80, and 0/100) via sequential cure method comprising of moisture cure and thermal cure steps. In the moisture cure step, Fourier Transform Infrared (FT‐IR) spectra revealed the network formation between NCO‐terminated group and moisture to firstly produce PU solid film. Then in the thermal cure step, the change of tri‐substituted benzene ring to tetra‐substituted benzene ring was observed suggesting polybenzoxazine network formation in this step. Moreover, the spectra reveal that isocyanate groups in polyurethane structure could react with phenolic hydroxyl groups of BA‐a to form biuret and allophanate groups. Dynamic mechanical analysis (DMA) confirms a synergistic behavior in glass transition temperature (T_g) of the alloys with the highest T_g value of 275°C which is uniquely observed in these alloys obtained from traditionally thermal cure method. The proposed sequential cure method above is found to be highly useful for uniform coating or film casting process which lacks in traditional, low A‐stage viscosity, benzoxazine resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40502.     

Thermomechanical properties of arylamine‐based benzoxazine resins alloyed with epoxy resin

Effects of epoxy resin on various arylamine‐based benzoxazine resins, i.e., aniline (BA‐a), m‐toluidine (BA‐mt), and 3,5‐xylidine (BA‐35x), have been investigated. Processing windows of BA‐35x, BA‐mt, and BA‐a were found to be widened with the amount of the epoxy. Gel points of benzoxazine‐epoxy resin mixtures can be predicted by an Arrhenius equation, e.g., gel time of BA‐35x and epoxy mixture at 70:30 mass ratio can be estimated by t_gel = 0.7012 × 10^?7 exp (10.563/T). Glass transition temperature (T_g) of BA‐a and BA‐mt alloyed with epoxy exhibited a synergistic behavior with the maximum T_g value at the benzoxazine‐epoxy composition of 80:20 mass ratio. However, in the BA‐35x and epoxy mixture, the decreasing trend in T_g from 241°C to 223°C with an addition of epoxy was observed. Furthermore, flexural strength and strain‐at‐break of those alloys were found to increase with increasing amount of the epoxy while modulus increased with the polybenzoxazine mass fraction. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Morphology and properties of poly(benzoxazine‐co‐urethane)s based on bisphenol‐S/aniline benzoxazine

Poly(benzoxazine‐co‐urethane) was prepared by melt‐blending bisphenol‐S/aniline‐type benzoxazine (BS‐a) with isocyanate‐terminated polyurethane (PU) prepolymer based on 2,4‐toluene diisocyanate and poly(ethylene glycol), followed by thermally activated polymerization of the blend. The copolymerization reaction between BS‐a and PU prepolymer was monitored using Fourier transform infrared spectroscopy. The morphology, dynamic mechanical properties, and thermal stability of the poly(benzoxazine‐co‐urethane) were studied using scanning electron microscopy, dynamic mechanical analysis, and thermogravimetry. Homogeneous morphology is shown in scanning electron micrographs of the fracture surfaces of poly(benzoxazine‐co‐urethane)s with different urethane weight fractions, and the roughness of the surface increases with urethane content increasing. Correspondingly, a single glass transition temperature (T_g) is shown on the dynamic mechanical analysis curves of the poly(benzoxazine‐co‐urethane)s, and the T_g is higher than that of the polybenzoxazine. With increase in the urethane content, the T_g and water absorption of poly(benzoxazine‐co‐urethane) increase, whereas the storage modulus and thermal stability decrease. POLYM. ENG. SCI., 53:2633–2639, 2013. © 2013 Society of Plastics Engineers     

Polybenzoxazine containing polysilsesquioxane: Preparation and thermal properties

Benzoxazine bearing trimethoxylsilane (BA‐b) was successfully synthesized via Mannich condensation among phenol, paraformaldehyde, and γ‐aminopropyltrimethoxysilane. The hydrolysis and condensation of the BA‐b catalyzed by hydrochloric acid can afford a soluble polysilsesquioxane bearing benzoxazine groups (denoted PSSQ‐b). By initiating the cocuring reaction of PSSQ‐b with difunctional benzoxazine of bisphenol A (BA‐a), the inorganic–organic hybrids of polybenzoxazine with polysilsesquioxane were prepared. The hybrids displayed enhanced T_g's in comparison with the control polybenzoxazine. In terms of initial decomposition temperature (T_d) and char and ceramic yields, the hybrids exhibited improved thermal stability as shown by thermogravimetric analysis (TGA). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 927–936, 2006     

Synthesis and characterization of a novel acetylene‐ and maleimide‐terminated benzoxazine and its high‐performance thermosets

A novel acetylene‐ and maleimide‐terminated benzoxazine, 3‐(3‐ethynylphenyl)‐3,4‐dihydro‐2H‐6‐(N‐maleimido)‐1,3‐benzoxazine (MBZ‐apa), was successfully synthesized with N‐(4‐hydroxyphenyl)maleimide, paraformaldehyde, and 3‐aminophenylacetylene. The structure of the benzoxazine is confirmed by FTIR and ¹H‐NMR spectroscopies. MBZ‐apa is easily dissolved in common organic solvents. Differential scanning calorimetry (DSC) was used to study thermal cross‐linking behavior of MBZ‐apa. The DSC curve shows only a single exothermic peak due to the oxazine ring‐opening polymerization and the polymerization of the acetylene and maleimide groups occurring simultaneously in the same temperature range. Dynamic mechanical analyses (DMA) reveals that the novel polybenzoxazine exhibits high glass‐transition temperature (T_g) (ca. 348°C). The storage modulus arrives at 4.5 GPa in the range of room temperature to 330°C. The polybenzoxazine exhibits good thermal stability as evidenced by thermogravimetric analysis (TGA). Pyrolysis‐gas chromatography/mass spectrometry (Pyrolysis‐GC/MS) was employed to characterize the polybenzoxazine. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of new polybenzoxazines from renewable resources for bio‐composite applications

Renewable natural resources such as eugenol, furfurylamine, stearylamine, and jute fiber were used to prepare polybenzoxazine composites. The purity of eugenol which is extracted from clove was confirmed by gas chromatography. FTIR, ¹H, and ¹³C NMR spectroscopic analysis were used to determine the structure of eugenol and the benzoxazine monomers namely 6‐allyl‐3‐furfuryl‐8‐methoxy‐3,4‐dihydro‐2H‐1,3‐benzoxazine (EF‐Bz) and 6‐allyl‐3‐octadecyl‐8‐methoxy‐3,4 dihydro‐2H‐1,3‐benzoxazine (ES‐Bz) synthesized from it. The curing analysis from differential scanning calorimetric analysis shows that the onset of curing is shifted to lower temperature (161°C) for EF‐Bz, when compared with ES‐Bz (174°C). The thermal stability analyzed from thermogravimetric analysis shows that the polybenzoxazine EF‐Pbz has higher thermal stability (T_5% = 361°C) with that of ES‐Pbz (T_5% = 313°C). The storage modulus, tensile, and flexural strength of the EF‐Bz/Jute fiber composite show high value when compared with ES‐Bz/Jute fiber composites. POLYM. COMPOS., 37:1821–1829, 2016. © 2014 Society of Plastics Engineers     

Effects of high nano‐SiO2 contents on properties of epoxy‐modified polybenzoxazine

High‐performance nanosilica composites based on epoxy‐modified polybenzoxazine matrices are developed. Chemorheological study of benzoxazine–epoxy resin mixtures reveals that processing window of the benzoxazine resin (BA‐a) is substantially broadened with an addition of the liquid epoxy. Glass transition temperature (T _g) of the BA‐a copolymerized with epoxy resin shows a synergistic behavior with a maximum T _g value (174°C) at the benzoxazine–epoxy mass ratio of 80:20. The copolymer at this composition is also used as a matrix for nano‐SiO₂ composites. A very low melt viscosity of the benzoxazine–epoxy mixtures promotes good processability with the maximum attainable nano‐SiO₂ loading up to 35 wt%. From scanning electron microscopy investigation, fracture surface of the 35 wt% nano‐SiO₂‐filled benzoxazine–epoxy composite reveals relatively homogeneous distribution of the nano‐SiO₂ in the copolymer with good particle wet‐out. In addition, very high reinforcing effect was also observed in such high content of the nano‐SiO₂, i.e., about 2.5 times in modulus improvement. This improvement is attributed to the strong bonding between the copolymer matrix and the nano‐SiO₂ through ether linkage as confirmed by Fourier‐transform infrared investigation. POLYM. COMPOS., 38:2261–2271, 2017. © 2015 Society of Plastics Engineers     

Synthesis and characterization of sequential interpenetrating polymer networks of polyurethane acrylate and polybenzoxazine

High‐performance ultraviolet (UV) curable polyurethane acrylate (PUA) coating alloyed with thermally curable polybenzoxazine (PBA) is developed. The hybrid polymer networks of PUA and PBA‐a were prepared by sequential cure methods, i.e., UV cure of the PUA followed by thermal cure of the PBA fraction. The effects of sequential cure were investigated in terms of mechanical, thermal, and physical properties of the resulting polymer alloys. The fully cured PUA/PBA‐a alloy films showed only single glass transition temperature (T_g) suggesting high compatibility between the two polymer networks, possibly of an interpenetrating polymer network type. The storage modulus in a glassy state and T_g of PUA/PBA‐a alloys were found to substantially increase with increasing PBA‐a content. Furthermore, degradation temperature at 10% weight loss of the PUA/PBA‐a alloy films was relatively high whereas the char yield at 800°C was found to increase with a PBA‐a component. Hardness was enhanced, whereas water absorption and water vapor permeation rate of the alloy were suppressed by the incorporation of the PBA‐a into the polymer alloys. As a consequence, the properties of UV curable PUA networks can be positively tailored and enhanced by forming hybrid network with PBA‐a. POLYM. ENG. SCI., 54:1151–1161, 2014. © 2013 Society of Plastics Engineers     

Effects of aromatic carboxylic dianhydrides on thermomechanical properties of polybenzoxazine‐dianhydride copolymers

Enhanced thermomechanical properties of bisphenol‐A based polybenzoxazine (PBA‐a) copolymers obtained by reacting bisphenol‐A‐aniline‐type benzoxazine (BA‐a) resin with three different aromatic carboxylic dianhydrides, i.e., pyromellitic dianhydride (PMDA), 3,3′,4,4′ biphenyltetracarboxylic dianhydride (s‐BPDA), or 3,3′,4,4′ benzophenonetetracarboxylic dianhydride (BTDA) were reported. Glass transition temperature (T_g), of the copolymers was found to be in the order of PBA‐a:PMDA>PBA‐a:s‐BPDA>PBA‐a:‐BTDA. The difference in the T_g of the copolymers is related to the rigidity of the dianhydride components. Furthermore, the T_g of PBA‐a:BTDA, PBA‐a:s‐BPDA, and PBA‐a:BTDA films was observed to be significantly higher than that of the neat PBA‐a owing to the enhanced crosslink density by the dianhydride addition. This greater crosslink density results from additional ester linkage formation between the hydroxyl group of PBA‐a and the anhydride group of dianhydrides formed by thermal curing. Moreover, the copolymers exhibit enhanced thermal stability with thermal degradation temperature (T_d) ranging from 410°C to 426°C under nitrogen atmosphere. The char yield at 800°C of the copolymers was found to be remarkably greater than that of the neat PBA‐a with a value up to 60% vs. that of about 38% of the PBA‐a. Toughness of the copolymer films was greatly improved compared to that of the neat PBA‐a. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Flammability and thermomechanical properties of dianhydride‐modified polybenzoxazine composites reinforced with carbon fiber

Composites based on carbon fiber (CF) and benzoxazine (BA‐a) modified with PMDA were investigated. The flammability of the carbon fiber composites was examined by limiting oxygen index (LOI) and UL‐94 vertical tests. The LOI values increased from 26.0 for the CF/poly(BA‐a) composite to 49.5 for the CF‐reinforced BA‐a/PMDA composites as thin as 1.0 mm and the CF‐reinforced BA‐a/PMDA composites were also achieved the maximum V‐0 fire resistant classification. Moreover, the incorporation of the PMDA into poly(BA‐a) matrix significantly enhanced the T_g and the storage modulus (E') values of the CF‐reinforced BA‐a/PMDA composites rather than those of the CF/poly(BA‐a). The T_g values and storage moduli of the obtained CF‐reinforced BA‐a/PMDA composites were found to have relatively high value up to 237°C and 46 GPa, respectively. The CF‐reinforced BA‐a/PMDA composites exhibited relatively high degradation temperature up to 498°C and substantial enhancement in char yield with a value of up to 82%, which are somewhat higher compared to those of the CF/poly(BA‐a) composite, i.e., 405°C and 75.7%, respectively. Therefore, due to the improvement in flame retardant, mechanical and thermal properties, the obtained CF‐reinforced BA‐a/PMDA composites exhibited high potential applications in advanced composite materials that required mechanical integrity and self‐extinguishing property. POLYM. COMPOS., 34:2067–2075, 2013. © 2013 Society of Plastics Engineers     

Preparation and cure behavior of organoclay‐modified allyl‐functional benzoxazine resin and the properties of their nanocomposites

A new type of polybenzoxazine‐clay nanocomposites were prepared by the in‐situ polymerization of allyl‐functional benzoxazine monomer, bis(3‐allyl‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl)isopropane (B‐ala), in the presence of two different types of organoclay, allyldimethylstearylammonium‐montmorillonite and propyldimethylstearylammonium‐montmorillonite. The organoclays were mixed with molten B‐ala, followed by pouring into glass mold and then gradual curing up to 250°C. DSC and IR were used to follow the cure behavior of B‐ala in the presence of organoclay, indicating that organoclays catalyzed the ring opening of cyclic benzoxazine structure. The XRD of the nanocomposites showed featureless patterns, suggesting the exfoliation of the organoclay into the matrix. The viscoelastic properties of the hybrids showed that the glass transition temperatures (T_g) of the nanocomposites shifted to lower temperature in the presence of small amount of organoclay, but T_g started to increase with the increase of the organoclay content. This result suggests that, in the presence of organoclay, the curing reaction of ally and benzoxazine occurred in a different way, resulting in a different network structure. However, the presence of dispersed layered silicates into the matrix enhanced the thermal stability over the neat thermoset resin. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Synthesis and characterization of a hybrid material based on a trimethoxysilane functionalized benzoxazine

A polybenzoxazine/polysiloxane hybrid has been prepared by sol–gel process and ring‐opening polymerization. For this purpose, first a functionalized benzoxazine was synthesized from bisphenol A, paraformaldehyde and 3‐(trimethoxysilyl) propylamine, with initial molar ratio 1 : 4 : 2, and 95% yield. The structure of the monomer was characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance. The sol–gel process and curing behavior have been studied by FTIR spectroscopy and differential scanning calorimetry. The dynamic mechanical thermal analysis of the hybrid material (Bz‐PSi) showed higher T_g and storage modulus respect to the conventional polybenzoxazine (Bz‐BA). Also, the thermogravimetric analysis revealed a better thermal stability. The high limiting oxygen index (LOI) values (about LOI = 32) confirmed similar effective flame retardance properties of the hybrid material respect to conventional benzoxazine. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Flexible polybenzoxazine thermosets containing pendent aliphatic chains

The rich chemistry of polybenzoxazines allows a wide range of molecular structure design by using appropriate starting materials. A new class of polybenzoxazines has been developed from benzoxazine monomers containing pendent long aliphatic chains. The monomers have been synthesized by the reaction of phenol or bisphenol A with two different long‐chain aliphatic amines. The chemical structure of the monomers was confirmed by ¹H nuclear magnetic resonance and Fourier transform infrared spectroscopy. The polymerization behavior of the monomers studied by differential scanning calorimetry shows exothermic peaks due to the ring‐opening polymerization of benzoxazine monomers centered at 247–255 °C. Dynamic mechanical analysis indicated that the glass transition temperatures T_g were in the range 81–92 °C. The thermal stability of the polymers was also examined by thermogravimetric analysis, demonstrating that the weight loss temperatures decreased in comparison with that of traditional polybenzoxazine. Copyright © 2011 Society of Chemical Industry     

Thermal analysis and mechanical characterization of maleimide‐functionalized benzoxazine/epoxy copolymers

Maleimide‐functionalized benzoxazine is copolymerized with epoxy to improve toughness and processibility without compromising the thermal properties. The incorporation of maleimide functionality into the benzoxazine monomer results in a high performance polymer. All three possible polymerization reactions are confirmed using Fourier transform infrared (FT‐IR) spectroscopy. While maleimide‐functionalized benzoxazine has a glass transition temperature, T_g, of 252°C, a further 25°C increase of T_g is observed when copolymerized with epoxy. The flexural properties are also measured, and the copolymers exhibit a flexural modulus of 4.2–5.0 GPa. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1670–1677, 2006     

Synthesis and characterization of poly(urethane‐benzoxazine)/clay hybrid nanocomposites

Poly(urethane‐benzoxazine)/clay hybrid nanocomposites (PU/Pa–OMMTs) were prepared from an in situ copolymerization of a polyurethane (PU) prepolymer and a monofunctional benzoxazine monomer, 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (Pa), in the presence of an organophilic montmorillonite (OMMT), by solvent method using DMAc. OMMT was made from cation‐exchange of Na‐montmorillonite (MMT) with dodecyl ammonium chloride. The formation of the exfoliated nanocomposite structures of PU/Pa‐OMMT was confirmed by XRD from the disappearance of the peak due to the basal diffraction of the layer‐structured clay found in both MMT and OMMT. DSC showed that, in the presence of OMMT, the curing temperature of PU/Pa lowered by ca. 60°C for the onset and ca. 20°C for the maximum. After curing at 190°C for 1 h, the exothermic peak on DSC disappeared. All the obtained films of PU/Pa–OMMT were deep yellow and transparent. As the content of OMMT increased, both the tensile modulus and strength of PU/Pa–OMMT films increased, while the elongation decreased. The characteristics of the PU/Pa–OMMT films changed from plastics to elastomers depending on OMMT content and PU/Pa ratio. PU/Pa–OMMT films also exhibited excellent resistance to the solvents such as tetrahydrofuran, N,N‐dimethylformamide and N‐methyl‐2‐pyrrolidinone. The thermal stability of PU/Pa were enhanced remarkably even with small amount of OMMT. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4075–4083, 2003     

High residual mechanical properties at elevated temperatures of bamboo/glass reinforced‐polybenzoxazine hybrid composite

We successfully added bamboo and glass fibers into bisphenol A‐aniline based benzoxazine (BA‐a) resin by hot‐pressing method. In order to improve the interfacial adhesion between bamboo fibers and the matrix, bamboo fibers were pretreated in 6 wt% NaOH solutions for 12 h. The results showed alkali‐treatment had a positive effect on mechanical properties of the composites at both room and elevated temperatures (60°C, 110°C, 160°C, and 210°C). Due to the incorporation of glass fibers, the bamboo/glass reinforced‐polybenzoxazine hybrid composites exhibited highest strength and modulus among all samples and had high residual mechanical properties at elevated temperatures (residual mechanical properties refers to the ratio of strength and modulus of the composites at elevated temperatures to that measured at room temperature). The fractured surface morphologies of the composites were observed by scanning electron microscope. The results showed with the increase of temperature, the debonding and fiber pull‐out became apparent, and the matrix softening could be clearly observed at 210°C. In addition, thermal and thermomechanical properties of neat benzoxazine and the composites were also investigated through thermogravimetric analysis and dynamic mechanical analyzer, respectively. POLYM. ENG. SCI., 59:1818–1829, 2019. © 2019 Society of Plastics Engineers     

Synthesis of branched benzoxazine monomers with high molecular mass,wide processing window,and properties of corresponding polybenzoxazines

Four cyclotriphosphazene‐based benzoxazine monomers (I, II, III, and IV) with relatively high molecular weight were synthesized by a nucleophilic substitution reaction, and their chemical structures were confirmed by ¹H‐NMR and ³¹P‐NMR. A new term, oxazine value (OV, similar to epoxy value), was first proposed to explain the structure–property relationship of the cured polymers. The polymerization behaviors of the four monomers were studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. The maximum exothermic peaks of the four monomers are in the range 244–248 °C. All monomers possess a wide processing window despite their high molecular weight. The thermal stability, glass‐transition temperature (T_g), and mechanical properties of each cured polymer were studied by thermogravimetric analysis and dynamic mechanical thermal analysis. The char yield at 850 °C, T_g, and storage moduli of PIV (polybenzoxazine obtained from monomer IV) are 60.0%, 218 °C, and 9.0 GPa, respectively. The surface property and humidity absorption character of the cured polybenzoxazines were also studied. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44453.