A new synthetic approach for difficult benzoxazines: Preparation and polymerization of 4,4′-diaminodiphenyl sulfone-based benzoxazine monomer

The first successfully synthesized benzoxazine in high purity from 4,4′-diaminodiphenyl sulfone (DDS), paraformaldehyde and phenol using high boiling point nonpolar solvent is reported. The solution method for benzoxazine synthesis is modified by using a nonpolar solvent of high boiling point. For comparison, the synthesis of such difficult benzoxazine monomer was prepared in high boiling point polar solvent, dimethylsufoxide. ¹H NMR indicates the purity of the monomer prepared by this novel method to be quite high in comparison with that obtained using dimethylsulfoxide (DMSO). The thermally activated polymerization of the monomer affords polybenzoxazine with T_g at ca. 203 °C. The 5% and 10% decomposition temperatures of the polymer are 324 and 368 °C with 58% char yield, reflecting the excellent thermal stability than the typical polybenzoxazine based on bisphenol-A and aniline.     

1,3‐bis(benzoxazine) from cashew nut shell oil and diaminodiphenyl methane and its composites with wood flour

Cashew nut oil‐based benzoxazine monomer has been synthesized applying solvent‐less method through the Mannich reaction of cashew nut shell oil as phenol, amine, and formaldehyde. A difunctional 1,3‐benzoxazine is synthesized using diaminodiphenyl methane as the amine component. ¹H and ¹³C‐nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy are used to characterize the structure of the monomers. Wood flour is used to prepare composites, making both reinforcement and matrix resin the materials derived from renewable resources. Observation of catalytic effects on DSC exothermic temperature and crosslink density by the added wood flour is discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of 2‐oxazoline‐benzoxazine compound and its polymer

A novel 2‐oxazoline‐benzoxazine (POB) was synthesized with 2‐(hydroxylphenyl)‐2‐oxazoline, 1,3,5‐triphenylhexahydro‐1,3,5‐triazine and paraformaldehyde. The chemical structure of the monomer was confirmed by FTIR, ¹H‐NMR, ¹³C‐NMR, and MS. The curing behavior of the monomer was studied by DSC and FTIR, and the ring opening reaction of the monomer was found to occur from 187.5°C. The results of DMA and TGA demonstrated that the thermal properties of polymer for POB monomer (P‐m) are better than polymer for POB precursor (P‐p), because that the oligomer in benzoxazine precursor decreased the perfection of the polymer's network structure; it was also found that the thermal properties of P‐m and P‐p are much better than the common polybenzoxazine and the composite material of benzoxazine and 2‐oxazoline. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci , 2008.     

Development of a novel,ultra‐performance polymer cement: In situ formation of benzoxazine monomer and subsequent formation of polybenzoxazine/cement composites

The feasibility of making a high strength, water resistant polymer cement with 6,6′‐bis(2,3‐dihydro‐3‐methyl‐4H‐1,3‐benzoxazinyl) isopropylidiene (bisphenol‐A) and methylamine‐based benzoxazine, is examined. The polymer cement composites are made by room temperature combination of monomer precursors, solvent, and alumina cement. The subsequent monomer formation, in both the presence and absence of cement, is measured with respect to time by ¹H nuclear magnetic resonance spectroscopic analysis (NMR) of the reaction products. The addition of high alumina cement to the monomer precursors results in accelerated benzoxazine monomer formation at room temperature. The mechanism of monomer formation is discussed. Decreased polymerization temperature of the benzoxazine monomer in the presence of cement is studied by thermal analysis. Solvent is found to have little to no effect on the monomer formation and cure. A compressive strength as high as 250 MPa and a 90 day room temperature water absorption of less than 3% is achieved with no further addition of modifiers. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Synthesis, characterization, and thermally activated polymerization behavior of bisphenol-S/aniline based benzoxazine

A difunctional benzoxazine monomer, 6,6′-bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazinyl) sulfone (BS-a), was synthesized via a solution method from bisphenol-S, aniline and formaldehyde. The chemical structure of the benzoxazine was confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and size exclusion chromatography. The ring-opening polymerization of BS-a monomer was investigated with FTIR under air and nitrogen atmospheres, and with differential scanning calorimetry (DSC) in both dynamic and isothermal conditions. The FTIR results show that the absorption intensities of C-O-C, C-N-C, and oxazine ring decrease gradually with temperature and time rising during the polymerization reaction. The change rates of some absorption intensities of oxazine ring are affected by different atmospheric environments, and a higher degree of conversion is obtained in nitrogen than that in air at the same reaction temperature and in equal time. Kinetic parameters of the dynamic polymerization DSC results were evaluated with Kissinger and Ozawa methods, respectively. The isothermal DSC results show that the polymerization reaction of BS-a monomer follows an autocatalytic mechanism.     

Synthesis and properties of a novel bio‐based benzoxazine resin with excellent low‐temperature curing ability

A novel bio‐based benzoxazine resin (diphenolic acid/furfurylamine benzoxazine resin, PDPA‐F‐Boz) was prepared by using bio‐based diphenolic acid, furfurylamine and paraformaldehyde as raw materials. The structure of DPA‐F‐Boz monomer was characterized by Fourier transform infrared spectroscopy, ¹H NMR and ¹³C NMR, and then its curing reaction and the thermal stability of the cured PDPA‐F‐Boz were analyzed. Compared with the traditional fossil‐based benzoxazine (bisphenol A/aniline benzoxazine, BPA‐A‐Boz) and the bio‐based benzoxazine (diphenolic acid/aniline benzoxazine, DPA‐A‐Boz), DPA‐F‐Boz monomer showed the lowest curing temperature, and PDPA‐F‐Boz had the highest residual char ratio at 800 °C and the lowest degradation rate at the peak temperature. Meanwhile, the total heat release, peak heat release rate and heat release capacity of PDPA‐F‐Boz were much lower than those of PBPA‐A‐Boz and PDPA‐A‐Boz. Thus, PDPA‐F‐Boz showed excellent low‐temperature curing ability and thermal stability. © 2019 Society of Chemical Industry     

Synthesis of linear polymers containing benzoxazine moieties in the main chain with high molecular design versatility via click reaction

Linear polymers with benzoxazine rings in the main chain have been synthesized applying click chemistry approach. These polymers possess molecular weights significantly higher than the benzoxazine polymers which have been chain extended via Mannich reaction. The number average molecular weight is estimated from size exclusion chromatography (SEC) to be between 20,000 and 40,000 Da. The structure of the polymers is confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is used to study crosslinking behavior of the polymers. The nature of the low temperature exotherm DSC peak observed in this work and the previous work of other authors is studied by model reactions. It is due to thermal coupling of the residual propargyl and azide end groups in the absence of active catalyst. In addition, a novel diazide-functional benzoxazine monomer has been prepared, showing a tremendous flexibility for applying click reaction to obtain various polymer architectures. Three types of polymers have been prepared from dipropargyl- and diazide-functional benzoxazine monomers. These polymers have been characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).     

Novel benzoxazine monomer containing diacetylene linkage: An approach to benzoxazine thermosets with low polymerization temperature without added initiators or catalysts

A novel benzoxazine monomer containing diacetylene linkage has been synthesized by applying an oxidative coupling approach. The structure is confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry (DSC) is used to study crosslinking behavior of synthesized material. The benzoxazine monomer exhibits unexpectedly low exothermic peak with the onset around 140 °C, which is significantly lower than conventional benzoxazines or benzoxazines containing additional crosslinking sites. Benzoxazine polymerization at this low temperature is also confirmed by FTIR. The initial model studies are made in order to understand this phenomenon and preliminary explanation is given. High thermal stability of the crosslinked thermoset was confirmed by thermogravimetric analysis (TGA).     

Preparation of oil-modified polycaprolactone and its further modification with benzoxazine for coating purposes

Sunflower oil-modified polyester (SOMPE) was prepared via the ring opening polymerization of ?-caprolactone (CL) using partial glycerides (PGs) and stannous octoate (SO) as the initiator and catalyst, respectively. In addition to being the initiator, PGs participate in the drying process of the film sample for coating purposes. The structure of the sample was characterized by FT-IR and ¹H NMR. The film of SOMPE cannot reach a fully dried state as a result of its less oil moiety content. By increasing the oil fraction, the chain length of polycaprolactone (PCL) decreased by changing the [monomer]/[initiator] mol ratio and shortening the reaction time. Even with these precautions, the molecular weight of SOMPE could not be reduced below 5000 g/mol, and this caused the film to become soft. Therefore, hydroxy-functional benzoxazine monomer (HFB-a) was prepared and used in a further modification of SOMPE. HFB-a was chemically combined with SOMPE via the urethane linkage formed from the reaction of 2,4-toluene diisocyanate, yielding SOMPE-HFB-a. Because the SOMPE-HFB-a sample also had a soft film, additional HFB-a was used to prepare the SOMPE-HFB-a/HFB-a blend. The cured blend prepared with SOMPE-HFB-a and HFB-a in a weight ratio of 1/8, [SOMPE-HFB-a/HFB-a:1/8], had good film properties. The cured film was examined by FT-IR and DSC following the curing process. After our modifications were applied, PCL and polybenzoxazine lost their softness and brittleness, respectively, and a binder with good film properties was formed.     

丁胺-芴基苯并噁嗪/环氧共混树脂的性能研究

以双酚芴、正丁胺和多聚甲醛为原料,二氧六环为溶剂,通过Mannich缩合反应,合成了高纯度丁胺-芴基苯并噁嗪单体（BF-n-b）。以差式扫描量热仪（DSC）研究了苯并噁嗪单体/E-51环氧共混树脂的固化行为,通过动态热机械分析（DMA）和热重分析（TGA）研究了共混树脂的热机械和热稳定性能。结果表明,采用改进的制备方法简化了苯并噁嗪单体的合成过程,单体收率和纯度显著提高;苯并噁嗪/环氧共聚物的玻璃化转变温度（Tg）达到165~178℃,初始热分解温度（热失重5%）达312~342℃,800℃时残碳率最高达22.4%。     

Studies on curing and thermal behavior of diglycidyl ether of bisphenol‐A and benzoxazine mixtures

This article describes the synthesis and characterization of benzoxazine monomers prepared by reacting the mixture of amine (aniline [A], 3‐chloroaniline [C], o‐toluidine [T]) and phenol (bisphenol‐A [B], phenol [P]) with formaldehyde [F]. The benzoxazine monomers prepared by reacting B and F with A, C, and T have been designated as BAF, BCF, and BTF, respectively. Structural characterization of benzoxazines was done using FTIR, ¹H NMR, and elemental analysis. The curing behavior of benzoxazine monomers was investigated by differential scanning calorimetry in the presence of diglycidyl ether of bisphenol‐A (DGEBA). In all the samples, the molar ratio of benzoxazine monomer:DGEBA, was varied as 1 :0, 3 : 1, 1 : 1, and 1 :3. The peak exotherm temperature (T_p) was lowest in all the samples having molar ratio of 3 : 1 benzoxazine:DGEBA and highest in samples having molar ratio of 1 : 3. The heat of polymerization (ΔH) was found to be maximum during curing of mixture of DGEBA and benzoxazine monomer prepared from phenol, aniline and formaldehyde (PAF). Thermal stability of benzoxazines:DGEBA mixture cured isothermally was evaluated by recording thermogravimetric traces in nitrogen atmosphere. The char yield was highest for a mixture having benzoxazine : DGEBA in the ratio of 3 : 1. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A novel benzoxazine monomer with methacrylate functionality and its thermally curable (co)polymers

Benzoxazine monomer with methacrylate functionality, namely 2-(2-(2H-benzo[e][1,3]oxazin-3(4H)-yl)ethoxy) ethyl methacrylate (BEM) was synthesized by simple esterification reaction of hydroxyl containing benzoxazine (B–OH) with methacryloyl chloride, and characterized. BEM was then copolymerized with styrene in 1:4 mol ratio by free radical polymerization using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. The structure, chemical composition, and molecular weight characteristics of the resulting copolymer were confirmed by FT-IR, ¹H-NMR spectroscopy, and GPC, respectively. The curing behavior and thermal properties of both monomer and copolymer were also studied by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA).     

Highly cross-linked thermosetting resin of maleimidobenzoxazine functionalized with benzocyclobutene

Maleimidobenzoxazine monomer functionalized with benzocyclobutene (BCB) and its cured resin has been successfully prepared. BCB-modified maleimidobenzoxazine monomer (HMI–AB) was synthesized by the reaction of 4-aminobenzocyclobutene (AMBCB), p-hydroxyphenylmaleimide (HMI) and paraformaldehyde in dioxane under reflux. Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR) were used to characterize the structure of the monomer. The monomer HMI–AB possesses three kinds of polymerizable functional groups of BCB, maleimide and benzoxazine. The polymerization behavior of the monomer is studied by differential scanning calorimetry (DSC) and FTIR. DMA study demonstrates that the cured resin show high storage modulus and high T_g at ca. 350 °C. TGA study shows that the cured resin possess good thermal stability.     

Ultrasound‐assisted synthesis of benzoxazine monomers: thermal and mechanical properties of polybenzoxazines

A series of benzoxazine monomers (P‐aea2–P‐aea8) were prepared from appropriate aromatic diamines containing linear aliphatic ether chains with phenol and formaldehyde through the Mannich reaction under ultrasonication and conventional methods. Based on the reaction performance, the ultrasonication method has been found to be more facile and convenient for the synthesis of benzoxazine monomer than the conventional method. The synthesized monomers undergo curing at a lower temperature than that of conventional benzoxazine (Ba‐A) monomer as evidenced from differential scanning calorimetric analysis. The presence of an aliphatic ether core in the benzoxazine monomer aids in lowering the curing temperature, which seems to vary linearly with chain length. Thermally polymerized benzoxazine (poly(P‐aea_s)) shows an enhanced tensile and flexural strength. Copyright © 2012 Society of Chemical Industry     

Chemically bonded iron carbonyl for magnetic composites based on phthalonitrile polymers

Dicarboxylic acid‐containing 1,3‐benzoxazine was synthesized and chemically bonded on iron carbonyl particles using a post‐coating method. Novel organic–inorganic hybrid magnetic composites were prepared via the interfacial reaction between magnetic phthalonitrile prepolymers and the benzoxazine functional coatings that chemically modified the iron carbonyl particles. The results showed that, compared with pure iron carbonyl particles, the modified particles could cure the phthalonitrile prepolymers efficiently and improve the interfacial compatibility of the functional composites. The magnetic composites with chemically modified particles exhibited stronger magnetism in comparison to composites containing bare particles: the saturation magnetization of the magnetic composites with equal concentration (5 wt%) of Fe(CO)₅ increased from 41.12 to 48.82 emu g^?1. Also, the magnetic composites obtained demonstrated excellent thermal stability up to 500 °C. Copyright © 2010 Society of Chemical Industry     

Synthesis, characterization and thermally activated curing of polysulfones with benzoxazine end groups

Polysulfones with benzoxazine end groups (PSU-B-a) were obtained using monomer synthesis method from the phenol terminated polysulfone (PSU-OH), aniline and paraformaldehyde as starting materials. For this purpose, the precursor PSU-OHs with different molecular weights were prepared by condensation of bisphenol-A and bis(p-chlorophenyl) sulfone in presence of potassium carbonate. The structure of the polymers before and after functionalization was confirmed by proton nuclear magnetic resonance spectroscopy (¹H NMR) and Fourier transform infrared spectroscopy (FT-IR). Thermally activated crosslinking behavior of these polymers was investigated by differential scanning calorimetry (DSC). Thermal and tensile properties of the crosslinked polymers obtained from PSU-B-a alone or with low molar mass benzoxazine (P-a) were studied by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA).     

A novel polybenzoxazine containing styrylpyridine structure via the Knoevenagel reaction

In this article, a kind of styrylpyridine‐containing polybenzoxazine was obtained via the Knoevenagel reaction between benzaldehyde and methylpyridine groups. The benzoxazine monomer (MPBC) containing the benzaldehyde and methylpyridine groups was synthesized firstly and its structure was characterized by Fourier transform infrared (FTIR) spectra, ¹H NMR and ¹³C NMR. With the aid of differential scanning calorimetry, FTIR, and photoluminescent tests, the interesting curing behaviors were probed. The results showed that the ring‐opening polymerization occurred at lower temperature, and the Knoevenagel reaction further took place at elevated temperature. The amine and phenol moieties were bonded together to form the styrylpyridine structure. Due to these special crosslinking structures, the corresponding polybenzoxazine exhibited excellent thermal stability, and had a special high char yield of 74.5%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40823.     

Highly branched benzoxazine monomer based on cyclotriphosphazene: Synthesis and properties of the monomer and polybenzoxazines

A hyperbranched organic-inorganic hybrid benzoxazine monomer based on cyclotriphosphazene (CP) has been synthesized, which possesses six organic benzoxazine moieties distributed on the inorganic ring of CP. The high molecular weight (1491 g/mol) monomer showed excellent solubility in common organic solvents. Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) were used to study the thermal ring-opening polymerization reaction of the novel benzoxazine monomer. FT-IR spectrum implied that the characteristic absorption peaks of the benzoxazine ring disappeared completely after curing at 240 °C for 1 h, which illustrated that the completion of polymerization reaction. DSC plots indicated that the melting point of the new monomer was 77 °C and an exothermic peak was 225 °C owing to the ring-opening polymerization of the monomer. Due to its highly steric crosslinking structure with rigid and thermal stable inorganic CP as the core, the polybenzoxazine based on the new monomer showed excellent thermal stability and mechanic properties. The char yield of the polymer at 850 °C was 66.9% in nitrogen, and the T_g of the polybenzoxazine was 152 °C.     

Synthesis,curing behavior and thermal properties of fluorene-containing benzoxazines based on linear and branched butylamines

A series of fluorene-containing benzoxazine monomers based on linear and branched butylamines were successfully synthesized in high purity and good yield through a facile one-pot procedure by the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with paraformaldehyde and isomeric butylamines. The chemical structures of the target monomers were characterized by Fourier transform infrared (FT-IR), Elemental analysis, ¹H and ¹³C nuclear magnetic resonance (NMR). The curing behavior of benzoxazine monomers was studied by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polybenzoxazines were measured by DSC and thermogravimetric analysis (TGA). The results reveal that the polarity of solvent and the basicity of butylamines produce clear effects on the synthesis of the butylamine-based benzoxazine monomers. Also, the basicity and steric effect of butylamines exhibit significant effects on the curing behavior of benzoxazine monomers and the thermal properties of their polymers. The glass transition temperature and thermal stability of branched butylamine-based polybenzoxazines are higher than those of the corresponding linear butylamine-based polybenzoxazine and traditional bisphenol A-based polybenzoxazines.