RSC Advances

PAPER View Article Online View Journal | View Issue

Synthesis, characterization, and properties of a novel aromatic ester-based polybenzoxazine Cite this: RSC Adv., 2020, 10, 6953 Chunli Zhu, Xing Gao, Weixi Fan and Xiaofen Fu *

Polybenzoxazines with molecular design flexibility have excellent properties by using suitable raw materials. A new benzoxazine monomer terephthalic acid bis-[2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)]ethyl ester (TMBE) with bis-ester groups has been synthesized from the simple esterification reaction of terephthaloyl chloride and 2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)-ethanol (MB-OH). The chemical structure of TMBE was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H-NMR, 13C-NMR). Polymerization behavior of TMBE was studied by differential scanning calorimetry (DSC) and FT-IR after each cure stage. The cross-linked polybenzoxazine (PTMBE) gave a transparent film through the thermal casting method. The dynamic mechanical analysis of PTMBE Received 5th December 2019 showed that the T was 110 C. Thermogravimetric analysis reveals better thermal stability as evidenced Accepted 16th January 2020 g by the 5% and 10% weight-loss temperatures (Td5 and Td10)ofPTMBE, which were 263 and 289 C, Creative Commons Attribution 3.0 Unported Licence. DOI: 10.1039/c9ra10191h respectively, with a char yield of 27% at 800 C. The tensile test of the film revealed that the elongation rsc.li/rsc-advances at break was up to 14.2%.

1. Introduction exibility of polybenzoxazines with dramatically scarifying their heat resistance. Therefore, some main-chain type poly- 24,25 As a new phenolic-type resin, polybenzoxazines possess attractive benzoxazines were synthesized by Mannich reaction with properties, such as high glass transition temperature,1,2 ame polyether diamines of diﬀerent molecular weights or PDMS retardancy,3 low water absorption,4 and low cost.5 They are with diﬀerent molecular weights for the diamine terminal, This article is licensed under a applied to the eld of halogen-free ame retardant laminates, bisphenol A, and formaldehyde. Such high-molecular-weight vacuum pump rotors, printed circuit boards, friction materials, prepolymers exhibited signicantly improved toughness due composites, and other elds.6,7 Nevertheless, inherent brittleness to the so segments and generated a high cross-linking degree

Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. of polybenzoxazines, especially in aromatic polybenzoxazines, due to the polybenzoxazine component. limits their further development in the chemical industry. The other approach to improve toughness is indirectly There are generally three reported approaches to improve preparing of polybenzoxazine prepolymers using poly- 14 the toughness of polybenzoxazines. The rst approach is esterication, coupling reactions, alternating copolymeriza- 26 27 introducing rubber,8,9 the exible heat-resistant linear poly- tion of donor–acceptor monomers, Diels–Alder reaction, 28 29 mer10–14 into resins as the toughening agent to improve tough- polyetherication, hydrosilylation These synthetic ness. The second approach is designing inherently tough approaches also necessarily yield high-performance polybenzoxazine monomers containing so segments to aﬀord benzoxazines with improved toughness. The novel polyesters tough polybenzoxazines.15,16 The third approach is the tough- were synthesized from the polycondensation reaction of 0 ening of polybenzoxazines by inorganic nanoparticles.17–19 bisbenzoxazine-diol, pyromellitic dianhydride, and 4,4 -(hexa- 14 Among them, the designing of inherently tough benzoxazine uoroisopropylidene)diphthalic anhydride. The molecular monomers and polybenzoxazines prepolymers was a signicant weights of polyesters were in the range of 5800–7000 Da with approach to improve the exibility of polybenzoxazines from benzoxazine moieties in the main chain exhibited high exi- the molecular level, and to increase the degree of chemical bility induced by the so pentyl and esters groups and crosslinking between the two phases. comparable thermal stability concerning low molar mass 29 The tough benzoxazine monomers were synthesized, analogous. Aydogan prepared polysiloxanes containing ben- including monofunctional and difunctional benzoxazines from zoxazine units in the main chain by hydrosilylation of 1,1,3,3- available phenols containing exible groups, primary amines tetramethyldisiloxane and diallyl functional benzoxazines. To and formaldehyde.4,20–23 These monomers improve the further improve its exibility, polysiloxanes chain was extended by the reaction of poly (bisbenzoxazinedimethylsiloxane)s and octamethyl-cyclotetrasiloxane in the presence of tetrabuty- School of Chemistry and Biological Engineering, Qilu Institute of Technology, Jinan, lammonium hydroxide as a catalyst. 250200, P. R. China. E-mail: [email protected]

This journal is © The Royal Society of Chemistry 2020 RSC Adv.,2020,10, 6953–6959 | 6953 View Article Online RSC Advances Paper

Based on this idea, our work presents a facile route for with 1 L of 0.5 N aqueous NaOH and nally three times with 1 L synthesizing high-purity aromatic benzoxazine containing bis- of distilled water. The methylene chloride solution was dried  ﬀ ester groups. First, 2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)- with MgSO4, ltered, and concentrated under vacuum to a ord ethanol (MB-OH) was synthesized from formaldehyde solution crude product (1.6 g, yield: 61%). The product was puried by

(37%), ethanolamine, and p-cresol. Then, terephthalic acid bis- chromatography (vmethylene chloride :vethyl acetate ¼ 2 : 1) to aﬀord [2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)]ethyl ester (TMBE) white power solid. 1 with bis-ester groups has been synthesized from the simple H NMR (CDCl3, 300 MHz, d): 4.05 ppm (s, Ar–*CH2–N),

esterication reaction of MB-OH and terephthaloyl chloride. 4.88 ppm (s, O–*CH2–N), 3.18 ppm (t, N–*CH2–C), 4.52 ppm (t,

The crosslinked polybenzoxazine (PTMBE) gave transparent C–*CH2–O), 2.27 ppm (s, Ph–*CH3).   13 d –* – exible lm through the thermal casting method. The thermal C NMR (CDCl3, 300 MHz, ): 50.70 ppm (Ar CH2 N), –* – –* – – and mechanical properties of aromatic ester-based poly- 82.85 ppm (O CH2 N), 50.38 ppm (N CH2 C), 63.65 ppm (C * – –* – *] benzoxazine were studied and compared with respect to poly- CH2 O), 18.30 ppm (Ph CH3), 165.71 ppm (O C O). benzoxazines analogous. FTIR (KBr) n: 1019 cm 1 (C–O–C symmetric stretching), 1277 cm 1 (C–O–C asymmetric stretching), 1506 cm 1 (trisub- 2. Material and methods stituted benzene ring), 932 cm 1 (oxazine ring), 1720 cm 1 (C] O stretching). 2.1. Materials

Potassium hydroxide, p-cresol (98%) were purchased from 2.4. Polymerization of TMBE Sinopharm Chemical Reagent Co., Ltd. 2-Aminoethanol, The amount of TMBE was melted, stirred and transferred to dioxane, triethylamine (Et N), methylene chloride was obtained 3 a rectangular aluminum foil mold and then cured at 120 C/2 h, from Tianjin Fu Jin Fine Chemical Co., Ltd. Formaldehyde 140 C/2 h, 160 C/2 h, 180 C/2.5 h in an air-circulating oven. (37 wt% in water), terephthaloyl chloride, n-hexane was used as Aer that, samples were allowed to cool slowly to room 

Creative Commons Attribution 3.0 Unported Licence. received. Methylene chloride used a er distillation. temperature to be tested.

2.2. Synthesis of MB-OH 2.5. Characterizations MB-OH was synthesized according to the literature.12 Asuspen- FTIR spectra were obtained with Bruker Tensor 27 FTIR spec- sion of paraformaldehyde (15.3 mL, 210 mmol), 30 mL 1,4- trometer (Bruker, GM) in which samples were preparing as KBr dioxane were added to a 250 mL three-neck ask in an ice bath. pellets. 1H-NMR and 13C-NMR spectra were recorded on Then 2-aminoethanol (6.0 mL, 100 mmol) was added drop-wise a Bruker Avance 300 instrument (Bruker) using CDCl3 as the to the system. The mixture stirred at room temperature for solvent and TMS as the internal standard. Diﬀerential scanning 

This article is licensed under a about 30 min. A er adding p-cresol (10.6 mL, 100 mmol), the calorimetry (DSC) was conducted using a DSC SP instrument temperature was gradually increased to 70 C, and stirring was (Rheometric Scientic) at a heating rate of 10 C min 1 under continued for another 3.5 h. A yellowish viscous uid was ob- nitrogen. Thermogravimetric analysis (TGA) was performed on tained aer removing the solvent through a rotary evaporator. a TGA/DSC STARe System instrument (Mettler-Toledo) at Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. Then the viscous liquid was dissolved in dichloromethane, 1 a heating rate of 10 C min under N2 atmosphere. The gas washed with 1 L of 0.1 N aqueous KOH and nally three times ow rate was 100 mL min 1. The dynamic mechanical analysis with 1 L of distilled water. The methylene chloride solution was (DMA) of samples was carried out using a Mettler-Toledo DMA/ dried with MgSO , ltered, and concentrated under vacuum to 4 SDTA861e instrument (Mettler-Toledo). The specimen with aﬀord crude product. The crude product was recrystallized with dimensions of approximately 3.00 2.20 0.8 mm3 was tested MB-OH n-hexane to give pure white solid of (9.53 g, 51%). – 1 by a shear mode at 1 Hz in the temperature range of 30 200 C H NMR (CDCl , 300 MHz, d): 3.98 ppm (s, Ar–*CH –N), 3 2 at a heating rate of 3 C min 1. Tensile measurement were also 4.85 ppm (s, O–*CH –N), 2.95 ppm (t, N–*CH –C), 3.69 ppm (t, 2 2 recorded with Material Testing Machine Model UTM5105 at C–*CH2–O), 2.24 ppm (s, Ph–*CH3). 1 1 a crosshead speed of 1 mm min . Each sample with a dimen- FTIR (KBr) n: 1034 cm (C–O–C symmetric stretching), 3 sion of approximately 20.0 5.0 1.0 mm was tested from an 1232 cm 1 (C–O–C asymmetric stretching), 1502 cm 1 (trisub- average of at least 5 tests. stituted benzene ring), 940 cm 1 (oxazine ring).

2.3. Synthesis of TMBE 3. Results and discussion 3.1. Preparation of TMBE and its polymer Into a 100 mL dry round-bottom ask equipped with a calcium chloride drying tube, 20 mL dry methylene chloride, MB-OH Scheme 1 illustrates our strategy for the preparation of TMBE (1.9 g, 10 mmol), triethylamine (1.7 mL, 1.4 mmol) were added and PTMBE. First, according to reference, we synthesized con- and mixed at room temperature for about 30 min. Then ter- taining hydroxyl benzoxazine (MB-OH). Second, using triethyl- ephthaloyl chloride (1.0 mL, 5.0 mmol) was added at 5 C. The amine as deacid reagent, dry dichloromethane as solvent, mixtures were stirred at room temperature for 2 d and kept TMBE was obtained via the esterication reaction of MB-OH reuxing for 4 h. A yellow transparent solution was obtained and terephthaloyl chloride at a molar ratio of 2 : 1. TMBE was aer cooling to room temperature. The solution was washed easily soluble in common low-boiling organic reagents, such as

6954 | RSC Adv.,2020,10, 6953–6959 This journal is © The Royal Society of Chemistry 2020 View Article Online Paper RSC Advances

Scheme 1 Synthetic route to TMBE and PTMBE.

Creative Commons Attribution 3.0 Unported Licence. dichloromethane, chloroform, and tetrahydrofuran. Finally, 6.68 ppm, 6.75 ppm, and 6.95 ppm assigned to protons of PTMBE was formed by the cross-linking of TMBE under thermal benzene ring linked to the oxazine ring. curing reaction with polymerization temperature of 180 C. The 13C NMR spectrum presented from Fig. 2 further proved the structure of TMBE. The carbon resonances of the oxazine ring –* – –* – at 50.7 ppm for Ar CH2 N and at 82.9 ppm for O CH2 Nwere 3.2. Characterization of TMBE clearly observed, respectively. The carbon resonances at 50.38 and –* – –* – The chemical structure of TMBE was conrmed by NMR and FT- 63.65 ppm of N CH2 CandC CH2 O were clearly appeared, IR spectral analysis. As can be seen from Fig. 1 where the 1H respectively. The peak at 165.71 and 20.30 ppm were characteristic – *] –* This article is licensed under a NMR spectrum of TMBE is presented, the appearance of the absorptions of O C OandPh CH3,respectively.Thereso- nance at 128.46 and 133.96 ppm corresponded to carbon atoms in protons resonating at 4.05 ppm (–O–*CH2–N) and 4.88 ppm (Ar– the aromatic ring of terephthalate. Others were characteristic *CH2–N) was clear evidence for the benzoxazine ring formation on TMBE. Moreover, the peaks at 3.18 ppm and 4.52 ppm absorptions attributed to the aromatic ring of benzoxazine. Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. FT-IR spectra also give evidence for the formation of ben- assigned to protons of –N–*CH2–C– and C–*CH2–O– were observed, respectively. The integral ration of these peaks was zoxazine containing bis-ester groups (Fig. 3). The characteristic 1 – close to the theoretical ratio of 2 : 2 : 2 : 2. The signal peak peak at 932 cm due to the C H out-of-plane vibration in the –* benzene ring where an oxazine ring attached was clearly appeared at 2.27 ppm corresponding to the Ph CH3. The peak 1 appeared at 8.10 ppm corresponding to the protons of the observed. Additionally, the strong peak at 1720 cm was benzene ring linked to the ester group. The peaks appeared at characteristic absorption of the carbonyl in terephthalate.

Fig. 1 1H-NMR spectrum of TMBE.

This journal is © The Royal Society of Chemistry 2020 RSC Adv.,2020,10, 6953–6959 | 6955 View Article Online RSC Advances Paper

Fig. 2 13C-NMR spectrum of TMBE.

3.3. Polymerization of TMBE Creative Commons Attribution 3.0 Unported Licence. of temperature, the intensity of the characteristic absorption peak at 932 cm 1 due to benzoxazine structure gradually The DSC heating-scan thermogram of TMBE was depicted in decreased due to the opening of the oxazine ring and dis- Fig. 4. The sharp endothermic peak appearing at 139 C corre- TMBE TMBE appeared aer the 180 C for 2.5 h. The intensity of absorption sponds to the melting temperature (Tm)of . bands at 1502 cm 1 due to the trisubstituted benzene ring showed unimodal curing behaviour as observed from the single (stretching) also decreased. Meanwhile, some new absorption exothermic peak, which is from the ring-opening polymeriza- bands appeared at 3442 cm 1 due to the phenolic hydroxy and tion of the benzoxazine ring. The onset and peak top tempera- 1 at 1481 cm due to the tetrasubstituted benzene ring, sug- tures of the peak are 176 and 231 C, respectively. The gesting that the ring-opening polymerization of TMBE occurred. polymerization temperature of TMBE is similar to the values This article is licensed under a 30 Both DSC and IR spectroscopy indicates the formation of pol- reported to other traditional benzoxazine compounds. DSC result of curing TMBE show the presence of aliphatic chains ybenzoxazine by polymerization at 180 C. (C4) in the benzoxazine structure has little eﬀect on the poly- 3.4. Thermal property of PTMBE Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. merization behavior of TMBE and only a lower temperature is required for polymerization. Dynamic mechanical analysis (DMA) was performed to study the The polymerization behavior of TMBE was also monitored by viscoelastic properties of PTMBE (Fig. 6). At 30 and 80 C, the FTIR aer curing at each temperature (Fig. 5). With the increase storage modulus (G0) values are 168 and 100 MPa, respectively, whereas the loss modulus (G00) values are 11 and 27 MPa,

Fig. 3 FTIR spectrum of the TMBE. Fig. 4 DSC thermogram of TMBE.

6956 | RSC Adv.,2020,10,6953–6959 This journal is © The Royal Society of Chemistry 2020 View Article Online Paper RSC Advances

Fig. 7 TGA curve of PTMBE. Fig. 5 FTIR spectra of TMBE after curing at each temperature.

elongation at a break of 14.2% and the tensile strength of respectively. For poly(BA-a) (bisphenol-A and aniline-based poly-  0 3 11.3 MPa. It is reported that the PB-a lm is very brittle with benzoxazine), the storage modulus G of 1.9 10 MPa is higher 30 elongation at break of 1.3%. The elongation at break of than that of PTMBE due to their high aromatic content. It has PTMBE was larger than that of PB-a. Namely, PTMBE had been clearly demonstrated from DMA that the exibility of PTMBE remarkably improved toughness, and the lm is easy to bend. is better than poly(BA-a). The T was observed at 110 and 89 C g Interestingly, in spite of the introduction of the aromatic ester Creative Commons Attribution 3.0 Unported Licence. from the maximum loss factor and maximum loss modulus, group, PTMBE still showed the high elongation at break respectively. The decrease of T can be attributed to the exible 20 g comparing with polybenzoxazines only containing linear long alkyl chain in PTMBE because of a lower energy barrier for motion. aliphatic chains (C12). The toughness enhancement of PTMBE TGA was performed to determine the thermal stability of is attributed to the long exible alkyl chains, which enhances PTMBE. Fig. 7 shows the TGA thermograms of PTMBE.In the mobility of segments under load and thereby increases the nitrogen, 5 and 10% weight loss temperatures (T and T )of d5 d10 ultimate elongation. The tensile modulus of PTMBE is PTMBE were 263 and 289 C, respectively. The char yield of 248.0 MPa, lower than that of PBA-a (4.3 GPa) with rigid back- PTMBE was up to 27.0% at 800 C. The T and T of PTMBE 30 d5 d10 bone. Therefore, the incorporation of the long aliphatic chain were decreased by about 50 C compared with poly(BA-a). The char This article is licensed under a and aromatic ester group into PTMBE network structure gave yield of PTMBE at 800 C has a slight drop compared with poly(BA- exible polymer lm without excessively scarifying its heat a). PTMBE shows the lower thermal stability than poly(BA-a) resistance. attributed as mentioned previously to the exible aliphatic chain. A yellowish PTMBE lm (7 6cm2) with 150–200 mmin Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. thickness was obtained through the thermal casting method in  2 3.5. Mechanical properties of PTMBE Fig. 9(a). A larger-sized lm (20 20 cm ) was also prepared in our lab according to the same procedure. Besides, the PTMBE The stress–strain curve was showed to study the mechanical lm had remarkably improved toughness, and is easy to bend in property for the PTMBE lm (Fig. 8). The PTMBE lm showed Fig. 9(b).

Fig. 6 DMA curves of PTMBE. Fig. 8 Stress–strain curve of PTMBE.

This journal is © The Royal Society of Chemistry 2020 RSC Adv.,2020,10, 6953–6959 | 6957 View Article Online RSC Advances Paper

Fig. 9 Appearance of PTMBE ﬁlm (a) and (b).

4. Conclusions 4 H. Xu, W. Zhang, Z. Lu and G. Zhang, Synthesis and properties of thermosetting resin based on urushiol, RSC By utilizing a clean and facile route, we have prepared a high- Adv., 2013, 3, 3677–3682. purity aromatic ester-based benzoxazine monomer and its 5 N. N. Ghosh, B. Kiskan and Y. Yagci, Polybenzoxazines-new polymer. Thermally activated polymerization of benzoxazine high performance thermosetting resins: synthesis and monomer provided exible, uniform polymer lm. The novel properties, Prog. Polym. Sci., 2007, 32, 1344–1391. Creative Commons Attribution 3.0 Unported Licence. polybenzoxazine lm exhibited signicantly improved tough- 6 Y. Gu and Q. C. Ran, in Handbook of Benzoxazine Resins, ed. ness due to the long aliphatic chain. The storage modulus and H. Ishida and T. Agag, Elsevier, Amsterdam, ch. 28, 2011, pp. glass transition temperature of PTMBE were 168 MPa and 481–494. 110 C, respectively. Regarding thermal stability, PTMBE 7 M. Xu, M. Liu, S. Dong and X. Liu, Design of low temperature showed lower thermal stability than poly(BA-a) due to the self-cured phthalonitrile-based polymers for advanced glass aliphatic hydrocarbon chain. It is anticipated to nd applica- ber composite laminates, J. Mater. Sci., 2013, 48, 8108– tions of PTMBE as a self-healing material. 8116. 8 T. Takeichi, Y. Guo and T. Agag, Synthesis and  This article is licensed under a Conflicts of interest characterization of poly(urethane-benzoxazine) lms as novel type of polyurethane/phenolic resin composites, J. There are no conicts to declare. Polym. Sci., Part A: Polym. Chem., 2000, 38, 4165–4176. 9 T. Takeichi, T. Kano and T. Agag, Synthesis and thermal cure Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM. of high molecular weight polybenzoxazine precursors and Acknowledgements the properties of the thermosets, Polymer, 2005, 46, 12172– The authors are thankful for the nancial supports from 12180. Shandong Provincial Natural Science Foundation, China 10 A. Chernykh, T. Agag and H. Ishida, Synthesis of linear (ZR2018MB022). polymers containing benzoxazine moieties in the main chain with high molecular design versatility via click reaction, Polymer, 2009, 50, 382–390. References 11 B. Kiskan, Y. Yagci and H. Ishida, Synthesis, characterization, and properties of new thermally curable 1 X. Ning and H. Ishida, Phenolic materials via ring-opening polyetheresters containing benzoxazine moieties in the polymerization of benzoxazines: effect of molecular 46 structure on mechanical and dynamic mechanical main chain, J. Polym. Sci., Part A: Polym. Chem., 2008, , – properties, J. Polym. Sci., Part B: Polym. Phys., 1994, 32, 414 420. 921–927. 12 M. Baqar, T. Agag, H. Ishida and S. Qutubuddin, 2 M. Goto, Y. Miyagi, M. Minami and F. Sanda, Synthesis and Poly(benzoxazine-co-urethane)s: a new concept for crosslinking reaction of polyacetylenes substituted with phenolic/urethane copolymers via one-pot method, 52 – benzoxazine rings: thermally highly stable benzoxazine Polymer, 2011, , 307 317. resins, J. Polym. Sci., Part A: Polym. Chem., 2018, 56, 1884– 13 A. D. Baranek, L. L. Kendrick, J. Narayanan, G. E. Tyson, 1893. S. Wand and D. L. Patton, Flexible aliphatic-bridged 3 3 S. Gao, Y. Liu, S. Y. Feng and Z. J. Lu, Synthesis of bisphenol-based polybenzoxazines, Polym. Chem., 2012, , – borosiloxane/polybenzoxazine hybrids as highly efficient 2892 2900. and environmentally friendly ame retardant materials, J. 14 A. Tuzun, B. Kiskan, N. Alemdar, A. T. Erciyes and Y. Yagci, Polym. Sci., Part A: Polym. Chem., 2017, 55, 2390–2396. Benzoxazine containing polyester thermosets with improved

6958 | RSC Adv.,2020,10,6953–6959 This journal is © The Royal Society of Chemistry 2020 View Article Online Paper RSC Advances

adhesion and exibility, J. Polym. Sci., Part A: Polym. Chem., 23 D. B. Austin, L. K. Laken, N. Jananee, E. T. Ginger, W. Steven 2010, 48, 4279–4284. and L. P. Derek, Flexible aliphatic-bridged bisphenol-based 15 B. S. Rao and A. Palanisamy, A new thermoset system based polybenzoxazine, Polym. Chem., 2012, 3, 2892–2898. on cardanol benzoxazine and hydroxy benzoxazoline with 24 T. Agag, S. Geiger, S. M. Alhassan, S. Qutubuddin and lower cure temperature, Prog. Inorg. Chem., 2012, 74, 427– H. Ishida, Low-Viscosity Polyether-Based Main-Chain 434. Benzoxazine Polymers: Precursors for Flexible 16 T. Agag, S. Y. An and H. Ishida, 1,3-bis(benzoxazine) from Thermosetting Polymers, Macromolecules, 2010, 43, 7122– cashew nut shell oil and diaminodiphenyl methane and its 7127. composites with wood our, J. Appl. Polym. Sci., 2013, 127, 25 T. Takeichi, T. Kano, T. Agag, T. Kawauchi and N. Furukawa, 2710–2714. Preparation of high molecular weight polybenzoxazine 17 Y. P. Chen, A. Q. Dayo and W. B. Liu, Synthesis of cardanol- prepolymers containing siloxane unites and properties of based phthalonitrile monomer and its copolymerization their thermosets, J. Polym. Sci., Part A: Polym. Chem., 2010, with phenol-aniline-based benzoxazine, J. Appl. Polym. Sci., 48, 5945–5952. 2019, 136, 47505–47513. 26 B. Gacal, L. Cianga, T. Agag, T. Takeichi and Y. Yagci, 18 A. B. Rajput, S. J. Rahaman, G. Sarkhel, M. K. Patra, Synthesis and characterization of maleimide (Co)polymers S. R. Vadera, P. M. Singru, Y. Yagci and N. N. Ghosh, with pendant benzoxazine groups by photoinduced radical Synthesis, characterization, and properties of exible polymerization and their thermal curing, J. Polym. Sci., Part magnetic nanocomposites of cobalt ferrite- A: Polym. Chem., 2007, 45, 2774–2786. polybenzoxazine-linear low-density polyethylene, J. Appl. 27 C. I. Chou and Y. L. Liu, High performance thermosets from Polym. Sci., 2012, 128, 3726–3733. a curable Diels-Alder polymer possessing benzoxazine 19 S. Li, T. Zou, L. Feng, X. Liu and M. Tao, Preparation and groups in the main chain, J. Polym. Sci., Part A: Polym.

properties of cardanol-based polybenzoxazine/SiO2 hybrids Chem., 2008, 46, 6509–6517. 128 –

Creative Commons Attribution 3.0 Unported Licence. by sol-gel technique, J. Appl. Polym. Sci., 2012, , 4164 28 K. D. Demir, B. Kiskan, S. S. Latthe, A. L. Demirel and 4171. Y. Yagci, Thermally curable uorinated main chain 20 D. J. Allen and H. Ishida, Physical and mechanical properties benzoxazine polyethers via Ullmann coupling, Polym. of exible polybenzoxazine resins: eﬀect of aliphatic Chem., 2013, 4, 2106–2114. diamine chain length, J. Appl. Polym. Sci., 2006, 101, 2798– 29 B. Aydogan, D. Sureka, B. Kiskan and Y. Yagci, Polysiloxane- 2809. containing benzoxazine moieties in the main chain, J. Polym. 21 T. Agag, L. Jin and H. Ishida, A new synthetic approach for Sci., Part A: Polym. Chem., 2010, 48, 5156–5162. diﬃcult benzoxazines: preparation and polymerization of 30 T. Agag and T. Takeichi, Synthesis and characterization of 4, 4’-diaminodiphenyl sulfone-based benzoxazine novel benzoxazine monomers containing allyl groups and

This article is licensed under a monomer, Polymer, 2009, 50, 613–626. their high performance thermosets, Macromolecules, 2003, 22 T. Agag, A. Akelah, A. Rehab and S. Mostafa, Flexible 36, 6010–6017. polybenzoxazine thermosets containing pendent aliphatic chains, Polym. Int., 2012, 61, 124–128. Open Access Article. Published on 20 February 2020. Downloaded 9/30/2021 5:30:58 PM.