Autocatalysis Synthesis of Poly(benzoxazine-co

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

Autocatalysis Synthesis of Poly(benzoxazine-co-resol)-Based Polymer and Carbon Spheres Jianming Zhao,†,‡ Muhammad Rehan Hasan Shah Gilani,†,§,⊥ Jianping Lai,†,‡ Anaclet Nsabimana,†,‡ Zhongyuan Liu,† Rafael Luque,†,∥,# and Guobao Xu*,†,▽

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State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People’s Republic of China ‡ University of Chinese Academy of Sciences, Chinese Academy of Sciences, No. 19A Yuquanlu, Beijing 100049, People’s Republic of China § Department of Chemistry, the Islamia University of Bahawalpur, Bahawalpur, Pakistan ∥ Departamento de Química Orgánica, Universidad de Córdoba Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV, Km 396, Córdoba, E-14014, Spain ⊥ Department of Chemistry, Government College University Faisalabad, Layyah Campus, Pakistan # People’s Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya str., 117198, Moscow, Russia ▽ University of Science and Technology of China, Hefei, People’s Republic of China S Supporting Information *

ABSTRACT: The molecular-level design and controlled synthesis of materials are of key importance for advancing their applications. Based on the special structure of 3-aminophenol, containing both phenol and amine groups, a facile synthesis of highly monodisperse poly(benzoxazine-co-resol)-based polymer spheres was first reported by the autocatalysis polymerization of 3-aminophenol and formaldehyde without using any catalyst, surfactants, templates, and/or functional dopants at low temperature. The sizes of polymer spheres can be widely tuned from 372 to 1030 nm by changing the initial reaction temperatures and the concentrations of monomers. Based on FTIR, NMR, XPS, and EDX analysis, 3-amoniaphenol was evidenced not only to participate in the polymerization and form the structure of polybenzoxazine but also to catalyze the polymerization. Furthermore, they can be pseudomorphically and uniformly converted to the corresponding carbon spheres in high yield due to the excellent thermal stability of 3-aminophenol−formaldehyde resin.

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presence of Pluronic F127 surfactant.15 Our group successfully utilized 3-aminophenol (AP) and formaldehyde (F) as monomers to synthesize highly monodisperse resin polymer spheres (APFS) and their magnetic polymer composite spheres without any surfactants and templates.16,17 All of these kinds of resin polymer spheres can be converted to their spherical carbonaceous analogues in a high char yield. Coincidentally, 3aminophenol molecule contains phenol and amine groups simultaneously. Therefore, the polymerization system of 3aminophenol and formaldehyde maybe satisfies the conditions of phenolic resin organic sol−gels. Consequently, a curious question arises: can polymer and carbon spheres be synthesized by the polymerization of 3-aminophenol and formaldehyde without using any other catalyst, surfactants, templates, and/or functional dopants?

INTRODUCTION There has been a considerable interest in the molecular-level design and controlled fabrication of monodisperse colloidal spheres, including silica, polymer, carbon, and their composite spheres due to their wide promise applications in colloidal catalysis, photonic crystals, drug delivery, biological sensors, energy storage, and templates.1−7 These applications of colloidal nanoparticles strongly depend on their sizes, structures, and compositions.5,8 Recently, monodisperse resorcinol−formaldehyde-based polymer and carbon spheres have been conveniently synthesized by extending the wellknown Stö ber method because the sol−gel process of resorcinol−formaldehyde-based xerogels and aerogels is analogous to that of silica.9−13 However, ammonia may serve other functions than catalysis and protective agent.14 Based on benzoxazine chemistry, a new kind of highly uniform polybenzoxazine-based polymer and carbon nanospheres were prepared by the Mannich condensation of resorcinol, formaldehyde, and 1,6-diaminohexane in the © XXXX American Chemical Society

Received: June 10, 2018 Revised: June 27, 2018

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DOI: 10.1021/acs.macromol.8b01239 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Scheme 1. Synthesis Process of APFS

narrow-scan XPS spectra of the C 1s, N 1s, and O 1s of the samples, using adventitious carbon to calibrate the C 1s binding energy (284.5 eV). 13C NMR analyses were carried out on a Varian Infinity-plus 400 spectrometer operating at a magnetic field strength of 9.4 T. FTIR was recorded on a Bruker Vertex 70 spectrometer. Thermogravimetric analysis (TGA) measurements were carried out by using a PerkinElmer TGA-2 thermogravimetric analyzer under nitrogen from room temperature to 800 °C at 10 °C min−1. The nitrogen adsorption isotherm was measured at 77 K on a Micromeritics Tristar 3000 system with micropore analysis. The Brunauer−Emmett−Teller (BET) method was utilized to calculate the specific surface areas. Prior to measurements, the samples were outgassed at 120 °C for at least 6 h.

Herein, we report a novel molecular-level design and controlled synthesis of highly monodisperse poly(benzoxazine-co-resol) polymer spheres by the autocatalysis polymerization of AP and F (Scheme 1). APF is chose as precursor because AP simultaneously contains amine and phenol groups so that APF can form silica-like frameworks based on benzoxazine chemistry. We found that 3amoniaphenol not only to catalyze the polymerization but also to participate in the polymerization and form the structure of polybenzoxazine. The effect of the initial reaction temperatures and monomer condensations on the diameters and morphologies of the polymer spheres was investigated in detail. Furthermore, the polymer spheres can be carbonized into nitrogen-doping carbon spheres in high yield because of the excellent thermal stability of APF resin. The synthesis method is facile and versatile because no catalyst, surfactants, templates, functional dopants, and hydrothermal treatment are used during the reaction process. Thus, the approach is considered to be low cost, environmentally friendly, and more suitable for industrial production.

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RESULTS AND DISCUSSION Scheme 1 illustrates the fabrication process of APFS from the polymerization of AP and F in a mixture of water and ethanol. The method integrates the classical sol−gel method with benzoxazine chemistry based on the molecular-level design because 3-aminophenol molecule contains both phenol and amine groups.7,11,12,15,16 First, 3-aminophenol and formaldehyde react to form benzoxazine and hydroxymethyl derivatives, and then the emulsion droplets are formed through the hydrogen bond of water, alcohol, 3-aminophenol, formaldehyde, hydroxymethyl derivatives, and/or benzoxazine derivatives. Next, the ring-open polymerization and polycondensation take place from the inside of emulsion droplets, resulting in uniform APFS. The reaction took place very quickly at room temperature after the addition of formaldehyde into the 3-aminophenol/ethanol/water solution. The beginning process is the key to the morphology of APFS. The synthesis parameters are shown in Table S1. The scanning electron microscopy (SEM) image shows that APFS-4 is regularly spherical and its size is uniform (Figure 1 and Table S1). Interestingly, widely self-assembled periodic structures with close-packed two-dimensional (2D) hexagonal planes arranged along the (111) direction are observed in the large scale SEM image (Figure 1a), further indicating a good monodispersity of the obtained resin polymer spheres. 3D selfassembled periodic structures are also observed in the cross section of coffee ring of SEM sample (Figure S1). The highmagnification SEM image (Figure 1b) demonstrates that APFS-4 has smooth surface and a mean diameter of 617 nm, with a standard deviation of 25 nm. As shown in Figure S2, APFS-4 sample exhibits bright and shiny color after centrifugation and drying. This is another proof that the obtained colloidal spheres are highly uniform in size. The number of nuclei formed is a probable function of temperature;18 thus, the effect of the initial reaction temperatures (IRTs) on the size of APFS was investigated (Figure 2). The rate of reaction increased with the increase of initial

EXPERIMENTAL SECTION

Materials. 3-Aminophenol (≥99.0%) and formaldehyde (38−40 wt %) were purchased from Sinopharm Chemical Reagent Co., Ltd. Ethanol was purchased from Beijing Chemical Reagent (Beijing, China). All chemicals were used as received. Syntheses of 3-Aminophenol−Formaldehyde Spheres and Carbon Spheres. The detailed synthesis parameters are shown in Table S1. Typically, an aqueous−ethanol solution was prepared by mixing 8.4 mL of ethanol and 8.4 mL of distilled water. Subsequently, 0.0733 g of 3-aminophenol was added under stirring at 30 °C until a complete dissolution occurred. Twenty minutes later, 0.125 mL of formaldehyde was added to the above mixture for polymerization for 1 h under continuous stirring at 30 °C. Then, the reaction temperature was increased up to 75 °C, and the reaction system was stirred at 75 °C for 4 h. The 3-aminophenol−formaldehyde resin polymer spheres were obtained by centrifugation. The spheres were dried at 100 °C overnight. The resulting APFS was labeled as APFS-n where APFS refers to polymer spheres and “n” denotes the number in Table S1. In order to obtain nitrogen-doped carbon spheres, 3aminophenol−formaldehyde resin polymer spheres were carbonized under flowing nitrogen in a tube furnace using a heating rate of 1 °C/ min up to 350 °C and dwell for 2 h and resuming heating rate of 1 °C/min up to 800 °C and dwell for 4 h. The resulting carbon materials were labeled as NCS-n-T, where “NCS” refers to carbon spheres and “T” refers to the number of the carbonization temperature; for instance, for the carbon materials obtained at 700, 800, 900, and 1000 °C, T = 700, 800, 900, and 1000, respectively. Characterization. The morphology of the spheres was characterized by using a FEI/Philips XL30 ESEM FEG field emission scanning electron microscope operated at 20 kV. XPS measurements were conducted with a VG ESCALAB MKII spectrometer. The XPSPEAK software (Version 4.1) was used to deconvolute the B


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Macromolecules

Not only the IRTs but also the monomer concentrations have a significant effect on the sizes of APFS. The sphere sizes get larger as the amount of 3-aminophenol and formaldehyde increases (Figure 3). An increase in the aminophenol concentrations from 5 to 360 mmol/L caused a gradual increase in the average sphere size from 372 to 1030 nm, respectively. As shown in Figure 3c−k, the size of APFS is uniform when the concentration of 3-aminophenol ranges from 10 to 160 mmol/L. Importantly, self-assembled periodic structures with close-packed planes arranged along the (111) direction are observed in Figure 3e−j, further indicating the excellent monodispersity of the obtained APFS. To check the structure and composition of APFS, thermogravimetric (TG) analysis, energy-dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) were conducted for APFS-4 as an example. First, TG analysis was performed to examine the thermal behavior of APFS-4. As shown in Figure 4a, the TG curve of APFS-4 exhibits their excellent thermal stability under nitrogen. Even at 800 °C, ∼55.3% of the residues remained. Such a high char yield indicates that the resin is an excellent carbon precursor for the production of corresponding carbon nanomaterial. Elemental analysis confirms that the APFS exhibit high contents of nitrogen, 13.84 wt % and 12.47 at. % (Figure 4b). Further insight into the chemistry of APFS-4 is obtained with FTIR spectrum (Figure 4c). The absorption bands appearing around ∼1559 and 1348 cm−1 for APFS-4 can be assigned to aromatic C−N stretching and “breathing” mode, respectively.20 In addition, the peak at ∼1111 cm−1 is attributed to C−N stretching. The weak band at ∼922 cm−1 originates from the benzene ring to which oxazine is attached,21 showing the characteristics of the benzoxazine residues in the framework of as-made APFS (Scheme S1). The absorbance peaks at 1033 and 1223 cm−1 due to the C−O−C symmetric and asymmetric stretching modes, respectively, demonstrate the existence of the benzoxazine ring aromatic ether and/or anisole (Scheme S1).22 The spectral peaks at 1505, 1591, and 1620 cm−1 are due to the CC stretching in

Figure 1. SEM images of APFS-4: (a) large-scale SEM image and (b) high-magnification SEM image.

reactive temperatures. When the IRT was 0 °C, the size of the polymer spheres is not uniform as shown in Figure 2a. Their sizes are from 252 to 642 nm (the spheres with size less than 252 nm may be centrifuged out, Figure S3a), and even some part of product is not spherical. The reaction is slow and takes more than 13 min at 0 °C. The concentrations of monomers decreased gradually with the formation of polymer spheres, resulting in the polydispersity of polymer spheres. As shown in Figure 2b−f, the sizes of APFS were controlled from 605 to 627 to 557 nm when the IRTs increased from 10 to 40 to 60 °C. Furthermore, we found APFS self-assembled into not only periodic structures with close-packed two-dimensional planes arranged along the (111) direction (Figure 2e) but also those arranged along the (100) direction (Figure 2c,f) and even 3D self-assembled periodic (Figure 2d), corresponding to a type face of an fcc structure.19 The pictures of centrifuged samples demonstrate that the monodispersity of APFS prepared at 20, 40, and 50 °C is better (Figure S3), showing that we can synthesize high-quality APFS at that range of IRTs. They are additional proofs that the polymer spheres are highly monodisperse.

Figure 2. SEM images of APFS prepared at different IRTs: (a) 0 °C (APFS-1), (b) 10 °C (APFS-2), (c) 20 °C (APFS-3), (d) 40 °C (APFS-5), (e) 50 °C (APFS-6), and (f) 60 °C (APFS-7). The scales of (a)−(e) are same as that of (f). C


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Figure 3. SEM (a−i) of APFS synthesized at with different 3-amoniaphenol concentrations: (a) 5 mmol/L (APFS-9), (b) 7.5 mmol/L (APFS-10), (c) 10 mmol/L (APFS-11), (d) 15 mmol/L (APFS-12), (e) 20 mmol/L (APFS-13), (f) 25 mmol/L (APFS-14), (g) 30 mmol/L (APFS-15), (h) 50 mmol/L (APFS-16), (i) 60 mmol/L (APFS-17), (j) 80 mmol/L (APFS-18), (k) 160 mmol/L (APFS-19), and (l) 320 mmol/L (APFS-20). The scales of (a)−(k) are same as that of (l).

asymmetric C 1s XPS peak of APFS-4 can be fitted to four peaks of CC (284.5 eV), C−C (285.1 eV), C−N (and/or C−O) (285.7 eV), and C−N (and/or CO) (288.5 eV).28,29 In addition, only one distinguishable peak 398.9 eV in the N 1s spectrum corresponds to the N−C (Figure 4f). The XPS analysis of APFS-4 further supports its complex structure outlined in Scheme S1. On the basis of the characterization above, it can be reasoned that the minienvironments, such as steric hindrance, probably play important roles during the whole polymerization process, especially the formation of emulsion droplets, finally resulting in complex framework of APFS. Indeed, the carbonization of APFS gives corresponding nitrogen-doped spheres (NCS) due to their excellent thermal stability. As shown in Figure 5, we prefer pyrolysis of APFS-4 at 700, 800, 900, and 1000 °C under a N2 atmosphere, and all the NCSs obtained retain perfect spherical shape, high uniformity in sizes, and self-assembled close-packed periodic structures along the (111) direction. The diameters of NCS-4700, NCS-4-800, NCS-4-900, and NCS-4-1000 are 521, 502, 490, and 482 nm, respectively, which are smaller than that of the parent APFS-4 (617 nm). Apparently, this reveals that the diameter shrinkage of APFS-4 took place during the pyrolysis process. The result also proves that the thermal stability of APFS-4 is better than those of resorcinol−formaldehyde resin spheres12 and melamine−formaldehyde resin spheres30 due to the highly cross-linked APF resin structures. To show the excellent monodispersity of NCS, a typical SEM image recorded on a large area of NCS-4 is provided in Figure S5. As shown in Figure S6, N2 adsorption−desorption analysis revealed an apparent surface area of SBET = 578 m2 g−1 and pore volume Vp = 0.30 cm3 g−1 at P/P0 = 0.97. At higher pressures, a slow rise in the isotherm occurs because of the

the aromatic rings in the condensed APFS-4. The strong broad band at about 3223 and 3358 cm−1 can be correlated to be stretching vibrations of O−H and/or N−H, most probably related to OH···N, OH···O, and OH···π hydrogen bonding,22−24 indicating that lots of hydroxyl groups are produced during ring-opening polymerization of benzoxazine (Scheme 1 and Scheme S1).25 To better understand the mechanism underlying the formation of APFS, APFS-4 was characterized by 1H → 13C CP/MAS NMR analysis (Figure 4d). The resolved peaks at ∼17 and 30 ppm can be assigned to the signals of the methylene groups in Ar−CH2−Ar.26 The resonances at 46, 58, and 67 ppm are consistent with the methylene groups in Ar− CH2−N (NH) and N (NH)−CH2−N (NH).27 But the resonance at 67 ppm may be ascribed to methylene in Ar− CH2−O. The peak at ∼82 ppm may be assigned to methylene of N (NH)−CH2−O in oxazine. The strong and broad resonances with chemical shifts ranging from 95 to 170 ppm are attributed to the carbons in the aromatic rings of 3aminophenol-formaldehyde resin polymer networks.26 The resonance band of APFS-4 from 112 to 120 ppm is due to meta-unsubstituted phenolic carbons, while the peaks at ca. 154 and 129 ppm are due to hydroxyl- and amine-substituted carbons and the other phenolic carbons, respectively. The 192 ppm peak may be ascribed to the CO carbon produced by the oxidation of CH2 of Ar−CH2−N (NH) and/or to the phydroxybenzaldehyde −CHO carbons in the framework of APFS-4 (Scheme S1).27 Additionally, XPS analysis was utilized to investigate APFS4, and the resulting full scanned XPS spectrum (Figure S4) exhibits remarkable carbon, nitrogen, and oxygen peaks. Figures 4e and 4f show the C 1s and N 1s XPS highresolution spectra, respectively. As shown in the Figure 4e, the D


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Figure 4. (a) TGA curve, (b) EDX spectrum, (c) FTIR spectrum, (d) 1H → 13C CP/MAS NMR spectrum, and high-resolution XPS spectra of (e) C 1s and (f) N 1s of APFS-4.

existence of a small population of external mesopores in the matrix of NCS-4-1000. The total surface area was calculated to be 578 m2 g−1, with a micropore contribution of 512 m2 g−1 (88.6%) and mesopore contribution of 66 m2 g−1 (11.4%) from de Boer statistical thickness (t-plot) analysis.31 The presence of N and O in NCS-4-1000 was investigated by XPS (Figure S7). The C 1s XPS spectrum of the NCS-4-1000 sample shows that a high degree of graphitization (sp2 C, 284.5 eV) exists in the carbon matrix of NCS-4-1000, demonstrating their excellent electric conductivity (Figure S8). Furthermore, C 1s XPS spectrum of the NCS-4-1000 sample also indicates the characteristic peaks of several functional groups, such as C−N, C−O, CN, and CO.29 Additionally, the N 1s XPS spectrum was obtained to evaluate the nitrogen species. The result shows that two distinct N configurations exist in the matrix of NCS-4-1000, namely, pyridinic N at ca. 397.8 eV and pyrrolic N at ca. 400.5 eV (Figure S9).29,32 The Raman spectrum of NCS-4-1000 further demonstrates its structural defects and disorder (Figure S10). NCS with high surface area, abundant hierarchical framework structures, and plentiful heteroatom doping may provide promising carbon nanomaterials for energy conversion and storage, catalysis, and adsorption.

Figure 5. SEM images of NCS-4 fabricated by carbonization of APFS4 at different temperatures: (a) 700, (b) 800, (c) 900, and (d) 1000 °C. The scales of (a)−(c) are same as that of (d).

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(3) Liu, J.; Yang, T.; Wang, D.-W.; Lu, G. Q.; Zhao, D.; Qiao, S. Z. A facile soft-template synthesis of mesoporous polymeric and carbonaceous nanospheres. Nat. Commun. 2013, 4, 2798−2804. (4) Wang, L.; Sun, Q.; Wang, X.; Wen, T.; Yin, J.-J.; Wang, P.; Bai, R.; Zhang, X.-Q.; Zhang, L.-H.; Lu, A.-H.; Chen, C. Using Hollow Carbon Nanospheres as a Light-Induced Free Radical Generator To Overcome Chemotherapy Resistance. J. Am. Chem. Soc. 2015, 137, 1947−1955. (5) Xu, F.; Tang, Z.; Huang, S.; Chen, L.; Liang, Y.; Mai, W.; Zhong, H.; Fu, R.; Wu, D. Facile synthesis of ultrahigh-surface-area hollow carbon nanospheres for enhanced adsorption and energy storage. Nat. Commun. 2015, 6, 7221−7230. (6) Howes, P. D.; Chandrawati, R.; Stevens, M. M. Colloidal nanoparticles as advanced biological sensors. Science 2014, 346, 1247390. (7) Liu, J.; Wickramaratne, N. P.; Qiao, S. Z.; Jaroniec, M. Molecular-based design and emerging applications of nanoporous carbon spheres. Nat. Mater. 2015, 14, 763−774. (8) Deshmukh, A. A.; Mhlanga, S. D.; Coville, N. J. Carbon spheres. Mater. Sci. Eng., R 2010, 70, 1−28. (9) Al-Muhtaseb, S. A.; Ritter, J. A. Preparation and properties of resorcinol-formaldehyde organic and carbon gels. Adv. Mater. 2003, 15, 101−114. (10) Pierre, A. C.; Pajonk, G. M. Chemistry of aerogels and their applications. Chem. Rev. 2002, 102, 4243−4265. (11) Pekala, R. W. Organic aerogels from the polycondensation of resorcinol with formaldehyde. J. Mater. Sci. 1989, 24, 3221−3227. (12) Liu, J.; Qiao, S. Z.; Liu, H.; Chen, J.; Orpe, A.; Zhao, D. Y.; Lu, G. Q. Extension of The Stober Method to the Preparation of Monodisperse Resorcinol-Formaldehyde Resin Polymer and Carbon Spheres. Angew. Chem., Int. Ed. 2011, 50, 5947−5951. (13) Dong, Y.-R.; Nishiyama, N.; Egashira, Y.; Ueyama, K. 214 Basic amid acid-assisted synthesis of resorcinol-formaldehyde polymer and carbon nanospheres. Ind. Eng. Chem. Res. 2008, 47, 4712−4716. (14) Lu, A.-H.; Hao, G.-P.; Sun, Q. Can Carbon Spheres Be Created through the Stöber Method? Angew. Chem., Int. Ed. 2011, 50, 9023− 9025. (15) Wang, S.; Li, W.-C.; Hao, G.-P.; Hao, Y.; Sun, Q.; Zhang, X.Q.; Lu, A.-H. Temperature-Programmed Precise Control over the Sizes of Carbon Nanospheres Based on Benzoxazine Chemistry. J. Am. Chem. Soc. 2011, 133, 15304−15307. (16) Zhao, J.; Niu, W.; Zhang, L.; Cai, H.; Han, M.; Yuan, Y.; Majeed, S.; Anjum, S.; Xu, G. A Template-Free and Surfactant-Free Method for High-Yield Synthesis of Highly Monodisperse 3Aminophenol-Formaldehyde Resin and Carbon Nano/Microspheres. Macromolecules 2013, 46, 140−145. (17) Zhao, J.; Luque, R.; Qi, W.; Lai, J.; Gao, W.; Hasan Shah Gilani, M. R.; Xu, G. Facile surfactant-free synthesis and characterization of Fe3O4@3-aminophenol-formaldehyde core-shell magnetic microspheres. J. Mater. Chem. A 2015, 3, 519−524. (18) Tseng, C. M.; Lu, Y. Y.; Elaasser, M. S.; Vanderhoff, J. W. Uniform polymer particles by dispersion polymerizaiton in alcohol. J. Polym. Sci., Part A: Polym. Chem. 1986, 24, 2995−3007. (19) Míguez, H.; Meseguer, F.; López, C.; Mifsud, A.; Moya, J. S.; Vázquez, L. Evidence of FCC Crystallization of SiO2 Nanospheres. Langmuir 1997, 13, 6009−6011. (20) Zhou, H.; Xu, S.; Su, H.; Wang, M.; Qiao, W.; Ling, L.; Long, D. Facile preparation and ultra-microporous structure of melamineresorcinol-formaldehyde polymeric microspheres. Chem. Commun. 2013, 49, 3763−3765. (21) Allen, D. J.; Ishida, H. Effect of phenol substitution on the network structure and properties of linear aliphatic diamine-based benzoxazines. Polymer 2009, 50, 613−626. (22) Allen, D. J.; Ishida, H. Polymerization of linear aliphatic diamine-based benzoxazine resins under inert and oxidative environments. Polymer 2007, 48, 6763−6772. (23) Garcia, J. M.; Jones, G. O.; Virwani, K.; McCloskey, B. D.; Boday, D. J.; ter Huurne, G. M.; Horn, H. W.; Coady, D. J.; Bintaleb, A. M.; Alabdulrahman, A. M. S.; Alsewailem, F.; Almegren, H. A. A.;

CONCLUSIONS In summary, we have successfully developed a novel facile molecular-level design and controllable synthesis of polymer spheres through an autocatalysis polymerization process. The amine group of 3-aminophenol is of key importance to the polymerization of 3 minophenol and formaldehyde. The particle sizes of APFS can be finely tuned by varying reaction conditions. After carbonization, APFS can be converted to nitrogen-doped carbon spheres with a high yield. The method integrates the traditional sol−gel process of phenolic resins with benzoxazine chemistry without any catalyst, surfactants, templates, and/or dopants. It is considered to be low cost, environmentally friendly, and more suitable to the large-scale production of polymer spheres and carbon spheres. It can be speculated that by extending this method and based on the diverse options of monomers, more nanostructured resin and carbon materials with varieties of properties and morphologies could be designed at the molecular level and controllable synthesis. These polymer and carbon nanomaterials are expected to have potential applications in catalysis, electrochemistry, drug delivery, water treatment, building complex structures, nanocasting, and adsorption.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b01239. Table of synthesis parameters, photographs of centrifugation, dry and carbonization samples, SEM images, XPS spectra, structure scheme of APFS, and N2 adsorption− desorption isotherm (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (G.X.). ORCID

Jianming Zhao: 0000-0001-8469-3155 Rafael Luque: 0000-0003-4190-1916 Guobao Xu: 0000-0001-9747-0575 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project was supported by the National Natural Science Foundation of China (No. 21505128, and 21475123), the Ministry of Science and Technology of the People’s Republic of China (No. 2016YFA0201300), K.C. Wong Education Foundation, Chinese Academy of Sciences Visiting Professorships for Senior International Scientists (No. 2013T2G0024), the Academy of Sciences for the Developing World (TWAS), Chinese Academy of Sciences (CAS), and RUDN University Program 5-100.

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REFERENCES

(1) Zhao, Y.; Shang, L.; Cheng, Y.; Gu, Z. Spherical Colloidal Photonic Crystals. Acc. Chem. Res. 2014, 47, 3632−3642. (2) Zakhidov, A. A.; Baughman, R. H.; Iqbal, Z.; Cui, C.; Khayrullin, I.; Dantas, S. O.; Marti, J.; Ralchenko, V. G. Carbon Structures with Three-Dimensional Periodicity at Optical Wavelengths. Science 1998, 282, 897−901. F


Article

Macromolecules Hedrick, J. L. Recyclable, Strong Thermosets and Organogels via Paraformaldehyde Condensation with Diamines. Science 2014, 344, 732−735. (24) Chernykh, A.; Liu, J.; Ishida, H. Synthesis and properties of a new crosslinkable polymer containing benzoxazine moiety in the main chain. Polymer 2006, 47, 7664−7669. (25) Ishida, H.; Sanders, D. P. Regioselectivity and network structure of difunctional alkyl-substituted aromatic amine-based polybenzoxazines. Macromolecules 2000, 33, 8149−8157. (26) Hao, G.-P.; Li, W.-C.; Qian, D.; Wang, G.-H.; Zhang, W.-P.; Zhang, T.; Wang, A.-Q.; Schueth, F.; Bongard, H.-J.; Lu, A.-H. Structurally Designed Synthesis of Mechanically Stable Poly(benzoxazine-co-resol)-Based Porous Carbon Monoliths and Their Application as High-Performance CO2 Capture Sorbents. J. Am. Chem. Soc. 2011, 133, 11378−11388. (27) Zhang, X. Q.; Looney, M. G.; Solomon, D. H.; Whittaker, A. K. The chemistry of novolac resins 0.3. C-13 and N-15 nmr studies of curing with hexamethylenetetramine. Polymer 1997, 38, 5835−5848. (28) Wu, Z.-S.; Winter, A.; Chen, L.; Sun, Y.; Turchanin, A.; Feng, X.; Muellen, K. Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors. Adv. Mater. 2012, 24, 5130−5135. (29) Silva, R.; Voiry, D.; Chhowalla, M.; Asefa, T. Efficient MetalFree Electrocatalysts for Oxygen Reduction: Polyaniline-Derived Nand O-Doped Mesoporous Carbons. J. Am. Chem. Soc. 2013, 135, 7823−7826. (30) Friedel, B.; Greulich-Weber, S. Preparation of monodisperse, submicrometer carbon spheres by pyrolysis of melamine-formaldehyde resin. Small 2006, 2, 859−863. (31) Cote, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, crystalline, covalent organic frameworks. Science 2005, 310, 1166−1170. (32) Wang, D.-W.; Li, F.; Yin, L.-C.; Lu, X.; Chen, Z.-G.; Gentle, I. R.; Lu, G. Q.; Cheng, H.-M. Nitrogen-Doped Carbon Monolith for Alkaline Supercapacitors and Understanding Nitrogen-Induced Redox Transitions. Chem. - Eur. J. 2012, 18, 5345−5351.

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Autocatalysis Synthesis of Poly(benzoxazine-co

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