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. 2019 Jan 2;4(1):1–8. doi: 10.1021/acsomega.8b01590

Synthesis and Thermal Properties of Ethynyl Phenyl Azo Phenol-biphenylene Resin

Zhihua Li †,‡,*, Yujing Li †,‡, Junjie Li †,‡, Yuan Gao §, Xiaohong Gu §
PMCID: PMC6648784  PMID: 31459306

Abstract

graphic file with name ao-2018-01590b_0012.jpg

A novel addition curing ethynyl phenyl azo phenol-biphenylene resin (EPABN) was synthesized by introducing ethynylphenyl group into biphenyl novolac resin (BN) through diazo coupling reaction. Its synthesis reaction and curing mechanism were also proposed. Fourier transform infrared spectroscopy and 1H NMR spectroscopic analysis showed that the ethynylphenyl group was successfully linked to the BN molecular chain. By differential scanning calorimetry analysis, the curing process of EPABN resin was determined to be 150 °C/2 h + 172 °C/2 h + 203 °C/4 h + 255 °C/4 h + 300 °C/4 h. Gel permeation chromatography and elemental analysis showed that the introduction of ethynylphenyl group increased the number-average molecular weight and weight-average molecular weight of EPABN. Thermogravimetric analysis showed that the EPABN resin synthesized under the obtained optimum conditions has excellent heat resistance, ablation resistance, and mechanical properties. Td5 and Td10 of heat resistance of the cured EPABN resin are 463 and 531 °C, respectively, and its residual char yield at 700 and 1000 °C is 78.2% and 72.1%, respectively.

Introduction

Phenolic resin is widely used in adhesives, laminates, ablative composites, molding compounds, coatings, foams, and many other fields due to its heat resistance, flame retardancy, low cost, and higher char yield.1−6 However, with the rapid development of high-rise buildings, aeronautics, aerospace, and other special fields, the traditional phenolic resin can no longer meet the higher requirements of these fields in terms of material strength, stiffness, heat resistance, and flame retardancy. Therefore, the research of heat-resistant, higher char yield, highly flame-retardant new phenolic resin is of great significance.7−10 The heat resistance of phenolic resin can be improved by adding modifier, which can be roughly divided into inorganic elements,11−13 inorganic nanoparticles,14,15 synthetic organic substances,16−18 natural organic substances,19,20 and composite modification.21,22 New groups such as ethynyl,23−25 allyl,26 and phthalonitrile27,28 can also be introduced into the phenolic resin to obtain a novel addition curable phenolic resin and improve the heat resistance of the phenolic resin. Kawamoto11 prepared boron-modified phenolic resin (BPR) with salicyl alcohol and boric acid. The resin has good thermo-oxidative stability and mechanical properties. L. Asaro15 obtained a phenolic resin reinforced with carbon black and mesoporous silica particles (5 and 20 wt %), which increased the glass transition temperature and mechanical properties of the silica/resin composite. Wang23 synthesized a novel phenolic resin with high ethynyl contents by the diazo coupling reaction of phenol units with 3-ethynylaniline. Most of the modification work is researched around conventional phenolic resin, but there are few studies on the modification of the high-performance phenolic resin, especially the biphenyl novolac resin (BN).29

Biphenyl novolac resin is a kind of high-performance phenolic resin that is synthesized by introducing biphenyl group into molecular main chain through Friedel–Crafts reaction between phenol and diphenyl dimethyl ether. The introduction of high rigidity biphenyl structure can greatly reduce the content of phenolic hydroxyl groups in BN resin and improve its heat resistance, low moisture absorption rate, high thermal oxygen stability, and high intrinsic flame retardancy.28,30 On the basis of this, BN was synthesized first in our work, and then ethynylphenyl group was introduced into the biphenyl novolac molecular chain to obtain a novel addition curing ethynyl phenyl azo phenol-biphenylene resin (EPABN). To the best of our knowledge, EPABN resin has been rarely reported. The structure and thermal properties of EPABN were characterized in this paper. The best curing process and the optimized synthesis reaction conditions of EPABN were discussed in detail. The synthesis of EPABN resin and its possible curing mechanism were also described. This is a new high-performance phenolic resin with high temperature resistance, higher char yield, and good process performance, which can be widely used in many fields such as aviation and aerospace.

Results and Discussion

Characterization of EPABN

The FT-IR spectra of BN and EPABN samples are shown in Figure 1. It can be seen from the Fourier transform infrared (FT-IR) spectra of BN that the 3401 cm–1 peak is attributed to the −OH stretching vibration on the aromatic ring, the C–H stretching vibration peak at the aromatic ring is at 3022 cm–1, and the −CH2– stretching vibration is at 2907 cm–1. 1454 and 1365 cm–1 are peaks of −CH2– scissoring vibration. 1593 and 1496 cm–1 correspond to the peak of C=C stretching vibration of benzene ring. 1238 cm–1 belongs to the peak of C–O stretching vibration on phenolic hydroxyl group. The absorption peaks at 804 and 754 cm–1 are the out-of-plane bending vibration absorption peaks of the para- and ortho-disubstituted phenyl C–H bond on the aromatic ring, respectively.28 These peaks indicate that the synthesized product is BN.

Figure 1.

Figure 1

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FTIR spectra of BN and EPABN resin.

Compared with BN, the infrared absorption spectrum of EPABN is basically unchanged. Only the sharper and stronger ≡C–H stretching vibration peak appeared at 3288 cm–1, and the narrow and weak −C≡C– stretching vibration peak appeared at 2105 cm–1. The vibration peaks of 1,2,4,6-tetrasubstituted structure C–H in phenol nucleus appeared at 898 cm–1, and the ≡C–H out-of-plane deformation peak of alkyne appears near 638 cm–1. Strong out-of-plane bending vibration peaks of benzene ring 1,3-disubstituted C–H appeared at 798 and 691 cm–1. The presence of these peaks indicates that the ethynylphenyl group has been successfully linked to the BN molecular chain.

The 1H NMR spectra of the BN and EPABN samples are shown in Figure 2 (standardized against tetramethylsilane (TMS)). Figure 2a is a 1H NMR spectrum of BN, in which proton peaks from 9.6 to 9.3 ppm are attributed to internally associated phenolic hydroxyl hydrogen. Peaks from 7.6 to 7.1 ppm and from 7.1 to 6.8 ppm correspond to proton peaks of the unsubstituted hydrogen on biphenyl groups and phenol nuclear benzene rings, respectively. Peak from 4.05 to 3.75 ppm is the proton peak of methylene hydrogen. Because of the presence of isomers, the proton peak of methylene hydrogen splits into six peaks. The peak appearing around 3.4 is the proton peak of impurity water, and the peak at 2.5 is solvent dimethyl sulfoxide (DMSO) peak.23,31Figure 2b shows the 1H NMR spectrum of EPABN. Compared with Figure 2a, the hydrogen proton peak of the associated phenolic hydroxy group, the hydrogen proton peak, and the methylene hydrogen proton peak of the aryl ring were shifted to 10.9, 8.1, to 6.8, and 4.1 to 3.8 ppm, respectively. An acetylene hydrogen proton peak appeared at 4.1–4.4 ppm, confirming that ethynylphenyl group was successfully introduced into the resin’s molecular chain structure. In addition, the peaks of hydrogen proton peaks on the aromatic rings in the characteristic absorption peak of EPABN are relatively weak. This may be due to the introduction of ethynylphenyl group, making the molecular structure rigid, leading to its solubility in DMSO being not good.

Figure 2.

Figure 2

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1H NMR spectra of (a) BN and (b) EPABN resin (DMSO, TMS standard).

The gel permeation chromatography (GPC) profiles of BN and EPABN samples are shown in Figure 3 (polystyrene (PS) standard). The profiles of the GPC curves of the BN and EPABN samples are similar, indicating that they have similar molecular weight distribution characteristics. However, the retention time corresponding to the middle peak position in the GPC curve of the EPABN sample became short, so that the number-average molecular weight and viscosity became large. Typical parameters of GPC curves for BN and EPABN samples are given in Table 1. We can see that the introduction of ethynylphenyl group increases the number-average molecular weight and weight-average molecular weight of EPABN, but the polydispersity becomes smaller, and the molecular weight distribution is more concentrated.

Figure 3.

Figure 3

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GPC profiles of BN and EPABN resin (THF eluent, PS standard).

Table 1. Typical Parameters of GPC Curves for BN and EPABN Samples.

resin Inline graphic Inline graphic polydispersity
BN 600 900 1.50
EPABN 1200 1500 1.25
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Analysis on Curing Process of EPABN

The EPABN resin is obtained by a coupling reaction between ethynylphenyl diazonium salt and BN, and it has an addition-curable reactive functional group in its molecular chain. This type of phenolic resin can be self-cured by thermal addition polymerization of acetylene groups at a certain temperature without the need of an external curing agent and a catalyst to obtain a cured product having excellent heat resistance. The curing process parameters can be obtained by differential scanning calorimetry (DSC) analysis.

From the DSC curve of EPABN at different heating rates given in Figure 4, the EPABN resin is a single peak cure. As the heating rate increases, its peak shape gradually broadens and high, and the peak temperature also becomes larger. When the heating rate is 5 °C/min, the peak temperature is the lowest at ∼211 °C. The peak shape is the narrowest and the lowest. The reaction exothermic temperature range is 150–260 °C. The exotherm is gentle, and the curing reaction is easy to control. When the heating rate is 20 °C/min, the maximum peak temperature is ∼250 °C; the exothermic heat of the curing reaction becomes larger, but its peak shape is the widest, indicating that the EPABN curing reaction is still easy to control.

Figure 4.

Figure 4

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DSC curves of EPABN at different heating rates (N2).

The characteristic temperature of curing reaction of EPABN at different heating rates is shown in Table 2. As the heating rate increases, the initial curing reaction temperature (Ti), peak top temperature (Tp), and termination temperature (Tf) of EPABN increase. This is because, at a lower heating rate, the heat flow rate dH/dt is smaller; that is, the thermal effect of unit time is small. Thus, the curing rate is small, and the system has enough time for curing reaction, so its Ti is lower. As the heating rate increases, the dH/dt and curing rate increase, resulting in a corresponding increase in the temperature difference, and the exothermic peak of the curing reaction will correspondingly shift toward the higher temperature. According to the DSC curve, it can be roughly determined that the curing process of the EPABN resin is 150 °C/2 h + 172 °C/2 h + 203 °C/4 h + 255 °C/4 h + 300 °C/4 h.

Table 2. Characteristic Temperature of Curing Reaction of EPABN at Different Heating Rates.

β, °C·min–1 Ti, °C Tp, °C Tf, °C
5.0 179 211 266
10.0 194 227 274
15.0 203 236 286
20.0 208 244 297
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Optimization of Synthesis Reaction Conditions of EPABN

The Mass Ratio of Different 3-Aminophenylacetylene to BN

With ethyl alcohol absolute as the solvent, the molar ratio of 3-aminophenylacetylene to NaOH was 1:2.07. The GPC curves and N content of EPABN resins prepared from different 3-aminophenylacetylene to BN mass ratios are shown in Figure 5 and Table 3. The profile of the GPC curves of EPABN samples prepared with different 3-aminophenylacetylene and BN mass ratios are very similar, indicating that they have very similar molecular weight distribution characteristics. Table 3 shows the typical parameters of the GPC curve. As the mass ratio of 3-aminophenylacetylene to BN increases, the number-average molecular weight, weight-average molecular weight, polydispersity, and N content of EPABN increase slightly. The larger the mass ratio of 3-aminophenylacetylene to BN, the greater the amount of 3-aminobenzeneacetylene involved in the diazo reaction and the more acetylene diazonium salt positive ions available as electrophiles. The greater the chance of electrophilic substitution on the aromatic ring with biphenyl novolac, the higher the diazo coupling rate, the higher the N content in the EPABN molecule, the larger the molecular weight and the polydispersity.

Figure 5.

Figure 5

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GPC curves of EPABN prepared by different mass ratios of 3-aminophenylacetylene to BN (THF eluent, PS standard).

Table 3. EPABN Prepared from Different Mass Ratios of 3-Aminophenylacetylene to BN.
  EPABN molecular weight distribution
  
mass ratio of 3-aminophenylacetylene to BN Mn Mw Mw/Mn N content, wt %
1.25:1 1400 2600 1.85 8.49
1.4:1 1500 2800 1.87 8.51
1.5:1 1600 3000 1.88 8.55
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Different Molar Ratios of 3-Aminophenylacetylene to NaOH

With ethyl alcohol absolute as solvent, the mass ratio of 3-aminophenylacetylene to BN was 1.25:1. The GPC and N contents of EPABN resins prepared from different molar ratios of 3-aminophenylacetylene to NaOH are shown in Table 4. As the molar ratio of 3-aminophenylacetylene to NaOH increases, the number-average molecular weight and weight-average molecular weight of EPABN increase, and the molecular weight distribution coefficient first decreases and then increases. But the N content in EPABN molecules gradually decreases. When the molar ratio of 3-aminophenylacetylene to NaOH is 1:1.09, the N content of EPABN is the highest, but the number-average molecular weight is very low at only 200. EPABN resin has lower intrinsic viscosity and poor heat resistance. When the molar ratio of 3-aminophenylacetylene to NaOH is 1:1.73, the N content in EPABN molecule is 8.93 wt %, the lowest molecular weight distribution coefficient is only 1.25, and the molecular weight distribution is more concentrated. At this time, EPABN resin has better heat resistance. When the molar ratio of m-aminophenylacetylene to NaOH is greater than 1:1.73, the molecular weight of EPABN is larger, but the N content is smaller; the active acetylene group, which can be used for thermal addition curing, is less, so the heat resistance is poor. In general, the coupling reaction of a diazonium salt with a phenolic aldehyde is performed in a system having a pH of 8–10. The content of NaOH is small, the pH value is too low, the concentration of phenolic sodium salt on the phenol ring in the molecular structure of BN is too low, and the coupling reaction is incomplete. When the NaOH content is high and the pH is too high, diazo anions are easily formed, which is unfavorable to the coupling reaction, and the diazo coupling ratio is low, so the N content in the EPABN molecule is small.

Table 4. EPABN prepared from different molar ratios of 3-aminophenylacetylene to NaOH.
  EPABN molecular weight distribution
  
molar ratio of 3-aminophenylacetylene to NaOH Mn Mw Mw/Mn N content, wt %
1:1.09 200 1200 6.00 9.47
1:1.73 1200 1500 1.25 8.93
1:2.07 1400 2600 1.86 8.49
1:2.17 1700 4000 2.35 8.35
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Different Solvent Systems

The mass ratio of 3-aminophenylacetylene to BN is 1.25:1, and the molar ratio of 3-aminophenylacetylene to NaOH is 1:1.73. The GPC and N contents of EPABN resin prepared from different solvent systems are shown in Figure 6 and Table 5. It can be seen from Figure 6 that the profiles of the GPC curves of the EPABN samples prepared with different solvent systems are very similar, indicating that they have very similar molecular weight distribution characteristics. As the water content in the solvent system increases, the number-average molecular weight, weight-average molecular weight, and polydispersity of EPABN increase first and then decrease, while the N content in the EPABN molecule continuously increases. When the solvent system used is absolute ethanol, the number-average molecular weight, weight-average molecular weight, and N content of EPABN are the smallest, but the molecular weight distribution is relatively concentrated. When the volume ratio of anhydrous ethanol to water in the solvent system is 2:1, the N content in the EPABAN is up to 9.53 wt %. The number-average molecular weight and molecular weight distribution are also relatively moderate. At this time, EPABN has excellent heat resistance. This is because the coupling reaction between diazonium salts and phenols is usually performed in weakly basic aqueous solution, but the solubility of basic aqueous solution to some phenols with larger steric hindrance is poor. Therefore, the concentration of the generated phenol oxygen ions is too low, and the coupling reaction does not easily proceed. At this point, adding an alkaline substance such as ethanol or pyridine as a catalyst can accelerate the coupling reaction and increase the diazo coupling rate. However, when the selected solvent system is an anhydrous organic solvent, the solubility of NaOH and phenols deteriorates, and the diazo coupling rate becomes lower. The solvent water molecules can also act as catalysts to accelerate the reaction.

Figure 6.

Figure 6

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GPC curves of EPABN prepared from different solvent systems (THF eluent, PS standard).

Table 5. EPABN Prepared by Different Solvent Systems.
  EPABN molecular weight distribution
  
solvent system V(ethanol)/V(water) Mn Mw Mw/Mn N content, wt %
absolute ethanol 1200 1500 1.25 8.93
4:1 1400 2200 1.57 9.32
2:1 1400 1900 1.36 9.53
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Thermal Properties

EPABN Resins Prepared from Different 3-Aminophenylacetylene and NaOH Molar Ratios

The TGA curves of EPABN resin-cured products prepared from different 3-aminophenylacetylene and NaOH molar ratios are shown in Figure 7, and the typical parameters of the TG curves are shown in Table 6. With the increase of the molar ratio of 3-aminophenylacetylene to NaOH, the Td5, Td10, char residue at 700 and 1000 °C of the cured EPABN resin first increased and then decreased. When the molar ratio of 3-aminophenylacetylene to NaOH is 1:1.09, the Td5, Td10, char residues at 700 and 1000 °C of the cured EPABN resin are the lowest, and the thermal performance is poor. When the molar ratio of 3-aminophenylacetylene to NaOH is 1:1.73, char residues at 700 and 1000 °C of the cured EPABN resin are the highest, which are 76.1% and 70.1%, respectively. When the molar ratio of 3-aminophenylacetylene to NaOH is 1:2.07, the cured EPABN resins Td5 and Td10 reach the highest, but the residual char rate is lower. Combined with GPC and elemental analysis of EPABN, it was found that EPABN resin prepared from a molar ratio of 3-aminophenylacetylene to NaOH of 1:1.73 has excellent thermal properties.

Figure 7.

Figure 7

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TG curves of the cured EPABN resin prepared from different molar ratios of 3-aminophenylacetylene to NaOH (N2, 10 °C/min).

Table 6. Typical Parameters of the TG Curvea.
sample Td5, °C Td10, °C char yield at 700 °C (%) char yield at 1000 °C (%)
1:1.09 333 381 75.8 59.1
1:1.73 457 522 76.1 70.0
1:2.07 468 526 72.9 64.5
1:2.17 455 517 71.1 62.5
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a

Td5, the temperature at which 5% of the sample decomposes; Td10, the temperature at which 10% of the sample decomposes.

EPABN Resin Prepared from Different Solvent Systems

The TG curves of the cured EPABN resin prepared from different solvent systems are shown in Figure 8, and the typical parameters of the TG curves are shown in Table 7. The Td5, Td10, char residues at 700 and 1000 °C of the cured EPABN resin gradually increase with the increase of the water content of the solvent system. When the solvent system used was two-thirds ethanol and one-third water (v/v), the Td5, Td10, char residues at 700 and 1000 °C of the cured EPABN resin reached the highest, 463 °C, 531 °C, 78.2%, and 72.1%, respectively. Combined with GPC and elemental analysis of EPABN, it can be seen that the N content of EPABN molecules synthesized under this condition is the highest, indicating that the content of active alkyne groups in the resin molecular structure is the highest. The heat-polymerization of alkyne groups increases the cross-link density of the cured EPABN resin, which greatly improves the heat resistance and ablation resistance of EPABN resins.

Figure 8.

Figure 8

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TG curves of the cured EPABN resin prepared from different solvent systems (N2, 10 °C/min).

Table 7. Typical Parameters of the TG Curve.
sample V(ethanol)/V(water) Td5, °C Td10, °C char yield at 700 °C (%) char yield at 1000 °C (%)
absolute ethanol 457 522 76.1 70.0
4:1 460 527 77.9 70.4
2:1 463 531 78.2 72.1
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Resin Synthesis Reaction and Curing Mechanism

The EPABN resin is obtained by using BN as raw material and introducing ethynylphenyl group into the molecular chain through a diazo coupling reaction. The reaction mechanism and curing mechanism are as follows:

  • (1)

    The BN is a special phenolic resin prepared by Friedel–Crafts alkylation reaction under the action of an acidic catalyst with excess phenol and 4,4′-dichloromethylbiphenyl. The reaction mechanism is shown in Scheme 1. Under acidic condition, 4,4′-dichloromethyl biphenyl reacted with H+ to form 4,4′-dimethylpositive ion biphenyl, then it attacked the ortho and para position with higher electron cloud density in phenol structure as electrophilic reagent to form intermediate S-complex and lost one proton to obtain electrophilic substitution product. The obtained electrophilic substitution product can also be subjected to Friedel–Crafts alkylation reaction with 4,4′-dichloromethyl biphenyl, and the reaction is repeated so as to finally generate BN oligomer.

  • (2)

    EPABN is a novel addition-cure phenolic resin prepared by a diazo coupling reaction between a BN and 3-aminophenylacetylene. The reaction mechanism is shown in Scheme 2. Under acidic conditions, sodium nitrite reacts with H+ to form HNO2 and acts on 3-aminophenylacetylene to convert it into a positively charged ethynylphenyl diazo hydrochloride. Biphenyl novolac molecular chains contain a large number of phenol structures, and the ortho and para electron clouds of phenol are dense. At a pH of 8–9, ethynylphenyl diazo hydrochloride can act as an electrophile to attack carbon atoms with a higher density of electron clouds, form intermediate products, lose hydrogen protons, and finally obtain EPABN resin. Because of the influence of steric hindrance, diazonium ions generally attack the para position, and if the para position is occupied, they will attack the ortho-position site.

  • (3)

    EPABN resin is mainly self-cured by thermal addition polymerization of ethynyl groups in the molecular chain. The ethynyl groups in the resin may be converted into benzene rings, aromatic rings, multiolefins, trimers, tetramers, conjugated olefins, etc. by trimerization reaction, Glazer coupling reaction, Strauss coupling reaction, Diels–Alder reaction, or addition polymerization reaction. The possible curing mechanism is shown in Scheme 3.

Scheme 1. BN Synthesis Reaction Mechanism Diagram.

Scheme 1

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Scheme 2. EPABN Synthesis Reaction Mechanism Diagram.

Scheme 2

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Scheme 3. EPABN Resin Curing Mechanism Diagram.

Scheme 3

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Conclusion

In conclusion, EPABN resin was successfully synthesized by diazo coupling reaction in this experiment. Compared with conventional high-performance phenolic resins, this is a new type of addition-curing resin in which the former needs to be cured under the action of a curing agent or a catalyst, and the latter requires only heating to be cured. The introduction of ethynylphenyl group increases the number-average and weight-average molecular weights of the resin and improves the heat resistance of the resin. The high-rigidity biphenyl structure in the molecular chain can greatly reduce the phenolic hydroxyl content in the BN resin and improve its heat resistance. Therefore, Td5 and Td10 of heat resistance of the EPABN resin synthesized under the optimum conditions are 463 and 531 °C, respectively, and its residual char yields at 700 and 1000 °C are 78.2% and 72.1%, respectively. The cured EPABN has excellent heat resistance, ablation resistance, and mechanical properties, which can be widely used in aerospace and aviation as ablative materials and thermal structural materials.

Experimental Section

Materials

4,4′-Dichloromethylbiphenyl (>98%) was purchased from Jiangsu Ruifengda Chemical Materials Business Department. Phenol and anhydrous ethanol were purchased from Sinopharm Group Chemical Reagent Co. Ltd. Methanol was purchased from Tianjin Baishi Chemical Co. Ltd. 3-Aminophenylacetylene (>98%) was purchased from Jiaozhou Fine Chemicals Co. Ltd. Sodium nitrite (NaNO2) was purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co. Ltd. Concentrated hydrochloric acid was purchased from Zhuzhou Xingkuang Chemical Glass Co. Ltd. Urea was purchased from Taishan Yueqiao Reagent Plastics Co. Ltd. Sodium hydroxide (NaOH) was purchased from Tianjin Damao Chemical Reagent Factory.

Synthesis of BN

BN resin was prepared by reacting phenol with 4,4′-dichloromethylbiphenyl in the presence of an acid catalyst. Phenol, 4,4′-dichloromethylbiphenyl, methanol, and concentrated hydrochloric acid were taken in a four-necked flask and stirred at 90 °C in an oil bath. The reaction was continued for 5 h under stirring at 90 °C. After the reaction is completed, it is rapidly heated to 180 °C, and the unreacted raw materials were removed by reduced pressure distillation. After it cooled, a pale yellow biphenyl novolac resin was obtained.

Synthesis of Diazonium Salts

Hydrochloric acid solution (15 wt %) was taken in a three-necked flask. 3-Aminophenylacetylene was added dropwise to it and stirred at 60 °C for half an hour. NaNO2 aqueous solution (35 wt %) was added dropwise to the above system and stirred at −5 °C. After the addition is completed, the reaction is performed at 0 °C for 1.5 h. Finally, urea was added to neutralize unreacted nitrous acid and filtered to obtain a brown-red transparent diazonium salt solution.

Synthesis of EPABN

EPABN resins were prepared by coupling reaction between 3-ethynylphenyl diazonium sulfate and BN in the presence of a base catalyst. Ethanol, BN, and NaOH were taken in a four-necked flask and stirred for 2 h. The solution was stirred well and cooled to 0 °C. To this solution, the synthesized diazonium salt solution was added dropwise at 0 °C and stirred well. After the addition, the solution was kept at the same temperature for 5 h by occasional stirring. The reaction mixture was then added dropwise to distilled water, and the pH was adjusted to 7 by adding dilute H2SO4. The synthesized resin was filtered, washed by distilled water, and dried at 60 °C overnight to obtain a reddish-brown powder EPABN resin. EPABN was thermally cured as per the following schedule: 150 °C/2 h + 172 °C/2 h + 203 °C/4 h + 255 °C/4 h + 300 °C/4 h, to give the cured thermosets.

Characterization

Spectroscopy (FT-IR) of the sample was recorded using a Nicolet 6700 Fourier transform infrared spectrometer. The data acquisition range during FT-IR analysis was from 4000 to 500 cm–1 with a resolution of 4 cm–1. The sample to be tested (5 mg) was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) at a sample concentration of 10 mg/mL. The 1H NMR spectrum of 0–15 ppm was measured at room temperature with TMS as internal standard by means of nuclear magnetic resonance spectrometer (Avance III 400 MHz). The E2695 GPC was used to measure the molecular weight size and distribution of the product. The sample was dissolved in tetrahydrofuran (THF) solvent and eluted with THF at a flow rate of 1 mL/min. The concentrations of the samples were 0.6 wt %. The standard sample was monodisperse polystyrene. The organic element analyzer (Vanio EL CHNS) was used to analyze the type and content of the elements contained in the sample. The DSC analysis (STA449C synchronous thermal analyzer) uses N2 as the protective atmosphere; the flow rate is 60 mL/min, the heating rate is 5 °C/min, 10 °C/min, 15 °C/min, 20 °C/min, and the test temperature range is 20–350 °C. The SDTQ600 thermogravimetry differential thermal analyzer was used for thermogravimetric analysis (TGA; test temperature range of 20–1000 °C, N2). The flow rate was 60 mL/min, and the heating rate was 10 °C/min.

Acknowledgments

This work was supported by Central South University Open and Shared Fund for Instrument and Equipment (CSUZC2014008) Funded Project.

The authors declare no competing financial interest.

References

  1. Xue B.; Zhang X. L. Application and development trend of phenolic resin. Thermosetting Resin 2007, 22, 47–50. [Google Scholar]
  2. Nair C. P.R. Advances in addition-cure phenolic resins. Prog. Polym. Sci. 2004, 29, 401–498. 10.1016/j.progpolymsci.2004.01.004. [DOI] [Google Scholar]
  3. Abdalla M. O.; Ludwick A.; Mitchell T. Boron-modified phenolic resins for high performance applications. Polymer 2003, 44, 7353–7359. 10.1016/j.polymer.2003.09.019. [DOI] [Google Scholar]
  4. Hirano K.; Asami M. Phenolic resins-100 years of progress and their future. React. Funct. Polym. 2013, 73, 256–269. 10.1016/j.reactfunctpolym.2012.07.003. [DOI] [Google Scholar]
  5. Kuroe M.; Tsunoda T.; Kawano Y.; Takahashi A. Application of lignin-modified phenolic resins to brake friction material. J. Appl. Polym. Sci. 2013, 129, 310–315. 10.1002/app.38703. [DOI] [Google Scholar]
  6. Spina S.; Zhou X.; Segovia C.; Pizzi A.; Romagnoli M.; Giovando S.; Pasch H.; Rode K.; Delmotte L. Phenolic resin adhesives based on chestnut (Castanea sativa) hydrolysable tannins. J. Adhes. Sci. Technol. 2013, 27, 2103–2111. 10.1080/01694243.2012.697673. [DOI] [Google Scholar]
  7. Qi S. C.; Han G.; Wang H. R.; Li N.; Zhang X. A.; Jiang S. L.; Lu Y. F. Synthesis and characterization of carborane bisphenol resol phenolic resins with ultrahigh char yield. Chin. J. Polym. Sci. 2015, 33, 1606–1617. 10.1007/s10118-015-1712-1. [DOI] [Google Scholar]
  8. Li S. F. Synthesis of benzoxazine-based phenolic resin containing furan groups. Chin. Chem. Lett. 2010, 21, 868–871. 10.1016/j.cclet.2010.01.007. [DOI] [Google Scholar]
  9. Feng J. J.; Chen L. X.; Gu J. W.; He Z. Y.; Yun J.; Wang X. B. Synthesis and characterization of aryl boron-containing thermoplastic phenolic resin with high thermal decomposition temperature and char yield. J. Polym. Res. 2016, 23, 1–7. 10.1007/s10965-016-0966-9. [DOI] [Google Scholar]
  10. Feng J. J.; Li J.; Chen L. X.; Qin Y. S.; Zhang X. F.; Gu J. W.; Tadakamalla S.; Guo Z. H. Enhanced thermal stabilities and char yields of carbon fibers reinforced boron containing novolac phenolic resins composites. J. Polym. Res. 2017, 24, 176. 10.1007/s10965-017-1338-9. [DOI] [Google Scholar]
  11. Kawamoto A. M.; Pardini L. C.; Diniz M. F.; Lourenço V. L.; Takahashi M. F. K. Synthesis of a boron modified phenolic resin. J. Aerosp. Technol. Manage. 2010, 2, 169–182. 10.5028/jatm.2010.02027610. [DOI] [Google Scholar]
  12. Zhang G. Y.; Liu S. Q.; Liu W. C.; Guan Y. Y.; Li B.; Yu W. M.; Li B. H.; Wang J. Study on the Molybdic Acid Modified High-ortho Phenolic Resin. Chem. Adhes. 2017, 39, 192–193. [Google Scholar]
  13. Li S.; Chen F.; Zhang B.; Luo Z.; Li H.; Zhao T. Structure and improved thermal stability of phenolic resin containing silicon and boron elements. Polym. Degrad. Stab. 2016, 133, 321–329. 10.1016/j.polymdegradstab.2016.07.020. [DOI] [Google Scholar]
  14. Jiang L.Dielectric Constant and Mechanical Properties of Graphene and Graphite Nanoplateles Modified Phenolic Resin. Thesis, Harbin University of Science and Technology, 2016. [Google Scholar]
  15. Asaro L.; Manfredi L. B.; Pellice S.; Procaccini R.; Rodriguez E. S. Innovative ablative fire resistant composites based on phenolic resins modified with mesoporous silica particles. Polym. Degrad. Stab. 2017, 144, 7–16. 10.1016/j.polymdegradstab.2017.07.023. [DOI] [Google Scholar]
  16. Li S.; Li H.; Li Z.; Zhou H.; Guo Y.; Chen F. H.; Zhao T. Polysiloxane modified phenolic resin with co-continuous structure. Polymer 2017, 120, 217–222. 10.1016/j.polymer.2017.05.063. [DOI] [Google Scholar]
  17. Foyer G.; Chanfi B. H.; Boutevin B.; Caillol S.; David G. New method for the synthesis of formaldehyde-free phenolic resins from lignin-based aldehyde precursors. Eur. Polym. J. 2016, 74, 296–309. 10.1016/j.eurpolymj.2015.11.036. [DOI] [Google Scholar]
  18. Lin C. T.; Lee H. T.; Chen J. K. Preparation and properties of bisphenol-F based boron-phenolic resin/modified silicon nitride composites and their usage as binders for grinding wheels. Appl. Surf. Sci. 2015, 330, 1–9. 10.1016/j.apsusc.2014.12.193. [DOI] [Google Scholar]
  19. Yang J.Preparation and application of phenolic resins for friction material matrix modified by boron and linseed oil. Thesis, Jiangsu University, 2016. [Google Scholar]
  20. Huang S. J.; Zhai S. Y.; Chen Y. G.; Su Z. Z.; Zhu G. M.; Xie L. Synthesis technology of cashew nut shell liquid modified phenolic resin and properties of its composites. Polym. Mater. Sci. Eng. 2016, 32, 42–48. [Google Scholar]
  21. Hu X.; Zeng J.; Dai W.; Shi W.; Li L.; Han C. Y. EPDM/vinyl triethoxysilane modified phenol formaldehyde resin composite. Polym. Bull. 2011, 66, 703–710. 10.1007/s00289-010-0374-y. [DOI] [Google Scholar]
  22. Huang G. R.; Liu H. B.; Yang L.; He Y. D.; Xia X. H.; Chen H. Pyrolysis behavior of graphene/phenolic resin composites. New Carbon Mater. 2015, 30, 412–418. [Google Scholar]
  23. Wang M.; Yang M.; Zhao T.; Pei J. Acetylene-grafted resins derived from phenolics via azo coupling reaction. Eur. Polym. J. 2008, 44, 842–848. 10.1016/j.eurpolymj.2008.01.002. [DOI] [Google Scholar]
  24. Li Z. H.; Peng Q. Y.; Li J. J.; Xia X. Q.; Zou D. H.; Niu J.; Liu L. L.; Li W. Studies on the structure and properties of ethynyl phenyl azo novolac foam. Acta Polym. Sin. 2016, 8, 1121–1127. [Google Scholar]
  25. Nair C. P. R.; Bindu R. L.; Ninan K. N. Addition curable phenolic resins based on ethynyl phenyl azo functional novolac. Polymer 2002, 43, 2609–2617. 10.1016/S0032-3861(02)00003-4. [DOI] [Google Scholar]
  26. Nechausov S. S.; Bulgakov B. A.; Solopchenko A. V.; Serdan A. A.; Kalugin D. I.; Lyalin A.; Kepman A. V.; Malakho A. P. Thermosetting matrices for composite materials based on allyl/propagryl substituted novolac resins. J. Polym. Res. 2016, 23, 114. 10.1007/s10965-016-1004-7. [DOI] [Google Scholar]
  27. Yang Y.; Min Z.; Yi L. A novel addition curable novolac bearing phthalonitrile groups: synthesis, characterization and thermal properties. Polym. Bull. 2007, 59, 185–194. 10.1007/s00289-007-0765-x. [DOI] [Google Scholar]
  28. Luo Z. X.; Zhang B. X.; Zhou H.; Han W. J.; Zhao T. Preparation and properties of a novel phthalonitrie functional biphenyl-type novolac resin. Aerosp. Mater. Technol. 2011, 4, 20–23. [Google Scholar]
  29. Li Z. H.; Duan F. F.; Hua S. J.; Xia X. Q.; Zou D. H.; Niu J.; Liu L. L. Preparation and Properties of Phthalonitrile Biphenyl Novolac Resin Hollow Microspheres. Acta Polym. Sin. 2017, 4, 596–604. [Google Scholar]
  30. Zhu Q. R.; Li J. C.; Wang L. J.; Du X. Y.; Tan W.; Wu J. Synthesis and characterization of phenol-biphenylene resin. J. Chem. Ind. Eng. (China) 2009, 60, 1052–1056. [Google Scholar]
  31. Luo Z. H.; Yang M.; Wang M. C.; Zhao T. Addition-curable phenolic resin with arylacetylene groups: preparation, processing capability, thermal properties, and evaluation as matrix of composites[J]. High Perform. Polym. 2011, 23, 575–584. 10.1177/0954008311421832. [DOI] [Google Scholar]

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