journal of mineral, metal and material engineering, 21-27 21 ......22 journal of mineral, metal and...

Journal of Mineral, Metal and Material Engineering, 2020, 6, 21-27 21

E-ISSN: 2414-2115/20 © 2020 Scientific Array

Novel Polytriazole Resins Derived from Star-Shape Arylacetylenes with Silane Unit

Niping Dai, Zhuoer Yu, Jun Zhang, Junkun Tang and Farong Huang*

Key Laboratory of Specially Functional Polymeric Materials and Related Technology (Ministry of Education), School of Material Science and Engineering, East China University of Science and Technology, Shanghai 200237, China

Abstract: Novel polytriazole resins were synthesized from star-shape arylacetylenes with silane unit, N,N,N',N'-tetrapropargyl-4,4'-diaminodiphenylmethane (TPDDM) and 1,1'-bisazidomethyl-4,4'-biphenyl (BAMBP) by 1,3-dipolar cycloaddition. The rheological properties, curing behavior, thermal properties and mechanical properties of the polytriazole resins were investigated. The results show that the resins have low viscosity and could be cured at 80˚C(ca). The cured resins demonstrate excellent heat resistance and high mechanical properties. The glass transition temperature (Tg) and the flexural strength of the cured resins at ambient temperature arrive at over 254˚C and over 138.9 MPa, respectively. The flexural strength of T300 carbon fiber reinforced composites reaches as high as 527.4 MPa at room temperature.

Keywords: polytriazole resin derived from star-shape arylacetylene, 1,3-dipolar cycloaddition, silicon-containing arylacetylene resin, high performance resin, advanced composite.

INTRODUCTION

1,3-Dipolar cycloaddition of an azide compound and an alkyne compound offers a simple, reliable and efficient approach to synthesize a triazole compound or a polytriazole [1]. The cycloaddition usually takes place at low temperature and with less influence of reaction medium. Recently, many researches have focused on the syntheses of homopolymers, block copolymers, graft copolymers, star polymers, dendrimers, and hyperbranched polymers by 1,3-dipolar cycloaddition of azide and alkyne groups of monomers, oligomers, and polymers [6]. The cycloaddition reaction of azides and alkynes is also found to be a very useful way to develop a novel resin for low-temperature molding composites in applications where size accuracy and material cost of parts or components are considered to be important. Our laboratory has explored a series of thermosetting polytriazole (PTA) resins made from multipropargyl compounds and multiazide compounds by 1,3-dipolar cycloaddition [10].

The silicon-containing arylacetylene resins exhibit excellent thermal stabilities with Td5 over 600˚C after they are curd [11]. Recently, star-shape arylacetylene resins derived from silicon(TEPxS) with high heat resistance have been developed [16]. The star-shape arylacetylene resins with ethynyl or ethynylene groups are used as a component to produce a new polytriazole

*Address correspondence to this author at the Key Laboratory of Specially Functional Polymeric Materials and Related Technology (Ministry of Education), School of Material Science and Engineering, East China University of Science and Technology, Shanghai 200237, China; Tel: 86-21-64251110; Fax: 86-21-64251087; E-mail: [email protected]

resin with good processability and heat resistance. At

the same time, low temperature curing could be realized by 1,3-dipolar cycloaddition between ethynyl or ethynylene groups of the TEPxS and azide groups of an azide compound. In this article, novel polytriazole resins made from the star-shape arylacetylenes with silane unit and an azide compound via the cycloaddition are investigated.

EXPERIMENTAL

Materials

Tetrahydrofuran (THF) (AR) was purchased from Shanghai Titan Scientific Co., Ltd., China. N,N,N',N'-tetrapropargyl-4,4'-diaminodiphenylmethane (TPDDM) and 1,1'-diazidomethyl-4,4'-biphenyl (BAMBP) were synthesized in our lab [16]. The novel polytriazole resins derived from star-shape arylacetylenes with silane unit (TEPxS, x= H, M, P), tris(3-ethynyl phenylethynyl)silane(TEPHS), tris(3-ethynyl phenylethynyl)methylsilane(TEPMS) and tris(3-ethynyl phenylethynyl) phenylsilane(TEPPS), were synthesized through cycloaddition reactions [16]. T300 carbon fabric(carbon fiber cloth) was purchased from Toray Co., Japan.

Characterization

The solubility was determined based on the following tests. A resin(0.1 g) was putted into a solvent(10 ml) and the produced mixture was swayed to observe whether the resin was soluble or not. Rheological behavior was determined on a Thermo Haake RS600 Rheometer system (Thermo Electron

22 Journal of Mineral, Metal and Material Engineering, 2020, Vol. 6 Dai et al.

Corporation, Germany) in the range of 90-200˚C and the shear rate and heating rate for the viscosity measurements were 0.01 s-1 and 2˚C/min, respectively. The viscosity of a resin at a temperature was measured on a Brookfield DV-II+Pro viscometer (AMETEK Brookfield, USA). DSC analysis was carried out at the heating rate of 10˚C/min and flow rate of 50 mL/min of nitrogen on a TA Q2000 analyzer (TA, New Castle, USA). The dynamic mechanical analysis (DMA) of the cured resins was conducted on DMA 1 ((METTLER TOLEDO, Greifensee, Switzerland) at the heating rate of 5˚C/min from 35˚C to 500˚C with the oscillation frequency of 1 Hz, and the testing mode was three-point bending. The thermal stabilities were determined on TGA/DSC 1LF analyzer (METTLER TOLEDO, Greifensee, Switzerland) at the heating rate of 10 ˚C/min from 40˚C to 1000˚C in nitrogen or air with a flow rate of 50 ml/min. The flexural properties of the cured resins (size: 80 mm×15 mm×4 mm) and carbon fiber reinforced composites (size: 45 mm×15 mm×2 mm) were measured with CRIMS DDL100 tester (Changchun Research Institute for Mechanical Science

Co., Ltd., Changchun, China) according to GB/T 9341-2008 standard.

Synthesis of Novel Polytriazole Resins

Novel polytriazole resins derived from star-shape arylacetylenes with silane unit (named as TEPxS-PTA resins, x= M, P, H) were synthesized in the following process as shown in Scheme 1. For TEPMS-PTA resin synthesis, TEPMS, TPDDM and BAMBP were weighed in stoichiometric ratios and dissolved in THF with stirring. The molar ratio of total alkyne group in loaded TEPMS and TPDDM with each 50% percentage to azide group in BAMBP was 1.1:1.0. The solution with 75% concentration was heated to 70˚C and kept at 70˚C for 2 h. The transparent solution was obtained. Thereafter, the solvent THF was removed under vacuum to get solid TEPMS-PTA resin. Other resins, TEPPS-PTA and TEPHS-PTA, were synthesized in the similar way as described above by using TEPPS and TEPHS instead of TEPMS, respectively.

Scheme 1: Synthesis route of novel polytriazole resins derived from star-shape arylacetylenes with silane unit.

Novel Polytriazole Resins Derived from Star-Shape Arylacetylenes Journal of Mineral, Metal and Material Engineering, 2020, Vol. 6 23

Preparation of Cured Novel Polytriazole Resins

TEPxS-PTA resins, TEPMS-PTA, TEPPS-PTA, and TEPHS-PTA, were separately weighted and putted in a mold. The resins with the molds were moved in a vacuum oven and heated to 60˚C. After the gas embedded and the residual solvent in molten resins were removed under vacuum at 60˚C, the resins with the molds were then transferred to another oven and heated to and kept at 80˚C for 12 h, 120˚C for 2 h, 150˚C for 2 h, 180˚C for 2 h and 210˚C for 2 h to get cured resins.

Preparation of T300 Carbon Fabric Reinforced TEPxS-PTA Composites

A 35wt% resin solution was prepared from a TEPxS-PTA resin and THF. Then 12 pieces of T300 carbon fiber cloth in size of 150 mm×100 mm were immersed in the resin solution and then dried out to obtain a carbon cloth prepreg. The prepreg was moved to a vacuum oven and heated to 40˚C and kept at 40˚C for 2 h for further removal of residual solvent. Thereafter, the prepreg were putted into a mold and then pressed in a presser machine under the pressure of 1.0 MPa(ca). Molding procedure was showed as follows: 80˚C/12 h+120˚C/2 h+150˚C/2 h+180˚C/2 h+210˚C/2 h.

RESULTS AND DISCUSSION

Processability of TEPxS-PTA Resins

TEPxS-PTA resins are solid at room temperature. For thermosetting resins, excellent solubility will greatly expand the application of the resins, especially in the field of composites. As shown in Table 1, TEPxS-PTA resins have good solubility in common organic solvents at room temperature, such as toluene, acetone, and THF.

The viscosity responses of a resin to temperature and time are significant to the processing capability of

the resin. Rheological properties of TEPxS-PTA resins were evaluated by a rotational rheometer at a heating rate of 2˚C/min from room temperature to 200˚C. The results are shown in Figure 1. As shown in the figure, with the temperature increasing, the resins start melting at 45˚C and then become liquid, which result in obviously falling of viscosity. Thereafter, the viscosity remains at a low value. Finally, the viscosity of the resins increases rapidly at temperatures above 108˚C due to the further polymerization of the resins, i.e., the crosslinking reactions of the resins. The temperature range in which the resin maintains a melt state with low viscosity is defined as a processing window. As shown in Figure 1, the processing windows of TEPMS-PTA, TEPPS-PTA and TEPHS-PTA resins are located in 41-108˚C, 41-107˚C, and 40-104˚C, respectively. Obviously, the processing window for TEPHS-TPA is the narrowest among the resins. This possibly results from that the addition reaction between Si-H and acetylene(ethynyl and ethynylene) groups easily happens and accelerates the curing process. Anyway, these resins have wide processing windows (about 65˚C), which means that the polytriazole resins have good processability.

Figure 1: Rheological properties of TEPxS-PTA resins.

Table 1: Solubility of TEPxS-PTA Resins in Some Organic Solvents

Solvent Solubility Solvent Solubility

Cyclohexane - Tetrahydrofuran(THF) +

Toluene + N,N-dimethylformamide +

Dicholormethane + Dimethyl sulfoxide +

Chloroform + Methanol -

Acetone + Isopropanol -

Note: +: soluble; -: insoluble.


The important application of a thermosetting resin is as a matrix in fiber-reinforced resin composites. Low viscosity of a resin often means excellent fluidity, which makes the resin easy to impregnate the fiber. The viscosity of the polytriazole resins derived from star-shape arylacetylenes with silane unit changes with time was determined with a viscometer at 60˚C and the results are shown in Figure 2. The viscosities of TEPHS-PTA, TEPMS-PTA, and TEPPS-PTA resins at 60˚C are 45 mPa·s, 51 mPa·s, and 84 mPa·s, respectively. The resins have low viscosity and the viscosity changes with the side groups on silicon atom. The bigger the size of the side group on a resin, the higher the viscosity of the resin. Among them, TEPPS-PTA has highest viscosity, which may be due to the largest side group phenyl on silicon atom. As shown in Figure 2, the viscosity of the resins increase slowly with the time at 60˚C. The rate of the increase is higher for TEPHS-PTA and TEPMS-PTA resins. This is probably related with the reactivity of the resins.

Figure 2: Viscosity-time curves of TEPxS-PTA resins at 60˚C.

Thermal Behavior of TEPxS-PTA Resins

The thermal behavior of the resins was traced by DSC analysis technique and the results are shown in

Figure 3. The analysis data obtained by following the ISO 11357-5-2013 standard are listed in Table 2. As shown in Figure 3, all TEPxS-PTA resins have an endothermal peak and an exothermal peak. The former is attributed by the melting of the resins at about 45˚C, the latter is attributed by the curing reactions in the range of 80~200˚C. As shown in Figure 3 and Table 2, the initial temperature(Ti) and top temperatures(Tp) of the curing exothermal peaks are around 84˚C and 144˚C. This illustrates that the curing reactions of TEPxS-PTA resins take place at about 84˚C, which demonstrates that TEPxS-PTA resins have low temperature curing character. The highest exothermic enthalpy ΔH for TEPHS-PTA resin probably results from the addition reaction of Si-H group with acetylene groups.

Figure 3: The DSC curves of TEPxS-PTA resins(10˚C/min, N2).

Figure 4 shows the DSC curves for TEPMS-PTA resin recorded at different heating rates. With the heating rate increasing, the exothermic peak shifts to a high temperature region due to the thermal hysteresis effect. The apparent activation energy (Ea) for the curing reactions are evaluated by using the Kissinger and Ozawa methods [20]. The results are listed in Table 3 (also see supporting information). As shown in

Table 2: The DSC Analysis Results of TEPxS-PTA Resins (10˚C/min, N2)

Resins Tm/˚C Ti /˚C Tp/˚C Te/˚C △H/(J/g)

TEPHS-PTA 45 84 143 186 953

TEPMS-PTA 48 86 144 184 909

TEPPS-PTA 47 83 144 187 868

Tm: the top temperature of the endothermic peak; Ti: the temperature at onset of reaction, corresponding to the point at which the DSC curve departs from the initial extrapolated baseline; Tp: the temperature at maximum reaction rate, corresponding to the top of the peak; Te: the temperature at end of reaction, corresponding to the return of the DSC curve to the final extrapolated baseline.


Table 3, the apparent activation energy obtained by the two methods is very close. The apparent activation energies for the curing reactions of TEPHS-PTA TEPMS-PTA, and TEPPS-PTA resins obtained by Kissinger method are 88.9, 88.4, and 87.3 kJ/mol, respectively. These close data indicates that the apparent activation energy for the curing reaction of the resins is less related to the substituent on silicon atom. The low value also illustrates that the curing reactions of the resins easily occur.

Figure 4: DSC curves for TEPMS-PTA resin at different heating rates.

Mechanical Properties of Cured TEPxS-PTA Resins and their Composites

Mechanical property is very important for the application of a resin. The flexural properties of TEPxS-PTA resins and their fiber reinforced composites are tabulated in Table 4. As shown in the table, the flexural properties of cured TEPPS-PTA resin are the lowest

among TEPxS-PTA resins. This probably results from that the cured TEPPS-PTA resin has low crosslinking degree due to the steric hindrance of the phenyl group.

As shown in Table 4, T300 CF/TEPxS-PTA composites show a flexural strength over 500 MPa and a flexural modulus over 40 GPa. Especially, T300 CF/TEPHS-PTA composite exhibits the best performance. The flexural strength and flexural modulus of T300 CF/TEPHS-PTA at room temperature reach 521.9 MPa and 50.6 GPa, respectively. The addition reaction of Si-H with acetylene groups results in high crosslinking degree for TEPHS-PTA resin. As a consequence, the modulus of T300 CF/TEPHS-PTA composite is highest among the composites. The change tendency of mechanical properties for the composites is similar with that for the related cured resins.

Heat Resistance of Cured TEPxS-PTA Resins

Glass transition temperature (Tg) of polymers is usually detected by dynamic mechanical analysis(DMA). Generally, the temperature at damping peak of tanδ is identified as the glass transition temperature in DMA analysis curves at which point large decrease in modulus also occurs. The thermal mechanical properties of the cured TEPxS-PTA resins were determined in nitrogen atmosphere by DMA in the range of 40˚C to 500˚C. The obtained DMA curves are shown in Figure 5. As shown in Figure 5, Tgs of the cured TEPHS-PTA, TEPMS-PTA, and TEPPS-PTA resins are 285˚C, 254˚C，and 272˚C, respectively. During the curing process of TEPxS-PTA resins, several different polymerization reactions occur. One is the reaction of the alkyne groups in TPDDM with azide

Table 3: Apparent Activation Energy for Curing Reaction of TEPxS-PTA Resins

Ea/kJ·mol-1 Methods

TEPHS-PTA TEPMS-PTA TEPPS-PTA

Kissinger 88.9 88.4 87.3

Ozawa 91.0 90.7 89.6

Table 4: Mechanical Properties of Cured Resins and their T300 CF Reinforced Composites at Room Temperature

Cured Resins T300 CF Composites Resin

Flexural Strength/MPa Flexural Modulus/GPa Flexural Strength/MPa Flexural Modulus/GPa

TEPHS-PTA 145.4±1.9 3.7±0.2 521.9±9.0 50.6±1.5

TEPMS-PTA 141.5±4.2 3.4±0.3 527.4±6.1 42.2±1.6

TEPPS-PTA 138.9±2.8 3.1±0.1 506.7±7.6 40.6±1.1


groups in BAMBP, and another is the reactions of aryne groups in the star-shape arylacetylenes with silane unit with the azide groups in BAMBP. In addition, there are self-polymerization reaction of alkyne/aryne groups. TEPHS, TEPMS, and TEPPS contains ethynyl groups and ethynylene groups and have six aryne groups in all. The triazole ring formed by the addition reaction of aryne groups of TEPxS with the azide groups is directly connected to the benzene ring, and then more rigid segments has been formed. Therefore, the cured resins have high glass transition temperatures. As mentioned above, the addition reaction of Si-H group with alkyne/aryne groups results in higher crosslinking degree in TEPHS-PTA resin. The Tg of the cured TEPHS-PTA resin is highest among TEPxS-PTA resins. Higher Tg for the cured TEPPS-PTA resin is attributed by the steric hindrance of big phenyl group as compared with the cured TEPMS-PTA resin.

Figure 5: DMA curves of cured TEPxS-PTA resins.

The thermal stability of the cured resins was determined by TGA in nitrogen up to 800˚C at a heating rate of 10˚C/min, and the resulting TGA curves are shown in Figure 6. The star molecules have a higher average acetylene functionality [22] than the linear molecules, which eventually causes higher crosslinking degree. It can be seen that the cured resins have high onset degradation temperature. The degradation temperatures at 5% weight loss (Td5) and the decomposition residues (Yr) at 800˚C for the cured TEPHS-PTA, TEPMS-PTA, and TEPPS-PTA resins are 354˚C, 345˚C, and 352˚C, and 57%, 50%, and 54% in nitrogen, respectively. It is noted that the effect of side group on the thermal stability is not obvious. However, the thermal stability of cured TEPHS-PTA resin is highest among the cured TEPxS-PTA resins. The tendency is that high stability is related with high crosslinking degree for the resins.

Figure 6: TGA curves of cured TEPxS-PTA resins in N2.

CONCLUSIONS

A series of novel polytriazole resins were prepared from star-shape arylacetylenes derived from silane, TPDDM and BAMBP through 1,3-dipolar cycloaddition polymerization. The processing windows for TEPHS-PTA, TEPMS-PTA, and TEPPS-PTA resins are located in 40-104˚C, 41-108˚C, and 41-107˚C, respectively. The resins have a suitable processing window(about 65˚C) and could be cured at 80˚C, which demonstrates the resins have a good processability. The cured polytriazole resins have a good mechanical properties and heat-resistance. The flexural strength of the cured TEPxS-PTA resins reaches as high as 145.4 MPa. T300 carbon fiber reinforced composites have a flexural strength over 500 MPa and a flexural modulus over 40 GPa. The Tg of the cured TEPHS-PTA resin reaches 285˚C. TEPxS-PTA resins could be expected to be used as matrices for low-temperature molding composites.

DISCLOSURE STATEMENT

The author(s) declares no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

ACKNOWLEDGEMENT

This work is supported by Fundamental Research Funds for the Central Universities (Grant No. 50321042017001).

SUPPORTING INFORMATION

The supporting information can be downloaded from the journal website along with the article.


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Received on 25-07-2020 Accepted on 05-09-2020 Published on 08-09-2020 DOI: https://doi.org/10.31437/2414-2115.2020.06.4 © 2020 Dai et al.; Licensee Scientific Array. This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

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