Synthesis and characterization of epoxy resin composites modified by reactive polyimide containing hydroxyl groups

Abstract

Reactive polyimide (PI) containing phenolic hydroxyl groups was prepared by the polymerization of 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane and mixed thiodiphthalic anhydride. A series of epoxy resin composites were obtained by adding reactive PI to N,N,N′,N′-tetraglycidyl-4,4′-diamino-diphenylmethane (TGDDM) epoxy resin in different proportions. The effect of PI content on curing behavior, thermal properties, and mechanical properties was carefully investigated. Even a small amount of PI addition improved the mechanical properties and heat resistance of the epoxy resin, particularly the fracture toughness. Among them, epoxy resin composites EP-PI-1.5 with the addition of 1.5 wt% PI showed the best mechanical properties, whose impact strength, fracture toughness, and tensile strength were increased by 114%, 59%, and 34%, respectively. The phase morphology was also investigated to illustrate the fracture mechanism by scanning electron microscope (SEM) characterization.

Keywords

Polyimide morphology mechanical properties thermal properties modification

Introduction

Epoxy resin (EP) was extensively utilized in various industries, including aerospace, electronics, and automotive, due to its remarkable physical and chemical properties, such as excellent flexural strength, high hardness, good alkali stability, and processability.^1–3 However, the formation of a three-dimensional network structure after curing generally results in poor fracture toughness and low cracking strain. Additionally, the inadequate heat resistance also restricts its application in numerous engineering fields.^4–6 As a result, the development of modified EP with enhanced toughness and heat resistance has become a growing area of interest for scientists.

Except for rubber elastomer,^7–10 EP modified by thermoplastic resins is the optimal approach, which has been widely adopted, as it not only enhances the toughness of EP but also improves its heat resistance. The thermoplastic resins used to modify EP generally include polysulfone (PSF),^11–13 polyetherimide (PEI),^14–18 polyethersulfone (PES)^19–22 and polyimide (PI),^23–26 etc. For example, the incorporation of PSF at a concentration of 15 parts per hundred parts of resin resulted in a significant increase in the impact strength and fracture toughness of EP with 65% and 89%, respectively. However, the glass transition temperature (T_g) of modified EP was only improved to 160°C due to the low T_g of PSF.²⁷ As a result, researchers have continued to investigate the modification of EP with thermoplastic resins with high T_g. Among these, PEI that contains flexible and isopropyl groups with higher T_g is utilized for modifying EP. When 20 wt% of PEI was added into N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM), the tensile strength, and flexural strength of modified EP were increased by 22% and 35%, respectively.^28,29 However, the high addition of PEI limits the wide application of modified EP because of the high price of PEI in comparison with EP. Recently, we have reported a modified EP via blending with low addition of polythioetherimide. When the addition of polythioetherimide was 2 wt%, the impact strength, fracture toughness, elongation at break, tensile strength, and flexural strength of the modified epoxy increased by 78%, 50%, 25%, 30%, and 20%, respectively.³⁰ As we all know, besides the physical blending of PI without active groups, modification by reactive PI may be a better and more effective way to obtain ideal properties. However, there were few investigations on the application of PI with active groups in modification of epoxy.^31,32 It was reported that when the addition amount of reactive PI was 13 wt%, the tensile modulus of modified EP bisphenol A diglycidyl ether (DGEBA) increased by 100%, while the tensile strength decreased.³³ The modification effect of the lower content of PI on EP composite properties has not been reported. A systematic investigation of the application of PI with active groups in modifying epoxy is necessary and interesting. It is also a challenge to find an effective PI resin with low content to modify epoxy resin to obtain EP composites with significant improvement in mechanical and thermal properties.

Thus, in this work, a PI containing phenolic hydroxyl groups, thioether bonds, and trifluoromethyl groups was designed to enhance the mechanical properties and thermal properties of TGDDM epoxy as shown in Scheme 1. The effects of the introduction of phenolic hydroxyl-containing PI on the curing behavior, thermal characteristics, mechanical properties, and phase morphology of EP were investigated.

Experimental

Materials

N,N,N′,N′-Tetraglycidyl-4,4′-diamino-diphenylmethane (TGDDM, the epoxy equivalent is 114 g/eq), and internal release agent (HD-9182) were purchased from Hunan Salve New Material Technology Co., Ltd. 4,4′-Diaminodiphenyl sulfone (DDS) was obtained from Suzhou Yinsheng Chemical Co., Ltd. Mixed thiodiphthalic anhydrides (m-TDPA) (3,3′-TDPA: 3,4′-TDPA: 4,4′-TDPA = 8:42:50) were prepared by our group.³⁴ 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), toluene, and N, N-dimethylacetamide (DMAc) were supplied from Sinopharm Chemical Reagent Co., Ltd. The other reagents all came from the marketplace and didn’t need to be further purified.

Measurements

The intrinsic viscosity was measured in DMAc at 30 ± 0.1°C utilizing an Ubbelohde viscometer with a concentration of 0.5 g/dL. The ¹H NMR spectrum of PI powder was measured at 400 MHz using a Bruker AV/ANCE NMR spectrometer with dimethyl sulfoxide-d₆ as solvent. The molecular weights of PI powder were measured by a PL-GPC 220 using N,N-dimethylformamide (DMF) as eluent at a flow rate of 1 mL/min and polystyrene as the calibration standard at 40°C with PL gel 5 μm Mixed-C column. The differential scanning calorimetry (DSC) test was carried out at the Netzsch DSC 214 differential scanning calorimeter with a nitrogen atmosphere with a 10°C per minute heating rate. The second heating scan was used to determine the T_g and curing exothermic peak of the cured EP. Using a PerkinElmer Diamond TG/DTA instrument, a thermogravimetric analysis (TGA) was performed in a nitrogen atmosphere (flow rate 50 mL/min) with a heating rate of 10°C/min from 50°C to 800°C. A Thermo Nicolet 6700 ATR-FTIR spectrometer was applied to examine the samples' Fourier transform spectroscopy technique (ATR-FTIR), which has a scanning range of 4000-400 cm⁻¹ and an average of 32 cycles. The mechanical properties of samples were measured and averaged over at least five specimens that are 150 mm long, 20 mm wide, and 4 mm thick, by a room-temperature Instron 5567 tensile tester with a crosshead speed of 5 mm/min. The impact strength was measured and averaged over at least five samples (Dimensions: 80 mm long, 10 mm broad, and 4 mm thick), by a plastic impact tester at a crosshead speed of 3.46 m/s at room temperature. Single-edge notched three points bending measurement (SENB) based on ASTM D5045-14 was used to assess fracture toughness. For measurement, rectangular specimens with a notch length of 5 mm in the center and dimensions of 44 mm, 10 mm, and 5 mm were constructed. The cross-sectional morphologies of samples were characterized by Verios G4 UC thermal field emission scanning electron microscope (TFE-SEM) (Thermo Scientific, USA). The critical strain intensity factor was used to study the fracture toughness of EP/PI composites (K_IC). According to the ASTM D5045-14 standard, the K_IC values were calculated as follows:

K_{I C} = (\frac{P}{B w^{\frac{1}{2}}}) f (x),

(1)

where W is the depth (width) of the sample, B is its thickness, P is its loading weight, x is its ratio of the crack length to its depth, and f(x) is its calibration factor, which is denoted as follows:

f (x) = 6 x^{\frac{1}{2}} \frac{[1.99 - x (1 - x) (2.15 - 3.93 x + 2.7 x^{2})]}{(1 + 2 x) {(1 - x)}^{\frac{3}{2}}} .

(2)

The dynamic DSC experiments were conducted with heating rates of 5, 10, 15, 20 K/min. The activation energy (E_a) is calculated by Kissinger equation:

\frac{d [\ln (\frac{β}{T_{p}^{2}})]}{d (1 / T_{p})} = - \frac{E_{a}}{R},

(3)

Where R is the gas constant, β is the heating rate and T_p is the peak temperature.

Preparation of PI

6FAP (14.65 g, 4.0 mmol) was dissolved in 140 mL DMAc by magnetic stirring in the ice bath. Then m-TDPA (13.05 g, 4.0 mmol) was added to the solution. After fully dissolved, the reaction was maintained in an ice bath for 12 h. The solution was then stirred at 200°C for 8 h, and the resulting solution was slowly poured into an ethanol/water (1:1) solvent to precipitate. PI was obtained by filtration, boiling, and washing in ethanol/water (1:1) solvent, and drying in oven.

Preparation of EP/PI

The TGDDM (100.0 g), different contents of PI, curing agent DDS (54.3088 g), and internal release agent (HD-9182) (2.0 g) were added to DMAc (150 g) in batches, and then dissolved by mechanical stirring at 60°C. Then the mixture was distilled at 60°C for 3 h and 120°C for 2 h, and most of the DMAc was distilled. Finally, the liquid was poured into a mold and heated at 200°C and 240°C for 2 h, respectively. According to the different contents of PI, the modified resins, EP-PI-0, EP-PI-1, EP-PI-1.5, EP-PI-2, and EP-PI-3 were obtained, where the PI contents of EP-PI-0, EP-PI-1, EP-PI-1.5, EP-PI-2, and EP-PI-3 were 0, 1, 1.5, 2, 3 wt%, respectively.

Results and discussion

Synthesis and characterization of PI

The synthesis of reactive PI derived from 6FAP and m-TDPA in DMAc at 200°C was illustrated in Scheme 2. The inherent viscosity of PI was 0.28 dL/g in DMAc at 30°C. The weight average molecular weight of PI determined by GPC relative to polystyrene standards was 23,000 g/mol. It is important to maintain a moderate degree of polymerization for optimal performance of the modified EP, as excessive degrees increased the viscosity of PI leading to poor dispersion in EP.

The chemical structure of PI was confirmed by ¹H NMR and ATR-FTIR spectrum. As shown in Figure 1, the peaks around 10.5 ppm could be assigned to the protons of the phenolic hydroxyl group, the peaks in the range of 8.25–7.50 ppm could be assigned to the protons from dianhydride moiety of mixed thiodiphthalic anhydrides (m-TDPA), and other peaks in the range of 7.50–6.98 ppm could be the signals of aromatic protons from diamine moiety of 6FAP.³⁵ Figure 2 displayed the ATR-FTIR spectrum of PI. The distinctive PI absorption peaks were seen at 3398 cm⁻¹ (O-H stretching), 1775 cm⁻¹ (asym C=O stretching), 1707 cm⁻¹ (sym C=O stretching), 1378 cm⁻¹ (C-N stretching), 1245 cm⁻¹ (C-O stretching), and 740 cm⁻¹ (sym C=O bending), which demonstrated that the PI containing a hydroxyl group and imide ring was successfully synthesized.³⁶ Furthermore, there was no significant weight loss before 378°C in the TGA curve of PI (Figure S1), which indicated the complete imidization of PI.

Curing characterization of EP composites

Achieving a three-dimensional network structure through complete curing was crucial for obtaining the outstanding properties of EP. Thus, it was essential to ensure the complete curing of TGDDM by adding an adequate amount of DDS based on its epoxy equivalent. The modified EP composites were cured at 200°C for 2 h and 240°C for 2 h in an oven.³⁰

To confirm the full curing of EP/PI composites with varying contents of PI, their DSC curves and ATR-FTIR spectra were analyzed. Figure 3 demonstrated that there was only one T_g step present in the DSC curve with no exothermic peak, which indicated that the composites had been fully cured. Likewise, following curing at 200°C for 2 h and 240°C for 2 h, respectively, the distinctive peak at 915 cm⁻¹ for the epoxy group and the N-H characteristic peak of DDS at 1623 cm⁻¹ disappeared in Figure 4, which provided evidence of a completed curing reaction.^3,36

Curing behaviour of EP-PI-1.5 and EP-PI-0

DSC curves of curing reaction of EP-PI-0 and EP-PI-1.5 at different heating rates were shown in Figure 5. The curing kinetic analysis of EP-PI-1.5 and EP-PI-0 was performed using Kissinger method. According to Kissinger equation (equation (3)), the activation energy (E_a) can be obtained from the slope of the plots of ln (β/T_p²) versus 1/T_p.^37,38 By using the data of β and T_p in Table 1, the E_a of EP-PI-1.5 was calculated as 58.57 kJ/mol, which was lower than that of EP-PI-0 (59.02 kJ/mol). This showed that the introduction of PI would promote the curing of EP.

Table 1.

DSC results of curing reaction of EP-PI-1.5 and EP-PI-0 at different heating rates.

Sample	β (K/min)	T_p (K)	ΔH (J/g)
EP-PI-1.5	5	483.20	642.23
	10	503.72	630.51
	15	517.04	642.78
	20	527.09	678.03
EP-PI-0	5	484.44	652.45
	10	505.27	670.99
	15	518.59	654.06
	20	528.24	649.32

Thermal properties of the EP/PI composites

The T_g of EP/PI composites with varying contents of PI was analyzed using DSC, and the results were summarized in Table 2. Figure 3 illustrated that the T_g of EP/PI composites increased from 218°C to 231°C with an increase in PI content, but subsequently decreased from 231°C to 223°C. EP-PI-1.5 with the addition of 1.5 wt% reactive PI exhibited the highest T_g value at 231°C, which was maybe due to that the compatibility between PI and EP was optimal when the PI content was 1.5 wt%.^17,27 These EP/PI composites with 1–3 wt% of PI exhibited enhanced thermal stability with T_d5% values in the ranges of 333–349°C and 334–346°C in nitrogen and air atmosphere, respectively, which was increased more than 10°C compared with EP-PI-0 without the addition of PI. Furthermore, the T_d5% of the modified EP increased initially with an increase in PI content but then decreased when the content of PI was 2–3%. The T_d5% reached the highest value (349°C) when the content of PI was 2 wt%, which was 31°C higher than that of pure EP.³³ The carbon residue of the EP/PI composites was found to be nearly identical to that of pure EP, with char yield values ranging between 23–25%. The thermal stability of EP/PI composites in a nitrogen atmosphere was demonstrated in Figure 6. Both the EP/PI composites and the pure EP showed a similar thermal weight loss process and were largely influenced by the thermal characteristics of the EP due to the small content of PI added. The improvement of thermal performance maybe comes from two aspects, on the one hand, the PI displayed superior thermal properties with T_g of 286°C and T_d5% of 428°C, which was higher than those of the EP. On the other hand, the active hydroxyl groups in PI could react with the epoxy group in EP, allowing the chain segment of PI to participate in the curing reaction.²⁷ This integration of PI into the modified EP composites enhanced the bonding force between PI and EP, ultimately leading to improved thermal properties of EP.

Table 2.

Thermal properties of PI and EP/PI composites.

Samples	T_g (^oC)	T_d5% (^oC)		Char yield^a(%)
Samples	DSC	N₂	Air	Char yield^a(%)
EP-PI-0	218	318	321	23
EP-PI-1	222	333	334	25
EP-PI-1.5	231	347	346	24
EP-PI-2	225	349	344	25
EP-PI-3	223	339	338	24
PI	286	428	430	62

^aResidual weight (%) in a nitrogen atmosphere at 800°C.

Mechanical properties of EP/PI composites

Figure 7 displayed the mechanical characteristics of EP/PI composites. The EP/PI composites exhibited excellent mechanical properties with a tensile modulus of 3.5–4.0 GPa, tensile strengths of 40–51 MPa, flexural modulus of 3.6–3.7 GPa, and flexural strengths of 73–95 MPa. With the increase in PI content, the tensile properties of EP/PI composites increased first and then decreased. Composites EP-PI-1.5 showed the highest tensile modulus of 4.0 GPa and the highest tensile strength of 51 MPa. Compared with the blank sample EP-PI-0, the tensile strength and tensile modulus of EP-PI-1.5 was increased by 34% and 14%, respectively.²⁷ The flexural modulus of EP/PI composites was maintained the same while the flexural strength was decreased with the increase of PI content as shown in Figure 7(b), which may be attributed to the decrease of crosslinking density in the EP composites.^17,33

The toughness of the modified EP composites was comprehensively studied by evaluating both impact strength and fracture toughness, with results presented in Table 3. The impact strength of cured EP/PI composites was determined using a pendulum impact test. Additionally, fracture toughness was evaluated through a single-edge notched three-point bending measurement. As shown in Figure 8(a), compared with the pure EP, the impact strength of the EP/PI composites had a significant increase from 4.5 kJ/m² to 9.6 kJ/m². When the PI content was 1.5 wt%, the impact strength of the composite reached the highest value (9.6 kJ/m²), which was 114% higher than the pure EP. The impact strength of EP/PI composites somewhat became to decrease when the content of PI reached 2 wt%, but it was still greater than the impact strength of pure EP. In comparison with pure EP, the fracture toughness of EP/PI composites was higher with values from 0.62–0.89 MPa*m^1/2. The fracture toughness also showed a similar trend of initially increasing and then decreasing, which was consistent with impact strength. The EP-PI-1.5 composite displayed the highest value (0.89 MPa*m^1/2) as illustrated in Figure 8(b), which showed that the addition of PI could greatly improve the fracture toughness by 59%. Overall, the mechanical properties of EP/PI revealed that the addition of 1.5 wt% PI could optimize the performance, which was consistent with the results of thermal properties. The enhancement of the mechanical properties of the modified EP by reactive PI may be attributed to the exceptional mechanical properties of the PI itself and the improved bonding force of the PI with EP by the reaction between the phenolic hydroxyl groups and epoxy groups.^33,34 A decline in these properties of EP/PI composites with 2–3 wt% of PI could be attributed to the elevated viscosity of the EP/PI mixture with high PI content leading to reduced dispersibility of PI in EP and lowered miscibility.¹⁷

Table 3.

Mechanical properties of EP and EP/PI composites.

Sample	T_m^a (GPa)	T_s^b (MPa)	F_m^c (GPa)	F_s^d (MPa)	I_s^e (kJ/m²)	K_IC (MPa* m^1/2)
EP-PI-0	3.5	38	3.6	104	4.5	0.56
EP-PI-1	3.7	42	3.6	95	6.5	0.62
EP-PI-1.5	4.0	51	3.7	92	9.6	0.89
EP-PI-2	3.6	42	3.6	75	7.1	0.66
EP-PI-3	3.5	40	3.6	73	7.0	0.63

^aTensile Modulus.

^bTensile strength.

^cFlexural Modulus.

^dFlexural strength.

^eImpact strength.

Phase morphology of the EP/PI composites

To clarify the fracture mechanism of EP/PI composites and explore the relationship between structure and mechanical properties, the SEM characterization of the fracture surface of EP/PI composites after the impact properties test was investigated, which was shown in Figure 9. The left and right sides of the image are magnified 500 and 1000 times respectively. The EP-PI-0 showed regular cracks in Figure 9(a) and (b), demonstrating that brittle fracture was the mechanism of fracture for the pure EP, which was responsible for the poor toughness. The EP/PI composites seemed comparatively rough on the SEM image. The EP-PI-1 with the addition of 1 wt% PI showed a transition from regular cracks to cracks like branches in Figure 9(c) and (d), which indicated that the toughness of the corresponding modified EP was improved from brittle fracture to ductile fracture. As shown in Figure 9(e) and (f), the surface of EP-PI-1.5 with the addition of 1.5 wt% PI had more shear deformation and tortuous cracks, which was consistent with the best comprehensive performance of EP-PI-1.5 in the mechanical properties characterization. With the addition of PI increased to 3 wt%, the roughness of the fracture surface of EP-PI-3 decreased, which also corresponded to the decrease of the mechanical properties, as shown in Figure 9(g) and (h). When the resin samples were impacted, the pure EP would deform and produce regular cracks while the cracks of EP/PI composites with the incorporation of PI would deflect into tortuous cracks and shear deformation, making the fracture surface rougher to achieve the purpose of toughening EP.^12,39

Conclusions

Based on an effective reactive PI with phenolic hydroxyl groups derived from 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, a series of modified EP with low content of 1–3 wt% was prepared. The curing behavior, thermal characteristics, mechanical properties, and phase morphology of those EP/PI composites were thoroughly investigated. The EP/PI composites exhibited enhanced T_gs in the range of 222–231°C, T_d5% in the range of 333–349°C. The impact strength and fracture toughness of the EP/PI composites were in the range of 6.5–9.6 kJ/m² and 0.62–0.89 MPa*m^1/2, respectively, which were a significant increase compared with pure EP. The EP-PI-1.5 with the addition of 1.5 wt% reactive PI displayed the best performances with impact strength of 9.6 kJ/m², fracture toughness of 0.89 MPa*m^1/2, tensile modulus of 4.0 GPa, and tensile strength of 51 MPa, which was increased by 114%, 59%, 14% and 34%, respectively in comparison with pure EP. The SEM micrographs illustrated that incorporating PI could prevent deformation and crack extension within the EP matrix during the curing process. Overall, incorporating low content of reactive PI into EP can markedly enhance its thermal and mechanical properties, thereby demonstrating promising application prospects in industries such as aerospace, electronics, and automotive.

Supplemental Material

Supplemental Material Synthesis and characterization of epoxy resin composites modified by reactive polyimide containing hydroxyl groups

Supplemental Material for Synthesis and characterization of epoxy resin composites modified by reactive polyimide containing hydroxyl groups by Gang Xu, Liyun Tan, Yong Nie, Xingzhong Fang and Guofei Chen in High Performance Polymers

Footnotes

Declaration of conflicting interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by National Key Research and Development Program of China (2022YFB3803300), the “Science and Technology Innovation 2025” Major Project of Ningbo of China (No. 2020Z051), and the Key R&D Program of Zhejiang Province (2021C0112).

ORCID iDs

Xingzhong Fang

Guofei Chen

Supplemental Material

Supplemental material for this article is available online.

References

Sun

Xiao

Tao

, et al. Preparation of high-performance carbon fiber-reinforced epoxy composites by compression resin transfer molding. Materials 2019; 12(1): 13.

Yang

Guo

Luo

, et al. Self-healing, recoverable epoxy elastomers and their composites with desirable thermal conductivities by incorporating BN fillers via in-situ polymerization. Compos Sci Technol 2018; 164: 59–64.

Zheng

Sun

Liu

H-Y

, et al. Effects of carboxylated carbon nanotubes on the phase separation behaviour and fracture-mechanical properties of an epoxy/polysulfone blend. Compos Sci Technol 2018; 159: 180.

Sun

Zhuo

, et al. Microstructure and mechanical properties of aminated polystyrene spheres/epoxy polymer blends. Compos Part A-Appl S 2014; 66: 58–64.

Mishra

Pandey

Singh

. Enhancing the mechanical properties of an epoxy resin using polyhedral oligomeric silsesquioxane (POSS) as nano-reinforcement. Polym Test 2017; 62: 210–218.

Cicala

Recca

Carciotto

, et al. Development of epoxy/hyperbranched blends for resin transfer molding and vacuum assisted resin transfer molding applications: effect of a reactive diluent. Polym Eng Sci 2009; 49(3): 577–584.

Chen

Wang

. Dynamic mechanical properties of polysiloxane-modified, castor oil-based polyurethane/epoxy interpenetrating polymer network composites. High Perform Polym 2011; 23(5): 345–351.

Mahesh

KPO

Alagar

Kumar

. Synthesis and characterization of polyurethane-toughened epoxy-bismaleimide matrices. High Perform Polym 2016; 16(3): 391–404.

Quan

Ivankovic

. Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer. Polymer 2015; 66: 16–28.

10.

Vijayan

Puglia

Vijayan

, et al. The role of clay modifier on cure characteristics and properties of epoxy/clay/carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) hybrid. Mater Technol 2017; 32(3): 171–177.

11.

Giannotti

Galante

Oyanguren

, et al. Role of intrinsic flaws upon flexural behaviour of a thermoplastic modified epoxy resin. Polym Test 2003; 22(4): 429–437.

12.

Jin

Yang

Jin

F-L

, et al. Fracture toughness and surface morphology of polysulfone-modified epoxy resin. J Ind Eng Chem 2015; 25: 9–11.

13.

Solodilov

Gorbatkina

. Properties of unidirectional GFRPs based on an epoxy resin modified with polysulphone or an epoxy urethane oligomer. Mech Compos Mater 2006; 42(6): 513–526.

14.

Zhang

Yue

C Y

, et al. Thermal and morphological properties of polyetherimide modified bismaleimide resins. High Perform Polym 2000; 12(3): 419–428.

15.

Shin

Jang

. Toughness improvement of high-performance epoxy resin using aminated polyetherimide. J Appl Polym Sci 1997; 65(11): 2237–2246.

16.

Jang

J G

Lee

. Polyetherimide-modified high-performance epoxy-resin. Polym J 1994; 26(5): 513–525.

17.

Aravand

Falzon

. Phase morphology and mechanical properties of polyetherimide modified epoxy resins: a comparative study. Polymer 2019; 179: 121640.

18.

Korokhin

Shapagin

Solodilov

, et al. Epoxy polymers modified with polyetherimide. Part I: rheological and thermomechanical characteristics. Polym Bull 2020; 78(3): 1573–1584.

19.

Wang

Zhang

. Organoclay-reinforced polyethersulfone-modified epoxy-based hybrid nanocomposites. High Perform Polym 2011; 23(7): 526–534.

20.

Rosetti

Alcouffe

Pascault

J P

, et al. Polyether sulfone-based epoxy toughening: from micro- to nano-phase separation via PES end-chain modification and process engineering. Materials 2018; 11(10): 1960.

21.

Partridge

Maistros

. Phase separation in thermosetting blends studied by dynamic dielectric analysis. High Perform Polym 1996; 8(1): 1–17.

22.

Yang

J-P

Chen

Z-K

Feng

Q-P

, et al. Cryogenic mechanical behaviors of carbon nanotube reinforced composites based on modified epoxy by poly(ethersulfone). Compos Part B 2012; 43(1): 22–26.

23.

Zhang

, et al. Understanding the self-polymerization mechanism of dopamine by molecular simulation and applying dopamine surface modification to improve the interfacial adhesion of polyimide fibers with epoxy resin matrix. High Perform Polym 2021; 33(6): 601.

24.

Ying

Guo

Fang

. Synthesis, freestanding membrane formation, and properties of novel sulfonated hyperbranched polyimides. High Perform Polym 2018; 30(1): 3–15.

25.

Hay

Woodfine

Davies

. Toughening of epoxy resins by polyimides synthesized from bisanilines. High Perform Polym 1996; 8(1): 35–36.

26.

Chen

Sun

Hong

, et al. Layered structure formation in the reaction-induced phase separation of epoxy/polyimide blends. Macromolecules 2008; 41(20): 7469–7477.

27.

Sun

Chen

, et al. Enhancing the mechanical and thermal properties of epoxy resin via blending with thermoplastic polysulfone. Polymers 2019; 11(3): 461.

28.

Chen

Huang

, et al. Investigation of the relationship between morphology and tribological properties of an epoxy resin based on tetraglycidyl 4,4′-diaminodiphenylmethane modified with polyetherimide oligomers. J Appl Polym Sci 2014; 131(4): 39863.

29.

Chen

Cong

, et al. Mechanical strength and tribological properties of diglycidyl ether of bisphenol-A cured by poly(amide-amidic acid) and 4,4’-diaminodiphenylsulfone. J Macromol Sci B 2013; 53(1): 118–132.

30.

Tan

Liu

, et al. Enhancing the mechanical properties and heat resistance of epoxy resin via blending with polythioetherimide. Polym Eng Sci 2023; 63: 1772–1780.

31.

Shen

Zhang

Huang

, et al. Study on preparation and properties of novel reactive phenolic hydroxyl-containing polyimides. J Polym Res 2012; 19(5): 9857.

32.

Que

Yan

Qiu

, et al. Synthesis and characterization of trifluoromethyl-containing polyimide-modified epoxy resins. J Mater Sci 2016; 51(24): 10833–10848.

33.

Agag

Takeichi

. Synthesis and characterization of epoxy film cured with reactive polyimide. Polymer 1999; 40(23): 6557–6563.

34.

Han

Fang

X-Z

Zuo

X-X

. Synthesis and properties of novel melt processable isomeric polythioetherimides. High Perform Polym 2010; 22(8): 989–1003.

35.

Gao

, et al. Homogeneous reinforcement as a strategy for the efficient preparation of high-strength, insulating and high heat-resistant PBO composite paper. J Mater Sci 2022; 57(19): 8701–8713.

36.

Wei

Fang

Han

, et al. Synthesis and characterization of poly(thioether ether sulfone imide)s derived from isomeric bis(chlorophthalimide)s and bis(4-mercaptophenyl) sulfone. Eur Polym J 2010; 46(2): 246–253.

37.

Men

Cheng

Chen

, et al. Curing behaviour and thermal properties of epoxy resin cured by aromatic diamine with carborane. High Perform Polym 2015; 27(4): 497–509.

38.

Jang

Lee

. Curing behavior of tetrafunctional epoxy resin/hyperbranched polymer system. Polymer 2001; 42: 8339–8347.

39.

Lee

Jin

Park

, et al. Study of new fluorine-containing epoxy resin for low dielectric constant. Surf Coat Tech 2004; 180-181: 650–654.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.02 MB