Curing Kinetics and Thermal Properties of Aromatic Multifunctional

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1 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins Mingming Yu 1, Zhengwei Zhou 1, Hang Lu 2, Aijun Li 1, Ruicheng Bai 1, Jinliang Sun 1, Musu Ren 1, and Hefeng Hu 2 1 Research Center for Composite Materials, Shanghai University, , Shanghai, PR China 2 Department of Polymer Materials, Shanghai University, , Shanghai, PR China Summary In order to investigate the relationship between the chemical structure of multifunctional epoxy resins and their properties, two tetrafunctional epoxies with different aromatic rings content in the molecular main chain, N,N,N,N -tetraglycidyl-4,4 -diaminodiphenyl ether (4,4 -TGDDE) and N,N,N,N -tetraglycidyl-2,2-bis[4- (4-aminophenoxy)phenyl]propane (TGBAPP), were cured with 4,4 -diaminodiphenyl ether (4,4 -DDE) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), respectively. Then four amine curing systems (TGBAPP/ BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/BAPP and 4,4 -TGDDE/4,4 -DDE) were obtained. Additionally, the 4,4 -TGDDE and another TGDDE with m-glycidyl amino, named N,N,N,N -tetraglycidyl-4,4 -diaminodiphenyl ether (3,4 -TGDDE) were cured with methyl nadic anhydride (MNA). Then the anhydride curing systems (4,4 -TGDDE/MNA and 3,4 -TGDDE/MNA) were prepared. The curing kinetics and thermal properties of these systems were studied in detail. The results indicated that the anhydride curing systems exhibited higher curing reactivity than the amine curing systems, and the resins cured with the anhydride showed better thermal properties. Moreover, introducing more aromatic rings into the backbone would decrease the curing reactivity but enhance the thermal property of the multifunctional epoxy resins. And the tetrafunctional epoxy with p-glycidy amino groups had higher curing reactivity than the epoxy with p-glycidy amino groups, and the thermal property of the front epoxy was better. 1. Introduction As one of the most important thermosetting polymers, epoxy resins are widely used in many fields as coatings, adhesives and matrices for fiber composites due to their superior mechanical properties, excellent chemical resistance and good cohesiveness compared to many materials 1 2.With the development of advanced technology, many attempts have been made to prepare high performance epoxy resins, especially to improve their thermal properties which are not only effected by the crosslinking density but also by the molecular main chain 3-5. Although many multifunctional epoxy resins were synthesized, and Smithers Rapra Technology, 2014 the thermal stability were reported previously 6-13, the investigation of the curing kinetics of the aromatic multifunctional epoxy resins with different chemical structure and the relationships between the chemical structure and their thermal properties have, however been less reported In the present work, N,N,N,N - tetraglycidyl-4,4 -diaminodiphenyl ether (4,4 -TGDDE,EEW=120 g/ mol) and N,N,N',N'-tetraglycidyl- 2,2-bis[4-(4-aminophenoxy)phenyl] propane (TGBAPP) were cured with 2,2-bis[4-(4-aminophenoxy) phenyl]propane (BAPP) and 4,4 -diaminodiphenyl ether (DDE), respectively. And the TGDDE with m-glycidyl amino groups which named N,N,N',N'-Tetraglycidyl-4,4'- diaminodiphenyl ether (3,4 -TGDDE) Corresponding author: Aijun Li (Address: P.O. BOX 321, Yanchang Road 149, Shanghai, PR China; Tel: ; Fax: ; aijun.li@shu.edu.cn) and the other with p-glycidyl amino groups named N,N,N,N - tetraglycidyl-4,4 -diaminodiphenyl ether (4,4 -TGDDE) were cured with methyl nadic anhydride (MNA). The curing kinetics of these systems ( TGBAPP/BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/ BAPP, 4,4 -TGDDE/4,4 -DDE, 3,4 -TGDDE/MNA and 4,4 -TGDDE/ MNA) and the thermal properties of the cured resins were studied in detail. 2. Experimental 2.1 Materials 2,2-bis[4-(4-aminophenoxy) phenyl]propane (BAPP), 4,4 -diaminodiphenyl ether (4,4 - DDE) and 3,4 -diaminodiphenyl ether (3,4 -DDE) were purchased from Changzhou Sunlight Chem. Co., China. Epichlorohydrin (ECH), sodium hydroxide (NaOH), methyl isobutyl ketone (MIBK), ethanol and Polymers & Polymer Composites, Vol. 22, No. 1,

2 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu N,N-dimethylformamide (DMF) were obtained from Sinopharm Chemical Reagents Co., China. N,N,N,N - tetraglycidyl-4,4 -diaminodiphenyl ether (4,4 -TGDDE) was supplied by department of polymer materials of Shanghai University. Methyl nadic anhydride (MNA) and 2-ethyl-4- methy-imidazole (EMI-24) were purchased from Aldrich. The latter was used as a curing accelerator. 2.2 Synthesis of Tetrafunctional Epoxies The tetrafunctional epoxy based on BAPP (TGBAPP) was synthesized as shown in Scheme 1, and 3,4 -TGDDE was synthesized as Scheme A 200 ml ethanol solution containing 1.0 mol ECH (92.5 g) and 0.1 mol diamine (41.1 g BAPP or 20.2 g 3,4 -DDE) was added to a three necked flask. The reaction mixture was stirred at 80 C for a period of time (12 hours for TGBAPP system, 8 hours for 3,4 -TGDDE system). Subsequently, 40 g aqueous sodium hydroxide solution with 50 wt.% concentration was introduced drop wise over a period of 1 h with stirring. The system was maintained at 70 C for additional hours (6 hours for TGBAPP system, 1 hour for 3,4 -TGDDE system), and then filtered to remove the residual sodium chloride. Finally, the organic phase was extracted with MIBK, and then washed several times with deionized water to remove the residual sodium chloride. After precipitated from its cold water, the product distilled to remove excess epichlorohydrin and other solvent. Then the tetrafunctional epoxy was obtained. 2.3 Preparation of the Cured Epoxy Resins The chemical structure of epoxies and curing agents were shown in Table 1. The DMF solution containing stoichiometric ratio of amine curing agent according to epoxy equivalent weight (EEW) was mixed with the epoxy, homogeneously, which formed amine systems of TGBAPP/BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/ BAPP and 4,4 -TGDDE/4,4 -DDE. The mixtures were heated at 50 C for 2 h to take the solvent out. Additionally, two TGDDE with different chemical structure was mixed with a stoichiometric ratio of the anhydride curing agent (MNA) together with the curing accelerator (EMI-24), respectively, which formed two anhydride systems of 4,4 -TGDDE/ MNA and 3,4 -TGDDE/MNA. And then they were heated to 80 C under vacuum to remove air bubbles and moisture. All these systems were cured in their respective optimal curing condition which decided by their dynamic DSC methods results as listed in Table Characterization FTIR spectrum was recorded on a Nicolet 380 infrared spectrometer in the range of cm H NMR characterization was carried out using BRUKER AVANCE 500MHZ NMR spectrometer with deuterated chloroform as the solvent and tetramethylsilane as internal standard. The epoxy equivalent weight (EEW) was determined with the HCl/acetone titration method. Differential Scanning Calorimetry (DSC) was performed on a TA Q2000 with a constant nitrogen flow of 50 ml/min. About 5 mg of a sample (TGBAPP/BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/ BAPP, 4,4 -TGDDE/4,4 -DDE, 4,4 -TGDDE/MNA and 3,4 -TGDDE/ MNA) was weighted and put into a hermetic aluminium sample pan at 25 C, which was then sealed, and the sample was tested immediately. The dynamic scanning experiments were ranged from 50 to 280 C at heating rates of 5, 10, 15, 20 and 25 C /min, respectively. Scheme 1. Schematic diagram the synthesis of TGBAPP Scheme 2. Synthesis of 3,4 -TGDDE 2 Polymers & Polymer Composites, Vol. 22, No. 1, 2014

3 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins Thermo-gravimetric analysis (TGA) was performed with a TA Q500 at the heating rates of 10, 20, 30, 40 C/min in a nitrogen atmosphere from 50 to 750 C, and the thermal stable residue was formed. About 10 mg of a sample (the cured epoxy resin), which had been cured and ground into a powder, was put into a ceramic cell and placed on a detector plate. Dynamic mechanical analysis (DMA) was characterized with a TA Q800 in the air. The specimen of mm was loaded in a three-point bending mode at a heating rate of 5 C /min from 50 to 250 C with a frequency of 1 Hz. 3. Results and discussion 3.1 Characterization of the Tetrafunctional Epoxies The synthesized TGBAPP and 3,4 -TGDDE were characterized with FTIR and 1 H NMR. Figure 1 showed the FTIR spectrums of the tetrafunctional epoxies. The spectrum of TGBAPP was assigned as follows: 3045 cm -1, 2966 cm -1, 2917 cm -1 and 2865 cm -1 (C-H), 1612 cm -1 and 1501 cm -1 (phenylene), 1230 cm -1 (Ar-O-Ar), 902 cm -1 ( ). Besides, the FTIR spectrum of 3,4 -TGDDE was assigned as follows: 3050 cm -1, 2992 cm -1 and 2920 cm -1 (C-H), 1608 cm -1, 1507 cm -1 and 1453 cm -1 (phenylene), 1226 cm -1 (Ar-O-Ar), 906 cm -1 ( ), 827 cm -1 (p-phenylene), 758 cm -1 (m-phenylene). The 1 H NMR spectrums of TGBAPP and 3,4 -TGDDE were shown in Figure 2. The chemical shifts of TGBAPP were assigned as follows: ppm (singlet, methyl protons), ppm (singlet, CH 2 oxirane ring protons), ppm (singlet, CH oxirane ring proton), ppm (multiplet, methine protons), ppm (singlet, aromatic protons). And the peaks labeled a j correspond to the structures shown in Scheme 1 based on these chemical Table 1. Chemical structure of epoxies and curing agents Component Chemical structure Epoxy TGBAPP 4,4 -TGDDE 3,4 -TGDDE Curing agent BAPP DDE MNA EMI-24 Table 2. Curing conditions for curing epoxy resins Systems Crosslinking Curing Post-curing Temp. ( C) TGBAPP/BAPP 157 Time (h) Temp. ( C) 183 Time (h) Temp. ( C) 205 TGBAPP/4,4 -DDE ,4 -TGDDE/BAPP ,4 -TGDDE/4,4 -DDE ,4 -TGDDE/MNA ,4 -TGDDE/MNA shifts. Additionally, the chemical shifts of 3,4 -TGDDE were assigned as follows: ppm (singlet, CH 2 oxirane ring protons), 3.2 ppm (singlet, CH oxirane ring proton), ppm Time (h) (multiplet, methine protons), ppm (singlet, aromatic protons). The peaks labeled a h correspond to the structures shown in Scheme 2 based on these chemical shifts. 4 Polymers & Polymer Composites, Vol. 22, No. 1,

4 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu Figure 1. FTIR spectrums of TGBAPP and 3,4 -TGDDE Figure 2. 1 H NMR spectrums of TGBAPP and 3,4 -TGDDE The EEW of 172 g/mol for TGBAPP and 125 g/mol for 3,4 -TGDDE were determined with the HCl/acetone titration method. 3.2 Curing Kinetics of Epoxy Resins The curing activation energies (E) were simulated by Kissinger model and the order of reaction n were deduced from Crane Figure 3 showed the DSC curves of the epoxy curing systems at different heating rates, and the exothermic peak temperature (T p ) of the curing curves shifted to a higher temperature with an increasing heating rate (b). Kissinger model is based on the fact that the peak temperature (T p ) varies with the heating rates (b) and it assumes the maximum reaction rate (da/dt) occurs at the peak temperatures, the equation can be expressed as Equation (1). So the E k values of the curing reactions will be determined from a plot of ln(b/t p2 ) vs. 1/T p as shown in Figure 4. Ek = R d[ln(β / T 2 p )] d(1 / Tp) (1) where E k is the curing activation energy simulated by Kissinger s equation, b is the heating rate and T p is the maximum peak temperature, and R is the ideal gas constant. The calculated values of E k, as shown in Table 3, showed the anhydride curing systems exhibited lower curing activation energy than the amine curing systems. Moreover, the E k values of the amine curing systems increased with the increasing amount of aromatic rings in the main molecular chain. And the influence on the epoxies was quite obvious than that on the curing agents. This is because the amine curing systems were combined with the amine based epoxies and the aromatic amine, the curing reaction had enough tertiary amine from the amine based tetrafunctional epoxies as accelerators, then the influence from the curing agent was not obvious. Additionally, the curing reactions were influenced with the reactivity of the functional groups and the steric hindrance of the backbone. Since the reactivity of the epoxy groups of TGBAPP and 4,4 -TGDDE were close, while the steric hindrance of TGBAPP was higher than that of 4,4 -TGDDE duo to more aromatic rings into the main molecular chain, which could be also illustrated by the value of molecular volume of TGBAPP of 596A and 4,4 -TGDDE of 399A. So the curing 4 Polymers & Polymer Composites, Vol. 22, No. 1, 2014

5 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins reactivity would be decreased with introducing more aromatic rings into the main molecular chain. Besides, the results showed that the curing activation energy of the tetrafunctional epoxy with p-glycidyl amino groups was slightly higher than that of the epoxy with m-glycidyl amino groups. Figure 3. DSC curves of curing epoxy resins with different heat rates: (a) TGBAPP/BAPP; (b) TGBAPP/4,4 -DDE; (c) 4,4 -TGDDE/BAPP; (d) 4,4 -TGDDE/4,4 -DDE; (e) 4,4 -TGDDE/MNA; (f) 3,4 -TGDDE/MNA In addition, the calculated n values of these curing reactions were all close to 0.9, which illustrated that all these reaction could be approximately as the first order reaction. According to the Kissinger model, the pre-exponential factors (A) were calculated with the following equation, and the results were shown in Table 3. A be exp ( E / RT p ) 2 RT p (2) The values of E and A determined from the curing kinetics data were used to calculate the reaction rate constant (k) from an Arrhenius equation: k = A exp ( E / RT ) (3) The k values at different temperature, as shown in Figure 5, were increased with the increasing curing temperature, which illustrated the curing reactions rate increased with the increasing temperature. Moreover, the results indicated that the curing reaction rates of the anhydride systems were faster than those of the amine systems, which showed the anhydride systems had higher curing reactivity. Furthermore, it could be seen from the results that the curing reactivity of the amine curing systems could be considered as the order: TGBAPP/BAPP > TGBAPP/4,4 -DDE > 4,4 -TGDDE/ BAPP > 4,4 -TGDDE/4,4 -DDE, which showed introducing more aromatic rings into the backbone would decrease the curing reactivity. And the tetrafunctional epoxy with p-glycidyl amino groups had higher curing reactivity than the epoxy with m-glycidyl amino groups. Table 3. The curing kinetic parameters of curing resins Systems E k (kj/mol) n A (s -1 ) TGBAPP/BAPP TGBAPP/4,4 -DDE ,4 -TGDDE/BAPP ,4 -TGDDE/4,4 -DDE ,4 -TGDDE/MNA ,4 -TGDDE/MNA Since the starting temperature of the exothermic reaction (T i ) corresponded to the crosslinking temperature, the exothermic peak temperature (T p ) corresponded to the curing temperature, and the post-curing temperature is associated with the terminal temperature of the exothermic reaction (T f ), the curing temperature can approximately be determined by extrapolating b to zero, as Figure 6 shows. Therefore, the theoretical crosslinking temperature, the curing temperature, and the post-curing Polymers & Polymer Composites, Vol. 22, No. 1,

6 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu Figure 4. ln(b/t p2 ) and lnb vs. 1/T p of curing epoxy resins: (a) TGBAPP/BAPP; (b) TGBAPP/4,4 -DDE; (c) 4,4 -TGDDE/ BAPP; (d) 4,4 -TGDDE/4,4 -DDE; (e) 4,4 -TGDDE/MNA; (f) 3,4 -TGDDE/MNA temperature could be obtained, and the temperatures were shown in Table 4. Figure 5. Curing reaction rate constant (k) values of epoxy systems at different temperatures The results indicated that the anhydride curing systems exhibited lower curing temperature than the amine curing systems. Additionally, the curing temperature increased with the increasing amount of aromatic rings in the main molecular chain, and the curing temperature of the epoxy with was p-glycidyl amino groups slightly lower than that of the epoxy with m-glycidyl amino groups. All of these could be attributed to the different curing reactivity of the curing systems. 6 Polymers & Polymer Composites, Vol. 22, No. 1, 2014

7 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins Figure 6. Crosslinking temperature, curing temperature and post-curing temperature for curing epoxy resins: (a) TGBAPP/BAPP; (b) TGBAPP/4,4 -DDE; (c) 4,4 -TGDDE/BAPP; (d) 4,4 -TGDDE/4,4 -DDE; (e) 4,4 -TGDDE/MNA; (f) 3,4 -TGDDE/MNA 3.3 Thermal Properties and Decomposition Kinetics of Cured Epoxy Resins The thermal behaviors of the cured epoxy resins were studied with thermogravimetric analysis (TGA). Figure 7 showed the TGA curves of the cured epoxy resins at a heat rate of 10 C/ min. The values of 5% weight loss decomposition temperature (T 5% ), the temperature at the maximum rate of decomposition (T m ) and char yield at 750 were listed in Table 5. The thermal stability could be illustrated by the values of T 5% and T m, and the results indicated that the thermal stability increased with Table 4. Curing parameters for curing epoxy resins Systems Crosslinking temperature ( o C) Curing temperature ( o C) the increasing temperature values. Therefore, the epoxy resins cured with the anhydride showed better thermal stability than those cured with the aromatic amine. Furthermore, it could Post-curing temperature ( o C) TGBAPP/BAPP TGBAPP/4,4 -DDE ,4 -TGDDE/BAPP ,4 -TGDDE/4,4 -DDE ,4 -TGDDE/MNA ,4 -TGDDE/MNA be seen that the thermal stability could be improved by introducing more aromatic rings into the main molecular chain since the thermal stability of the amine cured epoxy resins decreased Polymers & Polymer Composites, Vol. 22, No. 1,

8 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu Figure 7. TGA curves of cured epoxy resins at a heating rate of 10 C/min log β = AE log E d f (α)r RT (4) ln β T 2 max = ln AR E + ln n(1 α max ) n 1 E RT max (5) where b is the heating rate, f(a) is the differential expression of a kinetic model function, T max is the temperature corresponding to the inflection point of the thermo-degradation curves which corresponds to the maximum reaction rate, a max is the conversion at T max, and n is the reaction order. A and R are pre-exponential factor and ideal gas constant, respectively. Table 5. The decomposition date of cured epoxy resins at 10 C/min System T 5% ( C) T m ( C) Char yield (%) TGBAPP/BAPP TGBAPP/4,4 -DDE ,4 -TGDDE/BAPP ,4 -TGDDE/4,4 -DDE ,4 -TGDDE/MNA ,4 -TGDDE/MNA as the order: TGBAPP/BAPP > TGBAPP/4,4 -DDE 4,4 -TGDDE/ BAPP > 4,4 -TGDDE/4,4 -DDE. And the tetrafunctional epoxy with p-glycidyl amino groups had better thermal stability than the epoxy with m-glycidyl amino groups. Since the chain breakage depended not only on the chemical structure but also on the degradation activation energy, the thermal degradation activation energies were studied with the dynamic method Figure 8 showed the TGA curves of the cured epoxy resins at four different heating rates. The decomposition activation energy at 5% weight loss (E d5% ) and the decomposition activation energy (E d ) were obtained with Flynn-Wall-Ozawa equation and Kissinger equation 27 as follows: The values of E d5% were calculated by logb vs. 1/T plots at 5% decomposition conversions as Figure 9 shown, and the E d values could be obtained by ln(b/ T 2 ) vs. 1/T as Figure 10 shown. max max The results, as shown in Table 6, indicated that the epoxy resins cured with the anhydride exhibited higher decomposition activation energy compared with those epoxy resins cured with aromatic amine at the beginning of the decomposition duo to their better developed networks. In addition, the decomposition activation energy of TGBAPP/BAPP was lower than those of the other epoxy resins cured with the aromatic amine, and the decomposition activation energy of the tetrafunctional epoxy with m-glcidyl amino groups was higher than the epoxy with p-glcidyl amino groups. All above, the results of the thermal stabilities and the decomposition activation energies of the cured resins showed that The backbone chemical structure of the aromatic tetrafunctional epoxies was important to the thermal properties of the cured resins. Moreover, the tetrafunctional epoxy with p-glycidyl amino groups had 8 Polymers & Polymer Composites, Vol. 22, No. 1, 2014

9 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins better thermal stability than the epoxy with m- glycidyl amino groups, and the thermal stability could be improved by introducing more aromatic rings into the main molecular chain. Figure 8. TGA curves of cured epoxy resins at four different heating rates: (a) TGBAPP/BAPP; (b) TGBAPP/4,4 -DDE; (c) 4,4 -TGDDE/BAPP; (d) 4,4 -TGDDE/4,4 -DDE; (e) 4,4 -TGDDE/MNA; (f) 3,4 -TGDDE/MNA 3.4 DMA Analysis of Cured Epoxy Resins The DMA curves of these cured resins were shown in Figure 11. The glass transition temperature (T g ) of the epoxy resins cured with aromatic amine were 166, 160, 162 and 155 o C for TGBAPP/BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/ BAPP and 4,4 -TGDDE/4,4 -DDE, respectively, which determined by the peaks temperature of the Loss modulus (E ) curves. The results showed that the T g values could be elevated by introducing more aromatic rings into the backbone. On the other hand, the T g of 4,4 -TGDDE/MNA and 3,4 -TGDDE/MNA were 238 C and 234 C, respectively, which were attributed to their higher crosslinking density of 4,4 -TGDDE/MNA. Moreover, all the results indicated that the tetrafunctional epoxies cured with the anhydride exhibited higher crosslinking density compared to those cured with aromatic amine. In addition, it could be seen that the T g values of TGBAPP/BAPP, TGBAPP/4,4 -DDE and 4,4 -TGDDE/4,4 -DDE were close, which caused by their high crosslinking density and the large steric hindrance from the aromatic rings in the backbone. And TGBAPP/ BAPP showed better retention of E at elevated temperature compared Figure 9. logb vs. 1/T5% of cured epoxy resins Table 6. The decomposition activation energy of cured epoxy resins System E d5% (kj/ mol) E d (kj/ mol) TGBAPP/BAPP TGBAPP/4,4 -DDE ,4 -TGDDE/BAPP ,4 -TGDDE/4,4 -DDE ,4 -TGDDE/MNA ,4 -TGDDE/MNA Polymers & Polymer Composites, Vol. 22, No. 1,

10 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu Figure 10. ln(b/t 2 ) vs. 1/T of cured epoxy resins max max with that of 4,4 -TGDDE/4,4 -DDE, which was related to the stiffness of molecular chain and a low degree of free conformational rotation of TGBAPP/BAPP. Additionally, it is worthwhile to mention that the cured TGBAPP/BAPP, TGBAPP/4,4 -DDE and 4,4 -TGDDE/BAPP systems showed two peaks temperature of tand curves, one caused by lower crosslink density matrix sphere and the other caused by high crosslink density microballoon sphere Conclusions Figure 11. DMA curves of cured epoxy resins at a heating rate of 5 C/min with a frequency of 1 Hz: (a) TGBAPP/BAPP; (b) TGBAPP/4,4 -DDE; (c) 4,4 -TGDDE/ BAPP; (d) 4,4 -TGDDE/4,4 -DDE; (e) 4,4 -TGDDE/MNA; (f) 3,4 -TGDDE/MNA Some tetrafunctional epoxies with different chemical structure were cured with the aromatic amine and the anhydride, respectively, and then four aromatic amine curing systems (TGBAPP/BAPP, TGBAPP/4,4 -DDE, 4,4 -TGDDE/ BAPP and 4,4 -TGDDE/4,4 - DDE) and two anhydride curing systems (4,4 -TGDDE/MNA and 3,4 -TGDDE/MNA) were obtained. The curing kinetics were studied by a non-isothermal DSC method. The results indicated that the anhydride curing systems exhibited higher curing reactivity than the aromatic amine curing systems. Moreover, the curing reactivity decreased with the increasing aromatic rings in the main molecular chain, and the influence was quite obvious by the epoxies. Besides, the tetrafunctional epoxy with p-glycidyl amino groups exhibited higher curing reactivity than the epoxy with m-glycidyl amino groups. The results of the thermal properties of the cured resins indicated that the backbone chemical structure of the aromatic tetrafunctional epoxies was important to the thermal properties of the cured resins. Moreover, the thermal properties could be improved by introducing more aromatic rings into the main molecular chain. And the tetrafunctional epoxy with p-glycidyl amino groups had better thermal properties than the epoxy with m-glycidyl amino groups. 10 Polymers & Polymer Composites, Vol. 22, No. 1, 2014

11 Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins ACKNOWLEDGEMENTS The work was supported by Shanghai Leading Academic Discipline Project under the grant No. s Financial support from the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning was also gratefully acknowledged. R.B. also acknowledged the Shanghai Science and Technology Commission for the Grant (No. 10ZR ). REFERENCES 1. Chen X.B., Handbook of Composites based on polymer, Beijing, PRC (2004). 2. Wang D.Z., Applications and production of Epoxy Resins, Beijing, PRC (2001). 3. Dai Z., Li Y.F., Yang S.G, Zong C.Z., Lu X.K. and Xu J., J. Appl. Polym Sci., 106(3) (2007) Tao Z.Q., Yang S.Y., Ge Z.Y., Chen J.S. and Fan L., Eur. Polym. J., 43(2) (2007) Liu W.B., Qiu Q.H., Wang J., Huo Z.C. and Sun H., Polymer, 49(20) (2008) Xie M.R., Wang Z.G., and Zhao Y.F., J. Polym. Sci., Part A: Polym. Chem., 39(16) (2001) Ayman M. Atta, Mansour R., Mahmoud I. Abdou and Ashraf M. El-sayed, J. Polym. Res., 12 (2005) Pan G.Y., Du Z.J., Zhang C., Li C.J., Yang X.P. and Li H.Q., Polymer, 48(13) (2007), Li H.W., Hu Z.Q. and Huang H.L., Chinese Patent, CN B., (2011). 10. Yu X.H., Liu W.Z., Bing H., Xu Y.F. and Zhao J.X., Chinese Patent, CN C., (2009). 11. Mustată F. and Bicu I., J. Appl. Polym. Sci., 77(11) (2000) Lu X.D., Huang Y.D., and Zhang C.H., J. Reinf. Plast. Comp., 26(16) (2007) Rasmika H.P. and Ranjan G.P., Thermochimica Acta, 160(2) (1990) Liu Y.F., Du Z.J., Zhang C., Li C.J. and Li H.Q., J. Appl. Polym. Sci., 103(3) (2007) Kamlesh G.A., Manish P.P. and Ranjan G.P., Angew. Makromol. Chem., 266 (1999) Liu W.L., Pearce E.M. and Kwei T.K., J. Appl. Polym. Sci., 30(7) (1985) He H.F., Wang Y., Cheng Q.L., Lu H., Lin F.J., Hu G.Y., Wu J.H., Ding Z.W., Ye W.G. and Min X.F., Chinese Patent, CN B., (2011) 18. Dai Z., Li Y.F., Yang S.G., Yang C.Z., Zhao N., Zhang X.L. and Jia X., Eur. Polym. J., 45(7) (2009) Barral L., Cano J., López J., López- Bueno I., Nogueira P., Abad M.J. and Ramı rez, C., Eur. Polym. J., 36(6) (2000) Park J.W., Oh S.C. and Lee H.P., Polym. Degrad. Stab., 67(3) (2000) Barral L., Díez F.J., García-Garabal S., López J., Montero B., Montes R., Ramírez C., and Rico M., Eur. Polym. J., 41(7) (2005) Wang Q.F. and Shi W.F., Polym Degrad Stab., 91(8) (2006) Ozawa T., Bull. Chem. Soc. Jpn., 38(11) (1965) Flynn J.H. and Wall L.A., Polymer Letter, 4(3) (1966) Ozawa T., Thermal Analysis, 2 (1970) Liu Y.J., He C.L., Deng J.G., Ji K.J., Zhang Y.S. and Sun S.X., Engineering Plastics Application, 33(6) (2005) Kissinger H.E., Analy. Chem. J., 29(11) (1957) Guo L.M., The dynamic mechanical thermal analysis for polymer and composites, Beijing, PRC, (2002). Polymers & Polymer Composites, Vol. 22, No. 1,

12 Mingming Yu, Zhengwei Zhou, Hang Lu, Aijun Li, Ruicheng Bai, Jinliang Sun, Musu Ren, and Hefeng Hu 12 Polymers & Polymer Composites, Vol. 22, No. 1, 2014