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Improving thermal and flame-retardant properties of epoxy resins by a new imine linkage phosphorous-containing curing agent.

INTRODUCTION

Epoxy resins have widely used in the fields of coatings, paintings, adhesives, composites and so on, owing to their excellent mechanical, adhesive, and electrical properties [1, 2]. However, poor flame retardancy of the epoxy resins limits their application in most fields that require high performance especially in modern electronic and microelectronic industries.

Although traditional halogenated epoxy resins meet the flame-retardant requirements, the existence of halogen elements is still an important health issue [3] because of the generation of toxic, corrosive gases and the release of toxic, endocrine-disrupting chemicals in combustion. Moreover, these halogenated epoxy resins also lead to environment problems. For example, the European Union proposed to restrict the use of brominated flame retardants in electric/electronic fields [4, 5]. Simultaneously, the World Health Organization and the US Environmental Protection Agency also recommended exposure limits and risk assessment of halogenous compounds [6].

Reduction in combustibility of the epoxy resins by using phosphorus-containing retardants has become a pivotal part of the development and application especially in aerospace industries and electrical/electronic fields [7-13]. Among these phosphorus-containing retardants, 9, 10-dihydro-9-oxa-10phosphaphenanthrene-10-oxide (DOPO) derivatives [14-28] are attractive because of their relatively high thermal stability and flame-retarding efficiency. Furthermore, phosphorus-containing reactive imine can be used as curing agent and flame retardant in epoxy resins [24], Using this "reactive" type flame retardant in curing process, which incorporates the flame-retardant elements into the epoxy networks by covalent bond, problems of "additive" type flame retardant, which incorporates the flameretardant elements into the epoxy networks by physical blending, can be avoided [29]. Because the additive is not chemically compatible with the polymer, it may be leached from the polymer by migration to the surface during combusting processing, particularly if it is used for external applications, or may even volatilize during use. In the combustion process, phosphorous and nitrogen-containing groups have a synergy effect that helps to form an insulating multicellular protective layer on the surface of epoxy resin. The formed shield would act as a barrier to heat, air and pyrolysis products [30, 31].

In this work, a novel DOPO-based epoxy curing agent via imine linkage was successfully synthesized by two-pot procedure. Furthermore, we developed a modified one-pot approach to simplify the above two-pot approach. The structure of this agent was confirmed by [sup.1]H NMR, [sup.13]C NMR and [sup.31]P NMR spectra. The resulting compound was combined with 4, 4'-diaminodiphenyl methane (DDM) to co-cure epoxy resins (E51) by cast molding, which covalently incorporated halogen-free DOPO organ groups into the epoxy networks. Besides, the dynamic mechanical thermal, thermal and flame-retardant properties of these new halogen-free flame-retardant epoxy resins were discussed.

EXPERIMENTAL

Materials

9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from Shanghai Eutec Chemical, China. Ethanol, tetrahydrofuran (THF), A'A'-Dimethylfonnamide (DMF) and 4,4'diaminodiphenyl methane (DDM) were supplied by Sinopharm Chemical Reagent, China. Isophthalaldehyde and 4-aminophenol were purchased from Aladdin Reagent, China. Diglycidylether of bisphenol A (E51, EEW 196 g/eq) was obtained by Wuxi Bluestar, China. All reagents and solvents were used as received.

Synthesis of 4,4'-(l, 3-phenyIdimethyleneimino)diphenol (1) Isophthalaldehyde (13.4 g, 0.1 mol), 4-aminophenol (21.8 g, 0.2 mol) and ethanol (200 mL) were introduced into a 500 mL round bottom glass flask equipped with nitrogen protection and a magnetic stirrer. The reaction mixture was stirred at room temperature for 5 h. The filtered precipitate was washed with ethanol and dried in vacuo at 80[degrees]C to give a yellow powder (yield = 93%).

FTIR (KBr): 3424 [cm.sup.-1] (Ph-OH), 1618 [cm.sup.-1] (-CH=N-), 794 and 692 [cm.sup.-1] (m-Ph). [sup.1]H NMR (ppm, DMSO-[d.sub.6]), [delta] = 6.82 (4H, [H.sup.2], [H.sup.15]), 7.26 (4H, [H.sup.3], [H.sup.14]), 7.62 (1H, [H.sup.8]), 8.00 (2H, [H.sup.7], [H.sup.9]), 8.44 (1H, [H.sup.10]), 8.71 (2H, [H.sup.5], [H.sup.12]), 9.55 (2H, OH). [sup.13]C NMR (ppm, DMSO-[d.sub.6]), [delta] = 115.6 ([C.sup.2], [C.sup.15]), 122.6 ([C.sup.3], [C.sup.14]), 127.2 ([C.sup.10]), 129.1 ([C.sup.8]), 130.6 ([C.sup.7], [C.sup.9]), 136.9 ([C.sup.6], [C.sup.11]), 142.3 ([C.sup.4], [C.sup.13]), 156.4 ([C.sup.1], [C.sup.16]), 156.6 ([C.sup.5], [C.sup.12]).

Synthesis of 4,4'-[1, 3-phenyl-bis(9,10-dihydro-9-oxa-10phosphaphenanthrene-10-Yl) dimethyneimino)]diphenol(2)

DOPO (21.6 g, 0.1 mol), (1) (15.8 g, 0.05 mol), and THF (200 mL) were introduced into a 500-mL round bottom glass flask equipped with nitrogen protection, a condenser and a magnetic stirrer. The mixture was stirred at 60[degrees]C for 8 h. After that, THF was removed by a rotary evaporator. Yellowish powder was obtained (yield = 95%).

FTIR (KBr): 3432 [cm.sup.-1] (-NH-), 3238 [cm.sup.-1] (Ph-OH), 1582 [cm.sup.-1] (P-Ph), 925 [cm.sup.-1] (P-O-Ph), 755 and 690 [cm.sup.-1] (m-Ph). [sup.1]H NMR (ppm, DMSO-8/6), 5 = 4.74 (0.6H, [H.sup.5], [H.sup.12] ), 5.24 (0.4H, [H.sup.5]',[H.sup.12]), 5.51 (0.4H, NH'), 6.05 (0.6H, NH), 6.36-6.56 (4H, [H.sup.2], [H.sup.3], [H.sup.2]', [H.sup.3]', [H.sup.14], [H.sup.15], [H.sup.14'], [H.sup.15]'), 6.66 (0.4H, [H.sup.26]', [H.sup.38]'), 6.95 (0.6H, [H.sup.26], [H.sup.38]), 7.06-7.23 (1H, [H.sup.10], [H.sup.10]'), 7.29 (1H, [H.sup.25], [H.sup.37], [H.sup.25]', [H.sup.37]'), 7.32-7.39 (2H, [H.sup.7], [H.sup.9], [H.sup.7]', [H.sup.9']), 7.42 (1H, [H.sup.27], [H.sup.39], [H.sup.27]', [H.sup.39]'), 7.52 (1H, [H.sup.19], [H.sup.31], [H.sup.19]', [H.sup.31]'), 7.65 (1H, [H.sup.8], [H.sup.8]'), 7.77 (1H, [H.sup.20], [H.sup.32], [H.sup.20]', [H.sup.32]'), 7.95 (0.4H, [H.sup.18]', [H.sup.30]'), 8.05 (0.6H, [H.sup.18], [H.sup.30]), 8.15 (1H, [H.sup.24], [H.sup.36], [H.sup.24]', [H.sup.36]'), 8.20 (1H, [H.sup.21], [H.sup.33], [H.sup.21]' , [H.sup.33]'), 8.48 (0.4H, OH'), 8.51 (0.6H, OH). [sup.13]C NMR (ppm, DMSO [d.sub.6]), [delta] = 56.9, 57.9 ([C.sup.5], [C.sup.12], [C.sup.5]', [C.sup.12]'), 115.0 ([C.sup.3], [C.sup.14], [C.sup.3]', [C.sup.14]'), 115.2 ([C.sup.2], [C.sup.15], [C.sup.2]', [C.sup.15]'), 120.0 ([C.sup.26], [C.sup.38], [C.sup.26]', [C.sup.38]'), 120.2 ([C.sup.10], [C.sup.10]'), 121.6 ([C.sup.22], [C.sup.34], [C.sup.22]', [C.sup.34]'), 124.0 ([C.sup.21], [C.sup.33], [C.sup.21]', [C.sup.33]'), 124.6 ([C.sup.25], [C.sup.37], [C.sup.25'], [C.sup.37]'), 123.7, 125.4 ([C.sup.17], [C.sup.29], [C.sup.17]', [C.sup.29]'), 125.6 (C.sup.24], [C.sup.36], [C.sup.24], [C.sup.36], 127.7 (C.sup.7], [C.sup.9], [C.sup.7]', [C.sup.9]'), 128.3 ([C.sup.19] , [C.sup.31], [C.sup.19]', [C.sup.31]'), 130.4 ([C.sup.8] , [C.sub.8]' ), 130.8 ([C.sub.27], [C.sub.39], [C.sup.27]', [C.sup.39]'), 131.7 ([C.sup.18]', [C.sup.30]'), 131.9 ([C.sup.18] , [C.sup.30]), 133.1 ([C.sup.23], [C.sup.35], [C.sup.33]', [C.sup.35]'), 133.6 ([C.sup.20], [C.sup.32], [C.sup.20]', [C.sup.32]'), 135.1 ([C.sup.6], [C.sup.11]', [C.sup.6]', [C.sup.11]), 139.2 ([C.sup.4], [C.sup.13], [C.sup.4]', [C.sup.13]'), 148.6 ([C.sup.1], [C.sup.16], [C.sup.1]', [C.sup.16]'), 149.4 ([C.sup.28], [C.sup.40], [C.sup.28]', [C.sup.40]'). [sup.31]P NMR (ppm, DMSO-[d.sub.6]), 5 = 28.1, 31.3.

Preparation of (2) by a Simplified Approach

Isophthalaldehyde (6.7 g, 0.05 mol), 4-aminophenol (10.9 g, 0.1 mol), DOPO (21.6 g, 0.1 mol), and DMF (200 mL) were introduced into a 500 mL round bottom glass flask equipped with nitrogen protection and a magnetic stirrer. The mixture was stirred at room temperature for 12 h. After that, the reaction mixture was poured into water. The precipitate was filtered and washed with water, and then dried in a vacuum oven. Yellowish powder (yield = 98%) was obtained.

Preparation of the Cured Epoxy Resins

Several DDM/(2) molar ratios were mixed by stoichiometric E51 with 0.2 wt% 1-cyanoethyl-2-ethyl-4-methylimidazole as the accelerator and stirred homogeneously in an aluminum mold, and then cumulative curing at 135[degrees]C for 14 h, 160[degrees]C, 190[degrees]C, and 220[degrees]C for 2 h in an air-circulating oven, respectively. Aiming to avoid cracking, the epoxy thermosets were slowly cooled down to room temperature. The prepared epoxy/ curing agent compositions are listed in Table 1.

Instrumentation

Infrared spectra (FTIR) were recorded by a Nicolet Avatar 360 FTIR. [sup.1]H NMR, [sup.13]C NMR, [sup.31]P NMR spectra were collected with the Bruker Advanced II 400M spectrometer with DMSO-[d.sub.6] as a solvent. Thermogravimetric analysis (TGA) was performed with a Netzsch STA 409EP at a heating rate of 10[degrees]C/ min under nitrogen and air conditions, respectively. The dynamic mechanical tests were carried out on a Dynamic Mechanical Thermal Analyzer (DMTA) (MKIV, Rheometric Scientific Inc., USA) in single cantilever bending model with the temperature ranging from 25 to 220[degrees]C. The frequency used is 1.0 Hz at the heating

rate 2[degrees]C/min. The specimen dimension was 30 mm x 10 mm x 2 mm. The LOI was determined with an Atlas Limiting Oxygen Index Chamber. The specimen dimension was 100 mm x 6 mm X 4 mm.

RESULTS AND DISCUSSION

Characterization of (1)

As can be seen in Scheme 1, the imine-containing intermediates (1) were synthesized by the condensation of 4-aminophenol with isophthalaldehyde. According to the [sup.1]H NMR spectrum (Fig. 1) of (1), a signal peak appeared at about 8.7 ppm standing for an imine linkage, which indicated that the condensation reaction between-CHO and-N[H.sub.2] occured and a chemical group of -CH--N-obtained. In the [sup.13]C NMR spectrum (Fig. 2) of (1), the characteristic peak of imine at around 156.6 ppm also confirmed the condensation reaction. The detailed assignment of other peaks in the 'H NMR and [sup.13]C NMR spectra was shown in Section 2, and it confirmed the structure of (1). Besides, the absorption peaks at 794 and 692 [cm.sup.-1] demonstrated that (1) was meta-substituent using isophthalaldehyde as a starting material.

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Characterization of (2)

The DOPO-containing compounds (2) via imine linkage used as epoxy curing agents were successfully synthesized by electrophilic addition DOPO on the imine linkage of (1). Since the aliphatic carbon and the adjacent phosphorus are both chiral centers, sixteen stereoisomers should be obtained in each compound. Each stereocenter can be either R or S configuration, and hence, the possible combinations are RRRR, RRSS, RRRS, RRSR, SSRR, SSSS, SSRS, SSSR, RSRR, RSSS, RSRS, RSSR, SRRR, SRSS, SRRS, and SRSR configurations. The sixteen stereoisomers can be grouped into eight pairs of enantiomers, resulting in eight diastereomers (RRRR+SSSS, RRSS+SSRR, RRRS + SSSR, RRSR+SSRS, RSRR+SRSS, RSSS+SRRR, RSRS+SRSR, and RSSR+SRRS), which are distinct molecules with different spectroscopic data. According to the [sup.31]P NMR spectrum in Fig. 3 (proton decoupling), eight peaks at 28.07, 28.10, 28.11, 28.15, 28.16, 31.09, 31.33, and 31.57 ppm were observed, confirming the existence of eight diastereomers in (2). These eight peaks were so close that they could be divided into two group peaks at 28.1 and 31.3 ppm, approximately. As shown in the [sup.1] NMR spectrum (Fig. 4) of (2), two hydroxy peaks (OH and OH') at 8.48 and 8.51 ppm, two secondary irnino peaks (NH and NH') at 5.51, 6.05 ppm and two methyne peaks ([H.sup.5], [H.sup.12], [H.sup.5]', and[H.sup.12]) at 4.74, 5.24 ppm confirmed the validity of the assignment similar to the 3IP NMR spectrum.

Figures 4 and 5 show [sup.1] NMR and [sup.13]C NMR spectra of (2), respectively. All the assignments correspond to the expected signals. The signals of Ar-H, assigned by the assistance of [sup.1]- [sup.1]H COSY, confirm the structure of (2). In the [sup.13]C NMR spectrum, due to the P-C [sup.1]J coupling, the signals of carbon 5 and carbon 12 split into two peaks. Because of the same reason, the signals of carbon 17 and carbon 29 also split into two peaks. The signals of aromatic carbon, assigned by the assistance of [sup.1]H-[sup.13]C HMQC NMR spectrum, also confirm the structure of (2). Besides, the absorption peaks at 755 and 690 [cm.sup.-1] demonstrate that (2) is meta-substituent using (1) as a starting material.

Synthesis (2) by a Simplified Approach

The epoxy curing agent, DOPO-containing compounds (2) via imine linkage can also be synthesized by a simplified, one-pot procedure (Scheme 2). In this approach, the first two steps: condensation reaction between -CHO and -N[H.sub.2] and electrophilic addition DOPO on the imine linkage were carried out in one reactor. Liu reported the nucleophilic addition of DOPO on aldehyde at high temperature [32]. So we kept the reaction condition at room temperature, the addition was successfully avoided in this method according to the NMR spectra. The yield of (2) by this procedure was as high as 98%. Compared to the previous two-pot procedure, this one-pot procedure simplified the synthetic procedure and increased the yield obviously.

Reactivity between DDM/(2) and E51

The performance of the reaction between DDM/(2) and the oxirane groups in E51 was observed with FTIR spectra. Figure 6 shows FTIR spectra of E51, EP-O, and EP-5, which represent the pure resin (E51), E51 only cured by DDM and E51 cured by DDM combining with (2), respectively. As can be seen in Fig. 6a and b, the disappearance of oxirane absorption at 913 [cm.sup.-1] and appearance of aliphatic C--N absorption at 1230 [cm.sup.-1] indicated that DDM was covalently incorporated into the cured epoxy resins. Furthermore, as shown in Fig. 6a and c, the disappearance of oxirane absorption at 913 [cm.sup.-1], appearance of C--N absorption at 1230 [cm.sup.-1], P--O--Ph absorption at 925 cm*1 and m-Ph absorption at 755 and 690 [cm.sup.-1] indicated that DDM and (2) were covalently incorporated into the cured epoxy resins.

Dynamic Mechanical Thermal Properties of the Cured Epoxy Resins

The dynamic mechanical thermal properties of the cured epoxy resins can be obtained from the glassy state, through [T.sub.g], and well into the rubbery plateau of each material. Figure 7a exhibits how the storage modulus (E') changes with temperature for all the networks. The crosslinking density can be investigated and evaluated from the equilibrium storage modulus (E') using the theory of rubber elasticity [33], As shown in Fig. 7a, the storage modulus of the epoxy systems in the rubbery state decreased as content of (2) increased. It indicated that relatively large volume DOPO pendant increased the molecular spacing between epoxy chains and made the epoxy networks more flexible.

Dynamic mechanical thermal analysis was also performed to evaluate the glass transition temperature ([T.sub.g]) of the cured epoxy resins. As can be seen in Fig. 7b, the value of [T.sub.g] was 170, 165, 161, 157 and 153[degrees]C for EP-0, EP-1, EP-2, EP-3, EP-4 and EP5, respectively. All these epoxy systems had a single [T.sub.g], which is in accordance with the DSC results showed in Fig. S1 in Supporting Information, indicating that all these systems were homogeneous in spite of the introduction of (2). The homogeneous morphology endows cured epoxy systems with good compatibility permanently and offers another perspective that (2) has been covalently bonded with epoxy resins. Moreover, the [T.sub.g] values decreased very slowly as the (2) content increased, which could be explained as follows. On one hand, the aromatic moieties in (2) increase free volume. Therefore, materials containing more (2) have lower [T.sub.g]'s. On the other hand, as far as the chemical structures of both (2) and DDM used as curing agents are concerned, although the functionality of (2) (f = 4) is equal to that of DDM (f = 4), lower flexibility of (2) than that of DDM will slow down this decreasing trend. It is well known that the analysis of height and width of a relaxation peak is a way to evaluate and characterize the crosslinking densities and homogeneities of networks. As shown in Fig. 7b, the height of tan <5 peak increased as the (2) content increased, which indicated that networks for the (2) rich samples were more relaxed. The peak width at half height broadens as the number of branching modes increases, which produces a wider distribution of structures [33]. The range of temperatures at which the different network segments gain mobility therefore increases. As can be seen in all samples, the width of tan [delta] peaks had no obvious difference, indicating that the branching distribution of these networks was similar.

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Thermal Properties of the Cured Epoxy Resins

The thermal properties of the cured epoxy resins were characterized with TGA under nitrogen and air conditions, respectively. Figure 8 shows the weight loss with the temperature for the epoxy networks as well as the derivative curves and the TGA data were summarized in Table 2.

In nitrogen, the initial temperature of 5% weight loss (assigned as onset point of weight loss, [T.sub.5%]) was 347, 331, 323, 314, 310, and 306[degrees]C for EP-0, EP-1, EP-2, EP-3, EP-4, and EP5, respectively. It can be noted that the initial decomposition temperatures of these samples were all above 300[degrees]C, showing good thermal stabilities. Moreover, the thermal degradation behavior of all these resins involved a one-stage process. It indicated that there was a similar decomposition mechanism for these resins. Under air condition, it can be seen that EP-0 and EP-1 resins showed a three step break in the decomposition curves, while the higher phosphorus content resins such as EP2, EP-3, EP-4, and EP-5 showed a two-step break in the decomposition curves. As can be seen in Table 2, the [T.sup.3b.sub.max] in the three decomposition pathway and the [T.sup.2b.sub.max] in the two decomposition pathway increased as the high phosphorus content increased, indicating that incorporating more (2) content could improve thermal stability obviously.

Both the char formation under nitrogen and air at 700[degrees]C increased sharply with increasing (2) contents of the cured epoxy resins, indicating that the synergy between phosphorus and nitrogen in the epoxy networks apparently enhanced the thermal stability of the epoxy resins. On one hand, a protective phosphorus-rich layer formed on the surface of the resins and combustible gases reduced at high temperatures for phosphorus-containing molecules [29, 32]. On the other hand, the nitrogen containing moieties could provide thermal insulation and prevent the combustion from spreading due to the highly porous char formed by the released inert gaseous by-products [34, 35].

Flame-Retardant Properties of the Cured Epoxy Resins

LOI values can be applied to evaluate the flame retardancy of the epoxy thermosets. The experimental results were shown in Table 2. It is noteworthy that the LOI values increased from 24.5 to 37.5 rapidly as the (2) content in the cured epoxy resins increased. On the basis of the results, it is evident that the incorporation of (2) can impact good flame retardancy to the conventional epoxy resin. Such an excellent flame-retardant property is attributed to the unique synergistic effect of phosphorus and nitrogen from (2), which chemically links DOPO groups to the backbone of the epoxy resin in a covalent way. This molecular structure is highly advantageous to the reactive flame retardancy induced by the synergistic of phosphorus and nitrogen.

CONCLUSIONS

A novel DOPO-based tetrafunctional epoxy curing agent via inline linkage was successfully synthesized by the condensation of 4-aminophenol with isophthalaldehyde and further addition DOPO on the imine linkage of (1). Furthermore, we developed a modified one-pot approach instead of the traditional two-pot approach to prepare high performance of epoxy networks by crosslinking E51 with DDM and (2). A serials of epoxy resins with different phosphorus and nitrogen contents were obtained by changing the DDM/(2) molar ratios. Dynamic mechanical thermal, thermal and flame-retardant properties were evaluated in detail. All samples had a single [T.sub.g], showing that these epoxy resins were homogeneous for long-term use. The synergistic effect of phosphorus and nitrogen increased char yields and the LOI values, which effectively endowed polymers with enhanced thermal stability and flame retardancy. This new halogen-free and reactive flame retardant for epoxy resins will have potential applications in electron/electronic fields with low toxicity and better eco-friendliness.

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Cong Xie, (1,2) Jifu Du, (1) Zhen Dong, (1) Shaofa Sun, (1) Long Zhao, (1,3) Lizong Dai (1)

(1) Environmental Functional Material Laboratory, Hubei Collaboration Innovative Center for Non-Power Nuclear Technology, Hubei University of Science and Technology, Xianning 437100, People's Republic of China

(2) Fujian Provincial Key Laboratory of Fire Retardant Materials, College of Materials, Xiamen University, Xiamen 361005, People's Republic of China

(3) Nuclear Chemical Engineering Laboratory, School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China

Correspondence to: C. Xie; e-mail: xiecong824@sina.com.cn or L. Dai; e-mail: lzdai@xmu.edu.cn

Contract grant sponsor: The National Natural Science Foundation of China; contract grant number: U1205113; contract grant sponsor: Xiamen Science and Technology Committee; contract grant number: 3502Z20150047 and 3502Z20120015; contract grant sponsor: The Scientific and Technological Innovation Platform of Fujian Province of China; contract grant number: 2014H2006; contract grant sponsor: The The Doctoral Scientific Research Foundation of Hubei University of Science and Technology; contract grant number: BK1433.

Additional Supporting Information may be found in the online version of this article.

DOI 10.1002/pen.24270

TABLE 1. Crosslinking data of E51 using DDM and (2) as curing agents.

                                        DDM (phr)   (2) (phr)
             DDM/(2)
                                              parts per
Samples   Molar ratio(%)   P(%) (w/w)      hundred of E51

EP-0          100-0            0          25.2          0
EP-1          90-10           0.6         22.7         9.5
EP-2          80-20           1.1         20.2        19.1
EP-3          70-30           1.6         17.7        28.6
EP-4          60-40           2.1         15.1        38.1
EP-5          50-50           2.5         12.6        47.7

TABLE 2. Thermogravimetric data and LOI values for the cured
thermosets.

                                 Nitrogen

          P(%)
Samples   (w/w)   [T.sub.5%] (a)   [T.sup.1.sub.max] (b)

EP-0        0          347                  377
EP-1       0.6         331                  366
EP-2       1.1         323                  361
EP-3       1.6         314                  353
EP-4       2.1         310                  349
EP-5       2.5         306                  340

                    Nitrogen

Samples   [T.sup.2.sub.max] (b)   Char (c)

EP-0               --                21
EP-1               --                25
EP-2               --                26
EP-3               --                30
EP-4               --                32
EP-5               --                37

                                 Air

          [T.sub.5%]   [T.sup.1.sub.max]   [T.sup.2.sub.max]
Samples      (a)              (b)                 (b)

EP-0         287              303                 369
EP-1         289              304                 448
EP-2         291              307                 576
EP-3         281              310                 594
EP-4         280              315                 603
EP-5         279              309                 610

                      Air

Samples   [T.sup.3.sub.max] (b)   Char (c)   LOI

EP-0               554               0       24.5
EP-1               565               3       31.5
EP-2               --                7       33.0
EP-3               --                14      35.0
EP-4               --                16      36.0
EP-5               --                17      37.5

(a) Temperature of 5% weight loss ([degrees]C).

(b) Temperature of the maximum weight loss rate in the n-stage
decomposition ([degrees]C).

(c) Char yield at 700[degrees]C (wt%).
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Author:Xie, Cong; Du, Jifu; Dong, Zhen; Sun, Shaofa; Zhao, Long; Dai, Lizong
Publication:Polymer Engineering and Science
Article Type:Report
Date:Apr 1, 2016
Words:4739
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