Synthesis and properties of poly(aryl ether ketone)-based phthalonitrile resins.
In the past 30 years, phthalonitrile resins have been an important class of high-temperature materials having a variety of potential uses in composite matrices, adhesives, films, and electrical conductors owing to their outstanding thermal and thermo-oxidative stability, excellent mechanical properties, superior moisture resistance, and fire resistance [1-14], Polymerization of these resins occurs through cyano groups with catalyst of organic amines by an addition cure mechanism to propagate through multiple reaction pathways involving polytriazine, polyimine, and polyphthalocyanine formations, which ensures that these materials are usually composed of aromatic/heterocyclic ring systems to achieve thermal and oxidative stability, and little or no volatiles are evolved during the polymerization leading to void-free crosslinked networks [2, 15-17], In addition, phthalonitrile monomers and oligomers possess a low complex melt viscosity, which enables facile processing by the cost-effective, nonautoclavable processing techniques such as resin transfer molding, resin infusion molding, and filament winding , However, polymerization of the neat phthalonitrile monomer is extremely sluggish, requiring curing additives such as organic amines, and extended heat treatment at elevated temperature to promote the cure of the phthalonitrile resins [1, 12, 14-18]. A small processing window (20-30[degrees]C) [8, 14] and high processing temperature prevent these resins from being fully utilized for extreme applications, such as in aerospace industry; meanwhile, these disadvantages also cause high cost and processing difficulties [8, 19, 20], Aromatic ether [7, 14, 21, 22], ketone , and sulfone [7, 14, 21, 23] linkages have been previously introduced into phthalonitrile systems, and this has resulted in polymers with outstanding thermal properties. It has been generally recognized that the incorporation of ether linkages into an aromatic polymer leads to a lower melting temperature or glass-transition temperature ([T.sub.g]) and processing advantages [7, 24].
In the light of these facts, we proposed to synthesize a series of poly(aryl ether ketone) oligomers containing phthalonitrile with variable main chain length and cyano side groups by using 4,4'-dihydroxybenzophenone, 2,6-difluorobenzonitrile, and the endcapping reagent 4-nitrophthalonitrile. Incorporating linear ether linkages and extra cyano functional groups into phthalonitrile terminals could efficiently lower melting point and improve the crosslink rate, thus better processability could be obtained without evidently sacrificing other properties necessary for high temperature applications.
4,4'-Dihydroxybenzophenone (DHBP, AR) was purchased from Shanghai Licheng Chemical. 2,6-Difluorobenzonitrile (DFBN, AR) and 4-nitrophthalonitrile (NPN, AR) were obtained from Yangzhou Tianchen chemicals, Ltd and Shijiazhuang Alpha chemicals, respectively. Bis[4-(4'-aminophenoxy)phenyl]sulfone (p-BAPS) was prepared according to the previous work . Toluene (AR), tetrahydrofuran (THF, AR), chloroform (CH[Cl.sub.3], AR), acetone (AR), (N,N-dimethylformamide (DMF, AR), dimethyl sulfoxide (DMSO, AR), N,N-dimethyl acetamide (DMAc, AR), N-melhyl-2-pyrrolidinone (NMP, AR) and potassium carbonate (AR) were purchased from Tianjin BODI chemicals. NMP was purified by distillation under reduced pressure over calcium hydride.
Differential scanning calorimetry (DSC) analysis was performed on a Mettler-Toledo Instrument DSC [821.sup.e] modulated thermal analyzer at a heating rate of 10[degrees]C [min.sup.-1] under a nitrogen purge of 200 ml [min.sup.-1]. Thermogravimetric analysis (TGA) was performed on a Perkin Elmer Pryis 1 TGA analyzer from 100 to 800[degrees] C at a heating rate of 20[degrees]C [min.sup.-1] under a nitrogen or air purge of 100 ml [min.sup.-1] for the thermal and thermo-oxidative stability measurement of the cured samples. Fourier transform Infrared (FTIR) spectra were recorded with a Nicolet Impact 410 FTIR spectrophotometer in KBr pellets. The gel permeation chromatography (GPC) analysis was carried out using PL-GPC 220 instrument with THF as an eluent at the flow rate of 1.00 ml/min, and polystyrene as the calibration standard at 40[degrees]C. Hydrogen nuclear magnetic resonance ([sup.1]H NMR) spectra were performed on a Bruker Advance 300 spectrometer. A Physica MCR 300 rheometer, in conjunction with an environmental testing chamber for temperature control, was used to monitor the rheological behavior of the melting powdered samples between the 25 mm diameter parallel plates in the test chamber of rheometer. The measurements were performed with a frequency of 1 Hz and a strain of 1% at different temperatures as a function of time in nitrogen. A TA Instruments DMA Q800 was used to monitor the glass transition temperature ([T.sub.g]), the storage modulus (E') and damping factor (tan [delta]) of the rectangular cured samples (dimensions 30 x 4 x 3 [mm.sup.3]) in air over the temperature ranging from 40 to 400[degrees]C in the single cantilever mode at a strain amplitude of 10 pm, an oscillatory frequency of 1 Hz, and a heating rate of 5[degrees]C/min.
Synthesis of Poly(aryl ether ketone) Oligomers Containing Phthalonitrile (PAEK-CN)
The typical procedure for the synthesis of poly(aryl ether ketone) oligomer containing phthalonitrile (PAEK-CN-II) was as following: To a 100 ml, three-necked flask fitted with a thermometer, a Dean-Stark trap with a condenser, and a nitrogen inlet were added DHBP (8.5688 g, 0.04 mol), DFBN (2.7822 g, 0.02 mol), anhydrous [K.sub.2]C[O.sub.3] powder (6.6341 g, 0.048 mol), toluene (7 ml), and NMP (26 ml). The resulting mixture was degassed with nitrogen at the ambient temperature, stirred, and heated to reflux at 135-145[degrees]C for 3 h to remove all water by azeotropic distillation. Until toluene was removed by distillation, the temperature of the reaction mixture held at 165-170[degrees]C for 2 h, then cooled to room temperature. NPN (6.9322 g, 0.04 mol) and NMP (16 ml) were added in one portion, and the reaction mixture was heated to 85[degrees] C for another 24 h. Then, the product was slowly poured into distilled water and washed with distilled water and ethanol several times. The light yellow precipitate was collected by suction filtration and dried at 85[degrees]C under vacuum for 48 h. The purified product PAEK-CN-II was obtained. Selected data of PAEK-CN-II oligomer was as follows: mp: 129[degrees]C. [sup.1]H NMR (300 MHz, DMSO-[d.sub.6]) [delta] (ppm): 8.17 (d, aromatic-H), 7.97 (d, aromatic-H), 7.92-7.87 (m, aromatic-H), 7.76-7.70 (m, aromatic-H), 7.61-7.58 (m, aromatic-H), 7.41-7.28 (m, aromatic-H), 7.00 (d, aromatic-H). The number-average molecular weight ([M.sub.n]) was 1759, and the polydispersity (PD) was 1.17 according to GPC. FTIR (KBr, [cm.sup.-1]): 3041 (stretch, ph), 2233 (stretch, -CN), 1652 (stretch, -C=O), 1590, 1501, 1309 (stretch, ph), 1282, 1248, 1214, 1165, 933 (stretch, Ar-O-Ar), 844, 775, 734 (bend, ph).
The oligomers labeled as PAEK-CN-I and PAEK-CN-III with different molecular chain length was also obtained by varying the mole ratio of DFBN to DHBP, respectively, according to the similar procedure above.
Preparation of PAEK-CN/p-BAPS Mixtures for DSC Analysis and Rheometric Measurement
To a 100 ml flask fitted with a plug were added PAEK-CN, p-BAPS and THF in one portion. The mixtures were stirred vigorously with magnetic stirring apparatus for 3 h to make them disperse evenly at the ambient temperature, and then THF was removed by distillation with rotatory evaporator, and the mixtures obtained were dried at 80[degrees]C under vacuum for 48 h. These samples were used for the DSC studies and the rheometric measurement, respectively.
The thermal crosslinking reaction of the PAEK-CN oligomers was performed by heating either the oligomer powder or its rectangular solid sample with p-BAPS (3 wt%) as curing agent in air atmosphere.
Samples containing oligomer and p-BAPS were evenly dispersed by vigorous stirring at 220[degrees]C for about 2 min. Then the prepolymers were cured via heating in an oven according to the typical curing procedure as follows: 240[degrees]C for 5 h, 260[degrees]C for 4 h, 280[degrees]C for 4 h, 300[degrees]C for 4 h, 325[degrees]C for 4 h, and 350[degrees]C for 4 h, respectively, under air atmosphere to obtain crosslinked samples. Once the samples were readily cooled, the resultant dark black products were well ground for the thermal crosslinking properties measurement.
Preparation of the DMA Samples
Rectangular solid samples of polymers were prepared in stainless steel molds with cavity dimensions 55 X 5 X 4 [mm.sup.3]. The samples (2 g) of the neat PAEK-CN oligomers were initially melted and degassed for 3 h. After the initial degassing, p-BAPS (3 wt%) was added to the melt with stirring for about 2 min. The molten prepolymers were poured into the molds, then further degassed and heated for another 5 h at 240[degrees]C. The gel-like samples were thermally cured by heating in an oven under an atmosphere of air as the curing procedure above. The samples were then removed from the molds, and sanded to a thickness of ~3 mm for the dynamic mechanical measurements.
The gel content of the powdered crosslinked samples was determined through Soxhlet extraction, using DMAc as solvent. Samples were refluxed in DMAc for at least 52 h to attain a constant weight. The residue after extraction was taken as the gel component, and the gel content was calculated according to Eq. 1, as follows:
Gel content (%)= [W.sub.2]/[W.sub.1] x 100 (1)
where [W.sub.1] and [W.sub.2] are the weights of the samples before and after refluxed in DMAc, respectively.
RESULTS AND DISCUSSION
Oligomers Synthesis and Structural Characterization
The PAEK-CN oligomers were synthesized by a direct solution polycondensation. DFBN containing lateral cyano group was introduced to the oligomer main chain to increase crosslinkable cyano content in curing system. As shown in Scheme 1, the potassium diphenolate intermediates were first obtained by different excess feed ratios of DHBP to DFBN, and then they were readily converted to cyano-terminated PAEK-CN oligomer, named as PAEK-CN-I, PAEK-CN-II, and PAEK-CN-III with the addition of NPN into the reaction mixture, respectively. The structures of all the oligomers were confirmed by FTIR and [sup.1]H NMR spectra. FTIR spectrum of PAEK-CN-II oligomer as typical example showed several characteristic absorption peaks at 2233 and 1652 [cm.sup.-1] attributed to stretching vibration of cyano group (C [equivalent to] N) and carbonyl (C=O), respectively. [sup.1]H NMR spectrum of PAEK-CN-II showed the corresponding proton signals in the aromatic region range of 7.00-8.17 ppm, which were correlated well with the expected chemical structure. Molecular weights of PAEK-CN oligomer were evaluated by [sup.1]H NMR and theoretical values. The detailed data was included in Table 1. In the case of the NMR analysis, the value of n, which represents as the degree of polymerization, was calculated from the peak area ratio of H-a to H-f shown in Fig. 1 using the following equation:
4n+4/2 = [I.sub.H-a]/[I.sub.H-f] (2)
where [I.sub.H-a] and [I.sub.H-f] represent the integration of characteristic peak for H-a and H-f, respectively. The calculated results and GPC results are summarized together in Table 1. The molecular weight values calculated by the [sup.1]H NMR analysis are found to be closer to the theoretical ones calculated by the reactant ratio than those determined by GPC. It is reasonable considering the fact that the former is an absolute value, whereas the latter is a relative value. As expected, the molecular weights of the oligomers were dependent on the feed ratio, i.e., an increase of feed ratio corresponds to the increment of molecular weight, which indicated that the molecular weight was well controlled by the reactant ratio.
FTIR spectra of PAEK-CN-II prepolymers with 6 wt% p-BAPS under the successive cure temperatures is shown in Fig. 2. Three temperatures points investigated were chosen from the curing procedure mentioned earlier. It is found that the normalized intensity of the characteristic absorption peak at 2233 [cm.sup.-1] attributed to cyano group decreased distinctly after prepolymer was cured at 240[degrees]C, while several new characteristic peaks located at 3289 [cm.sup.-1] attributed to phthalocyanine ring, 1526 and 1360 [cm.sup.-1] attributed to triazine ring were observed, which indicated that the new structures such as phthalocyanine ring [16, 17] and triazine ring [16, 17] had formed by these thermally activated reactions. After further heat treatment at 300[degrees]C, an increase in the intensity of the triazine absorptions and a decrease in the cyano absorption were found, respectively. Continue to cure the sample at 350[degrees]C, there was only a little change in the intensities of the corresponding characteristic absorption peaks, and some cyano groups always remained unreacted, which indicated that further reaction of these cyano groups appears to be unlikely due to steric hindrance, similar to a previous report . The characterization of these thermally activated reactions showed the polymerization happened and the intensity of new characteristic peaks changed along with the temperature, suggesting the increase of the extent of the polymerization of the oligomers.
The curing of neat phthalonitrile resins has been shown to proceed very slowly even during extended periods at elevated temperatures [1, 5]. Therefore, it is necessary to incorporate a curing additive to initiate the curing process more effectively. p-BAPS was chosen as the curing additive because of its thermal stability at the initial processing or curing temperature (~200[degrees]C) [26, 27],
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To examine the effect of the addition of p-BAPS on the curing of PAEK-CN, DSC trace of neat PAEK-CN-II powder is performed in nitrogen atmosphere as shown in Fig. 3. There was no obvious exothermic peak related to the crosslinking reaction of the cyano groups in the heating scan up to 300[degrees]C. These results indicated PAEK-CN-II could hardly undergo thermal crosslinking in the absence of p-BAPS. This can be explained by the fact that the high reaction activation energy of trimerization makes the crosslinking kinetically unfavorable. It is also observed from Fig. 3 that the exotherm peak enthalpy of prepolymer had an obvious increase when the concentration of the curing additive p-BAPS increased. Thus, the addition of p-BAPS to the curing system was found to be effective in decreasing the curing temperature and facilitating the thermal curing of PAEK-CN.
The crosslinking process of powdered PAEK-CN mixed with 3 wt% p-BAPS under nitrogen is investigated by DSC thermal analysis, and the results of the first and second heating scans are represented in Fig. 4a and b, respectively.
It is illustrated from Fig. 4a that melting transition peaks ([T.sub.m]s ) for the PAEK-CN oligomers were in the temperature range of 109-142[degrees]C, far less than 4, 4'-bis(3,4-dicyanophenoxy)benzophenone (BDBP)'s (214[degrees]C) [28, 29], and curing exothermic peaks were in the temperature range of 233-245[degrees]C due to the initial reaction of PAEKCN with p-BAPS. It was indicated that PAEK-CN could melt and flow at relatively low temperature, and crosslink at high temperature, so the processing window (103-124[degrees]C) was much larger than that of BDBP (~26[degrees]C) . Figure 4a also shows, with the same weight ratio of curing additive, the temperature of the polymerization exothermic peaks of PAEK-CN moved from 233 to 245[degrees]C with the length of aryl ether ketone linkages in bisphthalonitrile oligomers prolonged, while the exothermic heat flows decreased from 21.05 to 11.31 J/g. That indicated when the length of PAEK-CN increased, the concentration of cyano groups in curing system decreased, so the polymerization reaction became more and more difficult.
The [T.sub.m]s observed in the first scan disappeared in the second DSC scan shown in Fig. 4b up to 300[degrees]C. Besides, obvious [T.sub.g]S ranging from 97 to 133[degrees]C were detected for PAEK-CN prepolymers in the second DSC scan. These results confirmed that the partly thermal crosslinking of the mixtures of PAEK-CN with 3 wt% p-BAPS had occurred in the DSC sample cell during the heating scan.
The rheological behavior of PAEK-CN-II prepolymers was studied by varying the concentration of p-BAPS and curing temperature. A plot of viscosity as a function of time at 260[degrees]C for PAEK-CN-II prepolymers with different content of p-BAPS is shown in Fig. 5. The results indicated that the viscosity of the prepolymer increased more rapidly with higher concentration of p-BAPS. It was revealed that the rate of diamine-catalyzed phthalonitrile polymerization could be easily controlled by varying the diamine concentration. This was consistent with the result of DSC in Fig. 3. The time sweep viscosity curves of the PAEK-CN-II prepolymer at different temperatures (220, 240, and 260[degrees]C) are depicted in Fig. 6. As could be seen, the viscosity of the PAEK-CN-II prepolymer was low at the beginning of the curing reaction, and then increased sharply as soon as gelation occurred. Moreover, the higher the curing temperature, the faster the viscosity increased. These results indicated that high temperature had a great tendency to accelerate the polymerization reaction of the PAEK-CN-II prepolymer. Then, the observed viscosity changes were evidence that the PAEK-CN-II prepolymer was reacting to form crosslink networks. In addition, the results also apparently demonstrated that curing temperature had also positive effect on the crosslinking rate, which was similar to the effect of the concentration of p-BAPS on the aforementioned crosslinking rate.
One of the most important factors influencing the processing of thermosetting resins is gelation . In the liquid state, the viscous properties are predominant (G' < G" and tan [delta] > 1), whereas in the solid state, the elastic properties are predominant (G' >G" and tan [delta] < 1). Therefore, at the gel point G' = G", the loss energy is equal to the energy stored, and tan [delta] is 1 according to the previous work [30, 31], From Fig. 7, the effective cross point of G' and G" was observed at 1050 s, which indicated that the resin underwent gelation transition. It is obviously found that the storage modulus (G') increased quickly in the time region from 1050 to 1500 s, PAEK-CN-II prepolymer had been transferred from viscosity flow state to solid state, and at the same time the loss modulus (G") also increased. The tan (delta) curve exhibited one sharp peak at 920 s, which indicated that PAEK-CN-II could be polymerized with p-BAPS at 260[degrees]C. The gelation time (determined from the storage modulus and the loss modulus crossover point) for the PAEK-CN-II prepolymers is summarized in Table 2. These data revealed that the gelation time of the PAEKCN-II prepolymers decreased as the increase of concentration of p-BAPS and curing temperature.
The rheological behavior of the prepolymers demonstrated that PAEK-CN-II possessed good processability, which made it available for a variety of techniques to fabricate composites such as compression molding, filament winding process, and vacuum assisted resin transfer molding.
The solubility tests of both powdered uncured and cured PAEK-CN were also conducted to investigate the crosslinking behavior. The solubility of the samples is tested in common organic solvents by dissolving 0.04 g of the powered samples in 1 ml solvent, and the results are summarized in Table 3. The uncured PAEK-CN samples were soluble in several aprotic solvents such as NMP, DMAc, DMF, DMSO, and THF. The good solubility might be resulted from the incorporation of DFBN containing lateral cyano group into the oligomer main chain, which disordered the packing of the intermolecular chain and therefore made the synthesized oligomers organically soluble. As a result, it was easy to prepare pieces and coatings from the solutions of PAEK-CN oligomers. The cured samples became insoluble in organic solvents. Measuring gel content of cured polymers is a direct method to evaluate the extent of curing reaction. Thus, the gel content of the cured samples powder was tested by Soxhlet extraction according to ASTM D2765 method. As shown in Table 4, the gel content of the cured polymers of PAEK-CN-I, PAEK-CN-II, and PAEK-CN-III were 90.1%, 97.9%, and 98.3%, respectively. The gel content for the cured samples was as high as expected, probably ascribed to the trimerization of the terminal and lateral cyano groups during the formation of crosslinked network. The results suggested that the curing condition chosen was proper to obtain full-cured products.
Dynamic Mechanical Analysis
Dynamic mechanical analysis was used to study the dynamic mechanical properties of the cured phthalonitrile polymers, and estimate the glass transition temperature ([T.sub.g]). The samples were prepared as mentioned in the experimental section. The storage modulus, E', and the damping factor, tan [delta], of PAEK-CN, cured in the presence of 3 wt% p-BAPS were evaluated between 40 and 400[degrees]C in an air atmosphere. As shown in Fig. 8, the storage modulus for cured PAEK-CN-I, PAEK-CN-II, and PAEK-CN-III was 2645, 2211, and 1635 MPa, respectively at 40[degrees]C. These data showed that the storage modulus of the cured PAEK-CN decreased, as the length of aryl ether ketone linkages increased. The variation in the storage modulus of the polymers reflected changes in the polymer rigidity resulting from differences in crosslinking density. It was possibly reasoned that owing to the increase of the length of PAEK-CN, the density of crosslink units decreased, and this made it more difficult for the curing additive to find crosslink units and to continue with the propagating polymerization reaction. Thus, the cured PAEK-CN-II and PAEK-CN-III had a longer spacer between the crosslinked centers and relatively lower crosslinking density with respect to the cured PAEK-CN-I. With temperature increasing up to 350[degrees]C, the gradual decreases in the storage modulus were attributed to stress relaxation of the polymer network. Figure 8 also shows that no [T.sub.g]s were observed for the samples cured according to the curing procedure mentioned earlier, which indicated that cured PAEK-CN resin possessed an excellent heat-resistant property, which was due to stable crosslinked networks to hinder the segmental motion of the polymer. Thus, all the phthalonitrile polymers exhibited dynamic mechanical behavior characteristic of a glassy material up to 350[degrees]C. This is the evidence that the cured samples retained very good mechanical properties at elevated temperatures.
Thermal Stability Analysis
The thermal and oxidative properties of the cured PAEK-CN were evaluated between 100 and 800[degrees]C in a TGA chamber under nitrogen/air atmosphere. The TGA thermograms of the cured PAEK-CN are shown in Fig. 9. The results of thermal analysis for all investigated oligomers are summarized in Table 5. All the cured PAEK-CN showed good thermal stability up to 460[degrees]C and began to lose weight at higher temperatures and had a char yield of 67-70% at 800[degrees]C in an inert atmosphere of nitrogen. The temperatures for 5% weight loss ([T.sub.5%]s) were in the range of 507-515[degrees]C. Also the polymers had excellent thermooxidative stability with the initial decomposing temperatures above 460[degrees]C in air atmosphere. The temperatures for 5% weight loss were in the range of 496-516[degrees]C. In addition, the residual weight retentions were found to be 4675% on further heating to 600[degrees]C, and catastrophic degradation occurred between 500 and 800[degrees]C, implying that these polymers possessed good oxidative stability. From these results, it was obvious that the cured PAEK-CN polymers showed good thermal stability with high char yield.
A series of poly(aryl ether ketone) oligomers (PAEK-CN) containing phthalonitrile were synthesized by a two step, one pot method successfully. The formation of the oligomers was confirmed by FTIR and [sup.1]H NMR analysis. The number-average molecular weights ([M.sub.n]s) of the phthalonitrile oligomers were in the range of 1420-2429 by GPC analysis. The PAEK-CN oligomers exhibited low melting points, large processing windows and good solubility. Furthermore, they could also be easily fabricated to shaped components in the presence of p-BAPS, since the viscosity of the melt and the rate of the phthalonitrile polymerization could be easily controlled for the PAEK-CN oligomers as a function of the quantity of curing additive and temperature. FTIR indicated, with the curing reaction progressed, the amount of cyano group decreased distinctly while the new structures such as phthalocyanine ring and triazine ring had formed. Gel content tests showed cured PAEK-CN had high gel content over 90.1%, and thus high crosslinking density. The cured PAEK-CN did not exhibit a [T.sub.g] upon heating to 400[degrees]C, and also displayed relatively good thermal mechanical properties and outstanding thermal stability along with thermo-oxidative stability, and thus the oligomeric phthalonitrile resins were expected as a good candidate in the fabrication of structural composite components for advanced aerospace applications.
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Tao Liu, Yanhua Yang, Tingting Wang, Haibin Wang, Hang Zhang, Yu Su, Zhenhua Jiang
Engineering Research Center of Special Engineering Plastics, Ministry of Education, College of Chemistry, Jilin University, Changchun 130012, People's Republic of China
Correspondence to: Zhenhua Jiang; e-mail: firstname.lastname@example.org
Contract grant sponsor: National Natural Science Foundation of China; contract grant number: 51103055; contract grant sponsor: Science and Technology Development Plan of Jilin Province; contract grant number: 20130206065GX.
Published online in Wiley Online Library (wileyonlinelibrary.com).
TABLE 1. Molecular weights data of oligomer PAEK-CN. Molecular weights (g [mol.sup.-1]) DFBN/DHBP Samples ratio [M.sub.n] (b) [M.sub.n] (c) PAEK-CN-I 1:3 780 700 PAEK-CN-II 1:2 936 998 PAEK-CN-III 1:1.5 1250 1698 Molecular weights (g [mol.sup.-1]) Samples [M.sub.n] (a) [M.sub.w] (b) PD (a) PAEK-CN-I 1420 1666 1.17 PAEK-CN-II 1759 2065 1.17 PAEK-CN-III 2429 3166 1.30 (a) By determined number-average molecular weight and polydispersities by GPC calibrated with polystyrene standards. (b) From calculated number-average molecular weight from the molar ratio of DFBN to DHBP. (c) By determined number-average molecular weight by [sup.1]H NMR analysis. TABLE 2. Gelation time of the PAEK-CN-II pepolymers. Gelation time (s) Concentrations of p-BAPS (wt%) 220[degrees] C 240[degrees]C 260[degrees] C 2 -- -- 3600 3 1610 1250 1050 4 -- -- 530 TABLE 3. Solubility of PAEK-CN and PAEK-CN. Solubility Polymer NMP DMF DMAC DMSO THF PAEK-CN-I + + + + + + + + + + Cured PAEK-CN-I - - - - - PAEK-CN-II + + + + + + + + + + Cured PAEK-CN-II - - - - - PAEK-CN-III + + + + + + + + + + Cured PAEK-CN-III - - - - - Solubility Polymer CHCl3 Acetone Toluene PAEK-CN-I + + - Cured PAEK-CN-I - - - PAEK-CN-II + + - Cured PAEK-CN-II - - - PAEK-CN-III + + - Cured PAEK-CN-III - - - + + : soluble in room temperature; +: soluble on heating; -, insoluble. TABLE 4. Gel content of the cured PAEK-CN with 3 wt% p-BAPS, respectively. Polymers Gel content (%) Cured PAEK-CN-I 90.1 Cured PAEK-CN-II 97.9 Cured PAEK-CN-III 98.3 TABLE 5. Thermal and thermo-oxidative stability of the cured PAEK-CN with 3 wt% p-BAPS, respectively. [N.sub.2] Char [T.sub.5%] yield (%) Polymers ([degrees]C) (800[degrees]C) Cured PAEK-CN-I 515 70 Cured PAEK-CN-II 507 67 Cured PAEK-CN-III 509 67 Air Char [T.sub.5%] yield (%) Polymers ([degrees]C) (600[degrees]C) Cured PAEK-CN-I 516 75 Cured PAEK-CN-II 496 46 Cured PAEK-CN-III 498 53
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|Author:||Liu, Tao; Yang, Yanhua; Wang, Tingting; Wang, Haibin; Zhang, Hang; Su, Yu; Jiang, Zhenhua|
|Publication:||Polymer Engineering and Science|
|Date:||Jul 1, 2014|
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