Synthesis and Properties of Novel Soluble Polyamides Containing Both Fluorene or Xanthene Cardo Moieties and Fluorinated Phenoxy Pendant Groups.
Wholly aromatic polyamides (aramids) are considered to be high-performance organic materials because of their many desirable characteristics, such as outstanding thermal stability, good chemical resistance, and low flammability, along with excellent mechanical properties [1-12]. However, most of them have high melting or softening temperatures and poor solubility in organic solvents because of the highly regular and rigid polymer backbones and the formation of intermolecular hydrogen bonding. These characteristic properties of aramids make them generally intractable or difficult to process, thus restricting their widespread applications. Moreover, the high moisture absorptions of aramids, compared with other high-performance polymer materials, have resulted in obvious negative effect on their electrical insulating and dielectric performance and mechanical properties. To overcome these limitations, many efforts have been made to improve their solubility and dielectric properties without thermal stability and mechanical properties being sacrificed. The introductions of flexible segments--such as ether or sulfone linkages [13-15], bulky pendant [16-19] or cardo groups [6, 20-26], unsymmetrical [27-29], and noncoplanar structures [30-33]--into polymer backbone have been employed as successful approaches to modify aramid properties.
The incorporation of fluorine substituents and bulky pendant groups into the polymers is considered as effective ways to obtain a low dielectric constant property. In recent years, the introduction of fluorine into the polyamide backbones has been intensively explored because of the unique characteristics of fluorine substituents [7, 34-40]. Fluorine incorporation has been found to generally decrease the dielectric constant and moisture absorption, to improve the optical properties, and also to increase the thermal stability. However, it appears that aromatic polyamides containing both cardo moieties and fluorinated phenoxy pendant groups have not been reported in detail in the open literature. In a continuation of our studies on easily processable high-performance polymers [41-45], we report herein the synthesis of a series of novel aromatic polyamides containing both fluorene or xanthene cardo structures and fluorinated phenoxy pendant groups from two fluorinated isophthaloyl chlorides and four diamines containing cardo groups by the low-temperature solution polycondensation in N/N-dimethylacetamide (DMAc). We expected that the incorporation of both bulky fluorene or xanthene cardo structures and flexible fluorinated phenoxy pendant groups into polyamide backbone would endow the resulting polyamides excellent solubility, high thermal stability, and optical transparency as well as good electrical insulating and dielectric properties. The solubility, thermal, and mechanical properties as well as optical and electric behaviors of the obtained polymers were investigated.
All reagents and solvents were of analytical grade and were used without further purification unless stated otherwise. DMAc was purified by distillation over CaH2 and stored over 4-[Angstrom] molecular sieve prior to use. 5-(4-Trifluoromethylphenoxy)isophthaloyl chloride (3F-IPC) and 5-(3,5-bis(trifluoromethyl)phenoxy)isophthaloyl chloride (6F-IPC) were prepared according to the literature procedure , Three aromatic diamines containing cardo groups--9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAPF) , 9,9-bis[4-(4-amino-2trifluoromethylphenoxy)phenyl]fluorene (BAFPF) , and 9,9-bis[4-(4-aminophenoxy)phenyl]xanthene (BAPX) --were synthesized according to the reported methods.
Synthesis of 9,9-Bis[4-(4-Amino-2Trifluoromethylphenoxy)Pheny!]Xanthene (BAFPX)
9,9-Bis(4-hydroxyphenyl)xanthene (9.15 g, 25 mmol) and 1chloro-4-nitro-2-(trifluoromethyl)benzene (11.4 g, 50 mmol) were dissolved in AVV-dimethylformamide (DMF) (100 mL). Anhydrous [K.sub.2]C[O.sub.3] (6.9 g, 50 mmol) was added to this solution, and the suspension was then stirred at 160[degrees]C for 10 h. After cooling to room temperature, the mixture was poured into a mixed solvent of MeOH and water (300 mL, v/v = 1:1) to precipitate a yellow solid that was collected by filtration, washed with MeOH, and dried. The crude product was recrystallized from DMF/EtOH (v/v =1:1) two times and dried under vacuum at 100[degrees]C to afford BNFPX (14.3 g, 75%) as a yellow solid; m.p. 195-196[degrees]C; FTIR (KBr; [cm.sup.-1]): 1532, 1354, 1266, 1143, 1117; [sup.1]H NMR (CD[Cl.sub.3]; [delta], ppm): 8.57 (d, 7 = 2.4 Hz, 2H), 8.31 (dd, 7=8.8, 2.4 Hz, 2H), 7.36-7.33 (m, 2H), 7.23-7.20 (m, 2H), 7.14-7.08 (m, 6H), 7.05-6.95 (m, 8H); [sup.13]C NMR (CDC1,; [detla], ppm): 160.7, 152.8, 152.5, 143.5, 141.9, 132.1, 129.8, 129.4, 128.8, 128.5, 123.9 (q, [sup.3][J.sub.C-F] = 5.2 Hz), 123.3, 122.2 (q, [sup.1][J.sub.C-F] = 271.6 Hz), 121.0 (q, [sup.2][J.sub.C-F]=32.9 Hz), 120.1, 117.4, 116.9, 53.7. Elemental analysis: calculated for [C.sub.39][H.sub.22][F.sub.6][N.sub.2][O.sub.7]: C, 62.91; H, 2.98; N, 3.76. Found: C, 62.67; H, 2.84; N, 3.59.
A mixture of BNFPX (7.44 g, 10 mmol), hydrazine hydrate (10 mL), and 10 wt% Pd/C catalyst (0.15 g) in EtOH (60 mL) was refluxed overnight. The resulting solution was filtered hot to remove the catalyst. The filtrate was cooled to room temperature and precipitated into water. The product was collected by filtration, recrystallized from ethanol, and dried under vacuum at 60[degrees]C to afford BAFPX (4.05 g, 60%) as a white solid; m.p. 174-175[degrees]C; FTIR (KBr; [cm.sup.-1]): 3467, 3388, 1629, 1235, 1162, 1129; [sup.1]H NMR (CD[Cl.sub.3]; [delta], ppm): 7.25 (t, J = 7.6 Hz, 2H), 7.15 (d, 7=8.0 Hz, 2H), 7.05 (t, 7 = 7.4 Hz, 2H), 6.95-6.74 (m, 16H), 3.71 (br, 4H); [sup.13]C NMR (dimethyl sulfoxide (DMSO)-[d.sub.6]; [delta], ppm): 157.4, 151.9, 146.3, 142.7, 140.0, 131.2, 130.3, 130.2, 128.7, 124.0 (q, [sup.1][J.sub.C-F] = 270.9 Hz), 123.8, 123.6, 121.8 (q, [sup.2][J.sub.C-F] = 29.8 Hz), 119.0, 116.7, 116.6, 111.2 (q, [sup.1][J.sub.C-F] = 4.9 Hz), 53.0. Elemental analysis: calculated for [C.sub.39][H.sub.26][F.sub.6][N.sub.2][O.sub.3]: C, 68.42; H. 3.83; N, 4.09. Found: C, 68.19; H, 3.61; N, 4.21.
Synthesis of Polymers
The general procedure for the synthesis of novel aromatic polyamides containing both fluorene or xanthene cardo moieties and fluorinated phenoxy pendant groups can be illustrated by the preparation of polymer I.
A solution of 13 mL of DMAc containing pyridine (0.4 mL) and BAPF (1.065 g, 2 mmol) in a 50-mL flask was cooled to 0[degrees]C using an ice-water bath, and then 3F-IPC (0.726 g, 2 mmol) was added under a stream of N2. The mixture was stirred at 0[degrees]C for 5 h and the reaction was then continued overnight at room temperature. The resulting highly viscous polymer solution was poured slowly with stirring into methanol (100 mL). The precipitate was crushed, washed with methanol, and allowed to dry in air. The air-dried product was heated at 100[degrees]C overnight under vacuum to give polymer I as a white powder. The other polymers II-VIII were also prepared according to a similar procedure as mentioned above.
Elemental analysis was performed with Perkin-Elmer Model 2400 CHN analyzer. The FT-IR spectra of the monomers and polymers in KBr pellets (2%) were recorded using a Nicolet FT-IR (51 OP) spectrophotometer. [sup.1]H NMR (400 MHz) and [sup.13]C NMR (100 MHz) spectra were obtained with a Bruker Avance 400 MHz spectrometer at an operating temperature of 25[degrees]C using CD[Cl.sub.3] or DMSO-[d.sub.6] as a solvent. Inherent viscosities were obtained with a concentration of 0.5 g/dL in DMAc at 30[degrees]C using an Ubbelhode suspended level viscometer. The molecular weight distributions were measured by using a gel permeation chromatography (GPC). Tetrahydrofuran (THF) was used as the mobile phase and polystyrene as the standard. Differential scanning calorimetry (DSC) measurements were performed on a Mettler Toledo DSC 821e instrument at a heating rate of 10[degrees]C/min under nitrogen. The glass-transition temperature ([T.sub.g]) was taken in DSC curve as the center of the step transition in the second heating run. Thermogravimetric analysis (TGA) was performed on a Netzch Sta 449c thermal analyzer system at a heating rate of 10[degrees]C/min in nitrogen. The mechanical properties of the polymer films were measured on an Instron 1122 testing instrument at a cross-head speed of 10 mm [min.sup.-1] on strips (5 mm wide, 60 mm long, and ca 0.05 mm thick), and an average of at least three replicas was used. Wide-angle X-ray diffraction (WAXD) was measured with a Rigaku D/MAX-IIA X-ray diffractometer, using CuKa radiation, at 30 KV and 20 mA. The diffractograms were recorded at room temperature over the range of 10-40[degrees]. The dielectric constants were measured at 25[degrees]C and a frequency of 1 MHz using a dielectric analyzer (TA Instruments DEA 2970). Ultraviolet-visible (UV-vis) spectra of polymer films were recorded on a Shimadzu UV-1601 UV-vis spectrophotometer. Water uptake was determined by the weighing of the changes in the polymer film (50 X 50 X 0.05 [mm.sup.3]) before and after immersion in water at 25[degrees]C for 24 h.
RESULTS AND DISCUSSION
As outlined in Scheme 1, 9,9-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]xanthene (BAFPX) was synthesized in two steps according to a similar procedure for the synthesis of BAPX , The dinitro compound (BNFPX) was obtained by the aromatic nucleophilic substitution reaction of BHPX with 2-chloro-5-nitrobenzotrifluoride in the presence of [K.sub.2]C[O.sub.3] in DMF. The catalytic reduction of BNFPX to the diamine BAFPX was accomplished by means of hydrazine monohydrate as well as a catalytic amount of Pd/C. FT-IR, NMR spectroscopies, and elemental analysis were used to confirm the structure of BAFPX. FT-IR spectrum of BAFPX showed characteristic bands of amino group at 3467 and 3388 [cm.sup.-1] (N--H stretching) and the characteristic absorption of trifluoromethyl group at 1162 and 1129 [cm.sup.-1], respectively. [sup.1]H NMR spectrum of the diamine monomer showed N[H.sub.2] protons at 3.71 ppm, and assignments of other peaks are in good agreement with the proposed monomer structure. In addition, the elemental analytical results also revealed the successful preparation of BAFPX.
The low-temperature solution polycondensation technique was employed for the synthesis of novel aromatic polyamides containing both fluorene or xanthene cardo moieties and fluorinated phenoxy pendant groups as shown in Scheme 2. Polymers I--VIII were prepared via a one-step pathway by the polycondensation reaction of 1 equiv. of fluorinated isophthaloyl chloride with 1 equiv. of aromatic diamine in DMAc solution containing a trace of pyridine. The reaction temperature was maintained at 0[degrees]C in the initial 5 h. To obtain high-molecular-weight polymers, the reaction was then allowed to proceed overnight at room temperature. All polymerization proceeded homogeneously throughout the reaction, and the resulting polymers were isolated as fibers or powders with an almost quantitative yield (94-96%). The polyamides I--VIII had inherent viscosities of 0.75-0.88 dL/g (Table 1) and could be solution-cast into films. The number-average molecular weights ranged from 38,900 to 52,200, and the polydispersities ranged from 1.54 to 2.02. The elemental analyses of polymers I--VIII are also summarized in Table 1. The elemental analysis values were in good agreement with the calculated ones, and in all cases, the carbon values are found to be lower than the calculated ones for the proposed structures due to the absorption of moisture.
The chain structures of the polyamides I--VIII were confirmed using FTIR and [sup.1]H NMR spectroscopy. The FTIR spectra of all the polymers exhibited characteristic absorptions of the amide group around 3400 (N--H stretching), 1665 (C=0 stretching), and 1500-1550 cm-1 (combined N--H bending and C--N stretching), and a band around 1125 [cm.sup.-1] (C--F stretching). A strong absorption band was observed around 1240 [cm.sup.-1] due to the Ar--O--Ar linkage. Figure 1 shows the typical FTIR spectrum of polymer I. The [sup.1]H NMR spectra of the polyamides showed a sharp singlet around [delta]= 10-11 ppm corresponding to the formation of an amide group, and assignments of other peaks are also in good agreement with the proposed polymer structures. The [sup.1]H NMR spectrum of polymer I is illustrated in Fig. 2.
The crystallinities of the polymers were evaluated by WAXD. The results of WAXD measurement of the polymers I-VIII are shown in Fig. 3. All the polymers obtained displayed amorphous patterns. We can interpret the result by the presence of the flexible fluorinated phenoxy pendant groups and bulky fluorene or xanthene cardo structures, which inhibited the close packing of the polymer chains and weakened intermolecular hydrogen bonding, thus resulting in the amorphous nature of these polyamides.
The solubility behavior of polyamides I--VIII was tested in various organic solvents qualitatively, and the results are summarized in Table 2. It can be seen that all the polyamides were readily soluble in both strong polar solvents such as N-methyl2-pyrroIidinone (NMP), DMAc, DMF, DMSO, or m-cresol and some common organic solvents such as THF, pyridine (Py), and acetone. Moreover, when comparing the polyamides derived from 3F-IPC and 6F-IPC, it is found that the polyamides based on 6F-IPC exhibited better solubility than those based on 3FIPC because of the high fluorine content and steric hindrance. For example, the polyamides V-VIII exhibited higher solubility, which could even be dissolved in acetone at room temperature. It is evident that excellent solubility of the polyamides was affected by their amorphous structures. These new polyamides exhibited higher solubility than the conventional aromatic polyamides, which is attributed to the presence of fluorinated phenoxy pendant groups and bulky fluorene or xanthene cardo structures in the polymer backbone, which resulted in the decrease in the interaction of polymer chains by increasing the distance between polymer chains. Consequently, the solvent molecules can penetrate easily and solubilize the polymer chains.
The thermal properties of all the polyamides were evaluated by DSC and TGA, and the results are summarized in Table 3. Their amorphous characters were supported by no melting peak ([T.sub.m]) detected by DSC (Fig. 4). The [T.sub.g]s of the polymers were in the range of 237-259[degrees]C, depending on the structures of the polyamides. In general, the 6F-IPC-based polyamides showed lower [T.sub.g] values than the corresponding 3F-IPC-based polyamides. The [T.sub.g] value of polymer V is 18[degrees]C lower than that of polymer I (259[degrees]C). This result might be attributed to the fact that pendant 3,5-bis(trifluoromethyl)phenoxy group is more effective than pendant 4-(trifluoromethyl)phenoxy group for the increasing the conformational freedom of the polymer chain, which resulted in a decrease in [T.sub.g]. In addition, the polyamides containing xanthene cardo groups exhibited slightly lower [T.sub.g] values than the corresponding polyamides containing fluorene cardo groups because xanthene cardo group contains a flexible ether linkage. For example, the [T.sub.g] value of polymer III or IV is 6[degrees]C lower than that of the corresponding polymer I or II, respectively. Also, the [T.sub.g] value of polymer VII or VIII is 4[degrees]C lower than that of the corresponding polymer V or VI, respectively.
As shown in Table 3, the design of polyamides with the incorporation of fluorinated phenoxy pendant group and bulky fluorene or xanthene cardo structure provides not only excellent solubility but also high thermal stability. Polymers I--VIII had the onset decomposition temperatures in the range of 421-449[degrees]C, the temperatures at 5 and 10% weight loss in the range of 437-476 and 489-517[degrees]C, respectively. In addition, these polymers remained 53-62% of original weight at 800[degrees]C in nitrogen. The typical TGA curves of the polymers II, V, and VII are shown in Fig. 5.
All the polymers possessed outstanding film-forming properties. Highly transparent, flexible polyamide films were easily prepared by casting the homogeneous polymer solutions in DM Ac (10 wt% solid content) on a glass plate, followed by thermally baking with the following procedure: 80[degrees]C/12 h, 120[degrees]C/6 h, and 150[degrees]C/2 h. The mechanical properties of these polyamide films are listed in Table 4. The values of the tensile strength varied in the range of 70.6-87.5 MPa, the tensile modulus varied in the range of 2.23-2.78 GPa, and the elongation at break varied in the range of 5.8-8.7%. All the polyamides exhibited good mechanical properties, which suggested that these polyamides could be considered as engineering plastics.
The optical properties of these polymer films with thickness of ~50 [micro]m were evaluated by UV-vis spectroscopy, and the transmission UV--vis spectra of the typical polyamide films are presented in Fig. 6. The transparency of the polymer films was evaluated at the wavelengths from 200 to 800 nm, and the UV data of all the polyamides at several wavelengths are given in Table 5. As shown in Table 5, the cutoff wavelengths of these polymer films ranging from 352 to 368 nm were lower than 370 nm, indicating that all the polyamides were colorless and had high transmittance. For example, all the polyamide films exhibited high-optical transparency higher than 80% transmittance at 500 nm. The optical properties of the resulting polyamides were improved in two ways. Polyamides with a bulky cardo group or a bulky pendant group in the polymer chains had good optical transparency because of the restriction of molecular alignment, and therefore disturbed effective formation of charge-transfer-complex (CTC) between polymer chains. Moreover, the extent of donor-acceptor complex formation could also be further decreased by lowering of the degree of charge separation along the polymer chain through the introduction of electron-withdrawing C[F.sub.3] groups into the polymer backbone.
The electrical insulating properties of these polyamide films were evaluated on the basis of the dielectric constants, measured by the parallel plate capacitor method using a dielectric analyzer. The dielectric properties of polymer films were also affected by the water absorption. As can be seen from Table 5, polymers I-VIII had lower water uptakes in the range of 1.06-1.43% due to the fluorine incorporation. The polymers VI and VIII showed obvious low water uptakes--which are 1.06 and 1.09%, respectively--because of the high fluorine content. The dielectric constants of these polyamides were in the range of 3.24-3.45 (1 MHz, Table 5). All the polyamides exhibited lower dielectric constants than commercial Nylatron (ca 3.7 at 1 MHz) due to their lower water uptakes. The decreased dielectric constants of these fluorinated polyamides could be attributed to the incorporation of fluorine substituents into polymers because of the small dipole and the low polarizability of the C--F bond as well as the increase in the free volume and also because of the decrease in the water absorption [46, 47], Additionally, the incorporation of bulky fluorene or xanthene cardo groups into polymer backbones can result in a less efficient chain packing and further reduce the number of polarizable groups per unit volume, thus also decreasing the dielectric constant.
A series of highly organosoluble and optically transparent polyamides containing both fluorene or xanthene cardo structures and fluorinated phenoxy pendant groups were synthesized from two fluorinated isophthaloyl chlorides and four diamines containing cardo groups by the low-temperature solution polycondensation. Experimental results indicated that the obtained polyamides exhibited excellent solubility in many organic solvents and could form transparent, strong, and flexible films with good thermal stability and mechanical properties, low dielectric constants and water absorptions, and high optical transparency. These characteristics indicated that these polyamides could be considered as new possible candidates for processable high-performance engineering plastics and promising photoelectric materials for use in optical communication applications.
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Huan Wen, Bin Huang, Feihua Zou, Mingzhong Cai
Department of Chemistry, Jiangxi Normal University, Nanchang 330022, People's Republic of China
Correspondence to: M. Cai; e-mail: firstname.lastname@example.org Contract grant sponsor: National Natural Science Foundation of China; contract grant number: 21664008: contract grant sponsor: Natural Science Foundation of Jiangxi Province of China; contract grant number: 20132BAB203015.
Published online in Wiley Online Library (wileyonIinelibrary.com).
Caption: SCHEME 1. Preparation of BAFPX.
Caption: SCHEME 2. Preparation of polymers.
Caption: FIG. 1. FTIR spectrum of polymer I.
Caption: FIG. 2. [sup.1]H NMR spectrum of polymer I.
Caption: FIG. 3. WAXD patterns of polymers I-VIII.
Caption: FIG. 4. DSC curves of polymers I--VIII.
Caption: FIG. 5. TGA curves of polymers II, V, and VII.
Caption: FIG. 6. UV-vis spectra of various polyamide films (I, IV, V, and VIII).
TABLE 1. Physical properties and elemental analyses of polyamides I-VIII. Polymer [[eta].sub.inh] Polymer component (a) (dL/g) I 3F-IPC/BAPF 0.88 II 3F-IPC/BAFPF 0.82 III 3F-IPC/BAPX 0.79 IV 3F-IPC/BAFPX 0.75 V 6F-IPC/BAPF 0.80 VI 6F-IPC/BAFPF 0.85 VII 6F-IPC/BAPX 0.77 VIII 6F-IPC/BAFPX 0.78 Polymer [M.sub.n] (b) [P.sub.d] (c) I 52200 1.76 II 48600 1.92 III 43400 1.54 IV 39700 1.87 V 49100 1.63 VI 51400 2.02 VII 38900 1.59 VIII 41400 1.92 Elemental analysis Polymer C (%) H (%) N (%) I Calcd. 75.90 4.04 3.40 Found 75.62 4.29 3.13 II Calcd. 67.64 3.26 2.92 Found 67.38 3.07 2.65 III Calcd. 74.46 3.97 3.34 Found 73.59 4.12 2.83 IV Calcd. 66.53 3.21 2.87 Found 66.19 3.50 2.45 V Calcd. 71.46 3.62 3.14 Found 70.79 3.84 2.62 VI Calcd. 64.33 2.94 2.73 Found 63.45 2.75 2.47 VII Calcd. 70.20 3.56 3.09 Found 69.49 3.38 2.57 VIII Calcd. 63.35 2.90 2.69 Found 62.68 3.17 2.23 (a) Inherent viscosity determined at a concentration of 0.5 g/dL in DMAc at 30[degrees]C. (b) Measured by GPC in THF with PS as a standard. (c) The polydispersity ([P.sub.d]) was obtained by [M.sub.w]/[M.sub.n]. TABLE 2. Solubility behavior of polyamides I-VIII. (a) Polymer NMP DMAc DMF DMSO m-Cresol I ++ ++ ++ ++ ++ II ++ ++ ++ ++ ++ III ++ ++ ++ ++ ++ IV ++ ++ ++ ++ ++ V ++ ++ ++ ++ ++ VI ++ ++ ++ ++ ++ VII ++ ++ ++ ++ ++ VIII ++ ++ ++ ++ ++ Polymer Py THF CH[Cl.sub.3] acetone EtOH I ++ ++ - + - II ++ ++ - + - III ++ ++ - + - IV ++ ++ - + - V ++ ++ - ++ - VI ++ ++ - ++ - VII ++ ++ - ++ - VIII ++ ++ - ++ - (a) The solubility was determined at a 3% solid concentration. ++ = soluble at room temperature; + = soluble on heating at 60[degrees]C; +- = partially soluble on heating at 60[degrees]C; - = insoluble at 60[degrees]C. TABLE 3. Thermal properties of polyamides I-VIII. Polymer [T.sub.g] [T.sub.d] (a) [T.sub.5] (b) ([degrees]C) ([degrees]C) ([degrees]C) I 259 422 437 II 258 429 441 III 253 441 471 IV 252 425 442 V 241 449 476 VI 249 431 454 VII 237 434 461 VIII 245 421 441 Polymer [T.sub.10] (c) [R.sub.w] (d) ([degrees]C) (%) I 498 62 II 496 61 III 515 58 IV 493 54 V 517 57 VI 502 56 VII 511 58 VIII 489 53 (a) [T.sub.d]: onset decomposition temperature. (b) [T.sub.5]: the decomposition temperature at 5% weight loss. (c) [T.sub.10]: the decomposition temperature at 10% weight loss. (d) [R.sub.w]: residual weight retention at 800[degrees]C. TABLE 4. Mechanical properties of polyamides I-VIII. Polymer Tensile Tensile Elongation strength (MPa) modulus (GPa) at break (%) I 87.5 2.66 6.8 II 75.7 2.38 7.1 111 84.9 2.23 8.7 IV 74.2 2.25 6.2 V 79.8 2.52 6.6 VI 86.7 2.45 7.5 VII 81.1 2.78 5.8 VIII 70.6 2.67 6.3 TABLE 5. Optical transparency and dielectric constants of polyamides I-VIII. Polymer [[lambda].sub.cut] Transparency 600 (nm) (a) (nm) (%) at 500 (nm) I 368 84 85 II 354 85 87 III 367 81 84 IV 352 81 84 V 367 86 88 VI 368 83 87 VII 361 86 88 VIII 356 84 86 Polymer 700 (nm) [W.sub.u] [D.sub.c] (b) (%) (c) (1 MHz) I 86 1.39 3.43 II 88 1.23 3.36 III 85 1.43 3.45 IV 84 1.25 3.37 V 88 1.28 3.39 VI 87 1.06 3.24 VII 88 1.30 3.38 VIII 87 1.09 3.26 (a) [[lambda].sub.cut]: cutoff wavelength. (b) [W.sub.u]: water uptake. (c) [D.sub.c]: dielectric constant.
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|Author:||Wen, Huan; Huang, Bin; Zou, Feihua; Cai, Mingzhong|
|Publication:||Polymer Engineering and Science|
|Date:||Nov 1, 2017|
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