Synthesis and properties of new soluble poly(amide-imide-imide)s.
Aromatic polyamides, a kind of polymer material with superior mechanical strength (1, 2), are synthesized from aromatic diamines and aromatic dicarboxylic acids. DuPont Kevlar[R] [poly(p-phenylene) terephthalamide] and DuPont Nomex[R] [poly(m-phenylene)isophthalamide] are commercially marketed as high-performance polymers usually in fiber form. With their intermolecular hydrogen bonds, most polyamides have good solubility in polar amide solvents and are widely used for a variety of applications (1-5). Aromatic polyimides possess outstanding thermal behavior and are noted for their excellent physical and electrical/insulating properties (1, 3). However, polyimides are difficult to process because of their high softening or melting temperatures and their insoluble nature. To overcome this drawback, various copolymers have been developed and reported (6-12), among them poly(amide-imide)s, whose amide groups can improve the solubility.
Poly(amide-imide)s usually have been synthesized through three main routes. The first route goes through the amide-imide-forming reaction, by which trimellitic anhydride (TMA) reacts either with diisocyanate to produce poly(amide-imide) (13-16) or with thionyl chloride to synthesize TMA-chloride before the latter and diamine can produce poly(amide-imide) (17). The second route goes through the imide-forming reaction, with amide-containing monomer serving as a medium; for example, amide-containing diamine is polycondensed with dianhydride to provide the poly(amide amic acid), which is then dehydrated to obtain poly(amide-imide) (18, 19). The last route goes through the amide-forming reaction from imide-containing monomers such as dicarboxylic acids or diamines. Imide-containing dicarboxylic acids usually come from the thermal imidization of diamines and TMA (20-26), from the condensation of dicarboxylic anhydride and amino acids (27-29), or from the dehydration of aromatic amino acids and TMA (30-32). Therefor e, aromatic poly(amide-imide)s can be synthesized by the polycondensation of the imide-containing dicarboxylic acid obtained and aromatic diamines.
In our laboratory, the dicarboxylic acid, N,N'-bis(4-carboxyphenyl)-4,4'-oxydiphthalimide was prepared from the flexible ether group-containing ODPA and the symmetrical p-ABA. A series of poly(amide-imide)s (series IV, Fig. 1) was synthesized from the diacid and various aromatic diamines (33). However, these polymers showed limited solubilities and poor film-forming ability. Besides, it was found that polyimide (V) synthesized from ODPA and MDA had excellent mechanical property, but its solubility was also poor. In this study, MDA, p-ABA, and ODPA were used to prepare a new-type tetraimide-dicarboxylic acid, which then reacted with various diamines to form poly/amideimide-imide)s ([III.sub.a-i]) by direct polycondensation. It was expected that synthesized polymers had significant improvement in solubilities and mechanical properties. Various properties of the resultant poly(amideimide-imide)s will be investigated and are compared with those of corresponding poly(amide-imide)s IV.
ODPA, that is, 4,4'-oxydiphthalic anhydride (Chriskev), was recrystallized from acetic anhydride before use. p-Aminobenzoic acid (p-ABA, TCI) and m-phenylenediamine ([II.sub.a], TCI) were vacuum-distilled before use. Other diamines including 4,4'-oxydianiline ([II.sub.b], TCI), 4,4'-thiodianiline ([II.sub.c], Chriskev), 4,4'-methylenedianiline (MDA) ([II.sub.d], TCI), 1,4-bis(4-aminophenoxy)benzene ([II.sub.e], TCI), 1,3-bis(4-aminophenoxy)benzene ([II.sub.f], TCI), 2,2-bis[4-(4-aminophenoxy)phenyl]propane ([II.sub.g], Chriskev), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane ([II.sub.h], TCI), and 2,2-bis[4-(4-aminophenoxy)phenyl] sulfone ([II.sub.i], Chriskev) were used as received. N-Methyl-2-pyrrolidinone (NMP, Fluka) and pyridine (Py, Wako) were purified by distillation under reduced pressure over calcium hydride and stored over 4A molecular sieves. Triphenyl phosphite (TPP, TCI) was used as received. Commercially available anhydrous calcium chloride ([CaCl.sub.2]) was dried under reduced pressure at 150[degrees]C for 6 h prior to use.
Synthesis of Tetraimide-Dicarboxylic Acid (I)
A mixture of 2.192 g (l6 mmol) of p-ABA and 1.590 g (8 mmol) of MDA was first dissolved in 48 mL of NMP. After the mixture was completely dissolved, 4.960 g (16 mmol) of ODPA was added to it in one portion. The mixture was stirred at room temperature for 2 h. About 10 mL of toluene was then added, and the mixture was heated at the reflux for about 3 h until about 0.7 mL of water was distilled off azeotropically via a Dean-Stark trap. After complete removal of water, the residual toluene was then distilled off under reduced pressure. After cooling, the obtained solution was trickled into water and the precipitated product was collected by filtration, washed several times with water, and dried in a vacuum to give diacid I; main m.p. 334[degrees]C (by DSC).
IR (KBr): 3500-2500 (acid -OH), 1778 (imide, symmetric C=O stretching), 1720 (acid C=O stretching and asymmetric imide C=O stretching), 1377 (imide, imide ring vibration, axial), 1088 (imide, imide ring vibration, transverse) and 744 [cm.sup.-1] (imide, imide ring vibration, out of plane).
[H.sup.1] NMR (400 MHz, DMSO-[d.sub.6]): [delta] = 8.11, 8.09, 8.05 ([H.sub.a] + [H.sub.e]), 7.65, 7.62, 7.61 ([H.sub.b] + [H.sub.c] + [H.sub.d]), 7.45 ([H.sub.f]), 7.39 ([H.sub.g]), 4.10 ppm ([H.sub.h]).
[C.sup.13] NMR (100 MHz, DMSO-[d.sub.6]) [delta] = 168.75 ([C.sup.1]), 168.32, 168.13, 167.92, 167.76 ([C.sup.6] + [C.sup.7]), 162.88, 162.84, 162.70 ([C.sup.10]), 142.77 ([C.sup.5]), 137.35 ([C.sup.17]), 136.03 ([C.sup.14]), 131.60 ([C.sup.8]), 131.45 ([C.sup.3]), 130.74 ([C.sup.16]), 128.89 ([C.sup.12]), 128.64 ([C.sup.2]), 128.45 ([C.sup.4]), 127.75, 127.59 ([C.sup.13] + [C.sup.15]), 126.59 ([C.sup.11]), 115.17 ([C.sup.9]), 42.59 ppm ([C.sup.18]).
[C.sup.13] NMR (100 MHz, DMSO-[d.sub.6]) [delta] = 168.75 ([C.sup.1]), 168.32, 168.13, 167.92, 167.76 ([C.sup.6] + [C.sup.7]), 162.88, 162.84, 162.70 ([C.sup.10]), 142.77 ([C.sup.5]), 137.35 ([C.sup.17]), 136.03 ([C.sup.14]), 131.60 ([C.sup.8]), 131.45 ([C.sup.3]), 130.74 ([C.sup.16]), 128.89 ([C.sup.12]), 128.64 ([C.sup.2])128.45 ([C.sup.4]), 127.75, 127.59 ([C.sup.13] + [C.sup.15]), 126.59 ([C.sup.11]), 115.17 ([C.sup.9]), 42.59 ppm ([C.sup.18]).
Synthesis of Poly(amide-imide-imide)s
A typical example of polycondensation is described as follows. A mixture of 1.021 g (1 mmol) of tetraimidediacid I, 0.518 g (1 mmol) of diamine [II.sub.h], 0.30 g of [CaCl.sub.2] 0.9 mL of Py, 0.6 mL of TPP and 6.0 mL of NMP was heated while being stirred at 100[degrees]C for 3 h. The viscosity of reaction solutions increased after 1 h, and an additional 2.0 mL of NMP was added to the reaction mixture. At the end of the reaction, the obtained polymer solution was trickled into 400 mL of stirred methanol. The stringy polymer was washed thoroughly with hot water and methanol, collected by filtration and dried at 100[degrees]C under reduced pressure. The inherent viscosity of the polymer in DMAc at a 0.5 g/dL concentration at 30[degrees]C was 1.01 dL/g. All other poly(amide-imide-imide)s were synthesized in a similar procedure.
Preparation of the Poly(amide-imide-imide) Films
A polymer solution of approximately 10% was made by the dissolving of poly(amide-imide-imide) in DMAc. The solution was poured into a glass culture dish 9 cm in diameter that was placed in a 90[degrees]C oven overnight to remove the solvent. Then, the obtained semidried polymer film was stripped from the glass substrate and further dried in vacuum at 160[degrees]C for 6 h. The obtained films were about 0.05 mm thick.
[H.sup.1] and [C.sup.13] NMR spectra were determined on a Jeol EX-400 FT-NMR spectrometer. Infrared spectra were recorded on a Horiba Fourier-Transform Infrared Spectrometer FTIR-720. Elemental analyses were carried out with a Perkin-Elmer Model 2400 C, H, N analyzer. The inherent viscosities of all polymers were determined using a Cannon-Fenske viscometer. Differential scanning calorimeter (DSC) traces were measured on TA Instruments DSC 2010 at the rate of 15[degrees]C/min in flowing nitrogen (40 [cm.sup.3]/min). Glass transition temperatures were read as the midpoint of the heat capacity jump and were taken from the second heating scan after a quick cooling down from 400[degrees]C. Thermogravimetry analysis (TGA) was conducted with a TA Instrument TGA 2050. Experiments were carried out on 10 [+ or -] 2 mg samples heated in flowing nitrogen or air (100 [cm.sup.3]/min) at a heating rate of 20[degrees]C/min An Instron Universal Tester Model 1130 with a load cell of 5 kg was used to study the stress-strain beh avior of the sample. A gauge of 2 cm and a strain rate of 5 cm/min were adopted for this study. Measurements were performed at room temperature with film specimens (0.5 cm wide, 6 cm long, and about 0.05 mm thick), and an average of at least five individual determinations was reported.
RESULTS AND DISCUSSION
Synthesis of Tetraimide-Diacid and Poly(amide-imide-imide)s
Tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of MDA, ODPA, and p-ABA in a 1:2:2 molar ratio at room temperature in amide-type solvent (such as NMP or DMAc), followed by intramolecular cyclodehydration of the intermediate tetramic acid I' (Fig. 2). The addition of p-ABA. ODPA, and MDA may not form the structure of tetramic acid I' completely in the initial period, and some other diacids (Fig. 3) were produced. However, the exchange reaction of amic acid was carried out during a long stirring time (34), and the product with the lowest free energy was prepared. From the molar ratio of monomers, I' is a more stable structure among intermediates. Therefore, a higher purity of tetraimide-di-acid I might be obtained after the cyclodehydration of I'. The structures of diacid I were confirmed by elemental analysis and IR, [H.sup.1] NMR, and [C.sup.13] spectroscopy.
The FT-IR characteristic absorptions of diacid I are shown in Fig. 4. As the diacid was prepared, the characteristic absorption bands of the imide ring were observed at 1778, 1720, 1377, 1088, and 744 [cm.sup.-1], and those of the anhydride and carboxyl groups of monomers at 1851 (acid C=O) and 1269 (C-O-C) [cm.sup.-1] disappeared. The diacid I is also confirmed by NMR spectra. In the [H.sup.1] NMR spectrum (Fig. 5), the protons [H.sub.a] and [H.sub.e] adjacent to the carbonyl acid or imide ring (ortho-oriented protons) resonated at the farthest downfield region, owing to the inductive effect and resonance; the [H.sub.b] meta-oriented to carboxylic acid and [H.sub.c,d] ortho-oriented to aromatic ether shifted to the upfield region, due to the shielding effect. The [H.sub.f,g] appeared at higher filed than the rest protons in that it was less affected by other groups. To calculate purity of I, it was assumed that the structures of m = 0 and m = 1 were the main components, so that the proportion of m = 1 could be x and that of m = 0 could be y. From the integral ratios of protons [H.sub.b,c,d] and [H.sub.f,g] in Fig. 5:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]
It was noticed that x was about 70%; therefore, the structure of m = 1 was the main component in diacid I. The [C.sup.13] NMR spectrum of I shows 22 signals due to the different diacids in I (Fig. 6). The same carbon position of each diacid component in I might have different chemical environments.
A series of poly(amide-imide-imide)s [III.sub.a-1] was synthesized from I and various diamines by means of direct polycondensation with TPP/Py as the condensing agent in NMP in the presence of calcium chloride. Polymerization can also proceed directly using the resultant solution of diacid synthesis. The results of the preparation of poly(amide-imide-imide)s are summarized in Table 1. All the reactions went on smoothly in homogeneous solutions under conditions listed in Table 1. In some cases, higher molecular weights of these polymers could be obtained by using a higher initial reactant concentration and adding a proper amount of supplemental NMP into the viscous reaction medium before the formation of swollen gel. Besides, an advantage of poly(amide-imide-imide) synthesis from large molecular weight I is that a large product can be obtained by using a small amount of TPP. In other words, when the same amount of TPP is used, the same mole of a polymer in this study and in other reports is formed, but the wei ght of the polymer in this study is larger. Therefore, new-type poly(amide-imide-imide)s could significantly reduce the synthetic cost and were thus helpful in industrializing direct polycondensation.
The inherent viscosities of the III series polymers were 0.78-1.45 dL/g. Most of the poly(amide-imide-imide)s could be solution cast into transparent and tough films, indicating a high molecular weight. The composition and structures of these poly(amide-imide-imide)s were characterized by their IR spectra and elemental analyses. A typical IR spectrum is shown in Fig. 4. The FT-IR spectrum of polymer [III.sub.h] exhibited characteristic absorption bands for the imide ring at 1778, 1724 (asymmetrical and symmetrical C=O stretching vibration), 1373 (C-N stretching vibration), 1088, and 746 [cm.sup.-1] (imide ring deformation). The absorptions of amide groups appeared at 3363 (N-H stretch) and 1674 [cm.sup.-1] (C=O stretch). The results of the elemental analysis of all the poly(amide-imide-imide)s are listed in Table 1. In all cases, however, the carbon values were found to be lower than the calculated ones for the proposed structures. This is possibly caused by the hygroscopic nature of the amide groups of these polymers. The uptakes of water were in the range of 1.08%-2.28%, which could be calculated from the weight change of the vacuum-dried polymer samples after they were exposed in the air at room temperature for 1 h. When the values found were corrected by eliminating the amount of absorbed water, the correction values were in good agreement with the calculated ones.
The qualitative solubility of poly(amide-imide-imide)s in various solvents is listed in Table 2. Concentration for the solubility tests is 0.05 g/mL. All polymers had excellent solubilities in NMP, DMAc, DMSO, and mcresol. The solubilities of series III polymers varied with the structures of diamines used in the synthesis. [III.sub.a-f] had poor solubilities in DMF and Py, and [III.sub.d,o] with stiff Ar structures of diphenylmethane and paralinked triphenylene-diether were soluble in DMAc and DMSO after heating. [III.sub.g-i] with Ar structure of the flexible group (such as isopropylidene, hexafluoroisopropylidene, and sulfone) showed the best solubilities among these polymers and could be dissolved in all testing solvents at room temperature. Compared with [IV.sub.a-i] and V, the III series polymers clearly exhibited a better solubility. Moreover, the phenomenon of combining insoluble polyimide V with insoluble poly(amide-imide)s [IV.sub.b-f] to form soluble poly(amide-imide-imide)s [III.sub.b-f] was more i nteresting. It may be due to the fact that the mixed diacid I makes the polymer chain heterogeneous and chain-packing disordered, thus enabling solvent molecules to diffuse easily into the polymer chains.
With the exception of the brittle behavior of polymer [III.sub.i] all the poly(amide-imide-imide)s were cast into transparent, flexible, and tough films from polymer solutions of DMAc. All the polymers were structurally characterized by X-ray diffraction studies. Most of the polymers displayed a nearly completely amorphous pattern, whereas [III.sub.i] revealed a semicrystalline pattern. The mechanical properties of the polymer films were determined by an Instron machine. The results are summarized in Table 3. These films had strengths at break of 87-107 MPa. elongations at break of 9%-14%, and initial moduli of 2.0-2.4 GPa. Several poly(amide-imide-imide)s in this series necked under tension and exhibited moderate elongation to break, indicating a ductile nature. This series of poly(amideimide-imide)s all possessed good mechanical properties, suggesting that these poly(amide-imide-imide)s can be applied as new materials for engineering plastics. On comparing mechanical properties of polymers III with their an alogous IV, series III polymers showed good film-forming ability. Except for [IV.sub.a], the other polymers [IV.sub.b-i] could not be cast into films or formed brittle films, owing to poor solubility and high level of crystallinity (33). Polymers III bad mechanical properties similar to [IV.sub.a] and V, but most of them had yield strengths in the range of 94-107 MPa.
The thermal properties of all the poly(amide-imide-imide)s were evaluated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal behavior data of all polymers are listed in Table 4. DSC measurements were conducted at a heating rate of 15[degrees]C/min in nitrogen. Quenching from the elevated temperatures (approximately 400[degrees]C) to room temperature in air gave predominantly amorphous samples so that the glass transition temperatures ([T.sub.g]) of almost all poly(amide-imide-imide)s could be easily measured in the second heating traces of DSC. The [T.sub.g] values of the poly(amide-imide-imide)s III were in the range of 270[degrees]C-309[degrees]C, depending on the structure of the diamine component and following with the increasing stiffness of the polymer backbones. [III.sub.a] containing the mono-phenylene group in diamine, which had higher rigidity, exhibited the highest [T.sub.g] value. [III.sub.e], whose diamine structures were all para-oriented, showed higher [T.sub.g] values than did [III.sub.f], derived from meta-oriented diamines. A comparison of [III.sub.g] with [III.sub.h,i] revealed that [III.sub.i] with the polar sulfone groups in polymer backbones possessed the highest [T.sub.g] value among them. [III.sub.h] based on [II.sub.h] with a bulky hexafluoropropane group increased steric hindrances, so their macromolecular chains rotated at higher temperature. [III.sub.g] had structures analogous to [III.sub.h], but the substituent magnitude of -[CH.sub.3] was much smaller than that of -[CF.sub.3]. Therefore, free volume between [III.sub.g] main chains may be increased without a steric hindrance, leading to lower [T.sub.g] value. When comparing [III.sub.a-i] with [IV.sub.a-i], the III series displayed higher [T.sub.g] values than the corresponding IV. This was attributed to the higher proportion of the imide group in the III series polymer backbones.
The thermostabilities of the poly(amide-imide-imide)s were examined by TGA measurements. The temperatures at 10% weight loss ([T.sub.10]) in nitrogen atmosphere were determined from the original thermograms and are tabulated in Table 4. [T.sub.10] values of polymers III were in the range of 540[degrees]C-570[degrees]C. The thermogravimetric traces indicate that polymers III possess high thermal stability with no significant weight loss up to approximately 500[degrees]C. The char yields of all polymers at 800[degrees]C were above 52%. A comparison of diamines showed that [T.sub.10] of the p-diphenoxybenzene-containing [III.sub.e] was higher than that of m-diphenoxybenzene-containing [III.sub.f]. This might be due to the stiff structure that caused a higher packing density of polymer chains. The fluorine-containing poly(amide-imide-imide) [III.sub.h] had a slightly better thermal stability than its nonfluoro analogous [III.sub.g] did because the C--F bond of the [CF.sub.3] group is stronger than that of the [CH.sub.3] group. [III.sub.i] bearing a sulfonyl group in diamine moiety exhibited lower [T.sub.10] than the other polymers did because of the weak bonding of the C--S bond and the easy degradation in the heating process. When compared with polymers IV, most of series III had higher [T.sub.10] values and char yields as a result of a higher proportion of the thermo-stable imide group in the main chain. Polymers [III.sub.a-i] also exhibited excellent thermal stability as did polyimide V. and their solubilities were improved.
A series of new-type poly(amide-imide-imide)s [III.sub.a-i] with moderate to high molecular weights was successfully synthesized. These polymers showed excellent solubilities and could be made into transparent and tough films upon casting from DMAc solution, reflecting good film-forming ability. The mechanical properties of the polymer films were flexible and tough, and some polymers exhibited yield points. Besides, these polymers were characterized by excellent thermal stability as well as high transition temperatures, demonstrating a good combination of properties and processability.
[FIGURE 4 OMITTED]
[FIGURE 6 OMITTED]
Table 1. Synthesis and Elemental Analysis of Poly(amide-imide-imide)s. Additional amount of [CaCl.sub.2] [eta]inh (b) Polymer (a) NMP (mL) (g) (dL/g) [III.sub.a] -- 0.30 0.83 [III.sub.b] 4 0.30 0.80 [III.sub.c] 2 0.30 0.78 [III.sub.d] 2 0.30 1.16 (c) [III.sub.e] 4 0.35 1.45 (c) [III.sub.f] 2 0.30 0.89 [III.sub.g] -- 0.30 0.93 [III.sub.h] 2 0.30 1.01 [III.sub.i] -- 0.30 0.84 Formula Polymer (a) [M.sub.W] [III.sub.a] [([C.sub.65][H.sub.36][N.sub.6] Calcd [O.sub.12]).sub.n] [(1093.03).sub.n] Found Corrected [III.sub.b] [([C.sub.71][H.sub.40][N.sub.6] Calcd [O.sub.13]).sub.n] [(1185.13).sub.n] Found Corrected [III.sub.c] [([C.sub.71][H.sub.40][N.sub.6] Calcd [O.sub.12]S).sub.n] [(1201.19).sub.n] Found Corrected [III.sub.d] [([C.sub.72][H.sub.42][N.sub.6] Calcd [O.sub.12]).sub.n] [(1183.16).sub.n] Found Corrected [III.sub.e] [([C.sub.77][H.sub.44][N.sub.6] Calcd [O.sub.14]).sub.n] [(1277.23).sub.n] Found Corrected [III.sub.f] [([C.sub.77][H.sub.44][N.sub.6] Calcd [O.sub.14]).sub.n] [(1277.23).sub.n] Found Corrected [III.sub.g] [([C.sub.86][H.sub.54][N.sub.6] Calcd [O.sub.14]).sub.n] [(1395.41).sub.n] Found Corrected [III.sub.h] [([C.sub.86][H.sub.48][N.sub.6] Calcd [O.sub.14][F.sub.6]).sub.n] [(1503.35).sub.n] Found Corrected [III.sub.i] [([C.sub.83][H.sub.48][N.sub.6] Calcd [O.sub.16]S).sub.n] [(1417.38).sub.n] Found Corrected Elemental analysis (d) (%) Moisture uptake (e) Polymer (a) C H N (%) [III.sub.a] 71.43 3.32 7.69 69.80 3.48 7.50 2.28 71.39 3.40 7.67 [III.sub.b] 71.96 3.40 7.09 70.38 3.47 6.91 2.06 71.83 3.40 7.05 [III.sub.c] 70.99 3.36 7.00 69.38 3.47 6.82 2.27 70.95 3.39 6.97 [III.sub.d] 73.09 3.58 7.10 71.75 3.64 6.91 1.83 73.06 3.57 7.04 [III.sub.e] 72.41 3.47 6.58 71.34 3.55 6.41 1.48 72.40 3.50 6.50 [III.sub.f] 72.41 3.47 6.58 71.37 3.50 6.47 1.44 72.40 3.54 6.56 [III.sub.g] 74.02 3.90 6.02 72.99 4.02 5.89 1.39 74.00 3.96 5.97 [III.sub.h] 68.71 3.22 5.59 67.97 3.28 5.52 1.08 68.70 3.24 5.58 [III.sub.i] 70.33 3.41 5.93 69.19 3.55 5.85 1.62 70.31 3.49 5.94 (a)Polymerization was carried out with 1 mmol of each monomer, 0.6 mL of triphenyl phosphite and 0.9 mL of pyridine in 6 mL of NMP at 100[degrees]C for 3 h. (b)Measured at a concentration of 0.5 g/dL in DMAc at 30[degrees]C. (c)Measured at a concentration of 0.5 g/dL in DMAc + 5% LiCi at 30[degrees]C. (d)For C and N: Corrected value = found value X (100% + moisture uptake %). For H: Corrected value = found value X (100% -- moisture uptake %). (e)Moisture uptake (%) = [(W - [W.sub.0])/[W.sub.0]] X 100%; W = weight of polymer sample after standing at room temperature for 1 h, and [W.sub.0] = weight of polymer sample after dried in vacuum at 100[degrees]C for 10 h. Table 2 Solubility Behaviour (a) of Poly(amide-imide-imide)s. Solvent (b) Polymer NMP DMAc DMF DMSO m-Cresol Py [III.sub.a] ++ ++ [+ or -] ++ ++ -- [III.sub.b] ++ ++ [+ or -] ++ ++ -- [III.sub.c] ++ ++ [+ or -] ++ ++ -- [III.sub.d] ++ +h -- +h ++ -- [III.sub.e] ++ +h -- +h ++ -- [III.sub.f] ++ ++ [+ or -] ++ ++ -- [III.sub.g] ++ ++ ++ ++ ++ ++ [III.sub.h] ++ ++ ++ ++ ++ ++ [III.sub.i] ++ ++ ++ ++ ++ ++ [IV.sub.a] ++ ++ ++ ++ ++ S [IV.sub.b] S S -- S -- S [IV.sub.c] S S -- S -- -- [IV.sub.d] -- -- -- -- -- -- [IV.sub.e] -- -- -- -- -- -- [IV.sub.f] -- -- -- -- -- -- [IV.sub.g] ++ S S S S S [IV.sub.h] ++ +h ++ ++ ++ ++ [IV.sub.i] ++ S S S S S V -- -- -- -- [+ or -] [+ or -] (a) Measured at a polymer concentration of 0.05 g/mL. Solubility: ++ soluble at room temperature + h soluble after heating [+ or -] Partially soluble S swelling -- insoluble (b) DNAc N N-dimethylacetamide NMP N-methyl-2-pyrrolidinone DMF N,N-dimethylformamide DMSO dimethylsulfoxide Py: pyridine. Table 3 Mechanical Properties of Poly(amide-imide-imide) Films. (a) Strength Strength Elongation Initial at yield at break at break Modulus Polymer (MPa) (MPa) (%) (GPa) [III.sub.a] -- 107 9 2.3 [III.sub.b] 107 105 14 2.4 [III.sub.c] 101 97 13 2.4 [III.sub.d] 103 103 14 2.1 [III.sub.e] -- 87 10 2.0 [III.sub.f] 103 102 10 2.2 [III.sub.g] 94 90 14 2.1 [III.sub.h] -- 97 11 2.0 [IV.sub.a] -- 101 9 2.5 V -- 91 8 2.1 (a)Films were cast from slow evaporation of polymer solutions in DMAc. Table 4 Thermal Properties of Poly (amide-imide-imide)s. DSC TGA [T.sub.10] [T.sub.g] (a) (b) [N.sub.2] Char yield Polymer ([degrees]C) ([degrees]C) (c) (%) [III.sub.a] 309 552 61 [III.sub.b] -- 552 52 [III.sub.c] 298 559 61 [III.sub.d] 298 558 62 [III.sub.e] 285 570 60 [III.sub.f] 270 556 57 [III.sub.g] 271 555 62 [III.sub.h] 279 564 62 [III.sub.i] 292 540 54 [IV.sub.a] 249 514 56 [IV.sub.b] 238 532 58 [IV.sub.c] 248 528 60 [IV.sub.d] 243 522 50 [IV.sub.e] -- 533 51 [IV.sub.f] 245 520 66 [IV.sub.g] 246 539 60 [IV.sub.h] 243 548 57 [IV.sub.i] 246 556 52 V 277 555 61 (a)From the second heating DSC trace conducted at a heating of 15[degrees]C/min in nitrogen. (b)Temperature at which a 10% weight loss was recorded by TG at a heating rate of 20[degrees]C/min. (c)Residual weight % at 800[degrees]C under a nitrogen atmosphere.
The authors are grateful to the National Science Council of the Republic of China for the support of this work (Grant NSC 90-2216-E-036-016).
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CHIN-PING YANG (*)
(*) Corresponding author.