J Polym Res (2012) 19:9902 DOI 10.1007/s10965-012-9902-9
ORIGINAL PAPER
Synthesis and characterization of novel organosoluble and thermally stable polyamides bearing triptycene in their backbones Sheng-Huei Hsiao & Hui-Min Wang & Ji-Shian Chou & Wenjen Guo & Teh-Hua Tsai
Received: 15 March 2012 / Accepted: 27 May 2012 # Springer Science+Business Media B.V. 2012
Abstract New triptycene-containing polyamides were prepared from 1,4-bis(4-carboxyphenoxy)triptycene with aromatic diamines or from 1,4-bis(4-aminophenoxy)triptycene with aromatic dicarboxylic acids via the phosphorylation polyamidation reaction. These polyamides were essentially amorphous and showed a significantly increased solubility as compared with their analogs without the triptycene units. All the polyamides could be solution-cast into flexible and tough films. They also showed good thermal stability with glass transition temperatures of 252–295 °C and 10 % weight loss temperatures higher than 540 °C. These polyamides are considered to be promising processable hightemperature polymeric materials. Keywords Polyamides . Triptycene . Structure-property relationships . Solubility . Thermal stability
Introduction Wholly aromatic polyamides (aramids) have been well known for their high temperature stability, excellent mechanical strength and good chemical resistance, which qualify them as high-performance polymeric materials [1, 2]. Fibers obtained from anisotropic solutions of these highperformance materials have been used in applications where high thermal stability and mechanical strength are required. However, most aramids suffer poor processability due to limited solubility in common organic solvents and high S.-H. Hsiao (*) : H.-M. Wang : J.-S. Chou : W. Guo : T.-H. Tsai Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, Taiwan e-mail:
[email protected]
glass-transition (Tg) and softening (Ts) temperatures. Therefore, considerable effort has been made to increase the processability and solubility of aramids by structural modification. One of the most common approaches to increasing solubility and lowering Tg and Ts is the introduction of flexible bonds in the polymer backbone and/or bulky pendent groups along the main chain [3–17]. Soluble or thermoplastic aramids may broaden applications in films, separation membranes, coatings, polymer blends, and composites. Iptycenes are a class of structurally unique compounds that consist of a number of arene rings joined together to form the bridges of [2.2.2] bicyclic ring systems [18]. The name iptycene originated from the basic unit triptycene, which was first synthesized and named by Bartlett and coworkers in 1942 [19]. Later, triptycene has become readily available thanks to the well known work of Wittig [20, 21] on the preparation of dehydrobenzene (benzyne) and its interaction with anthracene. The chemistry of triptycene has been studied in comparative detail and has been summarized in an earlier review paper reported by the Russian researchers [22]. Perhaps the earliest efforts in the study of triptycene polymers were made at Eastman Kodak and DuPont in the late 1960s wherein bifunctional, bridgehead-substituted triptycenes were synthesized and used to prepare a series of triptycene polymers, including polyesters, polyamides, polyurethanes, and a polyoxadiazole [23, 24]. However, the synthesis and properties of triptycene-containing polymers have only begun to attract attention since 1998 [25–31]. The use of triptycene moiety as a rigid and shape-persistent component is a method to introduce molecular-scale free volume into a polymer film [32, 33]. As part of our continuing efforts in developing easily processable, thermally stable polymers with potential for
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1,4-bis(4-aminophenoxy)benzene (6e, TCI), 2,2-bis(4-aminophenyl)hexafluoro- propane (6f, TCI), terephthalic acid (8a, Wako), isophthalic acid (8b, Wako), 4,4′-biphenydicarboxylic acid (8c, TCI), 4,4′-dicarboxydiphenyl ether (8d, TCI), and 2,2-bis(4-carboxyphenyl)hexafluoropropane (8f, TCI) were used as received. 1,4-Bis(4-carboxyphenoxy)benzene (8e) (mp0322–324 °C) was synthesized by alkaline hydrolysis of 1,4-bis(4-cyanophenoxy)benzene resulting from the condensation of 1,4-dihydroxybenzene with p-fluorobenzonitrile in the presence of potassium carbonate according to a reported procedure [34]. Calcium chloride was dried under vacuum at 200 °C for 3 h prior to use.
use as advanced materials, it appeared interesting to us to synthesize new aromatic polyamides containing triptycene units. The rigid, three-dimensional triptycene units may decrease interchain interactions and hinder close chain packing. Thus, it was expected that the introduction of triptycene structure into the polymer backbone could improve the solubility and preserve moderately high Tg values of the polyamides. Some properties of these polyamides are also compared with those of homologous counterparts without the triptycene units.
Experimental Monomer synthesis Materials 1,4-Bis(4-cyanophenoxy)triptycene (2) As described previously [33], 1,4-bis(4-aminophenoxy) triptycene (5) (mp0186–187 °C) was prepared by the aromatic nucleophilic substitution reaction of p-chloronitrobenzene with 1,4-dihydroxytriptycene in the presence of potassium carbonate, followed by hydrogen Pd/C-catalyzed reduction of the intermediate bis(p-nitrophenoxy) compound. p-Fluorobenzonitrile (TCI), potassium carbonate (K2CO3, Showa), potassium hydroxide (KOH, Showa), N,N-dimethylformamide (DMF, Tedia), and triphenyl phosphite (TPP) were used without further purification. N-Methyl-2-pyrrolidone (NMP, Tedia) and pyridine (Py, Wako) were dried over calcium hydride for 24 h, distilled under reduced pressure, and stored over 4 Å molecular sieves in a sealed bottle. Commercially available aromatic diamines and dicarboxylic acids including p-phenylenediamine (6a, TCI), m-phenylenediamine (6b, TCI), benzidine (6c, Wako), 4,4′-oxydianiline (6d, TCI),
In a 300-mL, round-bottom flask, 5.7 g (0.02 mol) of 1,4dihydroxybenzene (1) and 5.5 g (0.04 mol) of potassium carbonate (K2CO3) were suspended in a mixture of 30 mL of dry DMF and 15 mL of toluene. Then the mixture was refluxed at 150 °C with a Dean-Stark trap for the azeotropic removal of water. After most of the toluene had been removed, p-fluorobenzonitrile (4.8 g, 0.05 mol) was added to the mixture, and heating was continued at reflux overnight. The resulting solution was allowed to cool to room temperature and then poured into 600 mL of methanol to give white precipitates. After being washed repeatedly with water, the product was collected by filtration and was recrystallized from acetonitrile to afford 6.1 g (yield 63 %) of pure white needles (mp0327–330 °C, by DSC at 2 °C/min). IR (KBr): 2225 cm−1 (C≡N). 1H NMR (500 MHz, DMSO-d6,
O toluene
O
AcOH
OH
HBr O
HO
O
1 NC 2 F
O
O
CN
K2CO3
KOH
toluene, DMF
H2O/ EtOH
CN
HOOC
O
2
O
COOH
O
NH2
3
1 K2CO3 2 Cl
O2 N
O
O
NO2
NO2
Pd/C
H2N
O
DMF
DMF
4 Scheme 1 Synthetic routes to the triptycene-containing bis(ether-carboxylic acid) 3 and bis(ether amine) 5
5
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J05.4, 3.2 Hz, 4H, Hd), 7.86 (d, J08.8 Hz, 4H, Hf). 13C NMR (125 MHz, DMSO-d6, δ, ppm): 47.0 (C4), 115.0 (C11), 117.2 (C9), 118.7 (-CN), 120.0 (C1), 123.9 (C7), 125.4 (C6), 134.6 (C10), 139.6 (C3), 143.9 (C5), 145.6 (C2), 161.4 (C8). 1,4-Bis(4-carboxyphenoxy)triptycene (3)
Fig. 1 IR spectra of bis(ether nitrile) 2 and bis(ether-carboxylic acid) 3
δ, ppm): 5.65 (s, 2H, Hb), 6.94 (s, 2H, Ha), 6.97 (d, J0 8.8 Hz, 4H, He), 7.01 (dd, J05.4, 3.2 Hz, 4H, Hc), 7.27 (dd,
Fig. 2 a 1H, b
13
A suspension of the intermediate dinitrile compound 2 (6.0 g, 0.012 mol) in a mixture of water (20 mL) and ethanol (50 mL) containing dissolved potassium hydroxide (5.6 g, 0.096 mol) was heated at reflux temperature until no further ammonia was generated. The resulting solution was filtered hot to remove the insoluble solids. The filtrate was acidified by aqueous hydrochloric acid to a pH value of near 3. The precipitated white solid was filtered, washed thoroughly with water, and dried to yield 5.0 g (79 % in yield) of dicarboxylic acid monomer 3 (mp0386–389 °C, by DSC at 2 °C/min). IR (KBr): 2500∼3500 (-OH), 1689 cm−1 (C0O). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 5.69
C, c H-H COSY and d C-H HMQC spectra of bis(ether nitrile) 2 in DMSO-d6
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(s, 2H, Hb), 6.88 (s, 2H, Ha), 6.95 (dd, J08.8 Hz, 4H, He), 7.01 (dd, J05.4, 3.2 Hz, 4H, Hc), 7.27 (dd, J05.4, 3.2 Hz, 4H, Hd), 7.96 (d, J08.7 Hz, 4H, Hf). 13C NMR (125 MHz, DMSO-d6, δ, ppm): 47.1 (C4), 116.3 (C9), 119.5 (C1), 123.9 (C7), 125.1 (C11), 125.3 (C6), 131.6 (C10), 139.3 (C3), 144.1 (C5), 146.0 (C2), 161.4 (C8), 166.7 (-COOH). Polymer synthesis The phosphorylation polycondensation method was used to prepare the polyamides. A typical example for the preparation of polymer 7d is given. A mixture of 0.4212 g (0.8 mmol) of the dicarboxylic acid monomer 3, 0.1602 g (0.8 mmol) of 4,4′-oxydianiline (6d), 0.15 g of calcium chloride, 0.9 mL of triphenyl phosphite, 0.25 mL of pyridine, and 1.0 mL of NMP was heated with stirring at 120 °C for 3 h. The resulting viscous solution was poured slowly with stirring into 150 mL of methanol, giving rise to a tough, fibrous precipitate. The precipitated product was collected by filtration, washed repeatedly with methanol and hot water, and dried to give a quantitative yield of polyamide 7d. The
Fig. 3 a 1H, b
13
inherent viscosity of the polymer was 0.75 dL/g, measured in DMAc (containing dissolved 5 wt.-% LiCl) at a concentration of 0.5 g/dL at 30 °C. The IR spectrum of 7d film exhibited characteristic amide absorption bands at 3300 cm−1 (amide N– H str.) and 1648 cm−1 (amide carbonyl str.). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 5.75 (s, 2H, Hb), 6.87 (s, 2H, Ha), 7.03 (overlapped doublets, 12H, Hc + He + Hh), 7.32 (br. s, 4H, Hd), 7.79 (d, J08.5 Hz, 4H, Hg), 8.02 (d, J09.0 Hz, 4H, Hf), 10.26 (amide protons). Preparation of the polyamide films A solution of polymer was made by the dissolution of about 0.6 g of the polyamide sample in 6 mL of hot DMAc. The clear solution was poured into a 7-cm diameter glass culture dish, which was placed in a 90 °C oven for 12 h for evaporation of the solvent. The cast film was then released from the glass substrate and was further dried in vacuo at 160 °C for 6 h. The obtained films were about 70 μm thick and were used for X-ray diffraction measurements, solubility tests, and thermal analyses.
C, c H-H COSY and d C-H HMQC spectra of bis(ether-carboxylic acid) 3 in DMSO-d6
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radiation. DSC analyses were performed on a Perkin-Elmer Pyris 1 DSC at a scan rate of 20 °C/min under a nitrogen flow. Glass-transition temperatures (Tgs) were read as the midpoint temperature of the heat capacity jump and were taken from the second heating scan after a quick cooling from 400 °C to room temperature. Thermogravimetric analysis (TGA) was performed with a Perkin-Elmer Pyris 1 TGA. Measurements were carried out on 3–5 mg film samples heated in flowing nitrogen or air (90 cm3/min) at a heating rate of 20 °C/min. Thermomechanical analysis (TMA) was conducted with a Perkin-Elmer TMA 7 at a scan rate of 10 °C/min with a penetration probe of 1.0 mm diameter under an applied constant load of 10 mN.
Measurements IR spectra were recorded on a Horiba FT-720 Fourier transform infrared (FTIR) spectrometer. 1H and 13C NMR spectra were measured on a Bruker Avance 500 MHz FT-NMR spectrometer. The inherent viscosities were determined with a Cannon-Fenske viscometer at 30 °C. Weight-average molecular weights (M w ) and number-average molecular weights (Mn) were obtained via gel permeation chromatography (GPC) on the basis of polystyrene calibration using Waters 2410 as an apparatus and THF as the eluent. The mechanical properties of the polymer films were measured with an Instron model 1130 tensile tester with a 5 kg load cell at a crosshead speed of 5 mm/min on strips approximately 40–60 μm thick and 0.5 cm wide with a 2 cm gauge length. An average of at least five individual determinations was used. An average of at least five individual determinations was used. Wide-angle X-ray diffraction (WAXD) measurements were performed at room temperature (ca. 25 °C) on a Shimadzu XRD-6000 X-ray diffractometer (40 kV, 20 mA), using graphite-monochromatized Cu-Kα HOOC
O
O
Results and discussion Monomer synthesis The two triptycene-based monomers, 1,4-bis(4-carboxphenoxy) triptycene (3) and 1,4-bis(4-aminophenoxy)triptycene (5), O C
COOH
O
O
O H C N
Ar
H N n
H2N
Ar
7
TPP/Py/CaCl2/NMP
NH2
120 oC 3h
3
6 HOOC
O
O C
COOH
O
O
O
O H C N
Ar
H N n
7'
H2N
HOOC
Ar
O
O
H N
NH2
O
O
8 O
n
120 oC 3h
5 H2N
O C
Ar
9
TPP/Py/CaCl2/NMP
COOH
H O N C
H N
NH2
O
O
O
H O N C
O C
Ar
n
9' CF3
Ar :
O
O
O
O
O
CF3
a
b
c
d
e
f g
Scheme 2 Synthesis of polyamides
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were successfully synthesized via the synthetic routes shown in Scheme 1. According to a reported method [19], the triptycene-hydroquinoe (TPHQ) 1 was obtained in a good yield starting from the Diels-Alder reaction of pbenzoquinone and anthracene and subsequent rearrangement reaction using acetic acid/HBr as catalyst. The intermediate compounds, 1,4-bis(4-cyanophenoxy)triptycene (2) and 1,4bis(4-nitrophenoxy)triptycene (4), were prepared by the nucleophilic aromatic halogen displacement of p-fluorobenzonitrile and p-chloronitrobenzene, respectively, with TPHQ 1 in the presence of anhydrous potassium carbonate in DMF. Then, dinitrile compound 2 was converted into dicarboxylic acid monomer 3 by alkaline hydrolysis, and dinitro compound 4 was reduced to diamine monomer 5 with hydrazine monohydrate and Pd/C catalyst in refluxing ethanol. The FTIR spectra of intermediate dinitrile compound 2 and the diacid monomer 3 are illustrated in Fig. 1. The IR spectrum of dinitrile compound 2 shows characteristic cyano peak at 2225 cm−1. After hydrolysis, the characteristic absorption of the cyano group disappeared and the carboxylic acid group showed a typical carbonyl absorption band at 1689 cm−1 (C0O stretching) together with the appearance of broad band around 2500–3500 cm−1 (O-H stretching). The NMR data of the intermediate dinitrile compound 2 are shown in Fig. 2. The 1H, 13C, H-H COSY, and C-H HMQC NMR spectra of the target diacid monomer 3 are compiled in Fig. 3. Assignments of each carbon and proton are also indicated in
these spectra, and they are in good agreement with the proposed structures of these two compounds. The IR and NMR data of dinitro compound 4 and diamine monomer 5 are essentially identical with those reported in a previous publication [33]. Polymer synthesis Two series of novel polyamides 7a-g and 9a-f were synthesized using the Yamazaki-Higashi [35] phosphorylation polyamidation procedure from bis(ether-carboxylic acid) 3 with various aromatic diamines 6a-6g and from bis(ether amine) 5 with various aromatic dicarboxylic acids 8a-8f, respectively (Scheme 2). All the polymerizations proceeded homogeneously throughout the reaction and afforded clear and highly viscous polymer solutions, which precipitated in a tough, fiber-like form when the resulting polymer solutions were slowly poured into methanol. As shown in Table 1, the resulting polymers had inherent viscosities higher than 0.27 dL/g and up to 1.02 dL/g. Table 2 shows the average molecular weights of 7f and 7g measured by GPC using polystyrene as standard and THF as solvent, and the weightaverage molecular weights (Mw) were 28,000 and 43,500 with polydispersity index (Mw/Mn) of 2.07 and 2.02, respectively. As shown in Scheme 2, all the 7 and 9 series polyamides could afford transparent, flexible and strong films via solution-casting from DMAc. Structural features of these
Table 1 Inherent viscosities, film quality and solubility behavior of polyamides Polymer code
7a 7b
ηinha (dL/g)
0.90 0.49
Film qualityb
F (–) F (F)
Solubility in various solventsc NMP
DMAc
DMF
DMSO
m-Cresol
THF
++(±) ++(++)
++(−) ++(++)
++(−) ++(++)
++(−) ++(++)
+(−) +(+)
±(−) ±(−)
7c
1.02
F (–)
++(±)
++(−)
++(−)
++(−)
±(−)
−(−)
7d 7e 7f 7g 9a 9b 9c 9d 9e 9f
0.75 0.79 0.27 0.45 0.58 0.30 0.65 0.43 0.62 0.32
F (–) F (–) F (B) F F (–) B (–) F (–) F (–) F (–) F (F)
++(+) ++(±) ++(++) ++ ++(−) ++(++) ++(±) ++(+) ++(±) ++(++)
++(−) ++(−) ++(++) ++ ++(−) ++(±) ++(−) ++(−) ++(−) ++(++)
++(−) ++(−) ++(++) ++ ++(−) ++(±) +(−) ++(−) ++(−) ++(++)
++(−) ++(−) ++(++) ++ ++(−) +(±) +(−) ++(−) ++(−) ++(++)
+(−) ++(−) +(+) + +(−) +(−) ±(−) +(−) +(−) +(+)
±(−) ±(−) ++(++) ± ±(−) ++(−) −(−) ±(−) ±(−) ++(++)
a
Inherent viscosity measured at a concentration of 0.5 g/dL in DMAc-5 wt % LiCl at 30 °C
b
B: brittle and cracked upon creasing; F: flexible; -Insoluble in any available organic solvents
c
The qualitative solubility was tested with 10 mg of a sample in 1 mL of stirred solvent. ++, soluble at room temperature; +, soluble on heating; ±, partially soluble on heating; -, insoluble even on heating. Solvent: NMP: N-methyl-2-pyrrolidone; DMAc: N,N-dimethylacetamide; DMF: N,Ndimethylformamide; DMSO: dimethyl sulfoxide; THF: tetrahydrofuran
d
Values shown in parentheses are those of structurally similar polyamides 7′ and 9′ without the triptycene group
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Table 2 GPC data of polyamides 7f anf 7g Polymer
Mna
Mw a
PDIb
DPc
7f
13500
28000
2.07
16
7g
21500
43500
2.02
22
a
Average molecular weights relative to polystyrene standard in THF by GPC
b
Polydispersity Index (Mw/Mn)
c
Degree of Polymerization
polyamides were verified by FTIR and NMR spectroscopy. As shown in Fig. 4, they exhibited characteristic absorption bands of the amide group around 3300 (N-H stretching) and 1650 cm−1 (C0O stretching), with strong absorptions of aryl ether stretching in the region of 1100–1300 cm−1. 1H NMR spectra of a typical set of isomeric polyamides 7d and 9d are depicted in Fig. 5. Assignments of each carbon and proton are also given in the figures, and these spectra agree well with the proposed polymer structures. For comparison, some structurally related polyamides 7′ and 9′ without the triptycene group were also prepared and characterized. Similar to that described previously [34], most of the referenced polyamides 7′ and 9′ precipitated from the reaction media and did not dissolve in available organic solvents for film casting. This implies that the incorporation of the triptycene group enhances the solubility and film-forming ability of polyamides. Properties of the polyamides The solubility behavior of all polyamides was qualitatively tested in a number of organic solvents, and the results are summarized in Table 1. All the triptycene-based polyamides showed excellent solubility in aprotic dipolar solvents, such
Fig. 4 IR spectra of a typical set of isomeric polyamides 7d and 9d
Fig. 5 1H NMR spectra of a typical set of isomeric polyamides a 7d and b 9d in DMSO-d6
as NMP, DMAc, DMF, and DMSO at room temperature or upon heating at 70 °C. Some of them were even soluble in less polar m-cresol and tetrahydrofuran (THF), especially for those containing the hexafluoroisopropylidene (-C (CF3)2-) units, such as 7f and 9f. In all cases, the 7 and 9 series polyamides containing the packing-disruptive triptycene group exhibited a significantly enhanced solubility than the corresponding ones (7′ and 9′) without the triptycene group and could afford flexible and tough films by solvent casting. The cast films generally exhibited high tensile strengths of about 70∼80 MPa. The enhanced solubility can be attributed to the bulkiness of triptycene groups which increased the disorder in the chains and hindered dense chain packing, thus, reducing the interchain interactions. The wide-angle X-ray diffraction (WAXD) patterns are illustrated in Fig. 6. The results revealed that the 7 and 9 series polyamides showed amorphous WAXD patterns. When comparing the diffraction patterns of the analogous 7′ and 9′, an obvious effect of the introduction of the triptycene group on decreasing the crystallinity of these
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Fig. 6 Wide-angle X-ray diffractograms of polyamides
polyamides was observed. Apparently, the introduction of the bulky, three-dimensional triptycene groups decreases the interchain interactions between amide groups and increases the free volume, which interferes with the close packing of polymer chains, thereby leading to an enhancement in organosolubility and a decrease in crystallinity. The thermal properties of the polymers evaluated by DSC, TMA, and TGA are summarized in Table 3. DSC experiments were conducted at a heating rate of 20 °C/min in nitrogen. Rapid cooling from 400 °C to room temperature produced predominantly amorphous samples, so the glass transition temperatures (Tgs) of all the polyamides could be easily read in the subsequent heating DSC traces. The glass-transition temperatures (Tgs) of the 7 and 9 series
polyamides were observed in the range of 249–295 and 252–285 °C, respectively, by DSC. The lowest Tg of 249 °C was observed for polyamide 7e derived from the multiring flexible diamine 6e. The highest Tg value associated with polyamide 7c can be attributed to the presence of rigid biphenyl unit in the diamine component that stiffens the polymer backbone. In general, the Tg values depend on the structures of diamine and diacid moieties and decreased with decreasing rigidity and symmetry of the polymer backbone. The triptycene-containing polyamides 7b, 7f and 9f exhibited Tg’s higher than their respective counterparts 7′b, 7′f, and 9′f. The result can be attributed to bulky triptycene units thus restricting the segmental mobility. The softening temperatures (Ts) of the polymer films were determined with
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Table 3 Thermal properties of polyamides Polymer code
7a 7b 7c 7d
a
Tgb (°C)
Tsc (°C)
268 (–f) h
259 (222) 295 (–) 262 (–)
Tm (°C)
Td at 10 wt % lossd (°C) In N2
In air
Char yielde (%)
272 (–g) 264 (225)
− (–) − (–)
558 (506) 546 (510)
540 (479) 570 (510)
74 (64) 70 (65)
308 (–) 266 (–)
− (–) − (397)
595 (520) 559 (522)
570 (497) 560 (493)
75 (68) 70 (54)
7e
249 (–)
252 (–)
− (379)
545 (544)
550 (498)
70 (61)
7f 7g
281 (246) 269
290 (225) 270
− (–) –
551 (517) 567
551 (520) 567
69 (61) 69
9a
278 (–)
273 (–)
− (–)
549 (499)
539 (535)
74 (64)
9b 9c
275 (–) 294 (–)
267 (–) 287 (–)
− (416) − (–)
555 (517) 575 (548)
543 (547) 556 (545)
70 (66) 75 (65)
9d
253 (–)
244 (–)
− (429)
550 (498)
537 (532)
71 (67)
9e
252 (–)
248 (–)
− (384)
550 (485)
540 (523)
66 (64)
9f
285(245)
284 (243)
− (–)
556 (535)
545 (553)
67 (63)
a
The polymer film samples were heated at 300 °C for 30 min before all the thermal analyses
The samples were heated from 50 to 400 °C at a scan rate of 20 °C/min followed by rapid cooling to 50 °C at −200 °C/min in nitrogen. The midpoint temperature of baseline shift on the subsequent DSC trace (from 50 to 400 °C at heating rate 20 °C /min ) was defined as Tg b
c
Softening temperature measured by TMA with a constant applied load of 10 mN at a heating rate of 10 °C/min
d
Decomposition temperature at which a 10 % weight loss was recorded by TGA at a heating rate of 20 °C/min and a gas flow rate of 20 cm3 /min
e
Residual weight percentages at 800 °C under nitrogen flow
f
No discernible transition was detectable by DSC
g
No available specimens for the TMA testing
h
Values shown in parentheses are those of structurally similar poly(ether-amide)s 7′ and 9′ without the triptycene group
TMA by the penetration method. The Ts value was read from the onset temperature of the probe displacement on the TMA curve. Typical TMA curves for the representative polyamides 7f and 9f are shown in Fig. 7. The Ts values of these polyamides were observed in the range 244–308 °C. In most cases, the Ts values obtained by TMA are comparable to the Tg values measured by the DSC experiments. Because of the high degree of crystallinity, most of the referenced polyamides (7′ and 9′) did not show discernible
Tgs by DSC. Although polymers 7′a and 9′a exhibited a crystalline WAXD pattern, well defined endotherms were not observed on the DSC trace before decomposition, possibly because of high melting temperatures. The incorporation of ether linkages decreased the structural rigidity; therefore, polyamides 7′d, 7′e, 9′d and 9′e showed a clear melting endotherm around 384∼432 °C. Figure 8 shows the DSC curves of some representative polyamides for
Fig. 7 TMA curves of polyamides 7f and 9f
Fig. 8 DSC curves of some polyamides
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these polyamides showed apparently decreased crystallinity and enhanced solubility. Thus, these properties made these triptycene-based polyamides promising solution-processable, high-performance polymeric materials.
References
Fig. 9 TGA curves of polyamides 7d and 9d at a heating rate of 20 °C/min
comparison. The polyamides 9d and 9e indicated no clear melting endotherms up to the decomposition temperatures on the DSC thermograms. This result also supports the amorphous nature of these polyamides. By contrast, polyamides 9′d and 9′e showed a clear melting endotherm at 429 and 384 °C, respectively, on the DSC traces. These results also confirmed that the introduction of pendent triptycene group is effective in inhibiting the close packing of polymer chains and thus leads to a decrease in crystallinity or crystallization tendency. The thermal and thermo-oxidative stability of the poly (ether-amide)s was evaluated by TGA in both nitrogen and air atmospheres. Typical TGA curves for polyamides 8d and 9d in both air and nitrogen atmospheres are reproduced in Fig. 9. The temperatures for 10 % weight loss (Td) of the 7 series polyamides in nitrogen and air atmospheres stayed within 545–595 °C and 540–570 °C, and for the 9 series polyamides within 549–575 °C and 537–556 °C. They left more than a 66 % char yield at 800 °C in nitrogen. The Td values of reference polyamides 7′ and 9′ are also included in Table 3 for comparison. All the polymers exhibited a higher Td value as compared with their corresponding counterparts without the triptycene group.
Conclusions Two novel triptycene-based dicarboxylic acid and diamine monomers, 1,4-bis(4-carboxyphenoxy)triptycene (3) and 1,4-bis(4-aminophenoxy)triptycene (5), have been successfully synthesized in high purity and high yields. Two series of novel aromatic polyamides were prepared from various combinations of 3 with aromatic diamines or from 5 with aromatic dicarboxylic acids via the Yamazaki–Higashi phosphorylation technique. Because of the presence of bulky, three-dimensional triptycene units in the main chain, all the polyamides were noncrystalline, displayed good solubility, and afforded flexible and tough films. In comparison with analogous polyamides without the triptycene group,
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