Synthesis of poly(m-phenyleneisophthalamide) by solid-state polycondensation of isophthalic acid with m-phenylenediamine

Article abstract of DOI:10.1002/pola.24934

The synthesis of poly(m-phenyleneisophthalamide) was performed by thermal solid-phase polymerization from isophthalic acid and m-phenylenediamine without using any solvents or condensation agents. The two-stage heating process was conducted. The oligo(m-p

Full text of DOI:10.1002/pola.24934

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Synthesis of Poly(m-phenyleneisophthalamide) by Solid-state
Polycondensation of Isophthalic Acid with m-Phenylenediamine
1
1
1
2
3
Cenyao Zhang, Yu Shoji, Tomoya Higashihara, Akimitsu Tsukuda, Takashi Ochi,
1
Mitsuru Ueda
1
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology,
2
-12-1-H120, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
2
Films & Film Products Research Laboratories, Toray Industries, Inc., 1-1-1, Sonoyama, Otsu, Shiga 520-8558, Japan
Technology Center, Toray Industries, Inc., 1-1-1, Sonoyama, Otsu, Shiga 520-8558, Japan
3
Correspondence to: M. Ueda (E-mail: ueda.m.ad@m.titech.ac.jp)
Received 9 July 2011; accepted 6 August 2011; published online 27 August 2011
DOI: 10.1002/pola.24934
KEYWORDS: high-temperature materials; polycondensation; polyamides; solid-state polymerization; viscosity
INTRODUCTION Super engineering plastics are currently
receiving considerable attention for their applications in the
aerospace, automotive, electronic, and related markets. Aro-
matic polyamides (aramids), such as poly(m-phenyeleneisoph-
thalamide) and poly(p-phenyleneterephthalamide), are impor-
tant in the commercial fiber industry because of their high
ing target of aramids is the synthesis of poly(m-phenyelenei-
sophthalamide) (trade name: Nomex), which has high T and
g
Tm values. Herein, we report the direct synthesis of poly(m-
phenyeleneisophthalamide) by the solid-state polycondensa-
tion of isophthalic acid with m-phenylenediamine. The optimi-
zation of the reaction conditions for the oligomerization and
polymerization are described. No catalysts and plasticizers
were used in the polycondensation to produce the pure
poly(m-phenyeleneisophthalamide).
1
–8
tensile strength and good flame resistance.
There have
recently been progresses in many applications based on high-
performance aromatic polyamides, such as optoelectronic
9
–11
application.
The synthesis of aramids is normally achieved
by the solution or interfacial polycondensation of aromatic
diacid chlorides with aromatic diamines due to the lower
reactivity of the aromatic amines compared to aliphatic
amines and their high melting temperatures. From the stand-
point of green chemistry, the direct synthesis of aramids from
aromatic dicarboxylic acids and aromatic diamines without
using any solvents and toxic chemicals is becoming increas-
ingly important and more straightforward, being an environ-
mentally benign transformation. However, no report on the
synthesis of aramids using a solid-state polymerization pro-
RESULTS AND DISCUSSION
Recently, Lange and coauthors investigated the thermal con-
densation of carboxylic acids with amines in the presence of
molecular sieves, and found that aliphatic carboxylic acids
smoothly reacted with primary and secondary aliphatic
ꢀ
amines as well as aromatic ones at 160 C for several
1
3
hours. On the other hand, the reaction of benzoic acid with
an aromatic amine, such as aniline, gave around a 50% yield
ꢀ
of benzanilide even at 160 C for 24 h. Therefore, before the
1
2
cess has been published except for our recent paper. We
reported the direct synthesis of aramids by the solid-state pol-
ycondensation of aromatic dicarboxylic acids and aromatic
diamines containing ether linkages which increased the mobil-
ity of the polymer chains, and decreased the glass transition
temperatures (T s) and melting points (T s) of the resulting
aramids. The polycondensation under a nitrogen atmos-
phere proceeded in the melt state during the first step of the
oligomer formation and then in the solid state to yield the
desired aramids with high molecular weights. These findings
suggested that other aramids with high melting points could
be prepared without decomposition by the solid-state poly-
condensation method at high temperature. The next challeng-
synthesis of the poly(m-phenyleneisophthalamide), the model
reaction of benzoic acid (1) with m-phenylenediamine (2)
was carried out in the melt state to investigate the feasibility
of the direct synthesis of poly(m-phenyleneisophthalamide)
(6) [Scheme 1(A)]. Considering the sublimation of 1, a small
excess amount of 1 to 2 was used. These results are sum-
marized in Table 1. All the reactions proceeded in homoge-
g
m
1
2
0
neous states and then N,N -1,3-phenylenebis(benzamide) (3)
ꢀ
was quantitatively obtained after 5 h at 240 C. It was con-
ꢀ
firmed that 1 reacted with 2 in the range of 220–240 C.
Based on the model reactions, the polycondensation of 2
with isophthalic acid (4) was carried out under various con-
ditions in an argon atmosphere [Scheme 1(B)]. We first
Additional Supporting Information may be found in the online version of this article.
2011 Wiley Periodicals, Inc.
V
C
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SCHEME 1 (A) Model reaction of 1 and 2. (B) Oligomerization and polymerization of 2 and 4.
investigated the appropriate conditions to obtain oligo
m-phenyleneisophthalamide) (5) by the direct polycondensa-
ratio of the carboxylic acid and amine terminated oligomers
(
can be estimated from the integral ratios of h and m. This
estimation is quite important because the ratio of h and m in
the oligomers should be 1.0 to obtain high molecular weight
polymers in a subsequent postpolymerization process. The
feed ratio R (¼[2]/[4]) was then varied in such a way that
the ratio of h to m became 1.0. The results are summarized in
Table 3. In the case of R ¼ 1.2, the ratio of h to m became
tion of 2 with 4 without any thermal decomposition and sub-
limation of the monomers. These results are summarized in
ꢀ
Table 2. The synthesis of 5 was carried out at 240 C, which
was the optimized temperature based on the model reaction.
When the reaction time was extended from 1 to 5 h at 240
ꢀ
C, the inherent viscosity slightly increased. To accelerate the
ꢁ
1.0, due to the sublimation of 2 during the heating process.
polycondensation, the reaction temperature was increased to
ꢀ
2
60 C. The oligoaramid 5 with the inherent viscosity of 0.12
In the thermogravimetry (TG)/differential thermal analysis
dL/g was obtained after 1 h (Run 4). Thus, the optimized con-
(
DTA) analysis, the decomposition temperature of the
ꢀ
1
dition for the oligomerization was determined to be 260
C
ꢀ
oligomer was observed above 400 C, and an endothermic
peak corresponding to the melting point of the oligomers
was observed around 408 C (see Supporting Information,
and 1 h. The structure of 5 was characterized by IR and H
NMR spectroscopies. The IR spectra showed the characteristic
absorptions of the NAH and the C ¼¼ O stretchings of the
ꢀ
Fig. S1). Thus, the temperature for the postpolymerization
–
1
amino and amide carbonyl groups at 3266 and 1650 cm ,
ꢀ
was set at 350 C [Scheme 1(B)]. In practice, the polymeriza-
1
ꢀ
ꢀ
respectively. Figure 1 shows a typical H NMR spectrum of 5,
tion was carried out at 350 C at a heating rate of 10 C/
ꢀ
in which the characteristic resonance of the amide protons at
min after the oligomerization with R ¼ 1.2 at 260 C for 1 h.
10.4 ppm appears. For accurate assignments of the terminal
These results are summarized in Table 4. The inherent vis-
cosity of 6 reached to 0.34 dL/g after the polycondensation
groups of 5, model compounds, 3-(phenylcarbamoyl)benzoic
acid (7) and N-(3-aminophenyl)benzamide (8) were synthe-
sized and characterized as representatives for the carboxylic
or amino terminal groups. As can be seen in Figure 1, the sig-
nals h and m correspond to the protons of the carboxylic acid
and amine terminated amide protons, respectively. Thus, the
ꢀ
for 80 min at 350 C. By increasing the polymerization tem-
perature to 360 C, the inherent viscosity of 6 was improved
ꢀ
to 0.37 dL/g. Then the polymerization was carried out under
ꢀ
reduced pressure (0.05 Torr) at 370 C to promote the poly-
condensation. Both the yield and inherent viscosity of the
a
a
TABLE 2 Results of Oligomerization
TABLE 1 Results of Model Reaction
Conditions
Conditions
ꢀ
b
Run
T
2
( C)/t
2
(h)
Yield (%)
ginh (dL/g)
ꢀ
Run
T
1
( C)/t
1
(h)
Yield (%)
1
2
3
4
5
a
240/1
240/3
240/5
260/1
260/3
88
82
82
96
96
0.099
0.11
0.12
0.12
0.12
1
2
3
4
5
6
a
220/5
220/7
240/3
240/4
240/5
240/7
88
92
88
94
95
97
Reactions were carried out with 1.0 mmol of 2 and 1.0 mmol of 4.
Inherent viscosities were measured at 30 C in NMP at a concentration
b
ꢀ
Reactions were carried out with 3.0 mmol of 1 and 1.0 mmol of 2.
of 0.5 g/dL.
4
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1
FIGURE 1 H NMR spectra of (A) oligomer 5, (B) carboxylic terminal model 7, and (C) amino terminal model 8.
1
resulting aramid 6 were improved to 90% and 0.45 dL/g,
respectively. To shorten the reaction time, the reaction tem-
perature was increased to 380 C, producing the aramid 6
and 34,000, respectively. From the H NMR spectrum (Sup-
porting Information, Fig. S2), the characteristic signals h and
m for the terminal units, as seen in the oligomers (Fig. 1),
almost disappeared, indicating the increase in the molecular
weights of the aramid 6.
ꢀ
with the inherent viscosity of 0.46 dL/g in 10 min. When the
reaction time was extended to 30 min, a partially insoluble
polymer in conc. H SO was formed, suggesting that side
2
4
EXPERIMENTAL
reactions such as crosslinking reactions and oxidation might
ꢀ
occur. Finally, the polymerization was carried out at 400 C
Materials
for 1 min to produce the aramid 6 with an inherent viscosity
of 0.55 dL/g. Number- and weight-average molecular
m-Phenylenediamine (2) was sublimated prior to use. Iso-
phthalic acid (4) purchased from Tokyo Chemical Industry
weights (Mn and M ) values of 6 (g ¼ 0.46 dL/g) deter-
w
mined by size exclusion chromatography (SEC) are 15,000
TABLE 4 Results of Polymerization
a
TABLE 3 Results of End Group Determination
Conditions
Yield
g
inh
a
ꢀ
b
c
Run
R
T
3
( C)/t
3
(min)
(%)
(dL/g)
Temp.
Yield
g
inh
ꢀ
b
c
d
e
d
Run
( C)/Time (h)
R
(%)
(dL/g)
h/m
1
1.2
1.2
1.2
1.2
1.2
350/80
360/80
370/360
380/10
400/1
81
80
90
87
94
0.34
0.37
0.45
0.46
0.55
d
2
1
2
3
4
5
a
260/1
260/1
260/1
260/1
260/1
1.0
1.1
1.2
1.3
1.5
96
96
99
98
99
0.12
0.13
0.12
0.11
0.099
6.2
1.2
1.1
0.6
0.2
e
3
e
4
e
5
a
The molar ratio of 2 to 4.
b
c
Isolated yield.
Inherent viscosity was measured at 30 C in conc. H
ꢀ
Reaction was carried out with 1.0 mmol scale under argon stream.
2
SO
4
at a concen-
b
c
The ratio of 2 to 4.
tration of 0.5 g/dL.
d
Isolated yield.
The polymerization was carried out with 1.0 mmol scale under an
argon atmosphere.
The polymerization was carried out with 1.0 mmol scale under
d
ꢀ
Inherent viscosity was measured at 30 C in conc. H
2
SO
4
at a concen-
e
tration of 0.5 g/dL.
e
1
Determined by H NMR.
reduced pressure of 0.05 Torr.
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ꢀ
was recrystallized from ethanol prior to use. Model materi-
als, 3-(phenylcarbamoyl)benzoic acid (7) and N-(3-amino-
phenyl)benzamide (8) were synthesized according to the lit-
(DMSO-d , d, ppm, 40 C): 10.4 (s, NAH, 1H), 8.03 (d, J ¼ 8.7,
6
ArH, 4H), 7.79 (d, J ¼ 9.0, ArH, 4H), 7.51 (d, J ¼ 8.4, ArH, 4H),
7.34 (t, J ¼ 8.4, ArH, 1H), 7.08 (d, J ¼ 9.0, ArH, 4H), 6.70 (dd, J ¼
8.3, 2.1, ArH, 2H), 6.60 (t, J ¼ 2.7, ArH, 1H).
1
4,15
eratures.
The other reagents and solvents were
commercially obtained and used as received.
CONCLUSIONS
Measurements
We directly synthesized poly(m-phenyleneisophthalamide) from
isophthalic acid with m-phenylenediamine by a solid-state poly-
condensation. The model reactions between low nucleophilic
m-phenylenediamine and benzoic acid quantitatively proceeded
simply by heating to yield the desired aromatic diamide. When
the feed ratio R (¼[2]/[4]) was 1.2, the oligomer with equimo-
lar carboxylic acid and amine terminal groups was obtained
under the optimized conditions. Based on the optimized condi-
FTIR spectra were recorded on a Horiba FT-720 spectrome-
1
ter. H NMR spectra were recorded with a Bruker DPX300S
spectrometer. Thermal analysis was performed on a Seiko
EXSTAR 6000 TG/DTA 6300 thermal analyzer at a heating
ꢀ
rate of 10 C/min for TG. Mn and Mw values were deter-
mined by SEC, calibrated by standard polystyrene samples,
on a JASCO PU-2080Plus system equipped with two polysty-
rene gel columns (TSKGELs; GMHHR-M). N,N-Dimethylforma-
mide (DMF) containing 0.01 M LiBr was used as a solvent at
ꢀ
tions, the polymerization was carried out at 400 C for 1 min
ꢀ
–
1
under reduced pressure after the oligomerization at 260 C for
h. As a result, poly(m-phenyleneisophthalamide) with a maxi-
a flow rate of 1.0 mL min .
1
0
Synthesis of N,N -1,3-Phenylenebis(benzamide) (3)
Benzoic acid (1) (0.366 g, 3.0 mmol) and m-phenylenediamine
mum inherent viscosity of 0.55 dL/g could be obtained. This
environmentally friendly method can be applied to the synthe-
sis of aramids with high melting points that are currently pro-
duced via the thionyl-chloride-based method.
(2) (0.108 g, 1.0 mmol) were placed to a Pyrex test tube (15
mL) equipped with argon gas inlet and outlet tubes. The mix-
ture was heated with an oil bath at 240 C under an argon
ꢀ
atmosphere for 4 h, and then allowed to cool to room temper-
ature. The solids were dissolved in DMF (3 mL), and the
This work is supported by Japan Science and Technology Agency
(JST), A-step feasibility study program (#AS2111128D).
resulting solution was poured into a 1 wt % NaHCO aqueous
3
solution (300 mL) to remove the excess of benzoic acid. The
ꢀ
precipitate was collected, dried in vacuo at 120 C overnight.
REFERENCES AND NOTES
The yield of the model compound was 0.297 g (94%): m.p.
ꢀ
ꢀ
–1
1 Preston, J. In Encyclopedia of Polymer Science and Engineer-
ing; Mark, H. F.; Bikales, N. M.; Overberger, C. G.; Menges, G.;
Kroschwitz, J. I., Eds.; Wiley: New York, 1988; Vol. 11, p 381.
2
46–250 C (lit. 239–240 C). IR (KBr), m (cm ): 3266
1
(
1
ANH), 1650 (C ¼¼ O). H NMR (DMSO-d , d, ppm, 300 MHz):
6
0.3 (s, NAH, 2H), 8.36 (s, ArH, 1H), 8.02 (d, J ¼ 6.9 MHz, rH,
2
Vollbracht, L. In Comprehensive Polymer Science; East-
4H), 7.67–7.47 (m, ArH, 8H), 7.36 (t, J ¼ 9.0 MHz, ArH, 1H).
mond, G. C.; Ledwith, A.; Russo, S.; Sigwalt, P., Eds.; Perga-
mon Press: Oxford, England, 1989; Vol. 5, p 375.
Synthesis of Oligo(m-phenyleneisophthalamide) (5)
In a 10-mL Pyrex tube equipped with a stirring bar and argon
gas inlet and outlet tubes, the monomer 2 (1.0 mmol) and
monomer 4 (1.0–1.5 mmol) were placed under a stream of
3
Gaymans, R. J. In Synthetic methods in Step-Growth Polymers;
Rogers, M. E.; Long, T. E., Eds.; Wiley: New York, 2001; p 57.
Sorenson, W.; Sweeny, F.; Campbell, T. W. In Preparative
Methods of Polymer Chemistry; Wiley: New York, 2003; p 135.
Morgan, P. W. In Condensation Polymers: By interfacial and
Solution Methods; Interscience: New York, 1965, p 190.
Garc ´ı a, J. M.; Garc ´ı a, F. C.; Serna, F.; de la Pe n˜ a, J. L. Prog
Polym Sci 2010, 35, 623–686.
4
ꢀ
argon. The mixture was gradually heated up to 260 C with a
5
heating mantle for 1 h, and then allowed to cool to room tem-
perature. The solid was dissolved in conc. H SO (1.5 mL),
2
4
6
and the solution was poured into water (300 mL). The solu-
tion was neutralized by NaHCO3 (4.5 g). The oligomer was
7
Marchildon, K. Macromol React Eng 2011, 5, 22–54.
ꢀ
collected, and dried in vacuo at 120 C for 1 day.
´
8
Espeso, J. F.; Lozano, A. E.; de la Campa, J. G.; Garc ı´ a-Yoldi,
´
I.; de Abajo, J. J Polym Sci Part A: Polym Chem 2010, 48,
743–1751.
Synthesis of Poly(m-phenyleneisophthalamide) (6)
In a 15-mL Pyrex tube equipped with a stirring bar and argon
gas inlet and outlet tubes, 4 (0.166 g, 1.0 mmol) and 2 (0.130 g,
1
9
Est e´ vez, P.; El-Kaoutit, H.; Garc ´ı a, F. C.; Serna, F.; de la Pe n˜ a,
J. L.; Garc ´ı a, J. M. J Polym Sci Part A: Polym Chem 2010, 48,
3
1
.2 mmol) were placed under a stream of argon. The mixture
823–3833
ꢀ
was heated with a heating mantle at 260 C under an argon
atmosphere for 1 h. The resulting oligomer was heated at 400
1
0 Wang, H.-M.; Hsiao, S.-H.; Liou, G.-S.; Sun, C.-H. J Polym
Sci, Part A: Polym Chem 2010, 48, 4775–4789.
1 Yen, H.-J.; Guo, S.-M.; Liou, G.-S. J Polym Sci, Part A:
Polym Chem 2010, 48, 5271–5281.
2 Shoji, Y.; Mizoguchi, K.; Ueda, M. Polym
680–681.
ꢀ
C for 1 min under vacuum and then allowed to cool to room
1
temperature. The solid was dissolved in conc. H SO (7 mL), and
2
4
the solution was filtered through the glass filter 3G-3. Additional
mL of conc. H SO was added to wash the Pyrex tube and the
1
J 2008, 40,
3
2
4
filter. The combined conc. H SO solution was poured into water
2
4
13 GooSsen, L. J.; Ohlmann, D. M.; Lange, P. P. Synthesis
(300 mL) to precipitate the polymer, followed by neutralization
2009, 1, 160–164.
with NaHCO (30 g). The polymer was collected, and dried in
14 Ueda, M.; Morishima, M.; Kakuta, M. Polym J 1991, 23,
1511–1517.
3
ꢀ
vacuo at 120 C for 1 day. The yield of polymer was 0.224 g
–1
1
(
94%). IR (KBr), m (cm ): 3429 (ANH), 1658 (C ¼¼ O). H NMR
15 Ueda, S.; Nagasawa, H. J Org Chem, 2009, 74, 4272–4277.
4
728
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