Synthesis and characterization of aromatic poly(amides) based on 3,5-diamino-N-cyclopropylbenzamide

Article abstract of DOI:10.1039/c4ra16859c

Three aromatic poly(amides) (PAs) were prepared, one of them containing a dimethyldiphenylsilane unit from a new aromatic diamine monomer with a bulky pendant polar group. All PAs were obtained in high yield and the inherent viscosities were in the range

Full text of DOI:10.1039/c4ra16859c

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PAPER
Synthesis and characterization of aromatic
poly(amides) based on 3,5-diamino-N-
Cite this: RSC Adv., 2015, 5, 23057
cyclopropylbenzamide
a
A. Tundidor-Camba, C. A. Terraza,a L. H. Tagle,a D. Coll,a I. Ojedaa and M. Pinob
*
Three aromatic poly(amides) (PAs) were prepared, one of them containing a dimethyldiphenylsilane unit
from a new aromatic diamine monomer with a bulky pendant polar group. All PAs were obtained in high
yield and the inherent viscosities were in the range of 0.30 and 0.47 dL gꢀ1. The obtained poly(amides)
showed excellent solubility in a variety of aprotic polar organic solvents. PAs evidence thermal stability
with thermal decomposition temperature (TDT10%) between 300–371 ꢁC and the glass transition
temperatures (Tg) values were high (between 215 and 250 ꢁC). PAs containing silicon atom in the main
chain captures the highest moles number of water per mole of repeating unit. Contact angles were also
tested in order to know the hydrophilicity of the polymer films.
Received 22nd December 2014
Accepted 23rd February 2015
DOI: 10.1039/c4ra16859c
www.rsc.org/advances
Rigid aromatic poly(amides) with other polar groups into the
main or side chain are interesting in the reverse osmosis eld
1. Introduction
because it increases the hydrophilicity of the membrane,
allowing better diffusion of water through the polymeric
matrix.16 Structural rigidity of this sort of polymers is a critical
property for the adequate functioning of the membrane.17 Such
high stiffness degree is usually associated with high Tg values.
This work reports the synthesis and characterization of a
novel aromatic diamine with a cyclopropylcarbamoyl pendant
group and three aromatic poly(amides) derived from it. One of
them contains a dimethyldiphenylsilane unit in the repeating
unit. Solubility, water uptake, contact angle, inherent viscosity
and thermal properties of the polymers are also investigated
and discussed.
Thermally stable polymers are important because they can
replace metals and ceramics in several elds of science.
Specically, aromatic poly(amides) exhibit excellent mechan-
ical, electrical and chemical properties, making them very
interesting for their study as high performance materials.1–3
However, their industrial processing is affected by their
remarkable intractability caused by the strong molecular
interactions through hydrogen bonding of amide groups.4
With the aim to reduce the intermolecular bonding energy,
many structural modications have been made in poly(amides),
such as the incorporation of exible units, 1,3-substituted
monomers, bulky pendant groups or heteroatoms in the main
chain.5–8 These chemical modications provide interchain
distance, and consequently, higher free volume and solubility,
2. Experimental
without
affecting
the
thermal
properties.9,10
Ada-
2.1. Materials
mantylcarbamoyl pendant group or other cyclic side group such
as uorene or phenylcyclohexane were effective to improve the
solubility of the polymers derivatives.11–13
Anhydrous N,N-dimethylacetamide (DMAc), 3,5-dinitrobenzoyl
chloride, cyclopropylamine, Pd/C (10% w/w), 4,40-sulfonyldi-
benzoic acid and tert-butylisophthalic acid were obtained from
Aldrich Chemical (Milwaukee, WI). Bis(4-carboxyphenyl)
dimethylsilane was synthesized following a procedure already
reported by our research group.18 Diethyl ether and n-hexane
were reuxed over metallic sodium under nitrogen atmosphere.
All other reagents and solvents were purchased commercially as
analytical-grade and used without further purication.
In other works, and also in our previous works, it was found
that the introduction of diphenylsilane units in the polymer
backbone improves the solubility and maintains the thermal
properties of the polymeric materials.7,14,15 Silicon atom has a
lower electronegativity than carbon atom causing a small dipole
moment inside the chain, which increases the polarity of the
polymeric chain and therefore, its solubility in specic solvents.
a
´
Organic Chemistry Department, Faculty of Chemistry, Ponticia Universidad Catolica
2.2. Instrumentation and measurements
de Chile, Box 306, Post 22, Santiago, Chile. E-mail: atundido@uc.cl; Tel: +56
IR-TF spectra (KBr pellets) were recorded on a Perkin–Elmer
(Fremont CA) 1310 spectrophotometer over the range of 4000–
450 cmꢀ1. Melting points (uncorrected) were obtained on a
223541199
b
´
Physicochemical Department, Faculty of Chemistry, Ponticia Universidad Catolica
de Chile, Box 306, Post 22, Santiago, Chile
This journal is © The Royal Society of Chemistry 2015
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SMP3 Stuart Scientic melting point apparatus. 1H, 13C and 29Si
3,5-diamine-N-cyclopropylbenzamide (2). A mixture of 5 g (20
NMR spectra were carried out on a 400 MHz instrument (Bruker mmol) of 3,5-dinitro-N-cyclopropylbenzamide (1), 10% palla-
AC-200) using DMSO-d6 as solvent and TMS as internal stan- dium on activated carbon (0.250 g) and 100 mL of absolute
dard. Viscosimetric measurements were made in a Desreux– ethanol were placed under an atmosphere of hydrogen (30 psi)
Bischof type dilution viscosimeter at 25 ꢁC (c ¼ 0.5 g dLꢀ1). and allowed to react with stirring for 10 minutes. When the
Glass transition temperature (Tg) values were obtained with a pressure of the system decreased, the reaction bottle was loaded
Mettler-Toledo (Greifensee, Switzerland) DSC 821 calorimetric with 30 psi of additional of hydrogen, until the pressure of
ꢀ1
ꢁ
system (10 C min under N2 ow). Thermogravimetric anal- hydrogen was kept constant. Catalyst was removed by ltration
yses were carried out in a Mettler (Switzerland) TA-3000 calori- through a Celite plug, and the solvent removed under reduced
metric system equipped with a TC-10A processor, and a TG-50 pressure to afford 3.5 g of a yellow solid. The crude product was
thermobalance with a Mettler MT5 microbalance (temperature recrystallized from ethanol to afford 3.2 g of yellow crystals.
range between 25 ꢁC and 900 ꢁC at 10 ꢁC minꢀ1 under N2 ow).
Elemental analyses were made on a Fisons EA 1108-CHNS-O
equipment. A dataphysics OCA 20 device with a conventional
goniometer and high performance video camera, controlled by
SCA20 soware, was used to measure the optical contact angle.
Water sorption measurements were determined gravimetrically
at room temperature. Powder polymer samples (0.3 g), previ-
ously dried at 120 ꢁC for 24 h, were placed in a closed desiccator
containing a saturated aqueous solution of NaNO2, which
provided a relative humidity of 65%. The samples were
frequently weighed during 15 h and then allowed to humidify
Yield: 92%. M.p.: 201–202 ꢁC. IR (KBr, n, cmꢀ1): 3460, 3378,
3341 (NH2); 3236 (N–H); 3080 (C–H arom.); 2998 (C–H aliph.);
1644 (C]O), 1593 (N–H bending); 1527, 1456 (C]C); 1283 (C–N
bending); 746 (1,3,5-arom. subs.). H RMN (DMSO-d6, d, ppm):
for 5 more days until constant weight.
1
0.51 (m, 2H(7,70)); 0.62 (m, 2H(7,70)); 2.77 (m, 1H(6)); 4.81 (s,
4H(9)); 5.93 (s, 1H(1)); 6.18 (s, 2H(3)); 8.00 (s, 1H(8)). 13C RMN
(DMSO-d6, d, ppm), 6.07 (C7,70); 23.28 (C6); 102.43 (C1); 102.54
(C3); 136.74 (C4); 149.24 (C2); 169.63 (C5). Elem. Anal. Calcd. for
2.3. Monomer synthesis and characterization
3,5-dinitro-N-cyclopropylbenzamide (1). To a two-necked round-
bottomed ask equipped with magnetic stirrer, 3 mL (43.37
mmol) of cyclopropylamine in 125 mL of dry diethyl ether were
added. The mixture was stirred under a gentle nitrogen stream.
Small amounts (500 mg) of 3,5-dinitrobenzoyl chloride in solid
state were added every 5 minutes, until a total of 5 g (21.68
mmol). Suspension was maintained with stirring at room
temperature for 30 minutes and then ltered. White precipitate
was washed three times with 50 mL of HCl/water mixture (1 : 1
v/v) and then with water until neutral pH. Finally, the white
solid was dried in a vacuum oven. Crude product was recrys-
tallized from dichloromethane to afford 5 g of white needles.
C
10H13N3O; (191.11): C, 62.81%; H, 6.85%, N, 21.97%. Found: C,
62.16%; H, 6.06%, N, 21.88%.
Aromatic acid dichlorides (3, 4 and 5, Scheme 2). The cor-
responding dicarboxylic acid (10.0 mmol), 30 mL of thionyl
chloride and a few drops of DMF were reacted in a round
bottomed ask at 90 ꢁC for 3 h. Thionyl chloride excess was
removed from the solution by simple distillation. Crude 3 was
washed with dry n-hexane and then recrystallized from n-hexane
to afford 2.8 g of crystalline solid. Crude 4 was dissolved in dry
ꢁ
n-hexane and then cooled overnight at ꢀ30 C. The solid was
ltered and washed with cold n-hexane to afford 2.0 g of crys-
talline solid. Crude 5 was washed with dry n-hexane and then
recrystallized from n-hexane/toluene mixture (1 : 1 vol/vol) to
afford 2.7 g of white uffy solid.
4,4'-(dimethylsilanediyl)dibenzoyl chloride (3). Yield: 83%.
M.p.: 78–80 ꢁC. IR (KBr, n, cmꢀ1): 3030 (C–H arom.); 2980 (C–H
aliph.); 1774 (C]O), 1589, 1492 (C]C); 1413, 1106 (Si–C arom.);
1375 (Si–C aliph); 832 (arom. p-subst.).
5-(tert-butyl)isophthaloyl dichloride (4). Yield: 77%. M.p.:
44–45 ꢁC. IR (KBr, n, cmꢀ1): 3087 (C–H arom.); 2967, 2905 (C–H
aliph.); 1757 (C]O), 1587, 1473 (C]C); 1396, 1367 (–C(CH3)3
bending); 752 (1,3,5-arom.).
4,4'-sulfonyldibenzoyl chloride (5). Yield: 78%. M.p.: 159–160
ꢁC. IR (KBr, n, cmꢀ1): 3093, 3041 (C–H arom.); 1782, 1745 (C]O),
1590, 1575 (C]C); 1328, 1154 (S]O bending); 881 (arom.
p-subst.).
Yield: 92%. M.p.: 158–159 ꢁC. IR (KBr, n, cmꢀ1): 3289 (N–H);
3099, 3086 (C–H arom.); 2871 (C–H aliph.); 1644 (C]O); 1536,
1343 (NO2); 1457, 1422 (C]C); 730 (1,3,5-arom. subs.). 1H RMN
(DMSO-d6, d, ppm): 0.65 (m, 2H(7,70)); 0.77 (m, 2H(7,70)); 2.93
(m, 1H(6)); 8.94 (s, 1H(1)); 9.01 (s, 2H(3)); 9.12 (s, 1H(8)). 13C
RMN (DMSO-d6, d, ppm), 5.97 (C7,70); 23.76 (C6); 121.05 (C1);
127.73 (C3); 137.21 (C4); 148.47 (C2); 163.46 (C5). Elem. Anal.
Calcd. for C10H9N3O5; (251.05): C, 47.81%; H, 3.61%, N, 16.73%.
Found: C, 47.18%; H, 3.35%, N, 16.66%.
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2.4. Polymer synthesis and characterization
PA-3. Yield: 86%. IR (KBr, n, cmꢀ1), 3442 (N–H); 3094 (C–H
arom.); 2935 (C–H aliph.); 1654 (C]O) 1560, 1543 (C]C); 855
A typical polymerization procedure for the synthesis of poly-
(amides) was as follows. To a three-necked round-bottomed ask
equipped with mechanical stirrer, was added 1.18 mmol of 3,5-
diamino-N-cyclopropylbenzamide (2) and 1.5 mL of dry DMAc.
When the solution was completed, it was cooled with an ice-water
bath and 1.18 mmol of the corresponding acid dichloride (3, 4 or 5)
and 1.0 mL of dry DMAc were added. The ice-water bath was
removed when acid dichloride was entirely dissolved. Then, the
mixture was stirred at room temperature during 6 hours. The
resulting mixture was poured into 300 mL of water with stirring.
White solid was ltered, washed thoroughly with water and dried
at 100 ꢁC during 12 hours. Thus, PA-1 was obtained from acid
dichloride 3, PA-2 from acid dichloride 4 and PA-3 using acid
dichloride 5.
1
(arom. p-subs.); 747 (1,3,5-arom. subs.). H NMR (DMSO-d6, d,
ppm), 0.58 (s, 2H(7,70)); 0.68 (s, 2H(7,70)); 2.87 (s, 1H(6)); 7.90 (s,
2H(3)); 8.20 (s, 8H(12,13)); 8.45 (s, 1H(1)); 8.50 (s, 1H(8)); 10.71
(s, 2H(9)). 13C NMR (DMSO-d6, d, ppm), 168.1 (C10); 164.8 (C5);
143.4 (C14); 140.0 (C2); 139.3 (C4); 136.3 (C11); 129.6 (C13);
128.2 (C12); 116.0 (C3); 115.7 (C1); 23.6 (C6); 6.1 (C7,70). Elem.
Anal. Calcd. for [C24H19N3O5S]n (461.49)n, C, 62.46%; H, 4.15%;
N, 9.11%. Found: C, 62.16%; H, 4.11%; N, 9.03%.
PA-1. Yield: 99%. IR (KBr, n, cmꢀ1), 3444 (N–H); 3021 (C–H
arom.); 2956 (C–H aliph.); 1643 (C]O); 1555, 1538 (C]C); 1415,
1093 (Si–C arom.); 1376 (Si–C aliph); 814 (arom. p-subs.); 746
1
(1,3,5-arom. subs.). H NMR (DMSO-d6, d, ppm), 0.49–0.60 (m,
10H(7,70,15)); 2.77 (m, 1H(6)); 7.62 (d, J ¼ 7.5 Hz, 4H(13)); 7.80
(s, 2H(3)); 7.89 (d, J ¼ 7.6 Hz, 4H(12)); 8.36 (s, 1H(1)); 8.37 (s,
1H(8)); 10.36 (s, 2H(9)). 13C NMR (DMSO-d6, d, ppm), 167.3
(C10); 165.1 (C5); 141.3 (C2); 138.6 (C4); 135.2 (C14); 134.9 (C11);
133.4 (C13); 126.4 (C12); 114.9 (C3); 114.8 (C1); 22.6 (C6); 5.2
(C7,70); 3.4 (C15). 29Si NMR (DMSO-d6, d, ppm), 8.47. Elem. Anal.
3. Results and discussion
3.1. Monomer synthesis and characterization
A
new diamine, 3,5-diamino-N-cyclopropylbenzamide, was
Calcd. for [C26H25N3O3Si]n (455.58)n, C, 68.55%; H, 5.53%; N, synthesized by reacting 3,5-dinitrobenzoyl chloride with cyclo-
9.22%. Found: C, 68.36%; H, 5.43%; N, 9.12%.
propylamine in anhydrous diethyl ether, followed by a reduc-
tion reaction using hydrogen gas, Pd/C as catalyst and absolute
ethanol as solvent (Scheme 1).
PA-2. Yield: 99%. IR (KBr, n, cmꢀ1), 3440 (N–H); 3088 (C–H
arom.); 2961 (C–H aliph.); 1654 (C]O); 1598, 1543 (C]C); 739
(1,3,5-arom. subs.). 1H NMR (DMSO-d6, d, ppm), 0.46 (m,
2H(7,70)); 0.56 (m, 2H(7,70)); 1.29 (s, 9H(16)); 2.74 (m, 1H(6));
7.80 (s, 2H(3)); 8.07 (s, 2H(13)); 8.36 (s, 1H(11)); 8.37 (s, 1H(1));
8.41 (s, 1H(8)); 10.52 (s, 2H(9)). 13C NMR (DMSO-d6, d, ppm),
168.2 (C10); 165.8 (C5); 151.8 (C14); 139.5 (C2); 136.1 (C4); 135.1
(C12); 128.1 (C13); 125.2 (C11); 116.4 (C3); 116.2 (C1); 35.4 (C15);
31.4 (C16); 23.6 (C6); 6.1 (C7,70). Elem. Anal. Calcd. for
[C22H23N3O3]n (377.44)n, C, 70.01%; H, 6.14%; N, 11.13%.
Found: C, 69.79%; H, 6.09%; N, 11.01%.
Scheme
cyclopropylbenzamide.
1
Synthetic
route
to
obtain
3,5-diamino-N-
Fig. 1 FT-IR spectra of both dinitro (1) and diamine (2) compounds.
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Dinitro compound 1 was insoluble in the medium reaction
(anhydrous diethyl ether), favoring the isolation process. The
next step (reduction reaction) was conducted in a dark media to
prevent color change due to photodegradation of the diamine 2
(this diamine derivative is sensitive to light, changing from
yellow to red color).
The FT-IR spectra in Fig. 1 conrmed the presence of both
compounds. The bands at 3289 cmꢀ1 and 1644 cmꢀ1 corre-
spond to stretching of N–H and C]O groups, respectively,
while those at 1536 and 1343 cmꢀ1 were assigned to the vibra-
tion of the nitro group. Disappearance of these two signals and
the appearance of sharp bands at 3460 and 3378 cmꢀ1, corre-
sponding to the stretching of the amino group, conrmed the
formation of the monomer.
The 1H NMR spectrum in Fig. 2 also conrmed the structure
of the diamine. The peak at 8.00 ppm was assigned to amidic
hydrogen. The singlet at 4.81 ppm, integrating for 4 nuclei
corresponds to the hydrogens of the amino groups. Also, a clear
pattern of cyclopropyl fragment was possible to observe. The
multiplet at 2.77 ppm was assigned to hydrogen H6, while one
of the hydrogens H7 appears at 0.62 ppm and the other at 0.51
ppm. The same happened for hydrogens H70. The difference in
Fig. 3 FT-IR spectra of all aromatic acid dichloride derivatives.
chemical shi of the hydrogens H7 and H70 is due to the axial
and equatorial positions of both in the cyclopropyl ring.
Meanwhile, the 13C NMR spectrum showed the seven expected
carbon signals. The peak at 169.6 ppm corresponds to the
carbonyl carbon of the amide group. The carbons C1 and C3
showed similar chemical shis due to the mesomeric effect
induced by the amine group, by shielding the carbon nucleus.
The FT-IR spectra in Fig. 3 conrmed the absence of OH
bands in the all aromatic acid dichloride. Characterization by
NMR techniques was not necessary in order to continue with
the synthesis of polymers.
3.2. Polymer synthesis and characterization
Poly(amides) were prepared in solution, by reacting the appro-
priate acid dichloride with the diamine in N,N-dimethylaceta-
mide as solvent (Scheme 2).
Successful conversion from acid dichloride and diamine to
amide was conrmed by the FT-IR spectra, in which the char-
acteristic absorptions due to the amide group moiety around
3440 cmꢀ1 (yN–H) and 1650 cmꢀ1 (yC¼O) can be clearly identied
(Fig. 4).
Fig. 2 1H and 13C NMR spectrum of aromatic diamine 2.
23060 | RSC Adv., 2015, 5, 23057–23066
Scheme 2 Synthetic route of poly(amides).
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repeating unit. The hydrogens H8 and H1 appeared with a very
similar chemical shi, as shown in the enlarged gure. The
signals of hydrogens H12 and H13 appear as doublets, charac-
teristic pattern of substitution in the para position of the
aromatic ring (AB system). Also, the coupling constant (J) of
hydrogens H12 and H13 was determined (J ¼ 7.5 Hz approxi-
mately). The chemical shis of hydrogens H7 and H70 appear
overlapped with the singlet at 0.5 ppm, which corresponds to
hydrogens of the methyl groups bound to the silicon atom.
The 13C NMR spectrum of PA-1 (Fig. 6) shows two peaks at
167.3 and 165.1 ppm, corresponding to carbonyl carbon C10
and C5 of the amide groups, respectively, which exhibit
different chemical environments. Aliphatic carbon C15 appears
with a d value below zero due to the lower electronegativity of
silicon atom respect to carbon. Thus, the respective signal is
shied to higher eld. Similar behavior was observed for the
methyl hydrogens in the 1H NMR spectra. Chemical shis of the
remaining carbons were in accordance with the proposed
structure.
Fig. 4 FT-IR spectra of poly(amides).
Fig. 5 shows the 1H NMR spectrum of PA-1 in DMSO-d6. The
singlet at 10.36 ppm conrms the formation of an amide
linkage. Other peaks were assigned to hydrogens of the
Polymeric samples were also characterized by 29Si NMR.
Fig. 7 shows the spectrum of PA-1, where a single signal at ꢀ8.47
Fig. 5 1H NMR spectrum of PA-1 in DMSO-d6.
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Fig. 6 13C NMR spectrum of PA-1 in DMSO-d6.
ppm is observed. This chemical shi is expected when the
silicon atom is surrounded by two aromatic rings and two
methyl groups.19,20
3.3. Inherent viscosity and solubility
Inherent viscosity was measured at a single point, in N-methyl-2-
pyrrolidone (NMP) solution at 25 ꢂ 0.1 ꢁC (0.5 g dLꢀ1). Inherent
viscosity values were in the range of 0.30 to 0.47 dL gꢀ1
.
On the other hand, the solubility of poly(amides) was tested in
various organic solvents, and the results are listed in Table 1.
Unmodied polyamides such as PPTA and PPMI were insoluble
in m-cresol and, in some cases; LiCl was required for their
complete dissolution. The chemical modications made on the
new poly(amides) improve solubility, mainly in polar aprotic
solvents and m-cresol.
Fig. 7 29Si NMR spectrum of PA-1 in DMSO-d6.
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the chain.7,22 DTGA curves show a complex degradative process
between 300–400 ꢁC. However, a peak near 500 ꢁC, corre-
sponding to the main polymer degradation, was observed. PA-3
exhibited the lower value of TDT10%. Taking into account the
values of inherent viscosity, PA-3 showed chains shorter than
the other PAs (lower inherent viscosity), which could be asso-
Table 1 Inherent viscosity and solubility results of PAs
Solubility
PA
hinh (dL gꢀ1 a
) DMSO NMP DMF DMAc m-cresol THF
PA-1
PA-2
PA-3
PMPI*
PPTA**
0.45
0.47
0.30
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
—
—
—
—
—
—
ciated to the low value of TDT10%
.
b
b
In all cases, the char yield at 800 ꢁC was nearly to 40%. High
aromatic content of all poly(amides) was responsible for the
high char yields aer calcinations.
b
b
b
—
a
Measured in NMP (0.5 g dLꢀ1 at 25 ꢁC) Solubility: +, Soluble at room
temperature; -, Insoluble. *Poly(m-phenylene isophthalamide) used as
ref. 21. **Poly(p-phenylene terephthalamide) used as ref. 21. 5% wt
of LiCl was required.
b
DSC analyses were performed in order to obtain the Tg values
of all poly(amides) and the results are summarized in Table 2.
Fig. 9 shows the DSC curves obtained from the second heating
scan. Polymers did not show melting peaks, indicating the
amorphous nature of the materials.
Table 2 Summary of thermal properties of the PAs
One transition was detected in all poly(amides) corre-
ꢁ
sponding to the Tg. PAs showed Tg values greater than 215 C.
PA
aTDT10% (ꢁC)
bTg (ꢁC)
cChar Yield (%)
PA-1 and PA-3 showed similar Tg values and they were larger
than those of PA-2. Regarding the structures of the poly-
(amides), PA-1 and PA-3 have para-position linkage while PA-2
has meta-position linkage. The chains in PA-2 could be less
packed. This, and the fact that repeating unit in PA-2 has the
lower aromatic content could be responsible for its lower Tg
value. In general, the Tg values were large compared to other
structurally modied poly(amides).14,23–25 These results could be
interesting for applications in the gas separation membrane
eld or reverse osmosis membrane eld. These technological
applications, from the point of view of thermal properties, seek
to obtain polymers with high values of the glass transition
temperature.26–28
PA-1
PA-2
PA-3
PMPI*
PPTA**
371
359
300
245
215
250
280
425
39
40
37
a
Thermal decomposition temperature at which 10% weight loss was
recovered by TGA at a heating rate of 10 ꢁC minꢀ1 in nitrogen
atmosphere. Glass transition temperature taken at 10 ꢁC minꢀ1 in
b
c
nitrogen atmosphere. Residual weight (%) when heated to 800 ꢁC.
*Poly(m-phenylene isophthalamide) used as ref. 21. **Poly-
(p-phenylene terephthalamide) used as ref. 21.
Table 2 also shows the Tg values for PMPI and PPTA. These
values are very high, indicating that the structural modica-
tions made on the poly(amides) synthesized in this work
allowed to reduce structural rigidity, favoring industrial proc-
essability and reducing energy costs in case that mold the
material to a temperature above the Tg be necessary.
3.4. Thermal properties
Thermal stability of all poly(amides) was evaluated by TGA and
DSC techniques under a nitrogen atmosphere and the results
are summarized in Table 2. Fig. 8 shows the TGA curves for all
PAs. Three PAs exhibited good thermal stability, with the 10%
weight loss temperature (TDT10%) in the range of 300–371 ꢁC.
PA-1 exhibited the highest thermal stability among them,
probably due to the presence of the silicon atom, which
increases the ionic character of the silicon–carbon bond along
3.5. Water uptake and contact angle
Water sorption measurements were performed gravimetrically
at room temperature using poly(amides) powder samples
previously dried at 120 ꢁC for 24 h. Samples were introduced in
a closed desiccator containing a relative humidity of 65%. The
samples were frequently weighed during 15 h and then allowed
to humidify for 5 more days until constant weight.
Table 3 shows the percentage of water uptake for each
poly(amide). PA-2 had the largest value of water uptake.
However, analyzing the moles of water per mol of repeat unit,
PA-1 has more moles of water in the repeat unit than PA-2. As
the amount of amide groups in both repeating units is the
same, the higher water content in the repeating unit of PA-1
could be associated to the presence of the silicon atom. It is
known that the affinity of silicon to oxygen is very strong,29
being there an additional interaction between the silicon atom
and the water oxygen.
PA-3 had the lowest value of water uptake and the least
amount of moles of water per mol of repeating unit. The most
Fig. 8 TGA and DTGA curves of PAs.
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Fig. 9 DSC curves of PAs.
Table 3 Summary of the water sorption and contact angles of PAs
dimethylacetamide polymer solutions onto a glass plate and
heating at 60 ꢁC overnight. Then, the lms were stripped off and
were dried in a vacuum oven at 100 ꢁC overnight and at 150 ꢁC
for 48 h. Table 3 also shows contact angles measured for PAs
and the image of the drop (Fig. 10) was captured ve seconds
aer placed.
PA-1 and PA-3 had higher contact angles than PA-2, there-
fore, the surface of PA-2 is the most hydrophilic, since it showed
the smallest contact angle. This result would be inconsistent
with those obtained in the experiment of water absorption, but
morphology of the lm sample is a very important issue in
wettability properties. The explanation to these results should
be sought in the capability that has the chain for adopting
different conformations and molecular packing. From this
point of view, PA-2 has only two aromatic rings in their
repeating unit, while PA-1 and PA-3 have three aromatic rings,
therefore PA-2 has the lower aromatic content, which implies a
lower hydrophobicity and therefore, more wettability.
mol H2O/mol mol H2O/mol
PA
Water uptake (%)a repeat unit
amide
q (ꢁ)b
PA-1
PA-2
PA-3
5.4
6.0
4.5
1.5
1.4
1.2
0.7
0.44
0.48
0.34
0.35
84 ꢂ 1.8
69 ꢂ 0.4
81 ꢂ 2.0
—
PMPI* 5.5
a
Measurements were performed using the same conditions as in ref.
30. Contact angle recorded at a rate of 10 mL sꢀ1 at 25 ꢁC. *Poly(m-
b
phenylene isophthalamide) used as ref. 30.
plausible explanation for this result is that the sulfone group
could form intra and/or intermolecular H-bonds with nearby
amide groups, thereby reducing the number of moles of water
per mol of amide groups. This fact is related with the large Tg
value obtained for PA-3. The greater structural rigidity would
hinder penetration of water molecules through the polymer
matrix.
For comparison, the results obtained from an unmodied
poly(amide), m-phenylene isophthalamide (PMPI),30 were
included in Table 3. This poly(amide) is used as membrane for
reverse osmosis separation.31 The poly(amides) prepared in this
work have similar values of water uptake and exhibit water
absorption values larger than 1.2 mol of water per repeating
unit, while PMPI only has 0.7. Preliminarily, the prepared
poly(amides) could have application in the eld of reverse
osmosis separation.
4. Conclusions
Based on the synthesis of a novel aromatic diamine containing
a bulky pendant polar group, a series of three aromatic poly-
(amides) were successfully prepared by low temperature solu-
tion polycondensation technique. One PAs had a silicon atom in
the repeating unit, which possibly contributes to the increased
water uptake per mole of the repeating unit. In general, all PAs
had water absorption values per repeating unit larger than
PMPI. All PAs were thermally stable and the glass transition
temperature values were in the range of 215–250 ꢁC. The
obtained PAs were characterized by good solubility in aprotic
Another technique to investigate the wettability of a surface
of lm samples is by contact angle measurements. Dense lms
were prepared from all PAs by casting 10% (w/v) ltered N,N-
Fig. 10 The profiles of a droplet on the PAs. A) correspond to PA-1, B) to PA-2 and C) to PA-3.
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solvents and m-cresol. PA-2 showed the smallest contact angle,
poly(ether-imide)s
obtained
by
Yamasaki-Higashi
indicating the most hydrophilic surface.
phosphorilation techique. Use of bis(4-(4-aminophenoxy)-
phenyl)ethylmethylsilane, Polym. Bull., 2014, 71(5), 1001.
15 M. Bruma and B. Schulz, Silicon-containing aromatic
polymer, J. Macromol. Sci., Polym. Rev., 2001, 41, 1.
Acknowledgements
Tundidor-Camba, A. acknowledges the nancial assistance by 16 R. L. Riley, et al., Poly(amide) reverse osmosis membrane
´
´
´
´
Comision Nacional de Investigacion Cientıca y Tecnologica,
fouling and its prevention: oxidation-resistant membrane
development, membrane surface smoothing and enhanced
membrane hydrophilicity, U. S. Department of the Interior
Desalination Research and Development Program Bureau of
Reclamation, September, 2000.
CONICYT, through Project 79130011.
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