Synthesis and properties of new aromatic polyisophthalamides with adamantylamide pendent groups

Article abstract of DOI:10.1002/pola.23939

A new diacid monomer containing a pendent adamantyl ring was reacted with various aromatic diamines to prepare novel aromatic polyisophthalamides (PIPAs). The polymers were obtained in high yield and high molecular weight by the Yamazaki-Higashi phosphory

Full text of DOI:10.1002/pola.23939

Synthesis and Properties of New Aromatic Polyisophthalamides with
Adamantylamide Pendent Groups
´
´
´ ˜
´
JORGE F. ESPESO, ANGEL E. LOZANO, JOSE G. DE LA CAMPA, INIGO GARCIA-YOLDI, JAVIER DE ABAJO
Departmento de Qu´ımica Macromolecular, Instituto de Ciencia y Tecnolog´ıa de Polı´meros, C.S.I.C, Juan de la Cierva 3,
28006 Madrid, Spain
Received 3 November 2009; accepted 18 January 2010
DOI: 10.1002/pola.23939
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A new diacid monomer containing a pendent ada-
mantyl ring was reacted with various aromatic diamines to
prepare novel aromatic polyisophthalamides (PIPAs). The poly-
mers were obtained in high yield and high molecular weight
by the Yamazaki-Higashi phosphorylation method of polycon-
densation. Inherent viscosities ranged from 0.40 to 0.82 dL/g,
which corresponds to weight-average and number-average
molecular weights (GPC) in the range 21,000–63,000 g/mol and
9000–31,000 g/mol, respectively. The polymers were essentially
amorphous and soluble in a variety of polar aprotic solvents,
and they afforded transparent, creasable films by the solution-
casting method. The great size of the polyhedral adamantyl
moiety brought about a significant restriction of segmental
mobility, which translated into a strong increase of Tg, so that
very high glass transition temperatures were observed, in the
range 335–370 ꢀC (DSC), which are 70–90 ꢀC above the glass
transition temperatures of homologous PIPAs without pendent
groups. Thus, it can be stated that these adamantyl containing
polyamides are among the soluble aromatic PIPAs with highest
Tg ever described. Conversely, the initial decomposition tem-
perature, as measured by thermogravimetric analysis, was
about 400 ꢀC, which is lower by 40–70ꢀ than that of unsubsti-
tuted counterparts. Polymer films exhibited good mechanical
properties, with tensile strengths over 65 MPa and tensile mod-
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uli between 2.0 and 2.6 GPa.
2010 Wiley Periodicals, Inc. J
Polym Sci Part A: Polym Chem 48: 1743–1751, 2010
KEYWORDS: adamantane; mechanical properties; pendent
groups; polyamides; thermal properties
INTRODUCTION Aromatic polyamides constitute a special
group of engineering organic materials, which are considered
among the so-called high performance polymers. Wholly aro-
matic polyisophthalamides (PIPAs) and polyterephthalamides
are the most important families among aromatic polya-
mides.1,2 They are characterized by a very favorable combi-
nation of thermal and mechanical properties, which enable
them to be used in the fabrication of, for instance, high-
strength/high-modulus fibers, high-temperature and fire-
resistant fibers, and high-performance films.3 On the other
hand, wholly aromatic polyamides show very poor solubility,
and they do not melt below their decomposition tempera-
tures; therefore, they show a remarkable intractability, which
limits their utilization in many modern fields of application
where good processability is required. Thus, in the last few
decades, many studies have been undertaken to chemically
modify the primary structure of polyamides to improve their
tractability without severely impairing their excellent ther-
mal and mechanical properties.3–9 Among the approaches
outlined for these purposes, the incorporation of bulky pend-
ent groups has proved to be a reasonably good alternative to
enhance the solubility (processability) of aromatic poly-
amides.10–12 In this regard, it is worth stressing that, as a
rule, aliphatic pendent groups do lead to an improvement of
solubility, but they bring about both a drop of the transition
temperature and a lowering of the initial decomposition tem-
perature. On the other hand, aromatic and heterocyclic pend-
ent groups generally improve the solubility and do not sub-
stantially impair the thermal properties, and their
incorporation into aromatic polyamides can even enhance
the thermal resistance and can substantially increase the
glass transition temperature.13 That is the case, for instance,
for PIPAs which were modified by introducing phthalimido,14
benzothiazole,15 benzoxazole,16 or benzimidazole17 pendent
groups.
As a contribution to a continuous effort to further improve
the properties of modified aromatic PIPAs, the systematic
incorporation of bulky pendent groups has now been
extended to the preparation of PIPAs with a bulky cycloali-
phatic group, viz., the adamantyl group. Aromatic condensa-
tion polymers containing adamantane groups in the back-
bone have repeatedly been reported in the past. Thus,
polyamides,18 polyimides,19,20 phenolic resins,21 polysul-
fones,22 and polycarbonates23 have been synthesized from
monomers based on the adamantane ring. As a rule, the
incorporation of these moieties into the polymer structure
has brought about an increase of both solubility and glass
transition temperatures, so that the incorporation of
Correspondence to: J. de Abajo (E-mail: deabajo@ictp.csic.es)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1743–1751 (2010) 2010 Wiley Periodicals, Inc.
SYNTHESIS AND PROPERTIES OF NEW AROMATIC PIPAs, ESPESO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
adamantyl pendent groups was foreseen as a suitable alter-
native to improve the properties of traditional PIPAs.
The novel polymers reported here were synthesized from a
new monomer derived from isophthalic acid, which served
as the bearer of the pendent group. Thus, the adamantyl
group was joined to the main chain through an amide link-
age, which was expected not to bring about any significant
loss of thermal resistance of the modified PIPAs, because its
dissociation energy should be comparable to that of the
main chain amide linkages.
The main purpose of this work was to study the effect of the
bulky adamantyl pendent group on the general properties of
PIPAs, in comparison with those of homologous unsubsti-
tuted PIPAs and other related polyamides containing pend-
ent groups. In particular, the effect of chemical structure on
solubility, thermal transitions, thermal resistance, and me-
chanical strength of films was the main target of this study.
EXPERIMENTAL
Materials
1-Chlorocarbonyladamantane (Aldrich), 5-aminoisophthalic
acid (Aldrich), and N,N-dimethylacetamide (DMA, Scharlau)
were used as received. Reagent grade lithium chloride was
dried at 300 ꢀC before use. N-Methyl-2-pyrrolidinone (NMP,
Aldrich) was purified by distillation twice under reduced
pressure over calcium hydride and stored over molecular
sieves (4 Å). Pyridine (Py, Aldrich) was refluxed over potas-
sium hydroxide overnight, distilled at atmospheric pressure,
and stored over molecular sieves (4 Å). Triphenyl phosphite
(TPP, Aldrich) was distilled twice at low pressure.
The diamines, m-phenylenediamine (Aldrich), bis(4-amino-
phenyl)ether (Aldrich), 4,40-diaminobenzanilide (Aldrich),
9,9-bis(4-aminophenyl)fluorene (Chriskev), and 2,2-bis(4-
aminophenyl)hexafluoropropane (Chriskev) were purified by
sublimation just before use. 4(5)-(1-Adamantyl)-1,3-bis(4-
aminophenoxy)benzene was synthesized and purified in our
laboratory, according to the previously reported method.5
FIGURE 1 IR and 1H NMR spectra of 4(5)-[(1-adamantylcarbonyl)
amino]isophthalic acid.
band I), 1575 (combination of CAN stretching and NAH
bending, amide band II) (Fig. 1).
Monomer Synthesis
1H NMR (300 MHz, DMSO-d6, d, ppm) 1.69 (s, 6H), 1.92 (s,
6H), 2.01 (s, 3H), 8.14 (t, J ¼ 1.55 Hz, 1H), 8.56 (d, J ¼ 1.55
Hz, 2H), 9.55 (s, 1H), 13.21 (br s, 2H); 13C NMR (300 MHz,
DMSO-d6, d, ppm): 27.72, 36.04, 38.18, 41.13, 124.54,
131.50, 140.14, 145.35, 166.70, 176.51 (Fig. 2).
5-(1-Adamantylcarbamoyl) Isophthalic Acid
To a three-necked glass flask equipped with magnetic stirrer
was added 45.3 g (0.25 mol) of 5-aminoisophthalic in 125
ꢀ
mL of dry DMA. The mixture was warmed to 80 C under a
gentle nitrogen stream, until a clear solution was obtained.
The solution was cooled to 10 ꢀC and a solution of 53.6 g
(0.27 mol) of 1-chlorocarbonyladamantane in 100 mL of
DMA was added dropwise during 1 h. The reaction mixture
was maintained at room temperature for 3 h, and then it
was poured into water. The white precipitate was filtered,
washed three times with warm water, and finally dried in a
vacuum oven. The crude product was recrystallized from a
mixture of DMA: H2O (50:50) to afford 81 g (92%) of white
ELEM. ANAL. Calcd. for C19H21NO5 (343.38 g/mol): C, 66.46%;
H, 6.16%; N, 4.08%. Found: C, 66.26%; H, 6.34%; N, 4.12%.
Polymers Syntheses
All of the polymers were synthesized by the Yamazaki-Higa-
shi phosphorylation polyamidation method, which is
described in detail for the case of polymer 2c (Scheme 2).
A three-necked flask equipped with a mechanical stirrer, was
flame dried and charged under a blanket of nitrogen with
NMP (10 mL), diacid 5-ADIP (3.434 g, 0.01 mol), lithium
chloride (1.4 g), and pyridine (6 mL). The mixture was
stirred at room temperature until the diacid was completely
ꢀ
needles, (mp: 304 C, by DSC).
IR (KBr, cmꢁ1): 3390 (NAH stretching), 3240 (OAH stretch-
ing), 2965–2832 (aliphatic CAH stretching), 1720 (C¼¼O car-
boxylic stretching), 1670 (C¼¼O amide stretching, amide
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ARTICLE
Measurements
Elemental analyses were made in a Carlo Erba EA1108 Ele-
mental Analyzer. FT-IR spectra were obtained on a Perkin–
Elmer Spectrum One FT-IR spectrometer on pressed powder
samples and thin films. 1H and 13C NMR spectra were
recorded on a Varian Inova-300 spectrometer at 299.95 and
75.43 MHz, respectively, with standard acquisition parame-
ters. 1H NMR spectra at 80 ꢀC of 2d and 2f were recorded
on a Varian Inova-400 spectrometer at 399.95 MHz. Solubil-
ities were determined by mixing 10 mg of polymer with
1 mL of solvent for 24 h at room temperature. Samples that
did not dissolve were heated to the solvent boiling tempera-
ture. Differential scanning calorimetry (DSC) analyses were
performed on a TA instruments TA-Q-2000 calorimeter at a
heating rate of 20 ꢀC/min under nitrogen. Thermogravimet-
ric analyses (TGA) were performed under nitrogen, with a
TA Q-500 analyzer at 10 ꢀC/min, on 2–3 mg samples. Addi-
tional high-resolution TGA analyses were carried out by
using the standard TA Hi-Res method implemented in the TA
Q-500 device. Inherent viscosities were measured on filtered
0.5 g/dL polymer solutions in DMA at 25.0 6 0.1 ꢀC, in an
automated Ubbelohde viscometer. The mechanical properties
were tested on a MTS Synergie 200 Universal Testing
Machine, using strips 5 mm wide, 50 mm long, and 40–60
lm thick, that were cut from polymer films. An extension
rate of 1 mm/min was applied with a gauge length of
10 mm. Wide angle X-ray diffraction patterns were obtained
by means of a Philips X-ray diffractometer using Cu Ka radia-
tion over polymer films.
FIGURE 2 1H NMR spectrum of polyamide 2c.
dissolved. After that, the diamine 2,2-bis(4-aminophenyl)hex-
afluoropropane (3.343 g, 0.01 mol) and TPP (6.826 g, 0.022
mol) were rapidly added with aꢀdditional NMP (10 mL), and
the solution was heated to 105 C and held at this tempera-
ture for 3 h. The resulting viscous solution was poured into
500 mL of ethanol and the polymer precipitate was washed
several times with hot water, extracted with ethanol for 24 h
in a Soxhletꢀ apparatus, and dried overnight in a vacuum
oven at 100 C. A yield of 98% was achieved.
1H NMR results for all polymers were the following:
Size exclusion chromatography (SEC) measurements were
carried out using PL gel columns (Polymer Laboratories) of
nominal pore sizes 500, 104, and 105 Å. N,N-Dimethylforma-
mide (DMF) with 0.1% LiBr was used as solvent, and the
measurements were done at 70 ꢀC with a flow rate of 1.0
mL/min using an UV detector. The columns were calibrated
with narrow standards of a suitable aromatic polyamide,
poly(m-phenyleneisophthalamide), and polystyrene.
Polymer NMR results: 2a: 1H NMR (300 MHz, DMSO-d6, d,
ppm) 1.70 (s, 6H), 1.95 (s, 6H), 2.02 (s, 3H), 7.35 (t, J ¼ 8.0
Hz, 1H), 7.52 (d, J ¼ 7.8 Hz, 2H), 8.20 (s, 1H), 8.34 (s, 1H),
8.43 (s, 2H), 9.58 (s, 1H), 10.49 (s, 2H).
1
2b: H NMR (300 MHz, DMSO-d6, d, ppm) 1.72 (s, 6H), 1.93
(m, 6H), 2.04 (s, 3H), 7.05 (d, J ¼ 8.9 Hz, 4H), 7.81 (d, J ¼
8.9 Hz, 4H), 8.19 (s, 1H), 8.43 (s, 2H), 9.60 (s, 1H) 10.46 (s,
2H).
RESULTS AND DISCUSSION
2c: 1H NMR (300 MHz, DMSO-d6, d, ppm) 1.70 (s, 6H), 1.94
(s, 6H), 2.02 (s, 3H), 7.37 (d, J ¼ 7.7 Hz, 4H), 7.91 (d, J ¼ 8.9
Hz, 4H), 8.19 (s, 1H), 8.45 (s, 2H), 9.60 (s, 1H), 10.67 (s,
2H).
Monomer Synthesis
The monomer 5-(1-adamantylcarbonylamino) isophthalic
acid (5-ADIP) was prepared by a synthetic route depicted in
Scheme 1, using as starting material 1-adamantanecarbonyl
2d: 1H NMR (400 MHz, DMSO-d6, d, ppm, T ¼ 80 ꢀC) 1.73
(s, 6H), 1.97 (s, 6H), 2.04 (s, 3H), 7.72 (d, J ¼ 20.5 Hz, 4H),
7.96 (d, J ¼ 19.9 Hz, 4H), 8.21 (s, 1H), 8.42 (s, 2H), 9.36 (s,
1H), 9.98 (s, 1H), 10.19 (s, 1H), 10.48 (s, 1H).
chloride in
a classical, high yield amidation synthesis.
Attempts to synthesize the diacid chloride of 5-ADIP, to use
it in a conventional polyamidation with diamines at low tem-
perature, were unsuccessful. This was due to the presence of
the amide groups in 5-ADIP, which leads to secondary reac-
tions when chlorinating agents such as thionyl chloride are
used.24
2e: 1H NMR (300 MHz, DMSO-d6, d, ppm) 1.68 (s, 6H), 1.92
(s, 6H), 2.00 (s, 3H), 7.11 (d, J ¼ 8.5 Hz, 4H), 7.35 (d, J ¼
14.2, 7.3 Hz, 4H), 7.48 (d, J ¼ 7.3 Hz, 2H), 7.65 (d, J ¼ 8.6
Hz, 4H), 7.92 (d, J ¼ 7.2 Hz, 2H), 8.10 (s, 1H), 8.37 (s, 2H),
9.54 (s, 1H), 10.40 (s, 2H).
Figure 1 shows the IR spectra of the dicarboxylic acid mono-
mer, with a narrow absorption band at approximately 3390
cmꢁ1 (amide NAH stretching); the characteristic wide band
of aromatic carboxylic acid with a maximum at 3240 cmꢁ1
(OAH stretching) and the carbonyl absorption band at 1720
cmꢁ1 (C¼¼O stretching); two intense, sharp bands at 2832
and 2965 cmꢁ1 (aliphatic CAH stretching); and the bands of
2f: 1H NMR (400 MHz, DMSO-d6, d, ppm, T ¼ 80 ꢀC) 1.68
(m, 12H), 1.92 (m, 18H), 6.42 (s, 1H), 6.66 (d, J ¼ 7.6 Hz,
1H), 6.97 (d, J ¼ 8.6 Hz, 4H), 7.28 (d, J ¼ 8.3 Hz, 1H), 7.74
(m, 4H), 8.13 (s, 1H), 8.36 (s, 2H), 9.34 (s, 1H), 10.20 (s,
2H).
SYNTHESIS AND PROPERTIES OF NEW AROMATIC PIPAs, ESPESO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
of the current PIPAs in organic aprotic polar solvents related
to unmodified PIPAS. For instance, they all were soluble in
aprotic polar solvents and, in particular polymer 2a with m-
phenylene moieties, readily dissolved in NMP, DMA, or DMF
at room temperature, whereas the corresponding unsubsti-
tuted aromatic polyamide [poly(m-phenylene isophthala-
mide), MPD-I], does not dissolve in organic solvents without
adding a significant amount of inorganic salts.26 On the other
hand, the current PIPAs were insoluble in common organic
solvents, that is, ketones, chlorinated hydrocarbons, alcohols,
and cyclic ethers such as tetrahydrofuran or dioxane.
SCHEME 1 Synthesis of 5-[(1-adamantylcarbonyl)amino]isoph-
thalic acid (5-ADIP).
secondary amide groups at 1670 cmꢁ1 (C¼¼O stretching) and
1575 cmꢁ1 (combination of CAN stretching and NAH bend-
ing). Figure 1 also shows the H NMR spectrum of the mono-
mer, where it can be seen that all of the signals are in good
agreement with the expected chemical structure.
The thermal behavior was evaluated by means of DSC and
TGA. The data presented in Table 3 and Figure 3 demon-
strate that the incorporation of adamantly amide groups as
pendent substituents of PIPAs caused a significant increase
in the glass transition temperature (Tg)ꢀrelated to PIPAs pre-
viously reported. Tgs ranged from 335 C for polymer 2b to
370 C for polymer 2e (Table 2), whereas the Tg of a wholly
aromatic, commercial PIPA such as MPD-I is about 275 ꢀC.
For instance, the Tg of poly(m-phenylene-5-benzoylaminoi-
1
Synthesis of Polymers
ꢀ
Polyamides were prepared from the monomer 5-ADIP and a
series of technical and experimental aromatic diamines by
the synthetic route depicted in Scheme 2. The phosphoryla-
tion method first described by Yamazaki et al.25 was used as
the general preparation method for all of the polymers, using
the system triphenylphosphite-pyridine as a condensing pro-
moter and LiCl as solubility enhancer. All of the polyconden-
sation reactions proceeded readily in homogeneous solutions
and high yields and relatively high-molecular weights were
obtained. FTIR and NMR spectroscopies were used to con-
firm the chemical structure of all of the polymers. As an
example, the 1H NMR spectrum of polymer 2c has been
reproduced in Figure 2.
sophthalamide), a related polyamide with a pendent benzoy-
25
ꢀ
ꢀ
lamino group, is 298 C, which is 67 C lower than the Tg
of 2a. They have also much higher Tg than the PIPA prepared
from isophthalic acid and an adamantane-based cardo dia-
18
ꢀ
mine, for which a Tg of 231 C has been reported.
The strong increase of Tg observed upon incorporating the
polyhedral, voluminous adamantane ring as a pendent group
deserves a more in depth discussion. On comparing the glass
transition temperature found for polymer 2a with that of
other PIPAs from m-phenylene diamine and 5-substituted
isophthaloyl units, a good correlation between Tg and volume
of the pendent group could be found. It can be seen in
Figure 4, where the Tg of different poly(m-phenylene iso-
phthalamides) were plotted versus the van der Waals
Tables 1 and 2 list the results of polycondensation, along
with the elemental analyses of the polymers. Inherent viscos-
ities up to 0.92 dL/g were achieved, which correspond to an
estimated number average molecular weight, Mn, of 31,000
g/mol, and weight average molecular weight, Mw, of 63,000
g/mol (based on SEC measurements) for polymer 2f using
standards of poly(m-phenyleneisophthalamide, MPD-I). Mn
of 62,000 and Mw of 158,000 g/mol were obtained using
polystyrene standards as reference. It can be presumed that
the values obtained from the MPD-I references are more reli-
able than those measured taking polystyrene as reference,
because of the structural similarity of samples and referen-
ces in the first case. The polydispersity (Mw/Mn) values,
between 1.7 and 2.6, suggested that a suitable polycondensa-
tion method and a careful purification of the final materials
were implemented. Furthermore, the molecular weights
achieved for the set of polyamides can be considered, as a
whole, as reasonably high but not very high, particularly in
comparison to those achieved for aromatic polyamides pre-
pared by the solution polycondensation method using diacid
chlorides at low temperature.
Polymers Properties
The presence of the pendent bulky groups greatly affected
the properties of these polymers compared with those of
unsubstituted PIPAs. The chain separation caused by the
adamantyl side groups contributed to enhance the solubility
SCHEME 2 Synthesis of polyamides from 5-ADIP and
diamines.
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ARTICLE
TABLE 1 Preparation of Polyisophthalamides Containing Adamantyl Pendent Groups
Elemental Analyses
Polymer
Yield (%)
95
Repeat Unit Mol. Formula
C
N
H
2a
C
C
C
C
C
C
25H25N3O3
31H29N3O4
34H29F6N3O3
32H30N4O4
44H37N3O3
47H47N3O5
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
calcd.
found
66.55
66.01
73.35
73.10
63.65
63.50
71.89
71.58
80.59
80.28
76.92
76.65
6.06
5.80
5.76
5.70
4.56
4.38
5.66
5.46
5.69
5.46
6.45
6.35
10.11
9.49
8.28
7.98
6.55
6.81
10.48
10.25
6.41
6.35
5.73
5.70
2b
2c
2d
2e
2f
97
98
98
97
99
volume of the monomeric unit, calculated using the Compass
force field using the program Materials Studio 4.4.27 The cor-
relation is quite good in spite of the different structures and
functional groups depicted in Figure 4. This clearly suggests
that the bulky adamantyl side groups brought about a
The polyamides 2a, 2c, 2d, and 2e exhibited the highest Tgs,
as was to be expected on considering the chemical structure
of the corresponding diamines. Diamine a (MPD) is a short,
wholly aromatic diamine, which imparts high density of
hydrogen bonds, diamine c (diamine 6F) is a fluorinated
symmetric diamine which provides high Tg thanks to its
voluminous hexafluoroisopropylidene group and by the po-
lar character of the CAF bonds, diamine d (4,40-diamino-
benzanilide) is a para-oriented diamine with an amide
linkage, which provides efficient molecular packing and
additional hydrogen bonds through its amide linkage, and
diamine e is a cardo diamine which is recognized to pro-
vide good solubility, high free volume and high Tg at the
same time. On the other hand, amines b and f contain
ether linkages, which impart chain flexibility and segmen-
tal rotational freedom, and these characteristics make for a
decrease of Tgs.
decrease of molecular mobility, leading to
a dramatic
enhancement of the Tg and, what is more important, without
any loss in solubility (processability). Furthermore, pendent
adamantane rings yielded PIPAs with higher Tg than those
containing pendent polar aromatic heterocycles such as
phthalimide, benzoxazole, and benzothiazole, which are the
moieties of condensation polymers with highest thermal re-
sistance. The explanation of this behavior is very probably
due to the much higher effective volume of adamantane rela-
tive to the volume of the heterocycles, which are essentially
planar. The biggest difference corresponds to the related
ꢀ
PIPA with phenoxy pendent groups, for which a Tg of 245 C
has been reported.28 In this regard, the presence of the
ACOHNA linkage that connects the adamantyl group with
the polymer chain, surely plays a significant role on preserv-
ing a high value for Tg, thanks to an increase of the cohesive
energy density through interchain hydrogen bonding.
No endothermic peak was detected on the DSC traces in any
case, which, in principle, indicated that the novel PIPAs did
not develop crystallinity. This was confirmed by wide angle
X-ray scattering, where an amorphous pattern was recorded
in all cases (Fig. 5). Hence, the family of PIPAs reported here
TABLE 2 Inherent Viscosities and SEC Data of Polyisophthalamides Containing Adamantyl Pendent Groups
Poly(m-phenyleneisophthalamide)
Polystyrene Standards
Standards
Polymer
ginh (dL/g)
Mn
Mw
Mw/Mn
Mn
9,000
Mw
Mw/Mn
2a
2b
2c
2d
2e
2f
0.41
0.52
0.61
0.66
0.69
0.92
19,000
26,000
32,000
34,000
37,000
62,000
42,000
48,000
73,000
51,000
91,000
158,000
2.2
1.9
2.3
1.5
2.5
2.5
19,000
21,000
32,000
25,500
40,000
63,000
2.1
1.9
2.3
1.7
2.4
2.0
11,000
14,000
15,000
17,000
31,000
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 3 Mechanical and Thermal Properties of Polyisophthalamides Containing Adamantyl Pendent Groups
a
b
c
Polymer
Tensile Strength (MPa)
Young Moduli (GPa)
Tg (ꢀC)
Td (ꢀC)
Td10 (ꢀC)
Y800 (%)
2a
2b
2c
2d
2e
2f
–
–
365
335
365
365
370
345
400
390
410
395
425
410
420
425
435
430
445
430
49
52
46
51
44
43
83
65
84
69
70
2.4
2.0
2.6
2.3
2.3
a
Temperature of first onset in the TGA curve at a heating rate of 10 ꢀC/min.
Temperature of 10% weight loss.
Residual wt % at 800 ꢀC.
b
c
should be considered as glassy materials, essentially amor-
phous and with very high Tgs.
firmed that this premature loss should be associated with
the break-down of the joining amide bond and simultaneous
splitting off of the pendent group.
The thermal resistance, in terms of initial decomposition
temperature (Td onset), was evaluated by TGA. All of the
polymers showed relatively high Tds in N2, around 400 ꢀC.
The small differences observed in Td, regardless the diamine
moiety, could be attributed to the fact that decomposition
always started with the thermal breakdown of the amide
linkage that connects the main chain with the adamantyl
pendent group. As an example, Figure 6 shows the TGA trace
of one of the current PIPAs, which was recorded by using
the TA Hi-Res method.29 It can be observed how a first
weight loss occurred from around 400 ꢀC to about 480 ꢀC,
which should be associated with the loss of the pendent
group. An accurate determination of this first loss amount
could not be done because a second strong loss, correspond-
ing to the extensive decomposition of the polymers, over-
lapped in every case. Yet, the two-step decomposition pro-
cess could be confirmed as two distinguishable peaks were
registered on the differential weight loss curve.
To figure out how the thermal breakdown of these polymers
proceeds, and in particular the side amide breakdown, a
A similar behavior had been previously observed for PIPAs
containing benzoylamino pendent groups, which also showed
24
ꢀ
a first weight loss onset at about 410 C. Thus, it was con-
FIGURE 4 Glass transition temperature of polyisophthala-
mides prepared from m-phenylenediamine and isophthalic
acid derivatives containing pendent groups versus the van der
Waals volume of the isophthaloyl unit. Tg values taken from
ref. 13.
FIGURE 3 DSC plot of polyamides 2a and 2c. [Color figure can
be viewed in the online issue, which is available at
www.interscience.wiley.com.]
1748
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 5 WAXS diagrams of polyisophthalamides containing
adamantyl pendent groups.
FIGURE 7 Molecular models employed for the theoretical
study of thermal breakdown: Optimized geometries at
UB3LYP/6-31þG(d) level: (a) N-phenylbenzamide and (b) N-(1-
adamantanyl)benzamide.
theoretical study was carried out on two models with amide
linkage (Fig. 7), one of them aromatic and the other one cor-
responding to the model with the pendant group studied in
this work. Theoretical calculations were carried out using
the Density Functional Theory (DFT) with the UB3LYP func-
tional30 and the 6-31þG(d) basis set.31 The base superposi-
tion error was corrected using the Counterpoise Method.32
All calculations were performed using the GAUSSIAN 03 pro-
gram.33 Models 7a and 7b correspond to amide units within
the main chain (N-phenylbenzamide or benzanilide) and on
the pendent units [N-(1-adamantanyl) benzamide], respec-
tively. Models were optimized at UB3LYP/6-31þG(d) level
and their homolytic bond dissociation energies were calcu-
lated for the CACO (B1), COAN (B2), and NAC (B3) bonds
marked in the figure at the same computational level (ener-
gies calculated as the difference between the molecule and
its dissociated parts). The weakest bond in both cases was
B2, with dissociation energies of ꢁ84.49 kcal/mol for 7a
(OCarAN) and ꢁ82.06 kcal/mol for 7b (OCadAN). It con-
firmed that the amide breakdown is more probable for ada-
mantanyl pendent groups than for amide groups inside the
main chain, in agreement with that observed by TGA. A
more detailed study of these systems should be carried out
for a better and quantitative comprehension, as the differ-
ence in dissociation energies for B2 and B1 bonds does not
unquestionably support the hypothesis. It must be borne in
mind that at the high temperature of initial decomposition,
bonds B2 and B1 can become almost equally labile, particu-
larly in the case of model 7b, which means that the first
thermal breakdown can occur in any of the two linkages.
Nonetheless, the decomposition process in two steps
observed by TGA would be the same because B1 dissociation
energy is also higher for 7a (OCarAN) than for 7b (OCadAN).
In agreement with these observations, temperatures of 10%
weight loss measured by TGA lie for all the polymers in a
narrow range, viz., between 420 and 445 ꢀC. Small differen-
ces were observed for the carbonaceous residue among the
current PIPAs and in comparison with classical ones, with
ꢀ
weight retention around 60% at 800 C in N2.
The tensile strength and the Young modulus of polyamide
films (Table 3), ranging between 65 and 85 MPa and 2.0–2.6
GPa, respectively, can be considered as acceptable for unor-
iented samples, made by casting on a laboratory scale and
without any post-treatment. Polymer 2a, because of its low-
FIGURE 6 TGA curves of polyisophthalamide 2c (nitrogen, 10ꢀ/
min).
SYNTHESIS AND PROPERTIES OF NEW AROMATIC PIPAs, ESPESO ET AL.
1749

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
4 de Abajo, J.; de la Campa, J. G.; Lozano, A. E.; Preston, J. In
Polymeric Materials Encyclopedia; Salamone, J. C. Ed.; CRC
Press: Boca Raton, FL, 1996.
molecular weight, did give brittle films with insufficient me-
chanical strength to be tested under standard conditions.
However, polymer 2b, which showed only slightly higher mo-
lecular weight did give creaseable films that could be prop-
erly tested. The less rigid oxydiphenylene moiety of polymer
2b respect to the short-rigid 1,3-phenylene moiety of poly-
mer 2a should be considered as responsible of this behavior.
In general, the mechanical properties compared fairly well
with values reported earlier for experimental aromatic poly-
amides and other engineering thermoplastic polymers.34
Nevertheless, the presence of the bulky side adamantyl
groups slightly lowered the mechanical strength compared
with wholly aromatic PIPAs. Conversely, the values of moduli
of the current PIPAs with the pendent adamantyl group
were comparatively high, matching the moduli of amorphous
aromatic polyamides without pendent groups.24
5 Espeso, J. F.; de la Campa, J. G.; Lozano, A. E.; de Abajo, J.
J Polym Sci Part A: Polym Chem 2000, 38, 1014–1023.
6 Huang, T. L.; Hsiao, S. H. J Polym Res 2004, 11, 2–21.
7 Cheng, L.; Wu, H.; Ying, L.; Yang, X. L.; Jian, X. G. Desig
Monom Polym 2004, 7, 225–234.
8 Ge, Z.; Yang, S.; Tao, Z.; Liu, J.; Fan, L. Polymer 2004, 11,
3627–3635.
9 (a) Mallakpour, S.; Kowsari, E.; Polym Adv Technol 2005, 16,
732–737; (b) Bennet, C.; Kaya, E.; Sikes, A. M.; Jarret, W. L.;
Mathias, L. J. J Polym Sci Part A: Polym Chem 2009, 47,
4409–4419.
10 Chern, Y. T.; Shiue, H. C.; Kao, S. C. J Polym Sci Part A:
Polym Chem 1998, 36, 785–792.
11 Hsiao, S. H.; Li, C. T. Macromolecules 1998, 31, 7213–7217.
CONCLUSIONS
12 (a) Maya, E. M.; Lozano, A. E.; de la Campa, J. G.; de Abajo,
J. Macromol Rapid Commun 2004, 25, 592–597; (b) Hsiao,
S.-H.; Liou, G.-S.; Wang, H.-M. J Polym Sci Part A: Polym
Chem 2009, 47, 2330–2343.
By a facile, high yield route, it was possible to prepare the
new condensation monomer 5-[(1-adamantylcarbonyl)amino]
isophthalic acid (5-ADIP), which was readily purified to poly-
condensation grade.
13 de Abajo, J.; de la Campa, J. G.; Lozano, A. E.; Alvarez, J. C.
High yields and high-molecular weights were achieved for
the synthesis of adamantyl pendent PIPAs by the direct poly-
amidation method of Yamazaki-Higashi using 5-ADIP and a
series of technical aromatic diamines. The results confirmed
that the bulky pendent group did not much effect the reac-
tivity of the carboxylic functions of the isophthalic acid.
Adv Mat 1995, 7, 148–151.
14 (a) Diakoumakos, C.; Mikroyannidis, J. A. Polymer 1994, 35,
1986–1990; (b) de Abajo, J.; Santos, E. Angew Makromol Chem
1983, 111, 17–27.
15 Lozano, A. E.; de la Campa, J. G.; de Abajo, J.; Preston, J.
Polymer 1994, 35, 872–877.
The presence of the pendent bulky groups greatly affected
the general properties of these polymers compared with
those of unmodified PIPAs. Better solubility and much higher
Tg values were measured for the modified polymers; Tgs in
the range 335–370 ꢀC qualify the current polymers among
the PIPAs with highest Tg ever reported. Furthermore, the
current polymers showed higher Tgs than homologous PIPAs
containing benzamido or heterocyclic moieties as pendent
groups. On the other hand, the incorporation of an adaman-
tane pendent group linked to the isophthaloyl moiety by an
amide group caused a decrease in thermal resistance, as ini-
tial decomposition temperatures around 400 ꢀC were some-
thing lower than those observed for classical PIPAs. Mechani-
cal resistance and moduli of films, from 2.0 to 2.6 GPa, were
reasonably high and comparable to those of other PIPAs pre-
viously reported.
16 Lozano, A. E.; de la Campa, J. G.; de Abajo, J.; Preston, J.
Polymer 1994, 35, 1317–1321.
17 Mikroyannidis, J. A. Polymer 1996, 37, 2715–2721.
18 (a) Hsiao, S.-H.; Lee, C.-T. J Polym Sci Part A: Polym Chem
1999, 37, 1435–1442; (b) Kung. Y.-C.; Liou, G.-S.; Hsiao, S.-H. J
Polym Sci Part A: Polym Chem 2009, 47, 1740–1755.
19 Hsiao, S.-H.; Lee, C.-T.; Chern, Y.-T. J Polym Sci Part A:
Polym Chem 1999, 37, 1619–1628.
20 Matheus, A. S.; Kim, I.; Ha, C.-S. Macromol Symp 2007,
249–250, 344–349.
21 Jensen, J. J.; Grimsley, M.; Mathias, L. J. J Polym Sci Part
A: Polym Chem 1996, 34, 397–402.
22 Pixton, M. R.; Paul, D. R. Polymer 1995, 36, 3165–3172.
23 Morisita, H.; Horoyuki, T.; Hamada, Y. U.S. Patent7,329,718,
2008.
24 de la Campa, J. G.; Guijarro, E.; Serna, F. J.; de Abajo, J.
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