Chemical modification of the pendant structure of wholly aromatic polyamides: Toward functional high-performance materials with tuned chromogenic and fluorogenic behavior

Article abstract of DOI:10.1002/pola.24168

This work describes the preparation of functional aromatic polyamides with pendant fluorescent chemical structures. The preparation of a parent copolyamide with a lateral fluorene moiety anchored to the main chain through a urea group is described, along

Full text of DOI:10.1002/pola.24168

Chemical Modification of the Pendant Structure of Wholly Aromatic
Polyamides: Toward Functional High-Performance Materials
with Tuned Chromogenic and Fluorogenic Behavior
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PEDRO ESTEVEZ, HAMID EL-KAOUTIT, FELIX CLEMENTE GARCIA, FELIPE SERNA,
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JOSE LUIS DE LA PENA, JOSE MIGUEL GARCIA
Departamento de Quı´mica, Facultad de Ciencias, Universidad de Burgos, Plaza de Misael Banuelos s/n, 09001 Burgos, Spain
Received 12 April 2010; accepted 24 May 2010
DOI: 10.1002/pola.24168
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: This work describes the preparation of functional aro-
matic polyamides with pendant fluorescent chemical structures.
The preparation of a parent copolyamide with a lateral fluorene
moiety anchored to the main chain through a urea group is
described, along with the chemical modification of the fluorene
moieties to render six copolymers with different fluorescent
behaviors. The easy and clean chemical modification of the poly-
amide structure permits the preparation of high-performance
materials with ‘‘a la carte’’ fluorescence properties. The charac-
teristics of these materials make them useful for cutting-edge
technologies associated with the fluorescence of the pendant fluo-
rene moiety and with the host behavior of the urea motif, that
is, fluorescent sensing of analytes or hybrid luminescent con-
verter—light-emitting diode systems. The chemical modification
of the polymer structure was carried out with chemicals and con-
ditions optimized for polyamide models. The influence of the
chemical structure of the pendant fluorene core has also been
addressed in terms of thermal properties, solubility, water uptake,
C
V
and so forth. 2010 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 48: 3823–3833, 2010
KEYWORDS: binding sites; copolyamides; fluorescence or fluo-
rescent; functionalization of polymers; luminescence; lumines-
cent converter; LUCO; polyamides; signaling units
INTRODUCTION Chemical functionalization of the structure
of high-performance materials, that is, aramids, expands
their applicability to new and cutting-edge fields.1 Thus, the
inclusion of chromogenic and fluorescent chemical moieties
in the lateral aromatic polyamide chains1 can give rise to
luminescent converter (LUCO) materials, which in combina-
tion with a primary pumping source, that is, blue light-emit-
ting diodes (LEDs), permits the preparation of LEDs with
tremendous potential in lighting and backlighting applica-
tions.1–19 In addition, if the chromogenic and fluorescent
moieties include a substructure capable of interacting selec-
tively with analytes, the variations in the chromogenic or
fluorescent behavior of the material permit the preparation
of chemical sensors that could be used to detect analytes
using the different spectral characteristics of light emitted by
hybrid LUCO/LED devices or by fine tuning the visual per-
ception of their emitted light (color). In parallel, if the func-
tionalization gives rise to colored host substructures, the
interaction with guest analytes may also lead to color
changes, which could give rise to ‘‘naked eye’’ colorimetric
sensing materials.20–24
of the chemical structure of a parent polymer. The latter has
advantages related to the economics of the process, and it
opens a way for total or partial modification of the parent
structure with the desired functionality while still retaining
the properties of the parental compound to a degree, includ-
ing the characteristics of the functional groups.
Chemical modification of high-performance materials, espe-
cially of aromatic polyamides, is rarely performed. Few suc-
cessful examples have been published in the literature due
to their insolubility and to the presence of amide linkages
that can undergo side reactions.
Herein, we describe the preparation of novel aromatic polya-
mides with pendant structures comprised of a fluorene-sub-
stituted urea group, where the urea group is an excellent
binding site and the fluorene acts as a signaling unit due to
its fluorescent and sometime chromogenic characteristics.
We previously succeeded in the use of these functional
groups to prepare polymers with specialty properties.17,25–28
The fluorene moiety was chemically modified to alter its flu-
orescent behavior by introducing the following groups: car-
bonyl, hydroxy, oxime, hydrazone, and dicyanomethylene.
The chemical modification of a parent polyamide permits the
preparation of a series of polymers presenting different
The design and preparation of organic functional materials
can be carried out by two methods: by synthesis of mono-
mers containing the desired functionality or by modification
Correspondence to: J. M. Garcı´a (E-mail: jmiguel@ubu.es)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 3823–3833 (2010) 2010 Wiley Periodicals, Inc.
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CHEMICAL MODIFICATION OF WHOLLY AROMATIC POLYAMIDES, ESTEVEZ ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
properties, such as fluorescent behavior, binding characteris-
tics, and reactive functional groups.
precipitated in 500 mL of slightly acidified water. The prod-
uct (1) was filtered off, washed thorouꢀghly with distilled
water, and dried in a vacuum oven at 80 C overnight. Yield:
We prepared and analyzed a chemically modified copolya-
ꢀ
95%. M.p.: 276 C (dec.).
mide consisting of 90% of structural units of poly(m-phenyl-
R
ene isophthalamide) (NOMEXV) and 10% of structural units
1H-NMR (400 MHz, [D6]DMSO, d, ppm): 9.31 (s, 1H, NH);
8.84 (s, 1H, NH); 8.36 (s, 2H, Ph); 8.10 (s, 1H, Ph); 7.83 (m,
3H, Ph); 7.57 (d, 1H, J ¼ 7.2 Hz, Ph); 7.45 (d, 1H, J ¼ 8.1 Hz,
Ph); 7.38 (t, 1H, J ¼ 7.2 Hz, Ph); 7.28 (t, 1H, J ¼ 7.5 Hz, Ph);
4.4 (q, 4H, J ¼ 6.9 Hz, CH2CH3); 3.93 (s, 2H, Fluorene); 1.38
(t, 6H, J ¼ 6.9 Hz, CH2CH3). 13C NMR (100.6 MHz, [D6]DMSO:
d, ppm); 165.68; 153.54; 154.00; 143.64; 142.04; 141.76;
139.28; 136.51; 132.00; 127.63; 126.82; 126.00; 123.50;
123.45; 120.48; 118.39; 116.35; 82.16; 37.40; 15.10.
containing the pendant fluorene groups. We used the copoly-
mer to maintain the outstanding mechanical and thermal
R
properties of NOMEXV to give rise to creasable films or
dense membranes to be used as colorimetric or fluorescence
sensing materials.1 Moreover, a 10% mole content of the
structural units with the urea binding site and fluorescent
fluorene group is adequate for measuring changes in the
fluorescence behavior upon interaction with analytes and
sufficient for giving rise to perceptible ‘‘naked eye’’ colori-
metric variations.
FTIR (cmꢁ1): mNAH: 3300; dNAH: 1614; mAr C¼C: 1563; mC¼O
1750;1730.
:
The ease and effectiveness of the polymer modification reac-
tions have been carried out following orthogonal and high
yielding reactions and were previously studied using model
compounds. This synthetic approach has proven to be a rally
adequate strategy to prepare new functional soft materials.29
The models chemically resemble the polymers, and their low
molecular weight permits studying the reactions in terms of
cleanliness, conversion, and yield using conventional purifi-
cation and characterization techniques. The reaction condi-
tions were optimized with the model compounds and then
applied to the polymers. These model compounds were also
used to study the chromogenic and fluorogenic behavior of
the polymers in solution, supposing that each model mimics
the behavior of its corresponding polymer, but with a
defined molecular weight and higher solubility.30,31
5-[3-(9H-Fluoren-2-yl)ureido]isophthalic Acid (2)
5-[3-(9H-Fluoren-2-yl)ureido]isophthalic diethyl ester (10.50 g,
24 mmol) was mixed with 70 mL of NaOH (10%) and 100 mL
of N,N-dimethylacetamide in a 100-mL round-bottomed flask fit
with a magnetic stirrer. The resulting solution was stirred at
70 ꢀC for 24 h and then precipitated in 500 mL of slightly
acidified water. The product (2) was filtered off, washed thor-
oughly with distilled water, and driꢀed in a vacuum oven at 80
ꢀC overnight. Yield: 92%. M.p.: 299 C (dec.).
1H NMR (400 MHz, [D6]DMSO, d, ppm): 13.23 (s, 2H, CO2H);
9.27 (s, 1H, NH); 8.93 (s, 1H, NH); 8.38 (s, 2H, Ph); 8.15 (s,
1H, Ph); 7.86 (m, 3H, J ¼ 8.0 Hz, Ph); 7.58 (d, 1H, J ¼ 7.6
Hz, Ph); 7.50 (d, 1H, J ¼ 8.0 Hz. Ph), 7.36 (t, 1H, J ¼ 7.2 Hz,
Ph ), 7.26 (t, 1H, J ¼ 7.2 Hz, Ph), 3.93 (s, 2H, Fluorene). 13C
NMR (100.6 MHz, [D6]DMSO, d, ppm): 167.73; 153.59;
144.93; 143.60; 142.12; 141.57; 139.52; 136.42; 132.83;
127.69; 126.85; 125.96; 124.23; 123.63; 121.19; 120.26;
118.40; 116.36; 37.52. FTIR (cmꢁ1): mNAH: 3280; mOAH: 3400
ꢁ 2750; mC¼O: 1716; 1640; dNAH: 1610; mAr C¼¼C: 1558.
EXPERIMENTAL
All materials and solvents were obtained commercially and
used as received unless otherwise indicated. N-Methyl-2-pyr-
rolidone (NMP; Aldrich) was vacuum distilled twice over
phosphorus pentoxide and then stored over 4-Å molecular
sieves. Lithium chloride (Aldrich) was dried at 400 ꢀC for
12 h before use. Triphenylphosphite (TPP; Aldrich) was vac-
uum distilled twice over calcium hydride and then stored
over 4-Å molecular sieves. Pyridine (Merck) was dried by
refluxing over sodium hydroxide for 24 h and then distilled
over 4-Å molecular sieves. m-Phenylenediamine (MPD) was
purchased from Aldrich and purified by double vacuum sub-
limation. Isophthalic acid (IA) was purified by crystallization
(3 g in 1.2 L of boiling water). 9H-Fluoren-2-yl isocyanate
(Aldrich, 98%) was used as received.
5-(3-9H-Fluoren-2-ylureido)-N,N0-diphenylisophthalamide
(M1)
Aniline (2 mL, 30 mmol), diacid (2) (3 g, 7.7 mmol), and
lithium chloride (1.08 g) were dissolved in a mixture of pyri-
dine (4.6 mL), TPP (4.87 mL, 18.5 mmol), and NMP (15.5
mL) in a 50-mL three-necked flask fit with a mechanical stir-
rer. The resulting solution was stirred and heated at 110 ꢀC
under dry nitrogen for 4 h. The system was then cooled to
room temperature and the solution was precipitated in 300
mL of methanol. The product obtained was filtered off,
washed with methanol, extracted with acetone for 24 h in a
ꢀ
Soxhlet apparatus and driedꢀin a vacuum oven at 80 C over-
MONOMER AND MODELS
night. Yield: 72%. M.p.: 268 C (dec.).
5-[3-(9H-Fluoren-2-yl)ureido]isophthalic Diethyl
Ester (1)
1H NMR (400 MHz, [D6]DMSO, d, ppm): 10.47 (s, 2H, CONH);
9.20 (s, 1H, NH); 8.94 (s, 1H, NH); 8.26 (s, 2H, Ph); 8.18(s,
1H, Ph); 7.86(m, 7H, Ph); 7.60 (d, 1H, J ¼ 7.2 Hz, Ph); 7.51
(d, 1H, J ¼ 8.4Hz, Ph); 7.44 (m, 5H, Ph); 7.29 (t, 1H, J ¼ 7.2
Hz, Ph); 7.17 (t, 2H, J ¼ 7.2 Hz, Ph); 3.96 (s, 2H, ). 13C NMR
(100.6 MHz, [D6]DMSO, d, ppm): 166.16; 153.49; 144.89;
143.62; 142.04; 141.23; 141.03; 140.00; 139.45; 136.85;
129.70; 129.60; 127.74; 127.63; 126.57; 126.39; 124.82;
5-Amino diethyl isophthalate (5 g, 24 mmol) was dissolved
in 100 mL of N,N-dimethylacetamide containing 3.70 mL (29
mmol) of trimethylchlorosilane in a 250-mL round-bottomed
flask fit with a magnetic stirrer. Then, 9H-fluoren-2-yl isocya-
nate (24 mmol) was added portionwise and the resulting so-
lution was stirred at room temperature for 24 h and then
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ARTICLE
121.25; 120.80; 120.20; 118.25; 116.22; 37.45. FTIR (cmꢁ1):
5-(3-(9-(Dicyanomethylene)-9H-fluoren-2-yl)ureido)-
m
NAH: 3284; mC¼¼O: 1692 ꢁ 1646; dNAH: 1607; mAr C¼¼C: 1561.
N,N0-diphenylisophthalamide(M4)
Elemental analysis for C34H26N4O3 (538.31): calc (%) C
75.82, H 4.87, N 10.40; found (%) C 76.20, H 4.92, N 9.79.
In a 25-mL Erlenmeyer flask fit with a magnetic stirrer, 0.50
g (1.0 mmol) of M2 was dissolved in 4 mL of N,N-dimethyl-
formamide and 0.14 g (2 mmol) of malononitrile. The result-
ing solution was stirred at 100 ꢀC for 6 days and then pre-
cipitated in 100 mL of water. The product was filtered off,
washed thoroughly with distilled water, extracted with ace-
tone for 24 h in a Soxhlet apparatus and then dried in a vac-
uum oven at 60 ꢀC overnight. Yield: 85.71%. M.p.: 297 ꢀC
(dec.).
5-(3-(9-Oxo-9H-fluoren-2-yl)ureido)-N,N0-
diphenylisophthalamide (M2)
5-(3-9H-Fluoren-2-ylureido)-N,N0-diphenylisophthalamide
(M1) (1.95 g, 3.62 mmol) was dissolved in 20 mL of di-
methyl sulfoxide and cesium carbonate (3.54 g, 10.86 mmol)
in a 100-mL round-bottomed flask. The resulting solution
was stirred at room temperature for 6 days and then pre-
cipitated in 100 mL of water. The product (M2) was filtered
off, washed thoroughly with distilled water, and dried in a
vacuum oven at 60 ꢀC overnight. Yield: 92.5%. M.p.: 226 ꢀC
(dec.).
1H NMR (400 MHz, [D6]DMSO, d, ppm): 10.44 (s,2H, CONH);
9.16 (s,1H, NH); 9.15 (s,1H, NH); 8.21 (s,2H, Ph); 8.18 (s,1H,
Ph); 8.13 (s,1H, Ph); 8.01 (d,1H, J ¼ 7.6 Hz, Ph); 7.85 (d,4H,
J ¼ 8.0 Hz, Ph); 7.78 (m,1H, Ph); 7.57 (m,2H, Ph); 7.49 (t,1H,
J ¼ 8.0 Hz, Ph), 7.43 (t,4H, J ¼ 7.6 Hz, Ph); 7.28 (t,1H, J ¼
7.6 Hz. Ph); 7.18 (t,2H, J ¼ 7.2 Hz, Ph). 13C NMR (100.6
MHz, [D6]DMSO, d, ppm): 166.18; 161.20; 153.50; 143.14;
141.50; 140.80; 140.00; 136.90; 136.20; 136.06; 136.00;
134.23; 129.60; 129.10; 126.70; 124.80; 124.60; 122.70;
121.36; 120.90; 116.90; 114.40; 114.10; 76.20. FTIR (cmꢁ1):
1H NMR (400 MHz, [D6]DMSO, d, ppm): 10.48 (s, 2H, CONH);
9.30 (s, 1H, NH); 9.18 (s, 1H, NH); 8.26 (s, 2H, Ph);
8.21(s,1H, Ph); 7.92 (s, 1H, Ph); 7.87 (d, 4H, J ¼ 8.0 Hz, Ph);
7.74 (d, 2H, J ¼ 7.2 Hz, Ph); 7.63 (m, 3H, Ph); 7.44 (t, 4H, J
¼ 7.6 Hz, Ph); 7.34 (t, 1H, J ¼ 7.2 Hz, Ph); 7.18 (t, 2H, J ¼
7.2 Hz, Ph). 13C NMR (100.6 MHz, [D6]DMSO, d, ppm):
194.08; 166.20; 153.53; 145.37; 145.22; 141.87; 141.07;
140.03; 138.28; 136.96; 136.31; 135.20; 134.38; 129.64;
129.30; 129.64; 124.80; 124.82; 122.62; 121.59; 121.33;
121.17; 115.10. FTIR (cmꢁ1): mNAH: 3280; mC¼¼O: 1704ꢁ1649;
mNAH: 3290; mCBN: 2213, mC¼O: 1680–1646; dNAH: 1610; mAr
C¼¼C: 1547. Elemental analysis for C37H24N6O3 (600.64): calc
(%) C 73.99, H 4.03, N 13.99; found (%) C 73.68, H 4.12, N
13.54.
dNAH
:
1597; mAr
:
1553. Elemental analysis for
C¼C
(5-(3-(9-(Hydroxyimine)-9H-fluoren-2-yl)ureido)-N,N0-
diphenylisophthalamide (M5)
C34H24N4O4 (552.59): calc. (%) C 73.90, H 4.38, N 10.14;
found (%) C 73.62, H 4.53, N 9.72.
In a 25-mL Erlenmeyer flask fit with a magnetic stirrer, 0.50
g (1.0 mmol) of M2 was dissolved in 5 mL of N,N-dimethyl-
formamide and 0.076 g (1.1 mmol) of hydroxylamine hydro-
5-(3-(9-Hydroxy-9H-fluoren-2-yl)ureido)-N,N0-
diphenylisophthalamide (M3)
ꢀ
chloride. The resulting solution was stirred at 80 C for 24 h
5-(3-(9-Oxo-9H-fluoren-2-yl)ureido)-N,N0-diphenylisophthala-
mide (M2) (1.0 g, 1.8 mmol) was dissolved in 10 mL of N,N-
dimethylacetamide and 0.13 g (3.36 mmol) of sodium boro-
hydride in a 25-mL round-bottomed flask fit with a magnetic
stirrer. The resulting solution was stirred at room tempera-
ture for 24 h and then precipitated in 100 mL of slightly
acidified water. The product (M3) was filtered off, washed
thoroughly with distilled water, and dried in a vacuum oven
and then precipitated in 15 mL of water. The product (M5),
an equimolecular mixture of Z and E isomers, was filtered
off, washed thoroughly with distilled water, extracted with
acetone for 24 h in a Soxhlet apparatus and then dried in a
vacuum oven at 60 ꢀC overnight. Yield: 76%. M.p.: 270 ꢀC
(dec.).
1H NMR (400 MHz, [D6]DMSO, d, ppm): 12.60 (s, 1H, OH);
12.55 (s, 1H, OH); 10.48 (s, 2H, CONH,); 9.22 (s, 1H, NH);
9.15 (S, 1H, NH); 9.12 (S, 1H, NH), 9.06 (S, 1H, NH), 8.61 (d,
1H, J ¼ 7.2 Hz, Ph); 8.35 (d, 1H, J ¼ 7.2 Hz, Ph); 8.26 (s, 2H,
Ph), 8.2 (s, 1H, Ph); 7.85 (m, 6H, Ph), 7.44 (m, 7H, Ph); 7.18
(t, 2H, J ¼ 7.2 Hz, Ph). 12.55 (s, 1H, OH); 10.48 (s, 2H,
CONH,); 9.12 (s, 1H, NH); 9.06 (S, 1H, NH); 8.26 (s, 2H, Ph),
8.20 (s, 1H, Ph); 8.02 (d, 1H, J 7.2 Hz, Ph); 7.85 (m, 6H, Ph),
7.72(d, 1H, J 7.2 Hz, Ph), 7.44(m, 7H, Ph); 7.18 (t, 2H, J 7.2
Hz, Ph).13C NMR (100.6 MHz, [D6]DMSO, d, ppm): 166.18;
153.51; 152.08; 141.38; 141.01; 140.71; 140.52; 140.00;
137.26; 136.94; 136.14; 135.22; 134.43; 131.73; 131.34;
129.63; 128.34; 124.74; 121.30; 121.07; 120.57; 120.05;
ꢀ
ꢀ
at 60 C overnight. Yield: 93%. M.p.: 272 C (dec.).
1H NMR (400 MHz, [D6]DMSO, d, ppm): 10.46 (s, 2H, CONH);
9.20 (s, 1H, NH); 8.98 (s, 1H, NH); 8.25 (s, 2H, Ph); 8.17(s,
1H, Ph); 7.88(s, 1H, Ph), 7.85 (d, 4H, J ¼ 8.0 Hz, Ph); 7.74
(m, 1H, Ph); 7.59 (d, 1H, J ¼ 7.6 Hz, Ph); 7.50(d, 1H, J ¼ 9.2
Hz, Ph); 7.42 (m, 6H, Ph); 7.28 (t, 1H, J ¼ 7.2 Hz, Ph); 7.16
(t, 1H, J ¼ 7.2 Hz, Ph), 5.89(d, 1H, J ¼ 7.2 Hz, OH ), 5.50 (d,
1H, J ¼ 7.2 Hz, CH).13C NMR (100.6 MHz, [D6]DMSO, d,
ppm): 166.15; 153.45; 148.89; 147.57; 141.06; 140.41;
140.00; 136.90; 135.76; 135.14; 134.42; 129.60; 129.50;
129.45; 127.39; 125.83; 124.73; 124.70; 121.25; 120.24;
119.34; 116.31; 74.53. FTIR (cmꢁ1): mNAH: 3310; mC¼O
:
111.29. FTIR (cmꢁ1): mNAH: 3340; mC¼O: 1710–1625; dNAH
:
1700–1630; dNAH: 1597; mAr C¼¼C: 1620–1680; mOAH: 3200–
2450. Elemental analysis for C34H26N4O4 (554.60): calc (%)
C 73.63, H 4.73, N 10.10; found (%) C 74.01, H 4.75, N 9.81.
1605; mAr C¼C: 1610–1685; mOAH: 3210–2510. Elemental anal-
ysis for C34H25N5O4 (567.60): calc (%) C 71.95, H 4.44, N
12.34; found (%) C 72.13, H 4.73, N 11.96.
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CHEMICAL MODIFICATION OF WHOLLY AROMATIC POLYAMIDES, ESTEVEZ ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Experimental monomer and model synthesis (M5 and M6 were obtained as equimolecular mixtures of Z and E
isomers).
5-(3-(9-Hydrazone-9H-fluoren-2-yl)ureido)-N,N0-
diphenylisophthalamide (M6)
1H, Ph); 7.85(m, 7H, Ph); 7.62 (d, 1H, J ¼ 7.2 Hz); 7.41 (m,
7H, Ph); 7.30 (t, 2H, J ¼ 7.2 Hz, Ph); 5.95(d, 1H, J ¼ 7.2 Hz,
NH2); 5.53(d, 1H J ¼ 7.2 Hz, NH2).13C NMR (100.6 MHz,
[D6]DMSO, d, ppm): 166.27; 163.30, 153.56; 149.01;
147.61;141.19; 140.52; 140.10; 137.00; 135.76; 134.52;
134.42; 129.70; 129.60; 127.49; 125.95; 124.83; 121.34;
In a 25-mL Erlenmeyer flask fit with a magnetic stirrer, 0.50 g
(1.0 mmol) of M2 was dissolved in 5 mL of N,N-dimethylforma-
mide and 1 mL (20 mmol) of hydrazine monohydrate. The
resulting solution was stirred at room temperature for 48 h
and then precipitated in 15 mL of methanol. The product (M6),
an equimolecular mixture of Z and E isomers, was filtered off,
washed thoroughly with distilled water, extracted with acetone
for 24 h in a Soxhlet apparatus and then dried in a vacuum
oven at 60 ꢀC overnight. Yield: 71%. M.p.: 275 ꢀC (dec.).
121.27; 120.21; 119.43; 119.40; 116.18. FTIR (cmꢁ1): mNAH
3310; mC¼¼O: 1700–1630; dNAH: 1597; mArC¼C: 1620–1680;
mOAH 3200–2450. Elemental analysis for C34H26N6O3
:
:
(566.62): calc (%) C 72.07, H 4.63, N 14.83; found (%) C
71.70, H 4.67, N14.44.
1H NMR (400 MHz, [D6]DMSO, d, ppm): 10.52 (s, 2H, CONH);
9.25 (s, 1H, NH); 9.03 (s, 1H, NH); 8.30 (s, 2H, Ph); 8.22(s,
The overall monomer and model synthesis is shown in
Scheme 1.
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ARTICLE
SCHEME 2 Synthesis and chemical structure of polyamide CP1.
Copolymer Synthesis
then stirring for 24 h at room temperature. Polymer films
were prepared by evaporation of cast solutions in NMP. In
most cases, a concentration of 10% by polymer weight was
used and the solvent was eliminated by heating at 100 ꢀC
The copolymerization of the diacid (2) to give the copolymer
CP (Scheme 2) was carried out as follows: MPD (20 mmol),
diacid (2) (2 mmol), IA (18 mmol), and lithium chloride (2.8
g) were dissolved in a mixture of pyridine (12 mL), TPP (44
mmol), and NMP (40 mL) in a 200-mL three-necked flask fit
with a mechanical stirrer, and the resulting solution was
ꢀ
for 4 h in an air-circulating oven and then at 120 C for 4 h
under vacuum (1 mm Hg). Water sorption values were
determined gravimetrically at room temperature. Powdered
polymeric samples of about 200 mg, previously dried at 120
ꢀC for 24 h over phosphorus pentoxide, were placed in a
closed box containing a ꢀsaturated aqueous solution of NaNO2
at a temperature of 20 C, which provided a relative humid-
ity of 65%. The samples were weighed periodically over 8
days until they equilibrated with their surroundings and pre-
sented no further changes in weight.
ꢀ
stirred and heated at 110 C under dry nitrogen for 4 h. The
system was then cooled to room temperature and the solu-
tion was precipitated in 300 mL of methanol to give a swol-
len fibrous precipitate. The obtained copolymer was filtered
off, washed with distilled water and acetone, extracted with
acetone for 24 h in a Soxhlet apparatus, and finally dried in
a
vacuum oven at 80 ꢀC overnight. The yield was
quantitative.
Chemical modification of the copolymer CP1 to yield the
modified copolymers (CP2-6) was carried out following the
procedures described in the preparation of the models M2-6
from model M1.
RESULTS AND DISCUSSION
Our work concerns the design, preparation, and characteriza-
tion of high-performance functional materials for future use
The copolymer synthesis and acronyms are depicted in
Schemes 2 and 3.
MEASUREMENTS AND INSTRUMENTATION
1H and 13C NMR spectra were recorded with a Varian Inova
400 spectrometer operating at 399.92 and 100.57 MHz,
respectively, using deuterated dimethylsulfoxide ([D6] DMSO)
as solvent. Low-resolution electron impact (EI-LR) mass
spectra were obtained at 70 eV on an Agilent 6890N mass
spectrometer. High-resolution mass spectrometry (HRMS)
was carried out on a Micromass AutoSpect Waters mass
spectrometer. Infrared spectra (FTIR) were recorded with a
Nicolet Impact spectrometer. Elemental analyses were per-
formed with a LECO CHNS-932 microanalyzer. Inherent vis-
cosities were measured with an Ubbelohde viscometer at 25
6 0.1 ꢀC with NMP as the solvent at a concentration of 0.5
g/dL. UV/Vis and fluorescence spectra were recorded on a
Varian Cary3-Bio UV–Vis spectrophotometer and a Varian
Cary Eclipse fluorometer, respectively. Thermogravimetric
analysis (TGA) data were recorded on 5 mg of sample under
nitrogen or oxygen with a TA Instruments Q50 TGA analyzer
at a scan rate of 10 ꢀC/min. Polymer solubility was deter-
mined by mixing 10 mg of sample with 1 mL of solvent and
SCHEME 3 Chemical structure and codes of the modified
copolyamides.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 1 Characterization of model M2 by (a) FTIR, (b) 1H NMR, and (c) 13C NMR.
in advanced applications, especially in molecular recognition
and in light-emitting hybrid LUCO/LED systems. Therefore,
we describe copoly(isophthalamide)s containing urea binding
sites in the polyamide backbone along with a substituted
fluorene motif as the fluorescent signaling subunit (Scheme 2).
The copolymers with different fluorene moieties were derived
from a parent copolymer containing the unmodified fluorene
group (Scheme 3).
mit further reactivity on the polymer, thereby opening new
possibilities in terms of the applicability of the Nomex-like
aromatic polyamides.
Monomer, Polyamide Models, and Polymer Synthesis
and Characterization
The diacid monomer 2 was previously prepared in an easy
clean way by reaction of 2-isocyanato-9H-fluorene with 5-ami-
noisophthalic acid to produce a diacid monomer containing the
urea binding site and a fluorene motif in high yield and purity.
Chemical modifications of the pendant copolymer structure
were carried out following easy and clean reactions. The
introduction of new chemical functions in position 9 of the
fluorene ring clearly modifies the overall electron density
over the fluorene and the urea group. This modification per-
mits the tuning of: (a) the fluorescence and the signaling
behavior of the group; and (b) the receptor capability of the
urea motif. Moreover, the introduced functional groups per-
The reaction of the diacid monomer 2 with 2 eq of aniline
using high-temperature polymerization conditions, the so-
called Yamazaki method,32 yielded model M1 (Scheme 1) in
a quantitative manner. The oxidation of the model with ce-
sium carbonate/air transformed the fluorene group into fluo-
renone. The carbonyl group of fluorenone could be reduced
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ARTICLE
(10%) in conjunction with the low sensitivity of the NMR
technique permits to assure that the conversion was signifi-
cantly high, and it is not possible to guarantee a quantitative
conversion.
The inherent viscosity of the parent copolymer CP1 is 0.87
dL/g, which is significantly higher than 0.5 dL/g and indi-
cates the formation of a high molecular weight copolymer. In
addition, the creasable films obtained from this polymer
upon casting are also suggestive of copolymer formation.
Chemical modification of the pendant fluorene group of CP1
to produce the other copolymers, CP2–CP6, influences the
inherent viscosity. Changes in viscosity lead to different
hydrodynamic volumes in solution of polymers with the
same average polymerization degree (see Table 1 for ginh data).
POLYMER PROPERTIES
Thermal Properties
The thermal behavior of the copolyamides was evaluated by
TGA, and the results are shown in Table 1. The decomposi-
tion temperatures (Td) of all polymers range between 254
and 332 ꢀC (Table 1). This degradation step corresponds
with a weight loss lower than 10% and accounts for the loss
of the lateral chain, thus giving rise to a nomex-like struc-
ture, which is responsible for the second degradation step
FIGURE 2 1H NMR spectrum of copolyamide CP1 and CP3.
ꢀ
around 400 C. In regards to the first degradation processes,
to an alcohol (racemic mixture) and reacted with malononi-
trile to give the dicyanomethylene derivative; or with hydra-
zine to yield the hydrazone; or with hydroxylamine to give
the oxime. The oxime and hydrazone were obtained as equi-
molecular mixtures of the Z and E isomers. Moreover, mono-
mers M5 and M6 could be transformed again into M1 by a
simple hydrogenation step using Pd/C as catalyst. The mod-
els were purified by extraction with acetone for 24 h in a
Soxhlet apparatus.
different authors have described the oxidative degradation of
urea units to occur at temperatures between 250 and 300
ꢀC in urea-formaldehyde resins.33,34 The derivative curves of
the TGA data show a different thermal behavior of the
copolymers in oxidizing and inert atmospheres (see Fig. 3).
ꢀ
In regards to the char residue at 700 C, the copolymers had
values higher than 50%, corresponding to heat-resistant
polymers. The char yield can be use to estimate the limiting
oxygen index (LOI) of the polymers using the experimental
Van Krevelen equation (LOI ¼ 17.5 þ 0.4 CR, where CR is
the char yield in % weight).35 The polymers had LOI values
higher than 36, meaning that the polymer can be classified
The intermediates, monomer, and models were characterized
by IR and 1H- and 13C NMR spectroscopy, fully confirming
the chemical structure of all of the products. As an illustra-
tive example, Figure 1 depicts the chemical characterization
of M2.
TABLE 1 Inherent Viscosities and TGA Data of the
Copolyamides
The copolyamide CP1 was synthesized by combining iso-
phthalic acid (0.9 eq), diacid 2 (0.1 eq), and MPD (1 eq) fol-
lowing the Yamazaki method (Scheme 2).32 Every reaction
with the model compounds was optimized to give higher
yield and purity so that these conditions could be applied to
the modification of the copolymer. Similar conditions were
used to modify the pendant fluorene structure of copolymer
CP1 to give copolymers CP2-6. Figure 2 shows the chemical
characterization of copolymers CP1 and CP3 as an example.
TGAa
N2 Atmosphere
O2 Atmosphereb
ginh
Char
Td (ꢀC) yield (%)
Polymer (dL gꢁ1
)
Td (ꢀC)
LOI
CP1
CP2
CP3
CP4
CP5
CP6
a
0.87
0.60
0.74
0.97
0.75
0.70
265
265
255
280
255
260
58
51
59
58
60
47
265
260
260
280
255
260
40.7
37.9
41.1
40.7
41.5
36.3
1
The peaks of the H spectrum were assigned based on spec-
tra of the model and were consistent with a quantitative
modification of the pendant fluorene moiety. The NMR spec-
tra showed a complete conversion of the parent polyamide
(CP1) to copolymers CP2–CP6. This was analyzed by means
1
of the disappearance of the H signal in position 9 of the flu-
Td is the initial temperature at the onset of the first stage of the ther-
orene ring (see Fig. 2). Nevertheless, the lower molar con-
tent of the diacid residue containing the fluorene motif
mal weight loss. Char yield at 700 ꢀC.
b
The weight loss at 700 ꢀC under oxygen is complete.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 TGA curves of polyamide CP2 under N2 and O2. [Color
figure can be viewed in the online issue, which is available
at www.interscience.wiley.com.]
as self-extinguishing polymers (LOI is defined as the mini-
mum fraction of oxygen in a mixture of oxygen and nitrogen
that will just support combustion after ignition. As air con-
tains ꢂ21% oxygen, any material with a LOI lower than 21
will probably hold up burning in an open-air situation).
FIGURE 4 Solution of models M1, M2, M3, M4, M5, and M6
(from left to right) in NMP (10ꢁ3 M): (a) upper photograph:
without added anion; (b) lower photograph: with a fluoride
concentration of
5
ꢃ
10ꢁ3
M (fluoride added as [CH3
(CH2)3]4NF). [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com.]
Solubility and Water Sorption
The copolymer solubilities are shown in Table 2. The solubil-
ities of the aromatic polyamides are high and comparable to
that of the nomex. Therefore, these copolymers can be easily
transformed upon solution by ‘‘casting’’ and we prepared
creasable films in NMP solutions of the copolymers.
water-treatment membranes or even in dense gas-separation
membranes is generally associated with better performance.
The copolyamides described herein have a nomex-like struc-
ture with two amide groups per structural unit and a polar
pendant structure in 10% of the diacid residue. The polarity
Aromatic polyamides are hydrophilic polymers due to their
polar amide groups, whose interactions with water lead to
water uptake from the environment. These water molecules
interact with amide groups by weakening the amide–amide
interactions that give the polyamides their high cohesive
energy and consequently their high thermal transitions and
resistance and superior mechanical properties. Therefore,
the water uptake determines the final application of these
high-performance materials as the absorbed water dimin-
ishes the Tg and influences the mechanical, electrical, and
dielectric properties. Conversely, in other technological fields,
such as membrane technology, greater water uptake in
TABLE 2 Solubilitya and Water Sorption of the Copolyamides
NMP, DMA, DMSO DMF m-Cresol Water Uptake (%)
CP1 þþ
CP2 þþ
CP3 þþ
CP4 þþ
CP5 þþ
CP6 þþ
a
þþ
þþ
þþ
þþ
þþ
þþ
þ
þꢁ
þ
ꢁ
þꢁ
þ
8.4
9.2
8.8
8.3
8.7
9.4
FIGURE 5 Fluorescence emission of a film (red line) and a
DMSO solution (blue line) of polyamide CP1 along with a fluo-
rescence image of the polyamide (right: film obtained by cast-
ing; left: 4 ꢃ 10ꢁ3 M solution in DMSO). [Color figure can be
viewed in the online issue, which is available at www.
interscience.wiley.com.]
þþ ¼ soluble at room temperature; þ ¼ soluble on heating; þꢁ ¼ par-
tially soluble; ꢁ ¼ insoluble.
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have an electron-withdrawing behavior (mainly in models
and copolymers M1, M2, CP1, and CP2). The color of the
model can be somewhat correlated with the HOMO–LUMO
gap,37 being this gap 4.03 eV for model M1, colorless, and
2.7 eV for model M4, highly colored.
The interactions of the model compounds and of the copoly-
mers with different anions are selective and give rise to
color changes. The color developed upon addition of Fꢁ to
aprotic organic solutions containing urea compounds has
been precisely described by Esteban-Go´mez et al.38 The phe-
nomenon was ascribed to an acid-base reaction and not to a
host-guest interaction. Thus, the unsolvated anion behaves as
a strong base in organic conditions, causing the deprotona-
tion of the urea group and giving rise to an even stronger
ITC. Nevertheless, not all our models experiments color de-
velopment or variations in solution upon addition of fluoride,
showing the complex nature of these kinds of phenomena. This
could be partially explained because our systems are more com-
plex as some of the models have AOH or ANH2 groups capable
of interacting with the carbonyl group of the urea and amide
moieties and also capable of giving rise to a relatively strong
interaction with the fluoride anion through halogen bonds.
FIGURE 6 Fluorescence image of copolyamides in solutions in
solid state (films). From left to right: CP1, CP2, CP3, CP4, CP5,
and CP6. The polymer concentration in solution of DMSO was
4 ꢃ 10ꢁ3 M (equivalents of fluorene residue/L). The photograph
was taken under irradiation with UV (365 nm).
of the pendant chain depends mainly on the highly polar
urea group and in the chemical functionalization of carbon 9
within the fluorene residue. Measurement of the isothermal
sorption of water at 65% relative humidity gave values in ac-
cordance with the polyamide chemical structure (Table 2).
The water uptake is high for fully aromatic polyamides and
depends on the functionalization of the fluorene moieties.
Thus, the presence of hydroxyl groups (CP3 and CP5) or
amine groups (CP6) increases the hydrophilic character of
the materials, thus increasing the water uptake.
Therefore, the model compounds and polymers could serve
as ‘‘naked eye’’ sensing materials, allowing for their use in
chromogenic sensing devices. As an example, Figure 4 depicts
the color changes obtained upon adding fluoride anions to
solutions of the model compounds. Further investigations are
under progress related to the sensing behavior of the polymers
and models both in solution and in the solid state.
Chromogenic and Fluorescence Behavior
As previously outlined, the chromogenic and fluorescent
behaviors of high-performance polymers are key properties
for many novel applications, such as for chromogenic and
fluorogenic sensing materials or for hybrid LUCO/LED emit-
ting devices.
The colors of the model compounds in solutions and of the
copolymers, both in solution and in the solid state, range
from colorless to brown or yellow. The completely colorless
solutions correspond to the model and copolymer containing
the unmodified fluorene moiety (M1 and CP1, respectively).
The functionalization of the sp3 carbon (C9) of the fluorene
gives rise to a color development in solution because of the
intramolecular charge transfer (ICT) between the feeble elec-
tron-donating urea groups36 and the chemical functions that
TABLE 3 Fluorescence Emission Maxima (nm) of Copolymers
and Models
Polymer
Solutiona
Solid State (film)
Model
Solutionb
CP1
CP2
CP3
CP4
CP5
CP6
a
424
569, 594c
460
M1
M2
M3
M4
M5
M6
425, 460c
569, 594c
420
577
420
422
569, 600c
521
575, 598
528
530, 570c
517
FIGURE 7 Fluorescence images of solutions of models M1, M2,
M3, M4, M5, and M6 and (from left to right) in DMSO (2 ꢃ
10ꢁ3 M): (a) upper photograph: without added anion; (b) lower
photograph: with a fluoride concentration of 10ꢁ2 M (fluoride
added as [CH3 CH2)3]4NF).
432
447, 514
467
4 ꢃ 10ꢁ3 M solution in DMSO.
2 ꢃ 10ꢁ3 M solution in DMSO.
b
c
A maximum (underlined) and a shoulder were observed.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
REFERENCES AND NOTES
Some of the model compounds and copolyamides are highly
fluorescent, exhibiting intense blue to orange fluorescence
both in solution and in the solid state as a thin film or pow-
der (Figs. 5 and 6). The nature of the fluorescence behavior
could be somewhat related with the ICT. Thus, the highly flu-
orescent models (M3 and M5) show a nearly colorless pat-
tern in DMSO solution, probably indicating that the strong
ICT could give rise to an energy-wasting pathway quenching
the fluorescence of the fluorophore.39
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