Copoly(peryleneimide)s containing 1,3,4-oxadiazole rings: Synthesis and properties

Article abstract of DOI:10.1002/pola.24209

New copolyimides containing perylenediimide, oxadiazole and hexafluoroisopropylidene moieties were prepared by one-step polycondensation reaction in solution at high temperature of aromatic diamines containing preformed oxadiazole ring with a mixture of a dianhydride having a perylene ring and another dianhydride with hexafluoroisopropylidene unit. The thermal stability and glass transition temperatures of these copolyimides were measured and compared with those of related polyimides. The solid polymers were also studied by polarized light microscopy and X-ray diffraction which revealed a semicrystalline state consisting of face-to-face arranged columns of perylenediimide units. The film-forming ability and properties of the resulting thin films were investigated by using atom force microscopy and scanning electron microscopy which showed that the films were organized into selfassembled rod-like structures. The UV-Vis and photoluminescence properties in solution and in solid state were also investigated.

Full text of DOI:10.1002/pola.24209

Copoly(peryleneimide)s Containing 1,3,4-Oxadiazole Rings:
Synthesis and Properties
RADU-DAN RUSU, MARIANA-DANA DAMACEANU, LUMINITA MARIN, MARIA BRUMA
‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda 41A, Iasi 700487, Romania
Received 20 May 2010; accepted 29 June 2010
DOI: 10.1002/pola.24209
Published online in Online Library (wileyonlinelibrary.com).
ABSTRACT: New copolyimides containing perylenediimide, oxa-
diazole and hexafluoroisopropylidene moieties were prepared
by one-step polycondensation reaction in solution at high tem-
perature of aromatic diamines containing preformed oxadia-
zole ring with a mixture of a dianhydride having a perylene
ring and another dianhydride with hexafluoroisopropylidene
unit. The thermal stability and glass transition temperatures of
these copolyimides were measured and compared with those
of related polyimides. The solid polymers were also studied by
polarized light microscopy and X-ray diffraction which revealed
a semicrystalline state consisting of face-to-face arranged col-
umns of perylenediimide units. The film-forming ability and
properties of the resulting thin films were investigated by
using atom force microscopy and scanning electron micros-
copy which showed that the films were organized into self-
assembled rod-like structures. The UV-Vis and photolumines-
cence properties in solution and in solid state were also
C
V
investigated. 2010 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 48: 4230–4242, 2010
KEYWORDS: crystallinity; high temperature materials; photo-
optical properties; polyimides; thin films
INTRODUCTION Polymeric electroluminescent devices (ELDs)
have received much attention in recent years because of their
color tunability, low operating voltages, ease of fabrication, and
especially potential application for self-emitting full color flat
panel displays.1
containing perylene in optoelectronic fields can rarely be
found so far,9,10 which may be due to the poor solubility of
perylenediimide polymers in common organic solvents.
Therefore, the design and preparation of soluble poly(perylene-
imide)s, to give satisfactory processability of products with-
out
a perceptible loss of favorable properties, is an
One of the major issues for real application of ELDs is their
degradation under continuous operation. To fabricate ELDs
with high stability, much research has been performed to
improve the stability of organic materials and the interface
between the metal electrode and the organic thin film.2
important and urgent problem in the chemistry of heat
resistant polymers. Being known that the introduction of
flexible groups or/and certain supplemental heterocycles
into the backbone of fully aromatic polymers can lead
to soluble products,11,12 a combined approach was under-
taken through the synthesis of copoly(peryleneimide)s con-
taining oxadiazole rings and flexible groups such as ether or
hexafluoroisopropylidene.
Polyimides have various outstanding characteristics such as
good adhesion to metal, high thermal stability, low thermal
expansion, excellent film-forming properties, and especially a
high glass transition temperature (Tg), of above 200 ꢀC,
which make them potentially useful as stable materials for
ELDs.3 Among the polyimides, those containing perylene
units appear to possess one of the highest thermal stability
because of the condensed aromatic perylene ring. Perylene-
diimides represent one of the most important n-type semi-
conductor organic materials, providing prospects for applica-
tions in organic photovoltaic devices, electrophotography,
artificial light-harvesting complexes, solar cells, field-effect
transistors and light-emitting diodes.4–7 Perylenediimides are
inexpensive and robust materials (the parent anhydride is a
common automobile paint pigment), and they are highly
fluorescent and exhibit singlet energy transfer over unusu-
ally long distances.8 However, research using polyimides
The use of 1,3,4-oxadiazole ring in the construction of co-
polyimides is based on the already known high performance
properties of aromatic polyoxadiazoles, such as high thermal re-
sistance, good hydrolytic stability, low dielectric constant, tough
mechanical behavior, and other special properties determined
by the electronic structure of this particular heterocycle.13,14
Poly(1,3,4-oxadiazole)s are of great interest for ELDs due to
electron-withdrawing character of the 1,3,4-oxadiazole ring that
can facilitate the injection and transport of electrons.15
On the other hand, it was shown that the inclusion of hexa-
fluoroisopropylidene (6F) units into polymers can increase
the solubility, thermal stability, flame retardancy, oxidation
resistance, transparency and environmental stability.16
Correspondence to: R.-D. Rusu (E-mail: radu.rusu@icmpp.ro)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 4230–4242 (2010) 2010 Wiley Periodicals, Inc.
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FIGURE 1 PLM images of bire-
fringent molten of copolyimides
(1H: first heating scan).
The incorporation of oxadiazole together with perylene-
diimide units and flexible hexafluoroisopropylidene groups
into the polymer chain is expected to provide a suitable
combination of high performance properties, solubility
and reasonable thermal transition temperatures, thus good
processability, particularly in thin films and coatings. There-
fore, this study is concerned with the synthesis and proper-
ties of new easy processable copolyimides containing both
oxadiazole and perylene units in the main chain. Such poly-
mers are expected to have a useful balance of material pro-
perties and processing capability, particularly for casting into
very thin films for various applications in optoelectronics.
The properties of these copolyimides such as solubility,
inherent viscosity, thermal stability, Tg, photo-optical and
liquid-crystalline properties, crystalline structure and film
quality were investigated.
Synthesis of the Monomers
2,5-Bis(p-aminophenyl)-1,3,4-oxadiazole, 1a, was prepared
by the reaction of p-aminobenzoic acid with hydrazine
hydrate in polyphosphoric acid (PPA), according to a published
procedure.18
1H NMR (DMSO-d6, 400 MHz, ppm), 1a: 7.73 (d, 4 H), 6.70
(d, 4 H), 5.89 (s, 4 H).
2,5-Bis[4-(p-aminophenoxy)phenylene]-1,3,4-oxadiazole, 1b,
and 2,5-bis[4-(m-aminophenoxy)phenylene]-1,3,4-oxadiazole,
1c, whose structures are shown in Figure 1, were synthe-
sized by a known procedure starting from 4-fluorobenzoic
acid and hydrazine hydrate which first reacted in PPA to
give 2,5-bis(p-fluorophenyl)-1,3,4-oxadiazole, followed by the
reaction of the latter with p- or m-aminophenol in 1-methyl-
2-pyrrolidinone (NMP) as solvent and in the presence of
K2CO3.19,20
1H NMR (DMSO-d6, 400 MHz, ppm), 1b: 8.00 (d, 4H), 7.02
(d, 4 H), 6.85 (d, 4 H), 6.67 (d, 4 H), 5.09 (s, 4 H); 1c: 8.08
(d, 4 H), 7.16 (d, 4 H), 7.08 (t, 2 H), 6.45 (d, 2 H), 6.33 (s,
2 H), 6.25 (d, 2 H), 5.33 (s, 4 H).
EXPERIMENTAL
Starting Materials
3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) was
purchased from Aldrich and purified following a procedure
described in the literature.17 4,40-(Hexafluoroisopropyli-
dene)-diphthalic dianhydride (6FDA) was purchased from
Aldrich and purified by recrystallization from a mixture of
glacial acetic acid and acetic anhydride, followed by
thoroughly washing with anhydrous diethyl ether. 4,40-Oxy-
dianiline and 1-methyl-2-pyrrolidinone (HPLC grade) were
purchased from Aldrich and used as received. All other
chemicals were of reagent grade and used as received
without further purification, and all the other solvents used
in this study were purified by standard methods.
Synthesis of the Polymers
Copolyimides I, II, and III have been prepared by one-step
polycondensation reaction of three different aromatic di-
amines, 1, with a mixture of PTCDA, 3a, and 6FDA, 3b, taken
in different molar ratios. The reactions were carried out in
NMP with 3.5% LiCl, at a concentration of 7% total solids,
ꢀ
under nitrogen stream, at high temperatures (200–210 C).
Copolyimide IV has been prepared by one-step polyconden-
sation reaction of 4,40-oxydianiline, 2, with a mixture 1:1 of
PTCDA, 3a, and 6FDA, 3b, in a solution of NMP with 3.5%
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
LiCl, at a concentration of 7% total solids, under nitrogen
stream, at high temperature.
Measurements
The inherent viscosities of the polymers were determined at
20 ꢀC, by using NMP-polymer solutions of 0.5 g/dL concen-
tration, with an Ubbelohde viscometer.
In case of the two dianhydrides with different reactivity, the
less active dianhydride monomer PTCDA was added in the
first stage of reaction to the solution of diamine in NMP, and
then the more active dianhydride monomer 6FDA was added
to achieve an even more random incorporation of the two
monomer units in the polymer chain. Owing to the low solu-
bility of PTCDA in NMP with LiCl at room temperature,
higher reaction temperature is necessary to achieve better
solubility. The reaction mixture was stirred and heated to
200–210 ꢀC and allowed to react for 10 h, then gradually
cooled to room temperature. The generated water was
removed through a gentle nitrogen flow, and hence the reac-
tion balance was moved to the formation of polyimide.
The infrared spectra of the polymers were recorded on FTIR
Bruker Vertex 70 Spectrophotometer in transmission mode,
by using KBr pellets or thin films having the thickness of
30–80 lm.
The thermal stability of the polymers was investigated by
thermogravimetric analysis (TGA) using a MOM Budapest
derivatograph, operating at a heating rate of 12 ꢀC/min, in
air, from room temperature to 750 ꢀC. The temperature of
5% weight loss on the TG curve was considered to be the
beginning of decomposition or the initial decomposition tem-
perature (IDT). The temperature of maximum rate of decom-
position which is the maximum signal in differential ther-
mogravimetry (DTG) curves was also recorded.
The following example illustrates the general procedure. In a
100 mL three-necked, round-bottomed flask, equipped with
a mechanical stirrer and nitrogen inlet and outlet, diamine
1a (756 mg, 3 mmol) and NMP with 3.5% LiCl (18 mL) as
solvent were introduced. After complete solubilization of the
diamine, dianhydride PTCDA (294 mg, 0.75 mmol) was
charged. The reaction mixture was stirred and purged with a
gentle nitrogen flow for about half an hour and then 6FDA
(999 mg, 2.25 mmol) and NMP with 3.5% LiCl (10 mL) were
added. The reaction mixture was stirred and heated to 200–
The Tg of the precipitated polymers was determined by
using
a Pyris Diamond DSC Perkin Elmer calorimeter.
Approximately 3 to 8 mg of each polymer were crimped in
aluminium pans and run in nitrogen with a heat-cool-heat
profile from room temperature to 380 C at 10 C/min. The
mid-point temperature of the change in slope of the DSC
signal of the second heating cycle was used to determine the
Tg values of the polymers.
ꢀ
ꢀ
ꢀ
210 C and allowed to react for 10 h, then gradually cooled
The polymer mesophases were investigated by observing the
textures with an Olympus BH-2 polarized light microscope
under cross polarizers with a THMS 600/HSF9I hot stage.
to room temperature. Part of the resulting dark red copoly-
imide solution, Ic, was poured onto glass plates in order to
prepare thin films, while the rest was poured into water to
precipitate the solid polymer. The dark red polymer was
washed with plenty of water and finally treated with ethanol
in a Soxhlet apparatus for 1 day in order to remove the
unreacted monomers and the high boiling solvent. Finally,
copolyimide Ic was obtained asꢀa red powder after drying in
an oven, under vacuum, at 100 C for 6 h.
Wide angle X-Ray diffraction (WAXD) was performed on
a Bruker D8 ADVANCE Difractometer, using the Ni-filtered
Cu-Ka radiation (k ¼ 0.1541 nm). A MRI-WRTC–temperature
chamber (with nitrogen inert atmosphere) and a MRI-
TCPU1-Temperature Control and Power Unit were used. The
working conditions were 36 kV and 30 mA. All the diffracto-
grams were investigated in the range 1.5ꢁ40ꢀ (2h degrees),
at different temperatures. Initial samples for X-Ray measure-
ments were powders obtained directly by polycondensation.
All diffractograms are reported as observed.
Preparation of Polymer Films
Films of copolymers I, II, III and IV were prepared by casting
a polymer solution of 7% concentration in NMP with LiCl
onto glass plates, followed by gradual heating from room
The quality of very thin films as-deposited on silicon plates
was investigated by atomic force microscopy (AFM) using a
scanning probe microscopy Solver PRO-M, NT-MDT equip-
ment made in Russia, in semi-contact mode, semi-contact
topography technique.
ꢀ
ꢀ
temperature up to 210 C, and kept at 210 C for 1 h. Dark-
red, opaque coatings resulted having strong adhesion to the
glass support. The resulting films were stripped off the
plates by immersion in boiling water, followed by drying in
oven at 105 ꢀC. The films had a very good adhesion to
the glass support and could be stripped off the plates only
with a razor blade. These films had the thickness in the
range of 30–80 lm and were used afterwards for various
measurements.
The morphology of the free-standing films was investigated
by scanning electron microscopy (SEM) using a Quanta
200 ESEM.
The UV-Vis absorption and photoluminescence spectra of
copolyimides were registered with Specord M42 apparatus
and Perkin–Elmer LS 55 apparatus, respectively, by using
very diluted polymer solutions (ꢂ10ꢃ5 M).
Very diluted polymer solutions in NMP with concentration of
0.5–1% were used to obtain very thin films having the thick-
ness in the range of nanometers onto silicon wafers by spin-
coating technique, at a speed of 5000 rpm. These films, as
deposited, were gradually heated up to 180 ꢀC in the same
way as described earlier to remove the solvent and were
used for atomic force microscopy (AFM) investigations.
RESULTS AND DISCUSSION
The copolyimides I, II, and III studied here are based on two
dianhydrides, one containing perylene unit, 3a, and another
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ARTICLE
one containing hexafluoroisopropylidene group, 3b, and vari-
ous aromatic diamines containing preformed oxadiazole ring,
1. The structures of the monomers are shown in Scheme 1.
One-step polycondensation reaction of diamines 1 with a
mixture of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),
3a, and 4,40-(hexafluoroisopropylidene)-diphthalic dianhy-
dride (6FDA), 3b, in a solution of NMP with LiCl, yielded
copolyimides I, II and III after heating at high temperature,
as shown in Scheme 2.
The copolyimide Ia precipitated during imidization and
therefore we increased the proportion of 6FDA until a
soluble polymer was obtained. The same procedure was
applied to copoly(perylene-imide)s II, since a mixture 1:1
PTCDA:6FDA gave a copolyimide that precipitated during
heating.
For comparison, a related copolyimide, IV, based on 4,40-oxy-
dianiline, 2, and a mixture of the same dianhydrides was
synthesized, its structure being shown in Scheme 3.
The FTIR spectra of the synthesized copolyimides provided
evidence that all of the perylene, hexafluoroisopropylidene
and oxadiazole units were successfully incorporated into the
copolyimide chain, as listed in Table 1. All the polymers
showed characteristic imide ring absorptions in the range of
1770–1780 cmꢃ1 (asymmetrical C¼¼O imide stretching),
1720–1730 cmꢃ1 (symmetrical C¼¼O imide stretching) and
720–730 cmꢃ1 (imide ring deformation). Characteristic
SCHEME 1 Structures of the monomers (diamines and
dianhydrides).
SCHEME 2 Synthetic route of copoly(peryleneimide)s I, II, and III. [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
six-membered anhydride has no strain.22 Similar results in
the literature confirm that the introduction of rigid perylene
moieties into polyimides hampers the formation of products
with high viscosity values.23,24
Thermal Stability
The thermal stability of these polymers was evaluated by
thermogravimetric analysis. The polymers are highly thermo-
SCHEME 3 Structure of copolyimide IV.
stable, with initial decomposition temperature (IDT) being
ꢀ
absorption peaks of 1,3,4-oxadiazole ring were also very above 465 C (Table 2). Copolyimides Ia, IIa and III begin to
evident in the range of 960–970 cmꢃ1 and 1010–1020 cmꢃ1 decompose at 465–470 ꢀC, while those with higher content
(ACAOAC¼¼ stretching). CAH linkage in aromatic rings of 6F groups, Ib, Ic and IIb start their decomposition at
showed absorption peak at 3100–3120 cmꢃ1 while the CAF 475–480 ꢀC, which shows that the thermal stability slightly
linkage showed absorption peak in the range of 1100– increases with the increasing of 6F content. Theꢀtemperature
1300 cmꢃ1
. The strong absorption bands at 1240– of 10% weight loss is in the range of 480–510 C, while the
1250 cmꢃ1 in the FTIR spectra of copolyimides II, III and IV temperature of the maximum decomposition rate as
were linked to the presence of aromatic ether stretchings.
evidenced by DTG curves is above 525 ꢀC. All these data
demonstrate that these copoly(peryleneimide)s have high
thermal stability, similar to that of other polyimides based
on the same perylene-3,4,9,10-tetracarboxylic dianhydride
but without oxadiazole rings,25 and other related poly(pery-
leneimide)s which do not contain 6F groups.22 Thus, the
thermal stability of the present copolyimides is not affected
by the introduction of flexible 6F unit in the main chain, nor
of 1,3,4-oxadiazole ring, while the solubility and the film-
forming ability of the resulting polymers are much improved
due to the presence of these groups.
It is known that conventional aromatic poly(peryleneimide)s
are insoluble in easily accessible and safe organic solvents,
being soluble only in m-cresol, due to the rigid nature of
perylenediimide unit which dictates the overall shape of the
corresponding macromolecules and thus facilitates the
strong interchain interactions and due to the compact
aggregation of the polymer chains which occurs during
imidization that is carried out at high temperatures.21 Our
copoly(peryleneimide)s are soluble in a convenient aprotic
amidic solvent which is NMP, at a concentration of 0.5–1%
due to the presence of flexible 6F groups and oxadiazole The differential scanning calorimetry (DSC) curves of co-
rings in the macromolecular structure of these copolyimides poly(peryleneimide)s I–IV were recorded during a heating-
that leads to a higher solubility compared with their ana- cooling-heating cycle at a heating rate of 10 ꢀC/min. All the
logues without 6F and oxadiazole units. Oxadiazole rings and studied polymers show in the first DSC scan a broad weak
the flexible groups, such as ether or hexafluoroisopropyli- endothermic peak and in the second heating scan a trace
dene, introduce a deviation from the linearity of the chain inflection corresponding to the glass transition. Only IIa
and disturb the tight packing of the polymer chains and shows a second endothermic peak in the first heating scan.
make the shape of the respective macromolecules to be far Such weak transitions are characteristic of liquid crystalline
from a linear rigid rod which is characteristic to aromatic perylene-containing polyimides due to the strong interac-
polyimides based only on PTCDA.
tions between the perylene moieties.26
The inherent viscosity values of copolyimides I to IV were in The Tg of the present copoly(peryleneimide)s, as evaluated
the range of 0.12–0.23 dL/g. These low values of the viscos- by differentiꢀal scanning calorimetry (DSC), are in the range
ity can be explained by the low reactivity of the PTCDA of 227–292 C. An increase in the 6F content leads to higher
monomer, which may be largely attributed to the fact that a Tg values, as it can be seen in the case of copolyimides I,
TABLE 1 FTIR (KBr Pellets, cm21) Analysis of the Synthesized Copolyimides
Band Assign
Ia
Ib
Ic
IIa
IIb
III
IV
Ar. imide, C¼O asym.
Ar. imide, C¼O sym.
C¼O bend.
oxadiazole, CAOAC str.
oxadiazole, CAOAC str.
CAF str.
1773
1730
720
1774
1728
720
1774
1726
720
1774
1730
723
1774
1729
723
1774
1730
721
1774
1730
722
–
1017
963
1017
963
1017
963
1016
961
1016
962
1025
962
–
1122
3119
–
1144
3120
–
1145
3119
–
1167
3118
1244
1151
3119
1244
1121
3120
1248
1145
3119
1238
Ar. CAH str.
Ar. CAOAC str.
Ar., aromatic; asym., asymmetric stretching; sym., symmetric stretching; bend., bending; str., stretching.
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TABLE 2 Thermal Properties of the Copolymers
be independent of the diamine monomer type and the mono-
mers ratio used in the polymers synthesis, the main differ-
ence between the XRD diffractograms being in the diffraction
intensity (Table 3). How easy can be observed in Table 3, the
diffraction intensity decrease with the decreasing of perylene
percent into polymer chain (I% Ia > I% Ib > I% Ic; I%
IIa > I% IIb).
Polymer
Tg (ꢀC)a
IDT (ꢀC)b
T10 (ꢀC)c
Tmax (ꢀC)d
Ia
Ib
Ic
265
282
292
266
267
227
245
470
480
480
465
475
467
475
480
485
496
480
482
510
508
528
535
535
IIa
IIb
III
IV
a
527, 587
530
This means that the intermolecular forces which control the
orientation and molecular packing into the samples are
generated by almost the same rigid segments. Moreover,
comparing the X-Ray diffractograms of our polymers with
those belonging to related semiflexible perylene-containing
polyimides,29 almost the same diffraction maxima can be
observed. In addition, the semiflexible perylene-containing
polyimides present a maximum in the small angle region
which reflects the intercolumnar distance corresponding to
the flexible spacer. On the other hand, similar polymers
containing oxadiazole rings and hexafluoroisopropylidene
groups, and without perylene units, synthesized by us, did
not show any degree of crystallinity.30 In the light of these
premises, we can assert that the supramolecular self-assem-
bly of our polymers is mainly dictated by strong p stacking
of the perylene units. The d-spacing calculated with Bragg’s
law by using the measured diffraction angle and the relative
intensities observed in X-Ray diffraction patterns for the
synthesized copolyimides are enclosed in Table 3.
550
540
Tg, glass transition temperature.
b
c
IDT, temperature of 5% weight loss.
T
10, temperature of 10% weight loss.
max, temperature of maximum rate of decomposition.
d
T
while the Tg values of copolymers II are not influenced by
the increase of the 6F content. Similar effect was noticed
previously: sometimes fluorination results in decreasing Tg,
sometimes has no effect upon these values, and other times
results in increasing Tg.15,27,28
Polarized Light Microscopy (PLM) and X-Ray
Diffraction Studies
All the synthesized copolymers contain a perylene unit, a
polyaromatic mesogenic core, which has the tendency to
form columnar phases because of the strong pAp inter-
actions. Additionally, these copoly(peryleneimide)s contain
oxadiazole mesogenic core which also has the ability of self
assembling in supramolecular architectures. The ability to
form columnar phases was checked by DSC, PLM and WXRD
measurements.
Usually, as confirmed by X-Ray diffraction of several single
crystals, the perylene mesogen units exhibit flat p-systems,
which are arranged in stacks showing a parallel orientation
of the neighboring, cofacially stacked perylene cores at a
distance between 3.34 and 3.55 Å.31,32 In the case of X-Ray
diffraction pattern of our polymers, the pAp stacking of
the perylene cores gives two peaks at 24.5ꢀ and 27.3ꢀ
(2h degree) situated above the diffuse halo, which indicates
that the columns are slightly disordered and can slide past
PLM measurements show for all the samples a slight bire-
fringence in solid state indicating a degree of crystalinity.
Except for polymer IV whose melting was not observed by
PLM, all the studied polymers show a birefringent molten at
the temperatures corresponding in DSC thermograms to the
broad endothermic peak. Representative PLM images are
shown in Figure 1. The polymers Ib, Ic and III form viscous
molten, while the copolyimides Ia, IIa and IIb show more
fluid birefringent molten. Except for polymer IV, all the poly-
mer samples form by cooling a birefringent glass which can
not be scratched by a spatula. The isotropisation was not
ꢀ
observed up to 350 C.
In order to investigate the structural changes which take
place in DSC and PLM measurements, X-Ray diffractograms
of copolymer powders were recorded at temperatures corre-
sponding to the different phase regions.
All the samples show similar X-Ray pattern consisting in an
amorphous halo in the range 10–30ꢀ (2h degree), and five
sharp peaks situated around 9.4ꢀ, 11.08ꢀ, 12.34ꢀ, 24.5ꢀ,
27.3ꢀ (2h degree). A diffuse weak halo was registered in the
region 3.5ꢀ–7.5ꢀ (2h degree), too (Fig. 2). This XRD pattern
indicates the presence of what we define as a semicrystalline
state, which was formed during solution polycondensation
reaction. The diffraction position and peaks shape seem to
FIGURE 2 XRD diffraction patterns at room temperature of
polymers Ia, IIb, and III. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 3 The Intensities of the Peaks Observed in X-Ray Diffraction Patterns for
the Studied Copolyimides
˚
2h
d (A)
I% Ia
I% Ib
I% Ic
I% IIa
I% IIb
I% III
I% IV
9.4
9.43
8.02
7.21
3.72
3.36
102
75
80
67
54
49
58
53
31
28
44
30
28
69
57
53
40
11.1
12.2
24.6
27.4
247
121
138
166
87
101
65
106
74
142
87
107
58
90
60
66
90
59
each other. The calculated d-spacing for these reflections cor-
responding to the intracolumnar disk-disk distance among
the perylene mesogenes is 3.72 Å and 3.36 Å respectively,
these values are very close to the distance of 3.35 Å which
was found in graphite.33–35 The close contact of the perylene
p-systems may lead to the good charge conduction. The
explanation for the close stacking into perylene columns
could be the rigid imide rings which restrict the rotation and
enhance the interactions of perylene discs to stabilize the
columns by facilitating face-to-face packing motifs.
conclusion is consistent with AFM and SEM images, as will
be discussed later. A crude diagram containing a proposed
model of columnar self-assembly of one representative poly-
mer in solid state is given in Figure 3.
The XRD pattern of the polymer samples at the temperature
corresponding to the end of the thermal transition (Tg), as it
was observed in DSC thermogram, shows some changes with
respect to the room temperature diffractogram. Since all
polymers showed similar features, only the X-Ray diffracto-
gram of polymer Ia is reproduced as a representative exam-
ple [Fig. 4 (a)].
In the small angle region the polymers showed only a diffuse
weak halo which reflects the disordered liquid character of
the statistic chains connecting the perylene cores. Due to the
fact that in macromolecular chain perylene cores are sepa-
rated from each other by chain units with different lengths,
the regular repetitions of these columnar layers is hindered.
The broad halo (3–7ꢀ, 2h degree) corresponds to a poly-
dispersity of the intercolumnar distances in the range of 30–
13 Å and reflects the statistical disposition of the perylene
cores columns.
It can be seen that after heating the peaks from the wide-
angle region shifted slightly to smaller angles and a new
reflection in the wide-angle region appeared [Fig. 4(b)].
These features suggest a decrease of the attractive forces
among perylene units, due to the increase of thermal energy
and thus of the conformational disorder of single tetrahedral
coordinated C atom and of O atom. The columnar structure
of the semicrystalline state is retained by virtue of strong
pAp perylene interactions and chain rigidity, but there is
one component of rotational disorder and poor translational
movement of chain segments, especially for the polymers Ia,
IIa, and IIb (see PLM measurements) which exhibit less
viscosity in PLM measurements. After cooling the reflections
position became similar to XRD pattern before heating
[Fig. 4(c)]. These scarce changes of the XRD patterns are
similar to other results reported in literature for perylene-
containing polymers,29 and reflect the strong interactions
among perylene mesogens.
Compared to related semiflexible perylene-containing poly-
imides, our polymers show in X-Ray difractograms a broad
wide angle halo centered at 15.7ꢀ, 2h degree. The calculated
value of spacing corresponding to the broad wide angle halo
is around 5.7 Å and it is attributed to the liquid like correla-
tion of the disordered chain units. The reflections in the
middle angle region (9.4ꢀ, 11.08ꢀ, 12.34ꢀ, 2h degree) corre-
spond to the distances of 9.43, 8.02, 7.21 Å. Taking into
account that the supramolecular architecture is dictated by
p-stacking of the perylene cores and exclude the ordering of
the other mesogenic segments, by analogy with rod like
mesogens, we attributed these distances to the tilted pery-
lene discs.36,37 This fact indicates that the columnar stacks
have various orientations.
Although the PLM observations, birefringence and fluidity,
correspond to the definition of the liquid crystalline state,
the analysis of the morphology of the samples by X-Ray
diffraction suggest that these polymers form at high temper-
atures a plastic mesophase,38 characterized by the perylene
columns with various orientations in an amorphous matrix.
By cooling, the plastic mesophase gives a continuous film
with very good adhesion to the glass support.
The packing efficiency of the perylene cores which is
reflected by X-Ray diffraction intensity depends on the poly-
mers structure. The longest columnar stacks are formed by
the most stiffened polymer (Ia), while the shortest ones are
formed by the polymer containing the biggest amount of
kinking groups (IIb). In conclusion, the X-Ray measurements
indicate that the supramolecular architecture of the semi-
crystalline copolyimides consist in columns of perylene units
arranged face-to-face, with different orientations and without
intercolumnar correlations. These perylene columns are stat-
istically distributed into amorphous part of the sample. This
The results show that in these systems, the mesomorphic
transition is very slow, due to the predominant intermolecu-
lar interactions between mesogenic units.
Morphological Studies of the Polymer Films
The good solubility makes the present polymers potential
candidates for practical applications in spin-coating and
casting processes. All these polymers possess film forming
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ARTICLE
deposited by spin-coating technique onto glass plates, by
using diluted solutions of polymers I, II and III (concentra-
tion of 1%). The quality and the morphology of these films
were studied by atomic force microscopy (AFM). These spin-
coated copolymer films are smooth and homogeneous,
without cracks or pinholes, and are self-organized into verti-
cally segregated structures, with average heights of 40 nm,
as it can be seen in the histogram. Typical AFM images and
the corresponding histogram are shown in Figure 5.
FIGURE 3 Crude diagram containing a proposed model of co-
lumnar self-assembly of polymer IIa. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com.]
ability. The polymer solutions (7%) in NMP with LiCl were
processed into thin films by casting onto glass plates. The
free-standing films having a thickness in the range of tens of
micrometers were flexible, tough, and maintained their integ-
rity after repeated bendings, except for films prepared from
polymers Ib and Ic, which proved to be brittle. Very thin
films having the thickness in the nanometer range were
FIGURE 4 The X-Ray powder diffraction pattern at room tem-
perature before- (a) and after a heating-cooling cycle (c) and at
high temperature (b) for the sample Ia. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.
com.]
FIGURE 5 AFM images: a) 2D image, b) 3D image, and c) the
corresponding histogram of copolyimide Ia. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ordered 1D crystalline arrangement. SEM images of the thin
free standing films of these copolyimides show that the poly-
mers are organized into self-assembled well-ordered building
blocks that form supramolecular rod-like structures which
tend further to aggregate into bigger rods. These aggregates
mainly result from the pAp stacking interactions of pery-
lenediimide units.
Photo-Optical Properties
There is currently much interest in polymeric electrolumi-
nescent materials, particularly those which are able to emit
blue light that is difficult to be attained with the already
known inorganic ones.39 In addition, the use of electrolumi-
nescent thin films made from highly thermostable polymers
would avoid the thermal degradation in the final device
while in service at elevated temperatures. Since during the
formation of polymeric thin films, by spin coating or dip-
coating, pinholes are likely to form and therefore will cause
the electroluminescent device to break during its operation,
there is a strong requirement that electroluminescent poly-
mers should have an outstanding capability to form pin
hole-free films, with a strong adhesion to various substrates.
Since 1,3,4-oxadiazole rings and perylenediimide units are
known as light-emissive,7,26 the light-emitting properties of
these oxadiazole-containing copoly(peryleneimide)s have
been investigated. The light-emitting ability of the polymers
containing both oxadiazole and perylenediimide chromo-
phores was assessed on the basis of the photoluminescence
spectra which were recorded for both polymer solutions in
NMP and polymer films cast from NMP solutions, after exci-
tation with light of different wavelengths.
The proeminent feature in these materials is their extended
conjugated p-system; such extension is mirrored by the
electronic absorption spectrum. Figures 7 and 8 show the
absorption spectra of NMP solutions and cast films from
NMP solutions of three representative copolyimides.
FIGURE 6 SEM images of copolyimide Ia (a: 20 lm, b: 10 lm,
c: 5 lm scale size).
The solid-state packing behavior of these copolymers was
hypothesized based on their aggregation characteristics in
solid state,28 and the morphology of the obtained supra-
molecular assembly was intuitively reflected in scanning
electron microscopy (SEM) images (Fig. 6), showing a well-
FIGURE 7 UV-Vis absorption spectra of polymers Ia, IIa, and III
in NMP solutions.
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ARTICLE
oxadiazoles 1b and 1c containing ether bridges in their
moieties presented an additional weak absorption peak at
373–378 nm, these maxima being attributed to spin-allowed
pAp* transitions involving the imide-phenyl framework.
A very small peak at 443 nm appeared in UV spectrum of
polymer Ic, due to negligible intermolecular interactions of
the conjugated perylenediimide segments of the polymer
chains. The absorbance spectra of solutions and thin films
allow us to compare the position of absorption bands kabs
,
as seen in Table 4. The small red-shift (2–10 nm) of the
absorption maxima from the highest wavelength characteris-
tic to perylenediimide units in solid state with respect to
solution could be explained by the fact that the surrounding
chromophore polarity became weaker, and the intermolecu-
lar interaction of the polymer backbones became stronger.
The absorption edge, being a long-wavelength wing of the
longest-wavelength band of the spectrum, moves to longer
wavelength (smaller energy) for the polymer films when
compared with the edge of solution of the same polymer.
This means that conformation of polymer chain can be
different depending on the surroundings.40
FIGURE 8 UV-Vis absorption spectra of polymer films Ia, IIa,
and III.
It was found that all the oxadiazole-containing copoly(pery-
leneimide)s show one strong UV absorption maximum at
303–313 nm, and three peaks at 459–464 nm, 492–494 nm,
and 526–529 nm, in NMP solutions, the spectra being quite
identical (Table 4). A weak absorption peak or shoulder at
about 375 nm in the UV spectra of polymers II, III and IV
was detected, as well. The absorption maxima at 303–313
nm of these polyimides are mainly determined by the di-
phenyl-1,3,4-oxadiazole unit, because the unsubstituted di-
phenyl-1,3,4-oxadiazole in hexane shows its absorption maxi-
mum at 284 nm.20 The absorption peaks at 459–464 nm,
492–494 nm, and 526–529 nm are due to the chain seg-
ments containing perylenediimide units and are lower in in-
tensity as compared with the absorption bands characteristic
of diphenyl-1,3,4-oxadiazole unit.7
The energy band gap (Eg) could be estimated from the fol-
lowing equation:
Egs ¼ h ꢄ c=kedge
where h is the Planck constant, c is the light velocity, and
kedge is the wavelength of the absorption edges of the optical
absorption spectra. This simple method allows estimating
and then comparing the energy gaps for the investigated
polymers in the form of solution and thin film, as it is gath-
ered in Table 4. The energy gap of these copolyimides under
study varies from 2.25 eV to 2.28 eV for polymer solutions
and from 1.97 eV to 2.18 eV for polymer films. The Eg values
do not seem to be influenced by the nature of the diamine
used for polymer synthesis. Also, the introduction of 6F
groups in the polymer chains has a very small effect on Eg
values, which means that the packing of the macromolecules
was disturbed in a very low amount. The Eg values of the
In films cast from NMP solution all copolyimides presented
two absorption maxima in the range of 493–501 nm and
501–538 nm, and most of them a maximum or a shoulder at
465–469 nm. All copoly(peryleneimide)s based on diamino-
TABLE 4 Optical Properties of Copoly(Peryleneimide)s in Solution and Solid State
c
c
UV, Sol
kmaxa, nm
UV, Sol
kedgeb, nm
UV, Film
kmaxa, nm
UV, Film
kedgeb, nm
Eg
,
Eg ,
Polymer
Sol (eV)
Film (eV)
Ia
Ib
Ic
313, 464s, 492, 529
303, 492, 526
549
547
545
548
550
550
549
467, 500, 534
494, 531
629
581
579
577
570
575
629
2.26
2.27
2.28
2.26
2.25
2.25
2.26
1.97
2.13
2.14
2.15
2.18
2.16
1.97
303, 494, 528
443, 493, 535
378, 469s, 500, 538
375s, 465s, 499, 537
373, 501, 539
376, 500, 538
IIa
IIb
III
IV
a
306, 374s, 463, 493, 529
304, 376s, 462s, 493, 529
304, 375, 463, 492, 529
375, 459, 492, 528
c
k
max, wavelength of the maximum absorption peak.
Eg, energy band gap.
b
kedge, wavelength of the absorption edges (onset) of the optical
absorption spectra.
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 5 Photoluminescence Properties of Copoly(Peryleneimide)s I-IV
PL (at 303–313 nm)
em, nm
PL (at 360 nm)
em, nm
PL (at 492–494 nm)
kem, nm
Polymer
k
k
Ia
403, 537, 577s
406, 537, 578
405, 534, 578
370, 538, 581
368, 538, 577
370, 536, 580
–
404, 534, 586s
406, 534, 577s
536, 578
536, 578s
535, 579s
538, 578
537, 577
538, 579
539, 578
Ib
Ic
406, 533, 586
IIa
IIb
III
407, 442, 538, 578
407, 443, 538, 577
407, 438, 536, 577
408, 442, 465, 538, 577
IV
copolyimide films I-IV are smaller than the Eg values of poly-
mer solutions, due to the more aggregated conformation of
polymer main chains in solid state.
was done with 360 nm (Table 5, Fig. 9). In the case of solu-
tion of polymer IV that does not contain oxadiazole ring and
was used as reference, the excitation with 360 nm resulted
in a spectrum with two absorption maxima in the blue
domain at 408 and 442 nm and other two in the green and
yellow spectral range, at 538 and 577 nm, respectively,
being similar to those of copolyimides II and III, as seen in
Figure 9. This means that the PL emission that shifted from
UV-domain to blue region by lowering the energy of
excitation is mainly determined by segments containing
imide rings having different conjugation length, and not by
the diphenyl-oxadiazole chromophore. The PL spectra of
polymers II, III and IV also show a very strong emission of
perylenediimide moieties, while the emission of oxadiazole
moieties is completely quenched in case of polyimides II and
III. Because the absorption maximum of diphenyl-oxadiazole
chromophore is aproximately 304–306 nm and the perylene-
diimide moieties did not directly absorb these wavelengths
light, an excitation energy transfer from oxadiazole to pery-
lenediimide moieties must have taken place for which the
oxygen bridge appear to be responsible. A similar effect
was previously noted by other authors.7 It appears that in
the excited state, the oxygen acts as a better bridge for the
delocalization of the charge, because the position of the
phenylene ring next to the oxygen determines the PL more
significantly in the case of copoly(peryleneimide)s containing
ether bridges, II, III and IV. The emission spectra of these
copoly(peryleneimide)s in NMP solution excited by a 492–
494 nm light, showed two peaks at 536–539 nm and 577–
579 nm, which corresponded to the emission of perylene-
diimide moieties (Table 5). Figure 9 shows representative
photoluminescence spectra of these copoly(peryleneimide)s
in solution by excitation with light of different wavelengths.
Maximum emission wavelengths values of copoly(perylene-
imide)s I–IV in solution are collected in Table 5. Since the
absorption spectra present characteristic absorption for each
individual chromophore, and even for conjugated parts con-
taining these chromophores or imide rings, we investigated
the photoluminescence (PL) ability of these polymers by
exciting with light of different wavelengths. Thus, by exciting
at the maxima absorption wavelengths characteristic to
diphenyl-1,3,4-oxadiazole chromophore and at 360 nm,
polymers I displayed similar spectra with one strong and
large emission band centered around 405 nm, in the blue
domain, due to the emission of oxadiazole, imide and phenyl-
ene rings, and two maxima in the green and yellow spectral
range, around 535 nm and 577 nm, respectively, due to the
emission of perylenediimide moieties (Fig. 9).
When excited with light of 304–306 nm, polyimides II and
III presented one broad weak emission maximum in the UV
domain, centered at about 370 nm, and two peaks within
536–538 nm and 577–581 nm range. The bands from UV
domain of these polymers are splitted and red-shifted to
407 nm and ꢂ440 nm (blue domain), when the excitation
No emission was observed in solid state. This is probably
due to the high content of perylenediimide cromophore
which leads to fluorescence quenching through aggregation.
CONCLUSIONS
Novel ternary copolyimides containing perylene, oxadiazole
and hexafluoroisopropylidene units in the backbone were
designed and successfully synthesized by one-step solution
polycondensation reaction at high temperatures. The
FIGURE 9 PL spectra of the copolyimides Ia, IIa and IV by exci-
tation with UV light of different wavelength.
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ARTICLE
8 Cormier, R. A.; Gregg, B. A. J Phys Chem B 1997, 101,
completion of imidization was confirmed by FTIR analyses.
These copoly(peryleneimide)s posses good solubility in NMP
and can be processed into thin and tough flexible films hav-
ing the thickness in the range of tens of micrometers. SEM
and WAXD data showed the p stacking rods of the copolyi-
mides in thin films. The very thin films deposited on glass
plates by spin-coating with thickness in the range of nano-
metres are smooth and homogeneous, without cracks or pin-
holes, and are self-organized into vertically segregated struc-
tures. The present copolyimides are highly thermostable, up
to 465 ꢀC, and display glass transition in the range of 225–
295 ꢀC, with a large interval between decomposition and Tg
that make these copolyimides appropriate for processing by
a thermoforming technique, as well. X-Rays measurements
indicate a semicrystalline state of the studied polymers, con-
sisting in columns of perylene units arranged face-to-face,
with different orientations and without intercolumnar corre-
lations, statistically distributed into amorphous part of the
polymer. By excitation with light of different wavelengths, all
copolyimides without ether bridges in the main chain exhib-
ited two strong PL maxima in the bluish and green–yellow
domains, due to oxadiazole chromophore and perylenedii-
mide moieties emission, respectively. The PL spectra of
polymers containing ether bridges consist of the emission of
perylenediimide chromophore and conjugated segments with
imide rings, without emission from oxadiazole chromophore,
due to the excitation energy transfer from oxadiazole to per-
ylenediimide moieties. No emission was observed in solid
state. Further research in this field is necessary to study the
suitable perylene content in order to overcome the fluores-
cence quenching through aggregation. The high-performance
properties of these polymers provide an important guideline
for the design of new alternating copolymers that can be
used to fabricate electroluminescent devices with high
stability.
11004–11006.
9 Posch, P.; Thelakkat, M.; Schmidt, H. W. Synth Met 1999,
¨
102, 1110–1112.
10 Niu, H.; Wang, C.; Bai, X.; Huang, Y. Polym Adv Technol
2004, 15, 701–707.
11 Bruma, M.; Sava, I.; Hamciuc, E.; Hamciuc, C.; Damaceanu,
M. D. Rom J Inform Sci Technol 2006, 9, 277–284.
12 Bruma, M.; Damaceanu, M. D.; Muller, P. High Perform
¨
Polym 2009, 21, 522–534.
13 Schulz, B.; Bruma, M.; Brehmer, L. Adv Mater 1997, 9,
601–613.
14 Bruma, M.; Ko†pnick, T. Adv Colloid Interface Sci 2005, 116,
277–290.
15 Damaceanu, M. D.; Rusu, R. D.; Bruma, M.; Rusanov, A. L.
Polym Adv Technol DOI 10.1002/pat.1519.
16 Bruma, M.; Fitch, J. W.; Cassidy, P. E. J Macromol Sci
Polym Rev 1996, 36, 119–159.
17 Lu, W.; Gao, J. P.; Wang, Z. Y.; Qi, Y.; Sacripante, G. G.;
Sundararajan, P. R.; Duff, J. D. Macromolecules 1999, 32,
8880–8885.
18 Hamciuc, E.; Hamciuc, C.; Bruma, M.; Schulz, B. Eur Polym
J 2005, 41, 2989–2997.
19 Bruma, M.; Schulz, B.; Mercer, F. J Macromol Sci Part A:
Pure Appl Chem 1995, 32, 259–286.
20 Iosip, M. D.; Bruma, M.; Robison, J.; Kaminorz, Y.; Schulz,
B. High Perform Polym 2001, 13, 133–148.
21 Butt, M. S.; Akhter, Z.; Zaman, M. Z.; Munir, A. Eur Polym J
2005, 41, 1638–1646.
22 Rusanov, A. L.; Elshina, L. B.; Bulyceva, E. G.; Mullen, K. In
¨
Polymer Yearbook 18, Pethrik, R.; Zaikov, G., Eds.; Polymer
Yearbook Series; Rapra Technology Ltd: Shropshire, UK, 2004,
p 7.
This work was financially supported by Romanian Programs
PNCD-2, contract no. 11008/2007 and TE is warmly acknowl-
edged TE/2010.
23 Icil, H.; Icil, S. J Polym Sci Part A: Polym Chem 1997, 35,
2137–2142.
24 Wang, Z. Y.; Qi, Y.; Gao, J. P.; Sacripante, G. G.; Sundarara-
REFERENCES AND NOTES
jan, P. R.; Duff, J. D. Macromolecules 1998, 31, 2075–2079.
25 Xu, S.; Yang, M.; Bai, F.
J Mater Sci Lett 2002, 21,
1 Yang, M.; Xu, S.; Wang, J.; Ye, H.; Liu, X. J Appl Polym Sci
1903–1905.
2003, 90, 786–791.
26 Yao, D.; Wang, Z. Y.; Sundararajan, P. R. Polymer 2005, 46,
2 Kim, Y.; Lee, J. G.; Han, K.; Hwang, H. K.; Choi, D. K.; Jung,
Y. Y.; Keum, J. H.; Kim, S.; Park, S. S.; Im, W. B. Thin Solid
Films 2000, 363, 263–267.
4390–4396.
27 Hougham, G.; Tesoro, G.; Shaw, J. Macromolecules 1994,
27, 3642–3649.
3 Kim, Y.; Keum, J. H.; Lee, J. G.; Lim, H.; Ha, C. S. Adv Mater
Opt Electron 2000, 10, 273–283.
28 Hougham, G. In Fluoropolymers 2: Properties, Hougham, G.;
Cassidy, P. E.; Johns, K.; Davidson, T., Eds.; Topics in Applied
Chemistry Series; Plenum Press: New York, 1999, p 233.
4 Chern, Y. T.; Chung, W. H. J Polym Sci Part A: Polym Chem
1996, 34, 117–124.
29 Liu, Y.; Wang, K. R.; Guo, D. S.; Jiang, B. P. Adv Funct
5 Schmidt-Mende, L.; Fechtenkotter, A.; Mullen, K.; Moons, E.;
¨
Mater 2009, 19, 2230–2235.
Friend, R. H.; MacKenzie, J. D. Science 2001, 293, 1119–1122.
6 Liu, Y. J.; Zhuang, P.; Liu, H.; Li, Y.; Lu, F.; Gan, H.; Jiu, T.;
30 Bruma, M.; Damaceanu, M. D. Collect Czech Chem Commun
2008, 73, 1631–1644.
Wang, N.; He, X.; Zhu, D. Chem Phys Chem 2004, 5, 1210–1215.
31 Zugenmaier, P.; Duff, J.; Bluhm, T. L. Cryst Res Technol
7 Xu, S. G.; Yang, M. J.; Cao, S. K. React Funct Polym 2006, 66,
2000, 35, 1095–1115.
471–478.
COPOLY(PERYLENEIMIDE)S SYNTHESIS AND PROPERTIES, RUSU ET AL.
4241

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
32 Struijk, C. W.; Sieval, A. B.; Dakhorst, J. E. J.; van Dijk, M.;
Kimkes, P.; Koehorst, R. B. M.; Donker, H.; Schaafsma, T. J.;
Picken, S. J.; van de Craats, A. M.; Warman, J. W.; Zuilhof, H.;
Sudholter, E. J. R. J Am Chem Soc 2000, 122, 11057–11066.
36 Marin, L.; Damaceanu, M. D.; Timpu, D. Soft Mater 2009, 7,
1–20.
37 Marin, L.; Destri, S.; Porzio, W.; Bertini, F. Liq Cryst 2009,
36, 21–32.
33 Hadicke, E.; Graser, F. Acta Crystallogr Sect C: Cryst Struct
¨
38 Damaceanu, M. D.; Marin, L.; Manicke, T.; Bruma, M. Soft
Commun 1986, 42, 189–195.
Mater 2009, 7, 164–184.
34 Hadicke, E.; Graser, F. Acta Crystallogr Sect C: Cryst Struct
¨
39 Segura, J. L. Acta Polym 1998, 49, 319–344.
Commun 1986, 42, 196–198.
40 Sek, D.; Iwan, A.; Jarzabek, B.; Kaczmarczyk, B.; Kasperczyk,
J.; Mazurak, Z.; Domanski, M.; Karon, K.; Lapkowski, M. Macro-
molecules 2008, 41, 6653–6663.
35 Klebe, G.; Graser, F.; Hadicke, E.; Berndt, J. Acta Crystallogr
¨
Sect B: Struct Sci 1989, 45, 69–77.
4242
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA