Synthesis and characterization of luminescent rod - Coil block copolymers by atom transfer radical polymerization: Utilization of novel end-functionalized terfluorenes as macroinitiators

Article abstract of DOI:10.1002/chem.200390115

Two novel, rigid, photoluminescent, substituted terfluorene derivatives were synthesized by utilizing direct bromination and Suzuki coupling reactions. These oligomers were used as initiators for the atom transfer radical polymerization (ATRP) of styrene and tert-butyl acrylate. Thus, diblock and triblock rod - coil block copolymers were prepared with well-defined structure, as far as their size and shape is concerned. Molecular weights up to approximately 21000 and polydispersity indices not exceeding 1.5 in most cases were obtained. The copolymers emit blue light in solution, and their luminescence properties remain practically invariable when passing from solution to the solid state. No ground-state aggregation or excimer formation were observed in the solid state, even after annealing at high temperatures.

Full text of DOI:10.1002/chem.200390115

FULL PAPER
Synthesis and Characterization of Luminescent Rod Coil Block Copolymers
by Atom Transfer Radical Polymerization: Utilization of Novel
End-Functionalized Terfluorenes as Macroinitiators
Panagiotis K. Tsolakis and Joannis K. Kallitsis*[a]
Abstract: Two novel, rigid, photolumi-
nescent, substituted terfluorene deriva-
tives were synthesized by utilizing direct
bromination and Suzuki coupling reac-
tions. These oligomers were used as
initiators for the atom transfer radical
polymerization (ATRP) of styrene and
tert-butyl acrylate. Thus, diblock and
triblock rod coil block copolymers
were prepared with well-defined struc-
ture, as far as their size and shape is
concerned. Molecular weights up to
approximately 21000 and polydispersity
indices not exceeding 1.5 in most cases
were obtained. The copolymers emit
blue light in solution, and their lumines-
cence properties remain practically in-
variable when passing from solution to
the solid state. No ground-state aggre-
gation or excimer formation were ob-
served in the solid state, even after
annealing at high temperatures.
Keywords: atom transfer radical
polymerization ¥ block copolymers
¥ fluorescence ¥ phase separation ¥
polymerization ¥ radical reactions
initiated towards the study of various PF homopolymers and
Introduction
10]
copolymers.[6
Light-emitting organic materials have been extensively stud-
ied in the past few years, with the focus mainly on their
potential use in photoluminescent and electroluminescent
devices.[1 3] The most recent developments in polymeric light-
emitting diode (PLED) materials require the synthesis of
conjugated polymers that allow thin film deposition with
controlled and reproducible techniques, and which produce
highly efficient blue light with low driving voltage. Oligo- and
polyfluorene (PF) derivatives, in general, have been found to
be excellent candidates for fulfilling the above requirements,
since they emit blue light both in solution and in the solid
state, exhibit thermal stability, and produce light with high
quantum yields.[4] Although polyfluorene (PF) derivatives
were investigated for electrooptical devices[5a] shortly after
the discovery of electroluminescence in polymers by Friend,
Holmes, and co-workers,[1a] no intensive work was devoted to
this field for a long time, owing to some structure irregu-
larities.[5b] However, new research efforts have recently been
The application of these materials is hindered by their
tendency to form aggregates, either during annealing or upon
passage of current, which lead to a red-shifted and less
efficient emission.[4a, 11] To minimize this tendency for aggre-
gation, several attempts have been made to use bulky
substituents,[12] copolymerization techniques,[8g,13] dendrimer
attachment,[8c, 14] or an oligomer approach.[3, 11, 15]
Among the above methods, the copolymer approach, and
especially the synthesis of rod coil copolymers[7a, 16, 17] with
well-defined conjugated segments as their rod portion,
combines the advantages of polymers, such as easy processing
and the absence of crystallization in the devices, with the
advantages of the oligomer approach, such as solubility and
well-defined conjugation length. Moreover, with a proper
combination of the structures of the rigid, conjugated segment
and the coil part, unique morphologies can be obtained (such
as liquid crystals and honeycomb structures).[16a] The incor-
poration of a light-emitting oligomer into a block copolymer
structure can also reduce the size of the luminescent clusters
to nanoscale dimensions, minimizing interchain interactions
and subsequently the tendency to aggregate.
[a] Prof. Dr. J. K. Kallitsis, P. K. Tsolakis
Department of Chemistry, University of Patras
265 00 Patras (Greece)
In our work we chose atom transfer radical polymerization
(ATRP)[18] to prepare rod coil copolymers that bear a
substituted terfluorene derivative as the light-emitting rigid
block. More specifically, compounds 3 and 4 (see Scheme 1)
were synthesized and used as initiator precursors for the
polymerization of styrene and tert-butyl acrylate (tBA) by
ATRP, which resulted in diblock and triblock rod coil
and Institute of Chemical Engineering and High-Temperature
Chemical Processes (ICE/HT)
P.O. Box 1414, 265 00 Patras (Greece)
Fax : (‡30)0030610-997122
E-mail: J.Kallitsis@chemistry.upatras.gr
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/chemistry/ or from the author.
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936 943
meth-
ical
polymerization
ods.[18, 19a, 19b] The synthetic
process that ATRPutilizes does
not demand strict reaction con-
ditions. On the other hand,
adjustment of the reaction con-
ditions (proper catalytic sys-
tem, initiator, solvent, molecu-
lar ratio between the reactants),
can lead to a linear increase in
the molecular weight with con-
version and quite low polydis-
persities because of the activa-
tion deactivation step during
polymerization. This allows the
preparation of macromolecules
with
varying
composition
(block, gradient, statistical, al-
ternating copolymers) and top-
ology (star, comb, graft, den-
dritic, hyperbranched copoly-
mers).[18, 19a]
In this work novel, rigid,
mono- and bifunctional lumi-
nescent oligofluorene-based in-
itiators for ATRPof various
vinyl monomers were synthe-
sized in satisfactory yields by
well-known organic reactions
(Scheme 1). The substituted
terfluorene III and its precur-
sors were synthesized and puri-
fied based on known procedur-
es.[7c, 16d, 15c] The substituted ter-
fluorene III was directly
brominated by two different
synthetic methods.[7c, 8e] Despite
the previously known difficul-
ties in the synthesis and purifi-
cation of brominated oligo-
fluorene products, we managed
to isolate compound 2 by col-
umn chromatography and to
characterize it by 1H and
Scheme 1.
13C NMR spectroscopy. Furthermore, having carefully select-
ed the stoichiometry of the reactants, the monobromo
compound 1 was selectively obtained along with a certain
amount of unreacted hexahexylterfluorene. The assumption
of dibromoterfluorene formation cannot be excluded in this
stage. This mixture, after it was separated from any other by-
products by column chromatography, was used in the next
step.
copolymers that emit light. The triblock copolymers were
found to emit blue light in both solution and the solid state;
they did not form any excimers or aggregates after thermal
treatment of their films.
Results and Discussion
The 1H NMR spectra of III and 2 clarify the structure of the
brominated product. The multiple peak appearing in the
range d ˆ 7.3 7.4 ppm of the spectrum of III is assigned to the
protons at the 6-, 7-, 8-, 6''-, 7''-, and 8''-positions (Fig-
ure 1a).[15a] This peak is completely absent in the spectrum of
2, and a new multiple peak appears at d ˆ 7.48 ppm because of
the change in the chemical shift of the protons that are
In recent years a variety of controlled radical polymerization
techniques have been developed.[18, 19] These advances in
polymer chemistry allowed the synthesis of new, well-defined
macromolecules of varying topology and chemical structure,
which were difficult or even impossible to obtain with
traditional polymerization techniques. ATRPbelongs to
this category as one of the most popular controlled rad-
Chem. Eur. J. 2003, 9, No. 4
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937

J. K. Kallitsis and P. K. Tsolakis
FULL PAPER
trimer, both 1 and 2 were subjected to Suzuki coupling[20a] with
boronic acid IV[20b] to give the mono- and bifunctionalized
initiator precursors (3 and 4) for ATRP, with eight and ten
phenyl rings in the main chain, respectively. After applying
proper modifications to the end-groups of these precursors,
the resulting mono- and bifunctional initiators (5 and 6) were
used to synthesize diblock and triblock polystyrene and
poly(tert-butyl acrylate) (PtBA) copolymers with controlled
structure and shape (Scheme 2).
The structures of the initiators were confirmed by 1H NMR
spectroscopy. A characteristic change upon transformation of
3 to 5 (and 4 to 6) is the shift of the signal due to the aromatic
protons next to the oxygen substituent from d ˆ 6.95 to
7.15 ppm. In the spectrum of 5 the integration ratio (4:1) of the
signals at d ˆ 2.05 ppm, due to the six methylenic groups that
are adjacent the to 9-, 9'-, and 9''-positions, and at d ˆ
1.80 ppm, due to the terminal methyl group of the main
chain, shows that the OH end group was substituted, resulting
in a monofunctional initiator. The corresponding integration
ratio for the initiator 6 was 2:1 (Figure 2a), confirming that
the preparation of a bifunctional initiator was also achieved.
An important issue in oligo- and polyfluorene synthesis is
that the alkyl substitution in the 9(H)-position of the fluorene
units should be complete to prepare materials with thermo-
stability and optimized optical properties. In cases where the
aforementioned substitution is deficient, there can be partial
oxidation of the C(9) center to a carbonyl group, either during
the workup procedure in air or by thermal treatment of the
material.[4a] The resulting fluorenone moieties, known as keto
defects, act as quenching sites for optical excitations or
charges, since they have the ability to ™trap∫ singlet excitons
and reduce the population in the excited state.[12a] This would
lead to the appearance of a low-energy band in the yellow/
orange region of the photoluminescence spectrum. In our
case, the absence of signals at about d ˆ 3.5 ppm or at about
Figure 1. 1H NMR spectra (aromatic region) in CDCl3 at room temper-
ature a) of III and b) of 2.
ˆ
d ˆ 180 ppm, assigned to H(9) and C(9) O, respectively, from
the 1H and 13C NMR spectra of the precursor compounds and
the final initiators, indicate that the synthesized rods are
oxidatively stable, defect-poor oligofluorene derivatives.
The synthesized diblock and triblock copolymers and their
molecular characteristics are given in Table 1. Molecular
weights up to about 21000 were obtained, and for the PS
copolymers the polydispersity index (PDI) did not exceed 1.5.
Polymerization of tBA gave relatively lower molecular
weights. The different architecture of the block copolymers
as well as the different monomers used for polymerization
provide the opportunity to control the overall morphology
and properties of the final material. With the previously
discussed synthetic method one can easily explore the
relationship between structure and properties by tailoring
various chemical and physicochemical parameters, such as the
aspect ratio of the rigid-rod block, the glass transition
temperature, and the molecular weight of the flexible chains,
to obtain the desired final properties.
adjacent to the inserted bromine atoms (Figure 1b). Integra-
tion showed that the multiple peak at d ˆ 7.35 ppm in the
spectrum of III results from six protons and the corresponding
one at d ˆ 7.48 ppm in the spectrum of 2 results from four
protons. This shows that two bromine atoms have been
inserted. In addition, the peak assigned to the protons in the
1-, 3-, 6''-, and 8''-positions of 2 seems to consist of two
separate peaks, one singlet and one doublet, which overlap
one another. This proves that the bromination occurred in the
7- and 7''-positions to give the 2,7''-dibromotrifluorene
derivative. If the bromine atoms were introduced in the 6-,
and 6''-positions there would be two doublet peaks at d ˆ
7.48 ppm. Therefore, it is clear that the desired product 2 was
obtained. The results obtained from 13C NMR spectroscopy
are in accordance with the corresponding ones from the
1H NMR spectra and further support the conclusion that the
isolated compound 2 is selectively and totally brominated in
the 7- and 7''-positions of III.
The incorporation of the initiator into the polymeric chain
and the initiation efficiency were confirmed by 1H NMR
spectroscopy and size exclusion chromatography. In Figure 2
the 1H NMR spectra of the initiator 6 and the copolymer 6-PS
2 are presented. Most of the characteristic signals of the rigid
To increase the persistence and conjugation length, as well
as to introduce the proper end-functionalization for this
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Luminescent Rod Coil Block Copolymers
936 943
Scheme 2.
block (Figure 2a), that is signals in the aromatic region in the
range of d ˆ 7.57 7.78 ppm and in the aliphatic region at d ˆ
1.05 and 0.70 ppm, are clearly shown in the spectrum of the
copolymer (Figure 2b). The integration ratio of the protons in
the aromatic region (d ˆ 7.55 7.90 ppm) to those of the
dilute solution and in the solid state. In Figure 5 the
luminescence spectra of 6 and 6-PS 1 are compared with
those of hexahexyl-terfluorene in both solution and the solid
state. All three spectra in solution (Figure 5a) have a
characteristic progressive vibronic structure, which is related
À
À
ˆ
terminal CH3 CH2 groups of the hexyl substituents is as
expected (1:1). It is also clear that the signal at d ˆ 4.6 ppm,
which is assigned to the terminal protons next to the halogen
atoms of the initiator, has totally disappeared after the
polymerization, while a new signal, due to the substituted
initiator, has appeared at d ˆ 3.7 ppm. This is consistent with
the fact that no trace of the initiator is apparent in the SEC
chromatograms of the copolymers. As an example, the SEC
chromatogram of 6-PS 1 is presented in Figure 3.
to the vibrational stretching of the C C bond (about
1600 cmÀ1).[4a] The bathochromic shift of 14 nm in the
spectrum of the initiator relative to that of the terfluorene
indicates an increase in the effective conjugation length[15a]
after the incorporation of the two biphenyl units at the 2- and
7''-positions, as has already been well proven by NMR
spectroscopy. The fact that the emission spectra of the
initiator and the respective copolymer are almost identical
shows that the flexible chains do not affect the luminescent
properties of the chromophore, as was expected. In the solid
state (Figure 5b), the spectrum of the terfluorene oligomer is
red-shifted by 20 nm, that of the initiator exhibits a red shift of
10 nm. This difference could mainly be attributed to the larger
torsion angle between the phenylene rings of the biphenyl
units, which suppresses the formation of totally planar
species.[21]
The thermal behavior of the synthesized initiators and
copolymers has been studied by differential scanning calo-
rimetry (DSC; Figure 4). Initiator 5 displays an endotherm at
154.58C during the first heating scan, while only a glass
transition temperature (Tg) at 38.58C is obtained during the
second heating scan. For the initiator 6, only a Tg at 43.08C
was obtained for both the first and the second heating scans.
The higher Tg of 6 is consistent with its more rigid structure.
The DSC thermograms of the diblock and triblock copoly-
mers are also depicted in Figure 4. Information for the phase
separation of these copolymers can be extracted from these
thermograms. Two Tg values were detected in most cases, one
in the temperature range of the oligofluorene Tg value and the
other one arising from the PS phase. This indicates that a
phase separation, on the scale where Tg is sensitive, is
obtained in these copolymers.
As far as the copolymer×s spectrum is concerned there
seems to be almost no difference between the solution and
solid states (Figure 5c). We believe that the reason for the
minimal differences between these two spectra is that the
intermolecular interactions between chromophore units, re-
sulting from the formation of aggregates, are significantly
diminished. This means that the rigid block gets diluted into
the polystyrene matrix, almost as if it were diluted in CHCl3.
Similar cases in which the emission spectra of polyfluorene
derivatives in solution and in the solid state had little
difference have been reported recently.[22] In these cases,
Initiator 6 and its respective polystyrene copolymers were
investigated with absorption and emission spectroscopy in
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J. K. Kallitsis and P. K. Tsolakis
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Figure 2. 1H NMR spectra in CDCl3 at room temperature of 6 (top) and 6-PS 2 (bottom).
Table 1. Reaction conditions and molecular weight characteristics of the
synthesized block copolymers.
GPC results[d]
Polymer[a]
monomer/solvent (v/v)
Mn
Mw
PDI
5-PS 1
5-PS 2
6-PS 1
6-PS 2
5-PtBA 1
6-PtBA 1
1.5
2
2
1.5
2[b]
10[c]
4150
5000
1.20
1.50
1.38
1.41
1.22
1.65
9950
15500
21000
2500
14900
21450
29600
3050
5200
8600
[a] Reaction conditions: Diphenyl ether, CuBr, PMDETA, 1108C.
[b] DMF was used as a solvent. [c] Instead of DPE, 10% w/v ethylene
carbonate (EC) was used. Reaction temperature: 908C. [d] Molecular
weights and polydispersity indices were determined with size exclusion
chromatography experiments (CHCl3, room temperature) using polystyr-
ene standards for instrument calibration.
Figure 3. Size-exclusion chromatograms of the copolymer 6-PS 1 (solid
line) and the initiator 6 (dashed line).
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Luminescent Rod Coil Block Copolymers
936 943
Figure 4. DSC thermograms of a) 5 (first run), b) 5 (second run), c) 5-PS 2
(second run), d) 6 (first run), e) 6-PS 1 (second run). The first and second
heating rates were 208CminÀ1
.
instead of n-hexyl groups, bulky aliphatic or aromatic chains,
or even dendrimers were used as substituents in the 9-position
of the fluorene species in order to prevent packing of the
polymer backbone because of b-phase formation.[4a, 8c, 14a]
To further support the deduction that our copolymers are
capable of producing pure blue light as a result of the
inhibition of aggregate formation by their flexible polymer
chains, we investigated the thermal resistance of the copoly-
mers towards aggregate formation in the solid state.[22] For
that reason a 6-PS 1 copolymer film was cast from CHCl3 onto
a quartz substrate and annealed for half an hour at 1408C,
which is a temperature much higher than Tg (Tg,6-PS1
ˆ
96.18C). From its photoluminescence spectrum before and
after annealing (see Supporting Information) it is obvious that
no peak that could be attributed to excimer or aggregate
formation is present.
Conclusion
Rod coil diblock and triblock copolymers containing sub-
stituted terfluorene derivatives as the rod block have been
synthesized by utilizing atom transfer radical polymerization.
These copolymers have the ability to emit blue light when
excited in the near-UV region both in solution and in the solid
state. Despite the use of nonbulky substituents in the
9-position of the fluorene units, the photoluminescent char-
acteristics in the solid state exhibit minimal differences when
compared with those in solution, mainly because of the
incorporation of the emissive unit into polystyrene or PtBA
flexible chains. Furthermore, DSC measurements revealed
the presence of a phase separation in the synthesized block
copolymers, making these materials very promising for
luminescence applications.
Figure 5. Fluorescence spectra at room temperature of III (solid line),
&
initiator 6 (dashed line), and triblock copolymer 6-PS 1 ( ) dissolved in
CHCl3 (a) and as thin films cast from CHCl3 onto a quartz substrate (b).
c) Fluorescence spectrum at room temperature of 6-PS 1 in CHCl3 (solid
line) and as thin film cast from CHCl3 onto a quartz substrate (dashed line).
Excitation wavelength was 360 nm.
and finally with water; it was then dried over sodium hydroxide and
calcium chloride pellets and fractionally distilled. Diphenyl ether (Merck)
was stored over molecular sieves (4 ä) and purged with argon for 30 min
before the polymerization was started. CuBr (Aldrich), N,N,N',N',N''-
pentamethyldiethylene triamine (PMDETA, Aldrich), and all the other
reagents and solvents were used as received. All reactions were run under
inert atmosphere (N2, Ar). Silica gel 60 (Merck, 0.082 0.2 mm) was used as
the stationary phase for column chromatography.
Experimental Section
General: Compounds I, II, III, and IV were synthesized based on known
procedures.[7c, 15c, 16d, 20b] Styrene, tBA, and DMF (Merck) were vacuum-
distilled from finely powdered calcium hydride. Dichloromethane was
washed with concentrated sulfuric acid, then with dilute sodium hydroxide,
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J. K. Kallitsis and P. K. Tsolakis
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Physical characterization: The structures of the synthesized compounds
were clarified by high-resolution 1H NMR spectroscopy with a Bruker
Avance DPX 400 MHz spectrometer and by 13C NMR spectroscopy with a
Bruker Avance DPX 75 MHz. Fluorescence was measured on an SLM
Aminco SPF-500 spectrofluorometer. The concentrations of the solutions
used for these measurements were 10À7 m in chromophore units. Molecular
weights (Mn and Mw) were determined by gel permeation chromatography
(Ultrastyragel columns with 500 and 104 ä pore size; CHCl3 (analytical
grade) was filtered through a 0.5 mm millipore filter and samples were
passed through a 0.2 mm millipore filter; flow 1 mLminÀ1; room temper-
ature) using polystyrene standards for calibration.
Synthesis of 2-(4'-hydroxy-1,1'-biphenyl-4-yl)-9,9,9',9',9'',9''-hexahexyl-
7,2':7',2''-terfluorene (3):
A vessel containing compound 1 (1.10 g,
1.02 mmol) along with IV (0.91 g, 3.06 mmol), and tetrakis(triphenylphos-
phine)palladium (0.06 g, 0.05 mmol) was degassed and filled with argon
three times. Previously deoxygenated toluene (50 mL) and aqueous sodium
carbonate solution (2n, 0.55 g Na2CO3, 5.19 mmol) were added, and the
mixture was heated at reflux under argon for 48 h. After the mixture had
been cooled, the organic layer was separated and washed with water. The
toluene solution was dried over magnesium sulfate and the solvent was
removed by evaporation. The reddish liquid was dried under reduced
pressure at 708C. The intermediate product, which bears the tetrahydro-
pyranyloxy group, was quantitatively deprotected by using a tenfold excess
of concentrated hydrochloric acid and THF/MeOH (4:1) as a solvent
mixture at reflux for 12 h. The organic solvents were evaporated, and the
crude solid was filtered, washed with plenty of water and methanol, and
dried under vacuum. The material obtained was purified using column
chromatography (toluene/ethyl acetate, 6:1) to give 3. The yield was 0.57 g
(0.49 mmol, 48%). 1H NMR (CDCl3, TMS): d ˆ 7.81 (m, 8H), 7.65 (m,
12H), 7.56 (half of AA'XX', 2H), 7.32 (m, 3H), 6.94 (half of AA'XX', 2H),
2.05 (m, 12H), 1.11 (m, 36H), 0.77 ppm (m, 30H).
Synthesis of 2-bromo-9,9,9',9',9'',9''-hexahexyl-7,2':7',2''-terfluorene (1):
Compound III (2.40 g, 2.40 mmol) was dissolved in CCl4 (10 mL), and
then I2 (70 mg, 0.28 mmol) and Br2 (0.12 mL, 384 mg, 2.4 mmol) were
added. The reaction proceeded in the dark for 48 h. Aqueous sodium sulfite
solution was added to the mixture to remove the unreacted Br2. The
organic solution was separated and washed with sodium sulfite solution and
water. The crude product was obtained after evaporation of the solvent and
was dried under vacuum at 708C. The glassy, yellow-orange compound was
partially purified by column chromatography (hexane/toluene, 10:1) and
was used for the next stage.
Synthesis of 2,7''-bis(4'-hydroxy-1,1'-biphenyl-4-yl)-9,9,9',9',9'',9''-hexahex-
yl-7,2':7',2''-terfluorene (4): A vessel containing compound
2 (0.84 g,
Synthesis of 2,7''-dibromo-9,9,9',9',9'',9''-hexahexyl-7,2':7',2''-terfluorene
(2): Compound III (2.32 g, 2.32 mmol) was dissolved in CHCl3 (10 mL)
and FeCl3 (12.6 mg, 0.078 mmol) and Br2 (0.29 mL, 0.90 g, 5.66 mmol) were
added to the mixture. The reaction proceeded in the dark for 48 h. From
this point the same workup procedure was followed as in the synthesis of
Compound 1. The glassy, yellow-orange compound was purified by column
chromatography (hexane/toluene, 10:1). The yield was 1.50 g (1.30 mmol,
56%). 1H NMR (CDCl3, TMS): d ˆ 7.81 (d, J(H,H) ˆ 8.0 Hz, 2H), 7.75 (d,
J(H,H) ˆ 8.0 Hz, 2H), 7.62 (m, 10H), 7.48 (m, 4H), 2.05 (m, 12H), 1.10 (m,
36H), 0.75 ppm (m, 30H); 13C NMR (CDCl3, TMS): d ˆ 153.28, 151.83,
151.14, 141.04, 140.39, 140.09, 139.86, 139.24, 130.02, 126.29, 126.24, 126.19,
121.53, 121.47, 121.06, 120.99, 120.01, 55.54, 40.28, 31.44, 29.62, 23.83, 22.54,
13.97 ppm.
0.73 mmol) along with IV (0.65 g, 2.18 mmol) and tetrakis(triphenylphos-
phine)palladium (0.04 g, 0.035 mmol) was degassed and filled with
argon three times. Previously deoxygenated toluene (30 mL) and aqueous
sodium carbonate solution (2n, 0.40 g Na2CO3, 3.77 mmol) were added to
the mixture. The workup procedure is similar to that of the synthesis of 3.
The white-yellow solid obtained was purified using column chromatog-
raphy (toluene/ethyl acetate, 4:1) to give 4. The yield was 0.46 g
(0.34 mmol, 47%). 1H NMR (CDCl3, TMS): d ˆ 7.74 (m, 12H), 7.60 (m,
18H), 6.94 (half of AA'XX', 2H), 2.05 (m, 12H), 1.11 (m, 36H), 0.77 ppm
(m, 30H).
Preparation of the initiators 5 and 6: Et3N (65 mL, 0.47 mmol) and
2-chloropropionyl chloride (CPC, 280 mL, 2.9 mmol) were added in three
equal portions every 6 h to a cooled (ice bath) solution of 3 (170 mg,
0.15 mmol) or 4 (200 mg, 0.15 mmol) in ClCH2CH2Cl (20 mL). The system
was refluxed for 48 h after the last addition. The red solution was
concentrated by evaporation of most of the solvent. Methanol (20 mL) was
added to the residue and the colorless precipitate was isolated, washed with
methanol, and dried under vacuum. Column chromatography (toluene/
hexane, 1:1) gave 5 (155 mg, 0.12 mmol, 80%) and 6 (167 mg, 0.11 mmol,
73%) as colorless solids.
Synthesis of 4-(tetrahydropyran-2-yloxy)-1,1'-biphenyl-4'-yl-boronic acid
IV: 4'-bromo-[1,1'-biphenyl]-4-ol (15 g, 0.06 mol) was dispersed in CH2Cl2
(300 mL), and 3,4-dihydro-2H-pyran (16.3 mL, 0.18 mol) and (Æ)-cam-
phor-10-sulfonic acid (0.41 g, 1.76 mmol) were added. The reaction
proceeded in the dark under argon atmosphere at room temperature for
18 h. Approximately half of the solvent was removed by evaporation, and
diethyl ether (150 mL) was added. A tenfold excess of 1n aqueous NaOH
solution was added to the mixture, which was vigorously stirred for 18 h.
The organic layer was collected and washed with plenty of water. The
solution was dried over magnesium sulfate and after the complete
evaporation of the solvent a dark-brown viscous liquid was obtained, to
which hexane was added. The mixture was stirred overnight to produce a
colorless solid material (THP-protected 4'-bromo-[1,1'-biphenyl]-4-ol,
yield: 14.78 g, 44.4 mmol, 74%). This compound was converted to IV
according to the following procedure: in a previously dried three-neck
round-bottom flask equipped with a thermometer, a dropping funnel with a
rubber septum, a gas inlet/outlet, and a magnetic stirring bar, 4-(tetrahy-
dropyran-2-yloxy)-4'-bromo-1,1'-biphenyl (11.50 g, 34.5 mmol) was dis-
solved in THF (200 mL). The system was degassed three times and filled
with argon. The funnel was then charged with nBuLi (1.6n solution in
hexane, 33 mL, 52.6 mmol). The system was cooled to À808C and the
nBuLi was added dropwise over about 20 min. The temperature was
allowed to rise to À408C and was maintained at that temperature for
approximately 3 h. The mixture was cooled again to À808C and trimethyl
borate (10 mL, 88.6 mmol) was added dropwise. The suspension was
allowed to reach room temperature while stirring overnight under argon
atmosphere. Deionized water was added to the yellowish solution so as to
hydrolyze the excess trimethyl borate along with the boronic ester groups.
The crude product was extracted with ethyl acetate. The acetate solution
was washed with water, dried over magnesium sulfate, and the solvent was
removed by evaporation. Hexane was added to the white-yellow solid and
the latter was filtered, washed with hexane, and dried under vacuum. The
yield was 8.20 g (27.5 mmol, 80%). 1H NMR (CDCl3, TMS): d ˆ 7.52 (half
of AA'XX', 2H), 7.47 (half of AA'XX', 2H), 7.41 (half of AA'XX', 2H),
7.12 (half of AA'XX', 2H), 5.47 (t, J(H,H) ˆ 2.8 Hz, 1H), 3.92 (m, 1H), 3.62
(m, 1H), 1.45 2.10 ppm (3m, 6H).
1
5: H NMR (CDCl3, TMS): d ˆ 7.81 (m, 8H), 7.65 (m, 12H), 7.57 (half of
AA'XX', 2H), 7.32 (m, 3H), 7.15 (half of AA'XX', 2H), 4.60 (q, J(H,H) ˆ
6.8 Hz, 1H), 2.05 (m, 12H), 1.81 (d, J(H,H) ˆ 6.8 Hz, 3H), 1.11 (m, 36H),
0.77 ppm (m, 30H); elemental analysis calcd (%) for C90H108O2Cl (1257.43):
C 85.96, H 8.67; found: C 85.85, H 8.73.
6: 1H NMR (CDCl3, TMS): d ˆ 7.74 (m, 12H), 7.60 (m, 18H), 7.15 (half of
AA'XX', 2H), 4.60 (q, J(H,H) ˆ 6.8 Hz, 2H), 2.05 (m, 12H), 1.81 (d,
J(H,H) ˆ 6.8 Hz, 6H), 1.11 (m, 36H), 0.77 ppm (m, 30H); 13C NMR
(CDCl3, TMS): d ˆ 151.81, 149.93, 140.92, 140.65, 140.52, 140.33, 139.93,
139.36, 139.07, 138.92, 128.15, 127.61, 127.50, 126.18, 125.97, 121.45, 120.01,
55.34, 52.33, 40.41, 31.46, 29.68, 23.85, 22.54, 21.39, 13.97 ppm; elemental
analysis calcd (%) for C105H120O4Cl2 (1517.15): C 83.12, H 7.99; found: C
82.96, H 7.82.
ATRP of styrene and tBA using the rigid macroinitiators: A mixture of the
initiator 5 (0.2 mmol) or 6 (0.1 mmol), CuBr (0.2 mmol), and PMDETA
(0.2 mmol) was degassed. The solvent (3.5 mL) and the monomer (7.0 mL)
were added with a syringe. The reaction mixture was heated (temperatures
are specified in Table 1) for 18 h. After cooling to room temperature, THF
(10 15 mL) was added to dissolve the polymer. The suspension was
filtered to remove most of the catalyst. Styrene copolymers were
precipitated by the addition of methanol (20-fold excess by volume). The
tBA copolymers were obtained by pouring the filtered solution into a
mixture of methanol and water (50:50 v/v; 20-fold excess by volume). Then
the precipitated tBA copolymers were dissolved in diethyl ether. The
solution was washed with plenty of water, and diethyl ether was evaporated
to give the final tBA block copolymers.
942
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Chem. Eur. J. 2003, 9, No. 4

Luminescent Rod Coil Block Copolymers
936 943
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Acknowledgements
This work was partially supported by the Operational Program for
Education and Initial Vocational Training on ™Polymer Science and
Technology∫ -3.2a, 33H6, administered through the Ministry of Education
and Religious Affairs in Greece.
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