Donor - Acceptor diblock copolymers based on PPV and C60: Synthesis, thermal properties, and morphology

Article abstract of DOI:10.1021/ma035643o

An improved synthetic method to nitroxide end-capped poly(p- phenylenevinylene)s is presented. The nitroxide-functionalized PPVs are extended with a second coillike block by employing them as macroinitiators in a nitroxide-mediated radical polymerization (NMRP) of monomers like styrene, 4-chloromethylstyrene, 4-vinylpyridine, and n-butyl acrylate. The observed thermotropic properties and morphology of films based on the rod-coil diblock copolymers are identified and described. Some of the block copolymers are subsequently subjected to a coupling with C₆₀ to incorporate electron-accepting properties into these PPV-based diblock copolymers. For this, a statistical copolymer built from styrene and azidomethylstyrene was used as the second coillike block, making it possible to adjust the built-in ratio of C₆₀. The morphology and thermotropic properties of films prepared with these diblock copolymers are investigated.

Full text of DOI:10.1021/ma035643o

Macromolecules 2004, 37, 3673-3684
3673
Donor-Acceptor Diblock Copolymers Based on PPV and C60: Synthesis,
Thermal Properties, and Morphology
Ma r leen H. va n d er Veen ,† Ber t d e Boer ,*,† Ulf Sta lm a ch ,
Ka r in I. va n d e Weter in g,‡ a n d Geor ges Ha d ziioa n n ou ‡
Department of Polymer Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4,
NL-9747 AG, Groningen, The Netherlands
Received October 31, 2003; Revised Manuscript Received February 27, 2004
ABSTRACT: An improved synthetic method to nitroxide end-capped poly(p-phenylenevinylene)s is
presented. The nitroxide-functionalized PPVs are extended with a second coillike block by employing
them as macroinitiators in a nitroxide-mediated radical polymerization (NMRP) of monomers like styrene,
4-chloromethylstyrene, 4-vinylpyridine, and n-butyl acrylate. The observed thermotropic properties and
morphology of films based on the rod-coil diblock copolymers are identified and described. Some of the
block copolymers are subsequently subjected to a coupling with C60 to incorporate electron-accepting
properties into these PPV-based diblock copolymers. For this, a statistical copolymer built from styrene
and azidomethylstyrene was used as the second coillike block, making it possible to adjust the built-in
ratio of C60. The morphology and thermotropic properties of films prepared with these diblock copolymers
are investigated.
In tr od u ction
one of these methods, and the nature of the end groups
is difficult to determine due to their high molecular
weight. We aim to control the end groups and modify
them to obtain diblock copolymers with a well-defined
structure. This can be accomplished in two different
ways. One approach is the synthesis of well-defined
conjugated oligomers,8-10 in which one has the advan-
tage of controlling the end groups and the molecular
weight exactly. Such a multistep route is rather time-
consuming when aiming at higher molecular weights.
Our approach is based on a second method: the one-
step synthesis of conjugated polymers with relatively
high, controllable molecular weight (around or above the
effective conjugation length) and a relatively low PD.11
The PPV-based homopolymers reported in this paper
do contain exactly one end group per chain, which can
be modified to obtain a macroinitiator for nitroxide-
mediated radical polymerization (NMRP).
The advantage offered by polymers over the tradi-
tional semiconductor materials is the low cost and
versatility of processing methods, which allows the
polymer film to attain virtually any desired shape.
Casting a thin film over a macroscopically large area is
feasible and particularly attractive when reducing the
processing costs. For this to become reality the parent-
conjugated polymers, which are often intractable be-
cause of their stiff backbone, have to be derivatized
without deterioration of their optoelectronic properties.
Besides the molecular structure, details of the process-
ing history could play a key role in determining the
properties and morphology of such polymeric materials.
Therefore, each step has to be carefully carried out and
studied in detail when aiming at controlled properties
of thin polymer films.
The majority of publications on conjugated polymers
and their applications describe polymers based on poly-
(1,4-phenylenevinylene) (PPV) that were synthesized by
a precursor route (Gilch,1 Wessling and Zimmerman,2
etc.), Heck coupling,3 Wittig4 (-Horner)5 condensation,
McMurry coupling,6 etc.7 These methods yield high
molecular weight polymers with a high content of the
desired trans double bonds such as for example poly-
[2-m et h oxy-5-(2′-et h ylh exyloxy)-1,4-ph en ylen evin -
ylene] (MEH-PPV), poly[2-methoxy-5-(3′,7′-dimethyloc-
tyloxy)-1,4-phenylenevinylene] (MDMO-PPV), and poly-
[(2,5-dioctyloxy)-1,4-phenylenevinylene] (DOO-PPV) or
its analogue DEH-PPV with 2,5-di(2′-ethyl)hexyloxy as
side chains. Unfortunately, most PPVs exhibit a high
polydispersity (PD), making them less applicable to
control the morphology in the solid state. Moreover, the
end-group functionality cannot be controlled exactly by
Conjugated polymers can be regarded as (rigid) rod-
like systems with restricted flexibility compared to con-
ventional polymers like polystyrene (coillike). This may
result in complex phase behavior for diblock copolymers
containing at least one conjugated block. The presence
of such a stiff block puts these diblock copolymers in
the class of rod-coil diblock copolymers.12,13 The rodlike
block may be the liquid-crystal-forming segment or so-
called mesogen,14-16 which plays an important role
during the microphase separation. Block copolymers
that contain such liquid-crystalline segments have
several thermal transitions, namely, a glass transition
temperature for each distinct block, a phase transition
temperature for the liquid-crystalline block, and the
order-disorder transition temperature. They may give
rise to an enhanced microphase separation14,17 and
morphologies distinctly different from the conventional
spheres, cylinders, or lamellar structures,18 which may
include arrowhead, zigzag, and wavy lamellae phases.14,15
Stupp and co-workers showed that even low molecular
weight rod-coil block copolymers can microphase sepa-
rate in highly ordered phases as a consequence of a
larger Flory-Huggins interaction parameter (ø).19-21 In
† Present address: Molecular Electronics, University of Gronin-
gen.
‡ Present address: Ecole Europe´enne de Chimie, Polyme`res
Mate´riaux (ECPM), Universite` Louis Pasteur Strasbourg, 25, rue
Becquerel, F-67087 Strasbourg Cedex 2, France.
* To whom correspondence should be addressed: e-mail
b.de.boer@phys.rug.nl.
10.1021/ma035643o CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/21/2004

3674 van der Veen et al.
Macromolecules, Vol. 37, No. 10, 2004
Sch em e 1. Syn th esis of th e DEH-P P V Hom op olym er
(Siegr ist Con d en sa tion ) a n d th e Tr a n sm eta la tion of
th e TIP NO Lin k er a
related studies by Yu and co-workers, the well-defined
rod-coil block copolymers based on substituted PPVs
and poly(isoprene) (PI),9 poly(methyl methacrylate)
(PMMA),22 or poly(ethylene oxide) (PEO) formed liquid-
crystalline phases which comprise the substituted
PPV.10,23 As in the work of Stupp and co-workers, low-
molecular-weight hairy-rod blocks were used, and the
microphase separation obtained suggests strong mutual
interactions of the liquid-crystalline blocks. Additional
results presented in our previous work24,25 have dem-
onstrated that changes in the thermodynamics of the
environment result in quite complex and yet unexplored
behavior of the rod-coil diblock copolymers in solution.
These forms of self-organization are likely to act as the
“nuclei” for solidification and will bring about the
morphology of the solid film obtained under certain
processing conditions. Thermal treatment of, for ex-
ample, a film of MEH-PPV was found to improve the
device efficiency of diodes, which was attributed to a
higher degree of interchain interaction.26,27 An enhanced
ordering of the microstructure is generally obtained
through annealing, both in homopolymers and in con-
ventional block copolymers. Likewise, thermal treat-
ment of films of rod-coil block copolymers results in an
enhanced ordering of the microphase-separated mor-
phology.9
On the basis of the reported thin film properties, it
appears advantageous to be able to correlate the mor-
phology with the optoelectronic properties. The device
performance depends on the balance between intrachain
and interchain electronic interactions. Hence, the mor-
phology of the thin polymer film plays an important role
in determining the optoelectronic properties of light-
emitting diodes (LEDs) and photovoltaic (PV) cells. In
PV cells, the combination of a poly(p-phenylenevi-
nylene)-type polymer as the donor (D) material and C60
as acceptor (A) has proven promising.28 Materials that
combine the physical properties of fullerene and the
processability of polymers can be obtained by covalently
connecting the C60 to the polymer.25,29 The PPV-based
diblock copolymers reported in this paper have a
controlled amount of C60 and are used in a systematic
study to correlate the morphology and processing condi-
tions to, ultimately, the device performance.
a
(i) Aniline, 60 °C, 1 h; (ii) KOtBu, DMF, 80 °C, 3 h; (iii)
t-BuLi, ether, -78 °C; (iv) Br2Mg‚OEt2, ether, RT.
previously reported methods, was found to be very
reproducible. The formation of the DEH-PPV-TIPNO
macroinitiator is easily visualized by the disappearance
of the aldehyde signal at 10.4 ppm in the 1H NMR
spectrum and the emergence of a signal at 5.9 ppm from
the -CH(OH)- group.
The macroinitiator DEH-PPV-TIPNO is chain ex-
tended with a statistical copolymer of styrene (S) and
4-chloromethylstyrene (CMS, Scheme 2). To estimate
the chain growth in time of the diblock copolymer,
samples were taken during the NMRP copolymerization
with DEH-PPVk)15-TIPNO (Table 1). The monomer
conversions were kept below 25% to ensure a low
viscosity of the reaction mixture. The monomer compo-
sition as well as the chain length of the P(S-stat-CMS)
was determined using 1H NMR spectroscopy, assuming
that the DEH-PPV block remains unchanged. The
nature of the copolymerization is elucidated in a plot of
the molecular weight of the growing P(S-stat-CMS)
block (MnPS) vs time (Figure 1). Using the DEH-
PPVk)15-TIPNO macroinitiator, a linear growth in time
and low polydispersities (Table 1) are observed, con-
firming the “living” character of the NMRP copolymer-
ization. The values of the comonomer composition given
in Table 1 clearly illustrate that the determined built-
in ratio of the respective monomers is lower than the
feed ratio. This is most likely due to the slightly higher
reactivity ratio of the CMS comonomer, resulting in a
preference to add CMS instead of S. To determine
whether the same “living” behavior is observed for a
macroinitiator bearing a longer DEH-PPV block, two
additional copolymerizations in separated batches were
performed with DEH-PPVk)21-TIPNO (Table 1, Figure
1). Working with the same relative amount of initiator,
Ac2O, free TIPNO, and the same total amount of
monomer (but with a different feed ratio), we diluted
the system twice by adding an equal amount of solvent
(relative to the total amount of monomer in the system).
In doing so, the concentrations of all components were
twice as low compared to the bulk copolymerization with
DEH-PPVk)15-TIPNO. Although we did not investi-
gate the growth in time of these copolymerizations, the
NMRP systems with DEH-PPVk)21-TIPNO are re-
garded as being “living” because the combined results
are in line with the bulk polymerization of DEH-
Resu lts a n d Discu ssion
NMRP Cop olym er iza tion w ith P P V-Ba sed Ma c-
r oin itia tor s. The DEH-PPV homopolymer was syn-
thesized via the Siegrist polycondensation of 1 (Scheme
1), which is originally described by Kretzschmann et
al.30 This condensation via a Schiff base results in a
narrow molecular weight distribution and exactly one
terminal aldehyde group per chain.24,25,31 To obtain the
NMRP macroinitiator, the aldehyde end group of the
low-molecular-weight polymer (Mn ) 7.9 × 103 g/mol for
DEH-PPVk)21) is converted to an alkoxyamine based
on TIPNO (Scheme 2).
Both syntheses published in the literature for the
comparable DOO-PPV macroinitiator, either via a
Grignard reagent25 or via an organolithium compound,31
could not be repeated successfully. The in situ formed
lithiated anion (generated from 2) is therefore converted
into the more stable Grignard reagent by reaction with
MgBr2 (transmetalation). A large excess of 3 guarantees
a complete conversion of the aldehyde group (Scheme
2). This improved procedure for the synthesis of the
NMRP macroinitiator, which is a combination of the

Macromolecules, Vol. 37, No. 10, 2004
Diblock Copolymers Based on PPV and C60 3675
Sch em e 2. Syn th etic Rou te to Don or -Accep tor
Diblock Cop olym er s via NMRP w ith th e DEH-P P V
(Don or ) Ma cr oin itia tor a n d Su bsequ en t C60
F u n ction a liza tion (Accep tor ) of th e Secon d
Cop olym er Block a
mer (Table 2). The results obtained with UV-vis spec-
troscopy are consistent with those values obtained via
1H NMR spectroscopy. Note that the copolymer compo-
sition can only be determined by 1H NMR. Alternatively,
the P(S-stat-CMS) block lengths may be determined by
means of GPC. However, this technique is only used to
determine the PD (Table 1) since it is not appropriate
for an absolute molecular weight determination when
rigid-rod-like polymers are involved.
F u n ction a liza tion of (Di)block Cop olym er s w ith
C
60. It is our objective to incorporate both the donor (D)
and acceptor (A) functionalities into one macromolecule
by functionalizing our PPV-based diblock copolymers
with C60. During this third step toward D-A diblock
copolymers the C60 is attached to the well-defined
statistical P(S-stat-CMS) block via the chloromethyl
groups (Scheme 2).
Previously, the multifunctional P(S-stat-CMS) block
had been functionalized with C60 by employing atom
transfer radical addition (ATRA).25 This approach has
proven to be successful. For example, DOO-PPVk)7-b-
P(S-stat-C60MS)19K[1.5:1] containing an average of 15 C60
molecules per chain was obtained via this method.
Unfortunately, material that is not sufficiently soluble
was obtained after employing ATRA. Several research
groups use ATRA to graft more than one monofunctional
polystyrene chain onto C60 yielding dendritic or starlike
macromolecules.32 A chlorine-C60 bond is left behind
after the addition of a polystyrene chain onto C60. This
chlorine bond is less stable than the one of the CMS in
our P(S-stat-CMS) copolymers, resulting in a high
concentration of “polystyrene-C60 radicals” during the
course of ATRA. Their recombination with other poly-
styrene-like radicals is very likely. Since we use mul-
tifunctional polystyrenic chains, the occurrence of intra-
and intermolecular cross-linking (multiadditions onto
C60) is very likely. The probability of intramolecular
cross-linking has been lowered through systematic
“dilution” of the reactive CMS groups with styrene
moieties (i.e., higher S:CMS built-in ratio). However, the
intermolecular cross-linking is hard to overcome by
optimization of all reaction parameters when working
with radicals as intermediates. Hawker et al. modified
the P(S-stat-CMS) copolymers with an azide group to
perform a cycloaddition to C60 and obtained soluble
polymers.33 The azidomethyl-substituted polystyrene
(the so-called “azide intermediate”, in our case DEH-
PPV-b-P(S-stat-N3MS)) reacts in this method with an
equimolar amount of C60 to yield triazoline 4 (Scheme
3). The thermal extrusion of nitrogen from this triazo-
line leads to the formation of aza-bridged fullerenes 5
and 6 (and maybe their bisadducts) referred to as
bridged iminofullerenes. These fullerenes can have a
bridge between five- and six-membered rings and be-
tween two six-membered rings (called [5,6]-bridged and
[6,6]-bridged, respectively).34,35 In addition, the isomers
may either have closed or open transannular bonds.36
Of the possible Kekule´ structures of C60 the ones that
have the energetically most favorable arrangement
contain exclusively [6,6] double bonds and [5,6] single
bonds. So far, and consistent with this “rule”, the closed
[6,6]-bridged monoadduct (analogous to 5) and open
[5,6]-bridged monoadduct (analogous to 6) have been
observed by Prato et al.35 The number of π-electrons
remains unchanged in the case of the open [5,6]-bridge
monoadducts.29 Recently reported (cyclic voltammetric)
data of some polymeric fullerene derivatives confirmed
a
(i) Ether, 35 °C, 16 h; (ii) styrene, 2-chloromethylstyrene,
Ac2O, cat. TIPNO, anisole, 125 °C, 50 min; (iii) NaN3, DMF,
130 °C, 16 h; (iv) C60, chlorobenzene, 60 °C, 20 h; (v) 130 °C,
1 h.
PPVk)15-TIPNO (Table 1). While the monomer concen-
tration has been lowered compared to this bulk copo-
lymerization, no significant reduction of the propagation
rate is observed during these copolymerizations. As
expected, the monomer built-in ratio of the copolymers
prepared with DEH-PPVk)21-TIPNO macroinitiator is
lower than the feed ratio. Fortunately, it is still possible
to adjust and control the monomer composition in the
resulting copolymers.
1
In addition to H NMR as characterization method,
UV-vis spectroscopy can be used to estimate the
relative amount of P(S-stat-CMS) in diblock copolymers.
Upon chain extension of the DEH-PPV block, its
weight-normalized absorbance decreases with increas-
ing P(S-stat-CMS) block length. This relative decrease
in absorption is related to the weight percentage (wt
%) of P(S-stat-CMS) incorporated in the diblock copoly-

3676 van der Veen et al.
Macromolecules, Vol. 37, No. 10, 2004
Ta ble 1. Diblock Cop olym er s Obta in ed w ith NMRP Cop olym er iza tion of S a n d CMS Usin g DEH-P P V Ma cr oin itia tor s
DEH-PPVk)15-TIPNO
DEH-PPVk)21-TIPNO
batch 1 batch 2
single batch
time (min)
feeda
0
4.0
40
100
4.0
3.0
52.1
1.7
120
4.0
3.0
63.4
1.8
140
4.0
3.0
71.4
2.2
0
3.2
50
0
3.6
80
4.0
3.7
22.5
1.2
3.2
2.1
22.4
1.5
3.6
2.6
38.8
1.8
built-ina
Mn (kg/mol)b
PD
6.1
1.2
8.2
1.2
8.2
1.2
a
b
Comonomer S:CMS ratio. Including the TIPNO end group.
not sufficiently soluble in common organic solvents like
1
chloroform and chlorobenzene. Nonetheless, a H NMR
spectrum of DEH-PPVk)21-b-P(S-stat-C60MS)[2.1:1] that
contained a minimum amount of dissolved product
clearly demonstrated that the signal of the azide
intermediate at 4.17 ppm disappeared after reaction
with C60. In addition, a characteristic C60 absorption
peak around 330 nm is clearly present in UV-vis
spectra of the filtered solutions (see Supporting Infor-
mation). Both observations seem to be an indication of
the covalent attachment of C60 to the polymer.
Other techniques to determine the amount of C60 in
polymers are DSC and TGA.25 The latter one is a
convenient method when dealing with poorly soluble
materials like our DEH-PPV-b-P(S-stat-C60MS). Figure
2 shows the TGA thermograms of the starting polymers,
C60-functionalized polymers, and pristine C60. The mo-
lecular weights given for the P(S-stat-CMS) block func-
tionalized with C60 are their theoretical values (i.e.,
assuming 100% conversion of azide to C60). Diblock
copolymers with the same copolymer composition ([n:
m]) are prepared from the same starting materials. In
the DEH-PPV-b-P(S-stat-C60MS) and P(S-stat-C60MS)
samples, the polymer backbone starts to decompose at
300 °C, leaving a C60 adduct which shows only minor
weight loss up to 600 °C. This decomposition of the
backbone is nearly complete at 550 °C (see the corre-
sponding reference compounds), and we can assume
that the residue difference at 575 °C corresponds to the
C60 content. This residue was thought not to be unre-
acted C60 given that these polymers are dissolved and
filtered twice in THF (solubility of C60 in THF is <0.01
mg/mL at RT).39 The P(S-stat-CMS)21K[2:1] can contain
a (theoretical) maximum amount of 68 wt % of C60 after
a complete conversion, which would result in P(S-stat-
C60MS)63K[2:1]. A value of 55 wt % C60 is found with the
TGA analysis indicating that 80% of the theoretical
F igu r e 1. Polymer chain growth in time during NMRP
copolymerization of S and CMS with DEH-PPVk-TIPNO
macroinitiators.
that the electronic properties indeed resemble those of
pristine C60.37 Therefore, we expect that the C60 moieties
will still serve as electron acceptor when incorporated
into the DEH-PPV-b-P(S-stat-CMS) diblock copoly-
mers.
The conversion of P(S-stat-CMS) copolymers (used as
a reference compound) to the corresponding azide
intermediate is a versatile method with yields varying
from 70 to 85%. The chlorine group is completely
converted to an azide when a large excess of NaN3 is
used. Both the preparation of DEH-PPVk)21-b-P(S-stat-
N3MS)14K[2.1:1] and of the reference compound P(S-stat-
N3MS)21K[2:1] is easily monitored by 1H NMR and IR
spectroscopy. The methylene proton peak of the P(S-
stat-CMS) copolymers shifts from 4.46 to 4.17 ppm,
1
which is in agreement with the H NMR data reported
by Ederle´ and Mathis.38 The covalent bond connecting
the TIPNO group to DEH-PPV-b-P(S-stat-CMS) dis-
sociates in radicals due to the high temperature of this
conversion (i.e., just as it does during NMRP). The loss
of the TIPNO group is confirmed by the absence of its
amount is incorporated, giving P(S-stat-C60MS)54K[2:1]
.
Higher amounts of C60 are found upon increasing the
reaction time. Almost 90% of the theoretical value is
incorporated when going from 16 to 20 h and using only
1 equiv of C60. However, the yields of the reactions are
rather low (about 25%). Yields of about 40% are ob-
tained with DEH-PPV-b-P(S-stat-C60MS) diblock co-
polymers when 2 equiv of C60 was used.
1
characteristic H NMR shift at 0.45 ppm. Moreover, a
small aldehyde signal at 10.41 ppm indicates a possible
formylation of this radical chain end. The second method
used to detect the azide intermediate is IR spectroscopy.
The intermediate possesses a strong characteristic band
for the azide group at 2094 cm-1. The complete disap-
pearance of this band after cycloaddition to C60 confirms
the completion of the reaction. The formation of the
azide and its subsequent functionalization with C60 are
both monitored with IR spectroscopy. Convenient meth-
ods to determine the covalent bonding of C60 and the
amount of C60, like 1H NMR spectroscopy, could only
be used to observe the structural changes after func-
tionalization with C60. The P(S-stat-C60MS)[2:1] reference
compounds as well as the DEH-PPVk)21-b-P(S-stat-C60-
MS)[2.1:1] diblock copolymers are, after complete drying,
The synthesized DEH-PPV-b-P(S-stat-C60MS) diblock
copolymers contain 41 and 57 wt % of C60 (Figure 2).
The latter one with a higher fraction of chloromethyl
groups in the starting material indeed gives rise to a
higher amount of C60. This agrees well with the initial
aim that these groups will determine the C60 content
in diblock copolymers. A similar trend has already been
observed in using ATRA as C60 functionalization
method.25 Although the above-presented results are
promising, a new problem arises. It seems that after
drying the product renders insoluble. Only samples that
have not been completely dried could be redissolved.

Macromolecules, Vol. 37, No. 10, 2004
Diblock Copolymers Based on PPV and C60 3677
Ta ble 2. Deter m in a tion of th e P (S-sta t-CMS) Am ou n t in Diblock Cop olym er s
1H NMR spectroscopy
UV-vis spectroscopy
a
NMRP time
total
Mn
calcd Mn
calcd wt %
P(S-stat-CMS)
absorbance
calcd wt %
P(S-stat-CMS)
a
c
(min)
P(S-stat-CMS)
(Abs/mg g-1
)
DEH-PPVk)21
DEH-PPVk)21-b-P(S-stat-CMS)
DEH-PPVk)21-b-P(S-stat-CMS)
0
50
80
8.2b
22.4
38.8
54.5
19.7
12.4
14.1
30.6
63
79
64
77
a
b
In kg/mol. Including the TIPNO end group. c At λmax ) 496 nm.
Sch em e 3. Cycloa d d ition of Azid e In ter m ed ia te DEH-P P V-b-P (S-sta t-N3MS) to C60 w ith Su bsequ en t th e Nitr ogen
Extr u sion fr om th e Tr ia zolin e In ter m ed ia tea
a
(i) C60, chlorobenzene, 60 °C, 20 h; (ii) chlorobenzene, 130 °C, 1 h.
However, no transition temperatures were found in DSC
scans of DEH-PPV-b-P(S-stat-C60MS) diblock copoly-
mers prepared via the azide intermediate. Instead, an
enormous exothermic heat flow during the first heating
scan is observed (data not given). After this once-only
event starting at 80 °C and ending around 220 °C, the
samples exhibit no thermal transitions at all in the first
cooling scan and the subsequent second heating scan.
Further examination with TGA confirms a physical
change of the materials: the premature weight loss
observed with TGA starting at 120 °C disappears after
the sample has been used for a DSC analysis (Figure
3). We hypothesize that the formation of aza-bridged
fullerenes is incomplete (the nitrogen extrusion from
triazoline 4, Scheme 3), resulting in exothermic reac-
tions and weight losses. Unfortunately, this hypothesis
could not be confirmed with Gibbs energy calculations
F igu r e 2. TGA traces of (di)block copolymers recorded under
N2 and a heating rate of 10 °C/min. The amount of residue
left at 575 °C represents the wt % C60 incorporated. Pristine
based on nitrogen extrusion and the total amount of
heat released in the first DSC scan. However, the weight
loss monitored with TGA seems to match well with a
loss of nitrogen during the DSC analysis. The weight
percentage of C60 in the presented polymer (Figure 3)
is 95% of the theoretical amount. Upon thermal extru-
sion of nitrogen from this polymer the maximum weight
loss would be 2.2% while a premature weight loss of
2.1% is found with TGA (difference in residue at 300
°C before and after the DSC scan). These values indicate
that the polymer and their intermediate triazolines are
not fully converted to aza-bridged fullerenes during the
C60 is used as reference compound.
Other groups have observed the same problem, and so
far its cause is not clarified.40 The complete removal of
solvents should therefore be avoided during the prepa-
ration of these C60-functionalized diblock copolymers.
A significant rise in the Tg of a polystyrenic backbone
is expected when the chain stiffness increases due to
C60 side groups. Therefore, DSC provides qualitative
evidence for the incorporation of C60 in the polymers.

3678 van der Veen et al.
Macromolecules, Vol. 37, No. 10, 2004
F igu r e 3. TGA traces of diblock copolymers before and after
a DSC scan recorded under N2 with a heating rate 10 °C/min.
synthesis. On the basis of our observations and the
above-mentioned solubility problems (also observed by
others), one could conclude that the azide intermediate
route is not yet a versatile method to functionalize
polymers with C60.
Solid -St a t e P r op er t ies of Dib lock Cop olym er s
F ilm s. Control over the structure and morphology in
the solid state of D-A diblock copolymers is important
for the optoelectronic properties of photovoltaic devices
based on these materials. Ba¨ssler proposed that charge
transport in disordered organic materials proceeds
mainly by means of hopping across the medium at three
levels: intrachain, interchain, and interparticle (across
grain boundaries).41 Factors determining intra- and
interchain transport are the conjugation length and
structural order, respectively. Side chains attached to
the polymer backbone have a contradictory effect on the
transport properties at microscopic level. They may
introduce torsions along the chain, decreasing thereby
the conjugation length42 or, as insulating side chains
will, increase the hopping distance between neighboring
chains. On the other hand, the hopping rate increases
when the side chains enhance the ordering of polymer
segments in the solid state. For example, highly regio-
regular polymers have an enhanced on-chain energetic
order and charge delocalization.43 Moreover, long side
chains may have their own crystallization and melt
behavior and can induce liquid crystallinity (LC) in
rigid-rod-like macromolecules such as PPV.44 PPV de-
rivatives and rod-coil diblock copolymers have shown
to possess a rich phase behavior.45 Oligophenylenevi-
nylenes with alkoxy side chains, so-called “hairy-rod”
molecules, are extensively studied because of their
reversible LC transitions.46 This crystallization can lead
to dramatic changes in the optical and electronic
properties of a material.47 The alignment of the back-
bones (with a π-stacking arrangement and side chains
acting as spacers) may for example promote the inter-
chain and intersegment electronic interactions. This
increased amount of electronic overlap between seg-
ments and reduced structural heterogeneity is expected
to enhance the charge transport.
F igu r e 4. Optical micrographs at RT of the as-cast film (a)
of DOO-PPVk)7 and (b) using crossed polarizers for the film
that was cooled from the isotropic melt to 90 °C.
tant. Moreover, the thermal stability of the conjugated
polymer itself is important. In this section we report
the thermal transitions of the homopolymers DEH-
PPVk)15,21 and DOO-PPVk)7 in the solid state and
compare them with those of the diblock copolymers. The
homopolymers are the same as used for the synthesis
of the corresponding diblock copolymers. The thermal
properties are studied by DSC, TGA, and optical mi-
croscopy. DSC was used to determine the thermotropic
transition temperatures like Tg, side-chain melting
temperature (Ts), and the liquid-crystal-to-isotropic
transition temperature (TLC-I). The LC structure of
polymer films was elucidated by optical microscopy
using crossed polarizers.
DOO-P P V-Based Diblock (Co)polym er s. The syn-
thesis of DOO-PPV and its block copolymers is de-
scribed in refs 25 and 31 and in the Experimental
Section. The DSC analysis of DOO-PPV reveals the
existence of thermotropic transitions at 55 and 185 °C,
of which the lower transition temperature is attributed
to melting of the octyloxy side chains (Ts) and the higher
one to the isotropic transition temperature (TLC-I). A 1
wt % solution of DOO-PPV in 1,2-dichlorobenzene (or
chloroform) was cast onto a glass slide, and the film was
investigated with optical microscopy. Figure 4a shows
the rough texture of the as-cast film. It reveals reddish
elongated domains that are randomly distributed in the
film (displayed as gray areas in Figure 4a). Crossed
polarizers were used to determine whether the film
exhibits highly ordered crystalline domains. The ab-
sence of any birefringence in the as-cast film shows that
it does not reveal any highly ordered crystalline do-
mains.
LC behavior appears in a restricted temperature
range between the crystalline phase and the isotropic
melt. Having this, so-called, thermotropic LC behavior
in the active layer of a PV device will introduce a
temperature-dependent operation mode making the
study of thermotropic transitions in thin films impor-
A reddish grainy texture (or polydomain texture) is
observed upon cooling from the isotropic melt at 250 to
90 °C (gray areas in Figure 4b). Such a birefringence

Macromolecules, Vol. 37, No. 10, 2004
Diblock Copolymers Based on PPV and C60 3679
Ta ble 3. Tr a n sition Tem p er a tu r es of DOO-P P V a n d
DEH-P P V-Ba sed Diblock (Co)p olym er s a n d Th eir
Cor r esp on d in g Hom op olym er s
Tg
(°C)
Ts
(°C)
TLC-I
Tdec
(°C)a
(°C)b
DOO-PPVk)7
55
185
160
190c
180
160
380
370
330
340
335
DOO-PPVk)9-b-PS22K
DOO-PPVk)9-b-P4VP12.1K
DOO-PPVk)9-b-PBA5.8K
DOO-PPVk)7-b-
95
150
-45
95
60
70
50
60
P(S-stat-CMS)9K[1.5:1]
DOO-PPVk)7-b-
P(S-stat-C60MS)19K[1.5:1]
P(S-stat-CMS)21K[2:1]
DEH-PPVk)15
DEH-PPVk)15-b-
P(S-stat-CMS)66K[3:1]
DEH-PPVk)15-b-
P(S-stat-N3MS)66K[3:1]
DEH-PPVk)21
DEH-PPVk)21-b-
P(S-stat-CMS)14K[2.1:1]
DEH-PPV50
110
90
65
160
300
320
360
325
55/75
85
200
210
100
100
85
n.d.d
260
80
90
200
210
n.d.
n.d.
85
110
285
390
a
b
In combination with optical microscopy. Given for 5 wt %
loss during TGA. c Determined by optical microscopy. n.d. ) not
determined.
d
texture is often observed near the isotropic-nematic
transition for polydisperse and high-molecular-weight
specimens in thick films. The fine grains are believed
to correspond to regions of uniform orientation intercon-
nected by disclinations within nematic structures.48
Hence, all diblock copolymers described below based on
this symmetrically substituted DOO-PPV moiety have
a rodlike diblock that exhibits liquid crystallinity. This
does not imply a priori that all diblock copolymers based
on this PPV block will also exhibit the same thermo-
tropic behavior.
F igu r e 5. Optical micrographs at RT using crossed polarizers
of (a) DOO-PPVk)9-b-P4VP12.1K as-cast and (b) after cooling
from the melt and annealing for 1 h at 150 °C.
melting temperature, resulting in higher values of Ts
compared to the that of DOO-PPV homopolymer. This
is attributed to the glassy environment induced by the
coillike block below its Tg. For the polydisperse DOO-
PPV one does not observe a clear isotropic transition
temperature (TLC-I) of the backbone with DSC, but
merely a continuous increase of the endothermic heat
flow above a certain temperature. Hence, the onset of
the increased heat flow is taken as the TLC-I of the
DOO-PPV backbone. The DOO-PPV-b-P4VP showed
a continuous increase of the heat flow directly above its
glass transition. The broad Tg of the P4VP block around
150 °C is close to the melting temperature of the PPV
backbone and masks the onset of the TLC-I. This latter
transition was therefore determined with optical mi-
croscopy, resulting in a slightly higher TLC-I compared
to a DSC analysis. In general, the series of DOO-PPV-
based diblock copolymers reveal distinct transition
temperatures for both blocks, suggesting that mi-
crophases are involved. For a homogeneous mixture only
one transition from the glassy state to the liquid state
would have been observed.
Drop-casting a 1 wt % solution of DOO-PPV-b-PS,
DOO-PPV-b-P4VP, or DOO-PPV-b-PBA in chloroform
onto glass slides and subsequent slow evaporation of the
solvent resulted in thick films that showed birefringence
when imaged by optical microscopy (Figure 5a). All
diblock polymers gave rise to similar grainy textures
as their corresponding homopolymer DOO-PPV (Figure
4b). Upon heating to the isotropic melt the DOO-PPV-
b-PBA started to dewet the surface at 180 °C, which
resulted in small cracks in the film. DOO-PPV-b-PS
and DOO-PPV-b-P4VP liquefied above their TLC-I, but
dewetting was not observed. The LC phases emerged
at temperatures that were 20-30 °C below the melting
temperatures of the DOO-PPV backbone. In Figure 5b,
The thermotropic transitions of the DOO-PPV diblock
(co)polymers obtained by a combination of DSC and
optical microscopy as well as the decomposition tem-
perature (Tdec) determined by TGA are given in Table
3. Although the Tg depends slightly on the molecular
weight of the second coillike block, they represent
typical Tg’s (within a margin of (5 °C) for the (di)block
polymers. Tg’s of the corresponding homopolymers (PS,
110 °C; PBA, -60 °C; P4VP, 145 °C)49 differ up to 15
°C. The variation is attributed to the local order and
the low molecular weight of the diblock polymers. The
statistical copolymer P(S-stat-CMS)21K[2:1] exhibits a
lower Tg compared to its corresponding diblock copoly-
mer. Upon functionalization of DOO-PPV-b-P(S-stat-
CMS) with C60 the polymer chain becomes stiffer, and
consequently, its Tg increases from 95 to 110 °C. The
Ts is only observed in the first heating scan of the DSC
analysis, implying that the crystallization of the octyloxy
side chains is a slow process and depends on the
(thermal) history of the sample. The melting tempera-
ture of the side chains also depends on the Tg of the
second block. With increasing Tg of this coillike block
the Ts shifts toward higher temperatures due to a
relative higher stiffness of their local environment.
Illustrative of this phenomenon is DOO-PPV-b-PBA
with a Tg of -45 °C. Its very low Tg results in soft and
flexible microdomains that allows the octyloxy side
chains to melt at lower temperatures. Vice versa, a PBA
homopolymer has a Tg of -60 °C, and the increased Tg
of -45 °C for the diblock polymer suggests the presence
of PPV blocks between the PBA domains. All other
diblock (co)polymers exhibit Tg’s above the side-chain

3680 van der Veen et al.
Macromolecules, Vol. 37, No. 10, 2004
F igu r e 6. Optical micrographs at RT using crossed polarizers of (a) DEH-PPVk)15, (b) DEH-PPVk)21, and (c) DEH-PPVk)21
b-P(S-stat-CMS)14K[2.1:1]
-
.
an optical micrograph of DOO-PPV-b-P4VP displays
the typical crystalline texture at RT that was obtained
by cooling from the melt down to 150 °C and subsequent
annealing at 150 °C for 1 h prior to the cooling to RT.
Generally, this cooling from the melt gave rise to larger
crystalline domains compared to the as-cast films
(Figure 5, b vs a, respectively). The drop-casting of more
diluted diblock copolymer solutions (0.1 wt %) followed
by rapid evaporation of the solvent did not give rise to
birefringence or crystalline domains. This is attributed
to a fast solidification process rendering a long-range
order in the polymer films. The microphases can be
ordered locally on a length scale of several tens of
nanometers (see AFM images in ref 24). On a large
scale, however, the films appear to be isotropic due to
the overall random orientation of small domains. Be-
cause the resolution of optical microscopy is limited to
the wavelength of light, one cannot reveal the local order
in these films using this technique and has to utilize
other techniques like AFM or TEM.31
DEH-P P V-Based Diblock Copolym er s. The DEH-
PPV homopolymers show a similar behavior as the
DOO-PPV with the PPV backbone as the mesogenic
group. The DEH-PPVk)15 shows two transitions at low
temperatures (55 and 75 °C, Table 3), which are both
attributed to melting of the side chains. For DEH-
PPVk)21 only a single transition is found, which covers
the same temperature range. Since we observed several
crystalline-like textures in films of this polymer (optical
microscopy is described below), it is reasonable to
assume that this single and broad transition comprises
to the two transition temperatures found for the DEH-
PPVk)15 homopolymer. Clear isotropic transition tem-
peratures of the DEH-PPV (TLC-I) are not found with
DSC. The observed continuous increase of heat flow may
be due to crystallites that differ in size and perfection.
To circumvent these difficulties, we used optical mi-
croscopy to determine the TLC-I as the onset of the fast
disappearance of birefringence.
diblock copolymer is only found during the first heating
scan. After crystallization upon cooling, the correspond-
ing endothermic peak in the following heating scan is
absent probably due to a smaller volume fraction of
crystalline material.
Optical microscopy reveals the presence of birefrin-
gent textures in thick films of DEH-PPV and DEH-
PPV-b-P(S-stat-CMS). The films were obtained after
drop-casting a 1 wt % solution in chlorobenzene onto
glass slides and a subsequent slow evaporation of the
solvent. The as-cast films appeared to be highly bire-
fringent when examined under crossed polarizers. They
exhibit reddish needlelike domains that are isotropically
distributed in the film (Figure 6). The amorphous do-
mains (black) as well as the crystalline domains increase
in size with increasing DEH-PPV block lengths (Figure
6, a and b, respectively). A significant increase in size
of both domains is observed in films of DEH-PPV-b-
P(S-stat-CMS) (Figure 6, b vs c). Apparently, this second
coillike block enhances the mobility of the DEH-PPV,
resulting in a facilitated crystallization from solution
and larger domains. Heating of the films resulted in
melting of the crystalline domains, but no reversible
birefringence was observed after the subsequent cooling
from the melt. This indicates that the crystallization of
the bulk polymer is a slow process. No efforts have been
made to (re)crystallize the polymer by means of anneal-
ing at temperatures just above the Tg or Ts as has been
done for DOO-PPV-b-P4VP (Figure 5b). In addition to
the randomly distributed needlelike domains, we find
spherical aggregates often called spherulites.
The thermotropic transitions of the C60-functionalized
DEH-PPV diblock copolymers are not included in this
study since they show exothermic reactions upon heat-
ing (i.e., extrusion of nitrogen, see discussion of Figure
3). The C60 incorporated in DOO-PPV-b-P(S-stat-CMS)
did increase the chain stiffness and changed its ther-
motropic LC behavior. Similar results are expected for
the DEH-PPV polymers, suggesting a temperature-
dependent operation mode for optoelectronic devices
based on these donor-acceptor diblock copolymers.
The amorphous P(S-stat-CMS) block in the DEH-
PPV diblock copolymers gives rise to a clear Tg transi-
tion. In line with the theory this Tg increases (from 85
to 90 or 100 °C) for increasing P(S-stat-CMS) block
lengths (14, 21, and 66 kg/mol, respectively). However,
the Ts is now more difficult to elucidate because it
coincides with the Tg of the P(S-stat-CMS) block. For
both chain extended DEH-PPVk)15,21 polymers the Ts
increases with 10 °C. The mobility of segments at
specific temperatures seems to be lower due to the
glassy environment introduced by the P(S-stat-CMS).
Furthermore, the Ts for the DEH-PPV-b-P(S-stat-CMS)
Con clu sion s
An improved synthesis of the NMRP macroinitiator
based on PPV and TIPNO is presented, which is used
for the preparation of donor-acceptor diblock copoly-
mers. A “living” character of the NMRP polymerizations
is observed for these PPV-based macroinitiators. The
block lengths as well as the built-in ratio of the comono-
mers in the second P(S-stat-CMS) block can be con-

Macromolecules, Vol. 37, No. 10, 2004
Diblock Copolymers Based on PPV and C60 3681
was necessary by means of filtration over basic aluminum
oxide (90 Active Base, 0.063-0.200 mm). Anisole was distilled
from Na, THF from Na/K alloy, CH2Cl2 from Ca, toluene from
Na/benzophenone, and ether from KOH and LiAlH4. DMF was
stored on molecular sieve 4 Å, while all other solvents were
used as received unless mentioned otherwise. All NMRPs were
carried out under a N2 atmosphere.
trolled during the course of the polymerization. The
macroinitiator allows for the adjustment of the donor-
acceptor ratio in the C60-functionalized diblock copoly-
mers. In addition, the method to introduce the C60 has
been improved by circumventing the formation of radi-
cals through the utilization of azide intermediates.
Further improvement of this new approach is necessary
to enhance the solubility of the donor-acceptor diblock
copolymers. This could be achieved by means of a
complete conversion of the azide intermediates.
The structure-property relationship of the (diblock
co)polymers is investigated using the DOO-PPV and
DEH-PPV homopolymers as reference compounds.
They are both liquid-crystalline and exhibit thermotro-
pic transitions at 55 and 185 °C for DOO-PPVk)7 and
80 and 200 °C for DEH-PPVk)21. The first transition
is attributed to the melting of the side chains, and the
second higher one is an isotropic transition. Conse-
quently, the diblock copolymers possess complex and
rich phase behavior due to the combination of a me-
sogenic rodlike block and the adjacent coillike block. An
additional thermotropic transition was identified for the
diblock copolymers that is attributed to the Tg of the
polystyrene-like block.
DOO-P P Vk-b-P 4VP . The macroinitiator DOO-PPVk)9
-
TIPNO (0.2 g, Mn,PPV ) 3.9 × 103 g/mol), freshly distilled
4-vinylpyridine (4VP, 10 g, 95 mmol), anisole (10 mL), acetic
anhydride (Ac2O, 0.2 g, 2 mmol), and 2,2,5-trimethyl-4-phenyl-
3-azahexane-3-oxy (TIPNO free radical, 2 mg, 0.009 mmol)
were degassed by freeze-pump-thaw cycles (3×), flushed with
N2, and polymerized at 110 °C. Samples were taken after 4
and 8 h and precipitated in hexane (1 L). The polymer was
precipitated from CHCl3 into hexane (1 L). Yields: 189 mg (4
h) and 373 mg (8 h). Molecular weight Mn ) 7.1 and 16.0 ×
1
1
103 g/mol, respectively, determined by H NMR. H NMR: δ
) 8.0-8.6 (br d, CarH), 7.4 (br s, ColefH), 7.11 (br s, CarH), 6.2-
6.6 (br d, CarH), 4.0 (br s, OCH2), 2.2 (br s, CarH3), 1.3-1.8 (m,
CH, CH2), 0.8 (s, CH3).
2,5-Di(2′-eth yl)h exyloxy-4-m eth ylben zaldeh yde (1). The
monomer is prepared via the etherification of methylhydro-
quinon with (2′-ethyl)hexyl bromide51 (purified by means of
Kugelrohr at 100 °C/ 0.01 mbar; yield 62%; yellow oil), followed
by a selective Rieche-Gross formylation with dichloro(methoxy)-
methane.52 After purification by means of Kugelrohr (117-
122 °C/ 0.7 mbar), monomer 1 was obtained as yellow oil (78%
We have shown that this approach of rational design
and controlled synthesis is a systematic method to
explore the correlation between (self-)organization of
rod-coil diblock copolymers and the morphology of films
thus produced (and ultimately the correlation between
self-organization and the device performance).
1
yield). H NMR: δ ) 10.38 (s, 1H, CHO), 7.17 (s, 1H, CarH),
6.75 (s, 1H, CarH), 3.7-3.9 (dd, 4H, OCH2), 2.22-2.42 (br s,
3H, CarCH), 1.7 (m, 4H, CH2), 1.2-1.4 (br m, 18H, CH, CH2),
0.9 (m, 12H, CH3).
DEH-P P Vk. The synthesis of DEH-PPV was accomplished
by the Siegrist polycondensation (originally described in ref
30) of compound 1. The average degree of polymerization (i.e.,
number of repeat units k) of the DEH-PPV is determined with
1H NMR spectroscopy using the ratio of integrals of the OCH2
groups and the terminal CH3 group. For a DEH-PPV polymer
prepared at 80 °C in 3 h, a k of 21 units is calculated by this
method. This so-called DEH-PPVk)21 has a polydispersity (PD)
of 1.23 (determined by means of GPC vs polystyrene stan-
dards) and a Mn ) 7.9 × 103 g/mol. By only changing the
temperature to 50 °C, the DEH-PPVk)15 was synthesized in
3 h with PD ) 1.16 and Mn ) 5.6 × 103 g/mol. Representative
1H NMR of DEH-PPVk)21: δ ) 10.41 (s, CHO/end group), 7.49
(br s, ColefH), 6.67-7.16 (br s, CarH), 3.91 (br m, OCH2), 2.20-
2.34 (br s, CH3/end group), 1.71-1.85 (m, CH2), 1.14-1.68 (m,
CH, CH2), 0.8-1.0 (m, CH3).
Exp er im en ta l Section
Mea su r em en ts. 1H NMR spectra were recorded on a
Varian Gemini-300 spectrometer operating at 300 MHz in the
Fourier transform mode. All measurements were performed
at room temperature (RT) in chloroform-d (CDCl3; internal lock
on the 2H signal). Absorbance spectra were recorded on a
Perkin-Elmer Instruments Lambda 900 UV/vis/NIR spectrom-
eter and normalized of clarity. Fluorescence spectra were
recorded on a Perkin-Elmer luminescence spectrometer LS50-B
using an excitation wavelength of 10 nm below the absorption
maximum and a 2.5 nm bandwidth. The optical measurements
were performed in Uvasol chloroform with quartz cuvettes
(light path 10 mm) unless mentioned otherwise. Gel perme-
ation chromatography (GPC) analyses were performed in THF
(HPLC grade) with PL-gel mixed-C columns in a Waters
Powerline setup (717plus autosampler, 600 controller, and a 610
fluid unit), equipped with a Waters 996 photodiode array
detector (on-line UV-vis measurements), a Wyatt Dawn DSP
laser photometer (light scattering detector), and a 410 dif-
ferential refractormeter. All solutions (∼1 mg/mL) were filtered
over a polystyrene filter (0.45 µm) prior to a duplicate injection
of 100 µL (flow 1 mL/min, run time 25 min, RT). The infrared
DEH-P P Vk-TIP NO. The Br2Mg-O(C2H5)2 is prepared
prior to the synthesis from a stirred mixture under a dry N2
atmosphere of Mg turnings (0.17 g, 7.0 mmol) and ether (5
mL). Via a syringe, 1,2-dibromoethane (0.55 mL, 6.38 mmol)
was slowly added, and the mixture was stirred at RT for 30
min. From the resulting two-phase mixture, a quarter of lower
gray layer was used in the synthesis of DEH-PPVk)21
-
TIPNO. For this, 2,2,5-trimethyl-3-[1-(4-bromophenyl)ethoxy]-
4-phenyl-3-azahexane53 (2) (0.62 g, 1.5 mmol) was dissolved
in ether (10 mL) and cooled to -80 °C (cryostat). After the
addition of tert-butyllithium (1.5 M in pentane, 2 mL, 3 mmol),
the solution was stirred for 30 min at -80 °C. During this time,
the originally colorless solution turned via yellow to orange.
After adding the freshly prepared Br2Mg-O(C2H5)2 (∼1.75
mmol), a cloudy, white suspension, containing compound 3,
was obtained. This was allowed to warm to RT. After 30 min,
the color turned to yellow when the stirred solution was
immersed in a thermostated oil bath kept at 35 °C. A solution
of DEH-PPVk)21 (1.4 g, 0.18 mmol) in ether (40 mL) was added
via a syringe and stirred for 16 h at 35 °C. The mixture was
quenched in water (150 mL) that contained HCl (37%, 3 mL)
and stirred for 30 min at RT. After this period, the mixture
was extracted with ether (200 mL), the organic layer was
washed with water (2 × 300 mL) and with saturated NaHCO3
(1 × 200 mL), dried over Na2SO4, and filtered, and the solvent
was removed under a reduced pressure at RT. The red solid
was dissolved in CHCl3 (10 mL) precipitated twice in cold
spectra were recorded on
a Mattson Instruments FT-IR
spectrometer. Optical microscopy was performed on a Zeiss
Axiophot microscope equipped with a high-resolution CCD
camera (Sony DKC 5000; connected to a frame grabber and a
personal computer). Heating of the polymer films was per-
formed in a Mettler FP82HT optical hot stage with a Mettler
FP90 controller. Thermogravimetric analyses (TGA) were
carried out using a Perkin-Elmer TGA7 (heating rate of 10
°C/min under a N2 atmosphere). Differential scanning calo-
rimetry (DSC) analyses were obtained with a Perkin-Elmer
DSC-7 (calibrated with indium).
Ma ter ia ls. The syntheses of DOO-PPVk)7 homopolymer,
DOO-PPVk)7-b-P(S-stat-CMS)9k[1.5:1], and DOO-PPVk)7-b-P(S-
stat-C60MS)19K[1.5:1] diblock copolymers are described in ref 25,
of DOO-PPVk)9-TIPNO and DOO-PPVk)9-b-PBA5.8K in ref 31,
and of DOO-PPVk)9-b-PS22K in ref 24. Styrene (S) and
4-chloromethylstyrene (CMS) were distilled before use from
CaH2 under reduced pressure. Additional purification of CMS

3682 van der Veen et al.
Macromolecules, Vol. 37, No. 10, 2004
methanol (400 mL, ca. -30 °C), washed with ethanol until a
colorless filtrate was obtained (to remove excess of 3), and dried
under reduced pressure (RT, 16 h). Yield: 1.08 g (76%) of red
powder. Using the same conditions, the reaction has also been
performed with DEH-PPVk)15, resulting in 0.39 g (68%) of
DEH-PPVk)15-TIPNO. 1H NMR: δ ) 7.49 (br s, ColefH), 6.67-
7.16 (br s, CarH), 5.90 (br m, CHOH), 4.85 (br m, OCHCH3),
3.91 (br m, OCH2), 3.37 (d, NCHCH), 2.96 (br s, CHOH), 2.20-
2.34 (s, CH3/end group), 1.71-1.85 (m, CH2), 1.14-1.68 (m,
CH, CH2), 0.8-1.0 (m, CH3), 0.50 (d, CH(CH3)2 TIPNO).
DE H -P P Vk -b-P (S-sta t-CMS)p [n :m ]. The macroinitiator
DEH-PPV-TIPNO was chain extended with a statistical
copolymer by mixing the appropriate amounts of styrene and
4-chloromethylstyrene. The nomenclature used for the second
block is as follows: p is the molecular weight (Mn × 103 g/mol)
of the statistical copolymer with a built-in S to CMS ratio
indicated by n and m, respectively. The molar ratio of macro-
initiator to comonomer was in all cases 1:1300. Relative to the
amount of DEH-PPV-TIPNO, 4 equiv of Ac2O and 0.1 equiv
of TIPNO free radical (6 mg/mL in anisole) were added. Equal
weights of anisole to comonomer were used (optional). The
resulting solution was mixed and degassed by freeze-pump-
thaw cycles (3×), flushed with dry N2, and subsequently
immersed in a thermostated oil bath at 125 °C. The mixture
was cooled to RT after the desired polymerization time. The
polymer was precipitated in large excess of cold methanol (ca.
-30 °C), filtered, and washed until a colorless filtrate was
obtained. After redissolving in CHCl3 (few milliliters), the
polymer was again precipitated into cold methanol, filtered,
and washed. After drying under reduced pressure (60 °C, 16
h), an orange powder was obtained.
DEH-P P Vk)21-b-P (S-sta t-N3MS)31K[2.6:1]. DEH-PPVk)21-
b-P(S-stat-CMS)31K[2.6:1] (1.0 g, 0.026 mmol), NaN3 (2.41 g, 37.1
1
mmol); yield: 0.87 g (85%). Representative H NMR of DEH-
PPVk)21-b-P(S-stat-N3MS)14K[2.1:1]
: δ ) 10.41 (s, CHO/end
group), 7.49 (br s, ColefH), 6.66-7.01 (br m, CarH), 4.17 (br s,
CH2N3), 3.91 (br m, OCH2), 2.20-2.34 (br s, CH3/end group),
1.04-1.9 (m, CH, CH2), 0.8 (br m, CH3). Representative IR
(FT-IR) of DEH-PPVk)15-b-P(S-stat-N3MS)67K[3:1]
: 3026 (w,
-Caryl-H), 2923 and 2854 (s, CH3 and CH2), 2094 (vs, CN3),
1601 (s, -CdC-aryl), 1493 and 1453 (s, -C6H5, in plane), 1264
(s, Caryl-OR), 1199 and 1029 (s, -Caryl-H ) , out-of-plane),
817 and 756 (w and vs, -Caryl-H ) , in-plane) cm-1
.
DEH-P P Vk-b-P (S-sta t-C60MS)p[n :m ]. The corresponding
(di)block copolymers and C60 (2 equiv relative to the amount
of N3MS comonomer) were dissolved in chlorobenzene and
degassed by bubbling dry N2 through the solution for 15 min.
The mixture was stirred at 60 °C for 20 h using a thermostated
oil bath. Subsequently, it was refluxed for 1 h at 130 °C (no
N2 atmosphere). After cooling to RT, saturated NaCl (10 mL)
was added, and the mixture was vigorously stirred for 1 h as
an attempt to remove unreacted azide groups. The organic
layer was washed with water (4 × 500 mL) and dried over
Na2SO4, and the solvent was almost completely removed. The
residue was diluted with THF (500 mL), filtered, and washed
until a colorless filtrate, and the THF was removed under
reduced pressure. After repeating this latter step, the polymer
was precipitated in methanol (200 mL), filtered, and taken up
in chlorobenzene (10 mL). This latter precipitation and filtra-
tion were repeated, and the product was either dried under
reduced pressure (70 °C, 16 h) or stored in chlorobenzene (10
mL).
DE H -P P Vk )15-b-P (S-sta t-CMS)65K[3:1]. DEH-PPVk)15
-
DEH-P P Vk)15-b-P (S-sta t-C60MS)167K[3:1]. DEH-PPVk)21
-
TIPNO (0.14 g, 0.025 mmol), S (2.84 g, 27.3 mmol), CMS (1.04
g, 6.81 mmol), Ac2O (10 µL, 0.11 mmol), TIPNO (0.62 mg, 0.003
mmol); bulk polymerization with samples taken after time
intervals; yields: 5 mg (40 min, PD ) 1.2), 0.14 g (100 min,
PD ) 1.7), 0.13 g (120 min, PD ) 1.8), and 0.58 g (140 min,
b-P(S-stat-N3MS)67K[3:1] (0.24 g, 0.0033 mmol), C60 (0.68 g, 0.94
mmol); yield: 0.24 g (42%) of reddish-brown powder (poorly
soluble in organic solvents).
DEH-P P Vk)21-b-P (S-sta t-C60MS)41K[2.1:1]. DEH-PPVk)21
-
b-P(S-stat-N3MS)14K[2.1:1] (0.40 g, 0.018 mmol), C60 (1.0 g, 1.4
mmol); yield: 10-15 mL (34 mg/g chlorobenzene) of reddish-
brown solution.
PD ) 2.2). The last sample has been functionalized with C60
DEH-P P Vk)21-b-P (S-sta t-CMS)14K[2.1:1]. DEH-PPVk)21
.
-
TIPNO (0.41 g, 0.05 mmol), S (5.47 g, 52.4 mmol), CMS (2.49
g, 16.3 mmol), Ac2O (20 µL, 0.21 mmol), TIPNO (1.1 mg, 0.005
mmol), anisole (7.96 g, 73.6 mmol); yield: 0.86 g (conversion
of 13% in 50 min, PD ) 1.5).
P (S-sta t-C60MS)63K[2:1]. This reference compound was pre-
pared from P(S-stat-N3MS)21K[2:1] (36 mg, 0.0017 mmol) and 1
equiv (!) of C60 (66 mg, 0.092 mmol); yield: 27 mg (26%) of
brown powder (poorly soluble in organic solvents). Representa-
1
DEH-P P Vk)21-b-P (S-sta t-CMS)31K[2.6:1]. DEH-PPVk)21
-
tive H NMR of DEH-PPVk)21-b-P(S-stat-C60MS)41K[2.1:1]: δ )
TIPNO (0.39 g, 0.05 mmol), S (5.43 g, 52.1 mmol), CMS (2.24
g, 14.7 mmol), Ac2O (20 µL, 0.21 mmol), TIPNO (1.1 mg, 0.005
mmol), anisole (7.98 g, 74.2 mmol); yield: 1.45 g (conversion
of 23% in 80 min, PD ) 1.8). Representative 1H NMR of DEH-
PPVk)21-b-P(S-stat-CMS)14K[2.1:1]: δ ) 7.49 (br s, ColefH), 6.66-
7.01 (br m, CarH), 4.46 (br s, CH2Cl), 3.91 (br m, OCH2), 2.20-
2.34 (br s, CH3/end group), 1.04-1.9 (m, CH, CH2), 0.8 (br m,
CH3), 0.45 (br s, CH(CH3)2 TIPNO).
DE H -P P Vk -b-P (S-sta t-N3MS)p [n :m ]. The corresponding
diblock copolymers and NaN3 (20 equiv relative to the built-
in amount of CMS comonomer) were mixed in DMF (100 mL).
After stirring for 16 h at 130 °C (no N2 atmosphere), the
reaction mixture was poured out in water (300 mL) containing
CHCl3 (50 mL). After stirring for 15 min, the mixture was
extracted with CHCl3 (2 × 50 mL). Water (300 mL) was then
added to the combined organic layers. After stirring for 15 min,
the water layer was extracted with CHCl3 (200 mL). Each
portion of the combined organic layers (200 mL) was separately
washed with water (400 mL). The organic layers were dried
over Na2SO4 and filtered, and the solvent was removed.
Dissolved in CHCl3 (10 mL), the polymer was precipitated
twice into cold methanol (400 mL, ca. -30 °C) and washed
until a colorless filtrate was obtained. The product was dried
under reduced pressure (30 °C, 16 h), resulting in an orange
powder.
10.41 (s, CHO/end group), 6.25-7.48 (br m, CarH, ColefH), 3.88
(br m, OCH2), 2.20-2.34 (s, CH3/end group), 1.04-1.9 (m, CH,
CH2), 0.8 (br m, CH3).
P (S-sta t-CMS)21K[2:1]. Styrene (S, 10.89 g, 104.6 mmol) and
4-chloromethylstyrene (CMS, 8.00 g, 52.4 mmol) were mixed
with an alkoxyamine based on TIPNO (i.e., 2,2,3-trimethyl-
3-(1-phenylethoxy)-4-phenyl-3-azahexane; synthesized accord-
ing to ref 53; 0.20 g, 0.61 mmol). After addition of Ac2O (0.21
g, 2.06 mmol), the mixture was degassed by freeze-pump-
thaw cycles (3×) and flushed with dry N2. Immersed in a
thermostated oil bath it was kept at 125 °C for 5 h. Samples
were taken (after 80, 110, 160swhen the reaction mixture
solidifieds, 180, 230, and 270 min), which were diluted with
CHCl3, precipitated twice in methanol, filtered, and washed.
The products were dried under reduced pressure (60 °C, 16
h). Yields of white powder: 0.48 g (from 1.19 g; 80 min, PD )
1.1), 0.34 g (from 0.56 g; 110 min, PD ) 1.1), 64 mg (from 0.13
g; 160 min, PD ) 1.2), 0.66 g (from 0.74 g; 180 min, PD )
1.2), 0.83 g (from 0.90 g; 230 min, PD ) 1.2), 0.83 g (from 0.89
g; 270 min, PD ) 1.2), and 13.7 g (from 14 g; final product
after 300 min). The sample taken at 110 min was used as
reference compound in subsequent syntheses (azide prepara-
tion and C60 functionalization). Representative 1H NMR
(sample of 110 min): δ ) 6.50-7.00 (br s, CarH), 4.33-4.47
(br d, CH2Cl), 1.36-1.73 (br s, CH, CH2), 0.16-0.48 (br s,
CH(CH3)2 TIPNO).
DEH-P P Vk)15-b-P (S-sta t-N3MS)67K[3:1]. DEH-PPVk)21-b-
P(S-stat-CMS)66K[3:1] (0.32 g, 0.004 mmol), NaN3 (0.83 g, 12.8
mmol); yield: 0.27 g (85%).
P (S-sta t-N3MS)21K[2:1]. The P(S-stat-CMS)21K[2:1] (0.3 g, 0.014
mmol) and NaN3 (1.08 g, 16.6 mmol) were mixed in DMF (50
mL). After stirring for 16 h at 130 °C (no N2 atmosphere), the
mixture was poured out in water (450 mL) containing CHCl3
(50 mL). After stirring for 15 min, the mixture was extracted
DEH-P P Vk)21-b-P (S-sta t-N3MS)14K[2.1:1]. DEH-PPVk)21
-
b-P(S-stat-CMS)14K[2.1:1] (0.83 g, 12.8 mmol), NaN3 (1.47 g, 22.6
mmol); yield: 0.50 g (76%).

Macromolecules, Vol. 37, No. 10, 2004
Diblock Copolymers Based on PPV and C60 3683
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g (67%) of white powder. 1H NMR: δ ) 6.50, 7.00 (br s, CarH),
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Ack n ow led gm en t. The following people are ac-
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Ekenstein, E. J . Vorenkamp, C. Melzer, J . Wildeman,
V. V. Krasnikov, S. Polychronopoulou, and H. Nijland.
We thank FOM, NWO-CW, and the EU (TMR scholar-
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Su p p or tin g In for m a tion Ava ila ble: Additional FT-IR
and UV-vis spectra of DEH-PPV-b-P(S-stat-CMS), DEH-
PPV-b-P(S-stat-N3MS), DEH-PPV-b-P(S-stat-C60MS), and
DEH-PPV-TIPNO (UV-vis only) visualize the functional-
ization with the azide group and incorporation of C60. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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MA035643O