Soluble head-to-tail regioregular polythiazoles: Preparation, properties, and evidence for chain-growth behavior in the synthesis via Kumada-Coupling polycondensation

Article abstract of DOI:10.1021/ma501213g

Head-to-tail regioregular poly(4-alkylthiazole)s containing silylethers in the side-chains were synthesized via Kumada-Coupling polycondensation of "reversed" monomers, that were metalated at the sterically hindered 5-position. Their optical, electrochemi

Full text of DOI:10.1021/ma501213g

Article
pubs.acs.org/Macromolecules
Soluble Head-to-Tail Regioregular Polythiazoles: Preparation,
Properties, and Evidence for Chain-Growth Behavior
in the Synthesis via Kumada-Coupling Polycondensation
Frank Pammer,*,† Jakob Jager,† Benjamin Rudolf,† and Yu Sun‡
̈
†Institute of Organic Chemistry II and Advanced Materials, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
‡Fachbereich Chemie, TU Kaiserslautern, Erwin-Schrodinger-Strasse 54, D-67663 Kaiserslautern, Germany
̈
S
* Supporting Information
ABSTRACT: Head-to-tail regioregular poly(4-alkylthiazole)s contain-
ing silylethers in the side-chains were synthesized via Kumada-Coupling
polycondensation of “reversed” monomers, that were metalated at the
sterically hindered 5-position. Their optical, electrochemical, and bulk
properties have been studied, and evidence is presented that indicates
the occurrence of quasi-living chain-growth behavior in the polymer-
ization process. Two polymers, PTzTIP and PTzDIBO, featuring
triisopropylsilyl and diisobutyloctadecylsilyl side chains, respectively,
were prepared. PTzTIP is largely insoluble, while PTzDIBO is fully
soluble in common organic solvents, including hexane, and readily gave
number-averaged molecular weights exceeding 100 kDa, corresponding
to an average degree of polymerization greater than 200, as determined
via gel-permeation chromatography (GPC) in CHCl3. The formation of
a regular head-to-tail regiostructure could be confirmed through comparison with a head-to-head−tail-to-tail regioregular
polybithiazole (PBTzTIP), synthesized via Yamamoto-polymerization of a head-to-head-linked bithiazole. Regioregular PTzDIBO
could be obtained via different polymerization protocols, including external initiation with two new aryl-nickel-complexes, which
furnished material with particularly low polydispersities (<1.4 at Mn > 100 kDa). Furthermore, a direct correlation between the
obtained molecular weight and the monomer/catalyst ratio was observed in series of batch polymerization experiments, in
agreement with a chain-growth polycondensation process. The incorporation of the precatalyst−aryl moiety into the polymer chains
could be proven by comparison with a model compound. The functionalized end-groups allowed to independently determine
1
the molecular weight via H NMR, which gave good agreement with the values obtained from GPC, further corroborating the
occurrence of chain-growth.
emerged as the method of choice.4 CTP protocols allow for the
controlled chain-growth polycondensation of AB-bifunctional
in the last decades.1 Polythiophenes (PTs) in particular are
arenes, and primarily involve the cross-coupling of in situ gene-
INTRODUCTION
■
Conjugated polymers have been the subject of intense research
rated Grignard and organozinc species, with nickel catalysts.
Recently, chain-growth polycondensation of via Suzuki-coupling
has also been reported.5,4b Quasi-living chain-growth behavior
could be observed for a number of electron-rich polyarenes, such
as rr-P3ATs,6 polyselenophene,7 polyfluorene,8 polypyrrole,9
and poly(dialkoxyphenylene).10 More electron-deficient poly-
mers, on the other hand, have been investigated to a much lesser
degree. Chain-growth behavior was observed in the synthesis of
polypyridines,11 a naphthalene diimide−bithiophene copolymer,12
and a poly(benzotriazole).13 Polythiophene bearing perfluoro-
alkyl side-chains,14 and poly(thieno[3,4-b]pyrazine15 could also
be synthesized via Kumada- and Negishi-type polycondensations,
among the most intensely studied polymeric semiconductors,
and have been widely employed in the fabrication of organic
electronic devices, such as organic field effect transistors,
organic light-emitting diodes, and organic photovoltaic cells.2
Also, functionalized PTs played important roles in conjugated
polymer-based sensors.3
The regioregularity of poly(3-alkylthiophenes) (rr-P3ATs,
Chart 1) has been shown to critically affect the materials prop-
erties, including the optical band gap and the electrical con-
ductivity after doping. A coplanar arrangement of the thiophene
rings in rr-P3ATs generally results in a larger effective con-
jugation length, and allows for aggregation via π-stacking in the
solid state which in turn is beneficial for charge carrier mobility
and overall performance of organic electronic devices. For
the preparation of highly regioregular rr-P3ATs and other
polyarenes, polymerization protocols summarized under the
term catalyst transfer polycondensation (CTP) have recently
Received: June 12, 2014
Revised: August 6, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
e.g., by Yamashita et al., who reported oligo-thiazole based n-
channel organic field effect transistors (OFETs) that exhibited
electron mobilities exceeding 1 cm2/(V s) and required a lowered
threshold voltage compared to their thiophene analogues.17
Thiazole and thiazole derivatives have been frequently employed
as electron-accepting comonomers in conjugated polymers.18,19
Reports on thiazole homopolymers, however, are largely limited
to works by Yamamoto20 and Curtis21 on the properties of head-
to-head−tail-to-tail regioregular polybithiazoles (PBTz, Chart 1).
Recently, we were able to report the synthesis and properties
of head-to-tail regioregular polythiazoles bearing n-alkyl-chains
in the 4-position (Chart 1, C9-PTz: R = n-C9H19, C13-PTz: R =
n-C13H27).22 In agreement with the properties of PTTz/
PTTTz,16 the investigated rr-PTzs exhibited optical and elec-
tronic band gaps comparable to rr-P3ATs, while their frontier
orbitals levels were stabilized by ca. 0.3−0.5 eV. Unfortunately,
C9-PTz and C13-PTz were largely insoluble in organic solvents.
The molecular weight of the bulk material could therefore not
be determined, and the polymerization process could not be
investigated in detail.
Chart 1
Herein, we report the synthesis of 2,5-dihalogenated thia-
zoles (1a/b, Scheme 1) with silyloxymethyl-side-chains that
furnish better soluble polythiazoles (PTzTIP, PTzDIBO, Chart
1). Their properties are discussed and evidence is presented for
the occurrence of a chain-growth process in the polymer synthesis
via nickel-catalyzed Kumada-coupling polycondensation.
respectively, but the occurrence of chain-growth was not
reported.
In our group we are interested in further expanding the scope
of CTP toward more electron-deficient heterocyclic building
blocks, in order to access new potential n-type materials.
To this end, we recently explored the synthesis and properties
regioregular poly(4-alkylthiazole)s (rr-PTzs, Chart 1) via CTP.
While thiazoles are isoelectronic to thiophenes, the electron-
withdrawing imine-nitrogen in the ring renders them com-
paratively electron-poor. Accordingly, partial substitution, of
thiophene against thiazole in an otherwise head-to-tail regio-
regular P3AT (PTTz, PTTTz, Chart 1) leads to increasing
stabilization of the frontier orbitals.16 The potential of thiazoles
in the fabrication of n-type materials has been demonstrated,
RESULTS AND DISCUSSION
■
Monomer and Polymer Synthesis. The monomers were
obtained via a five-step synthesis, as outlined in Scheme 1.
Starting from 1-bromoethylpyruvate (2) the thiazole ring was
built up (3), and was halogenated (4, 5), followed by conversion
of the carboxylic acid ester 5 to the corresponding thiazolyl-
alcohol 6. The alcohol was then reacted with trialkylchlorosilanes
Scheme 1. Monomer Synthesis and Polymerization Experiments
B
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to
furnish the corresponding silylethers featuring triisopropyl- (1a)
and diisobutyloctadecylsilyl groups (1b). Analogous to our
i
previous report, treatment of 1a/b with PrMgCl leads to
quantitative metalation at the 5-position, and the corresponding
AB-bifunctional Grignard species 7-Mga/b are formed (Scheme 1b,
Figure 1). Treatment of 7-Mga with copper(II) chloride results
Figure 2. (A) 1H NMR spectra of polythiazoles recorded in 1,2-
dichlorobenzene-d4 (ODCB-d4) at 100 °C (PTzDIBO, PBTzTIP)
and at 150 °C (PTzTIP). ∗ = end groups and low molecular weight
oligomers. (B) Close-up of the peak of PTzDIBO (Mn = 93.0 kDa) at
100 °C in ODCB-d4.
1
Figure 1. H NMR spectra of (a) hydrolyzed 7-Mga and (b) 1a in
CDCl3.
ODCB-d4 at 100 and 150 °C, respectively, the corresponding
signals are observed at 5.27 and 5.28 ppm. The corresponding
signal in the head-to-head−tail-to-tail regioregular PBTzTIP
appears at 5.00 ppm in the same solvent. This signal offset is
similar but somewhat smaller than the one previously reported
for head-to-head- and head-to-tail-dyads of oligo- and poly-
(4-alkylthiazole)s (ca. 0.4 ppm).22 A close-up of the signal of high
molecular weight PTzDIBO (Figure 2B, see also and Figures S30
and S33 in the Supporting Information) shows only trace signals
associated with possible head-to-head-defects. While this indicates
a high degree of regioregularity, tail-to-tail-defects may still
be present. Signals associated with inherent regio-defects can be
unambiguously observed only in lower molecular weight samples
(Mn < 15 kDa, e.g., Figure 7c). Here two individual peaks can be
resolved at 5.09 and 5.11 ppm (recorded at 50 °C in CDCl3),
that can be observed as a shoulder only for higher molecular
weight samples. Since the minor signal is not detectable in high
molecular weight samples, we tentatively attribute it to chain-end
dyads. However, it may also be associated with regio-defects
generated in the initiation steps. The regioregularity of PTzDIBO
can also be inferred from 13C NMR data that shows four well-
resolved signals for the thiazole ring and the α-methylene-group at
157.0, 154.7, 131.7, and 60.0 ppm (Figure S34 in the Supporting
Information). Extensive regio-defects are expected to lead
to multiple signals in the 13C NMR,29 or cause severe signal
broadening.30
Optical and Electronic Properties. The electronic prop-
erties of PTzDIBO and PTzTIP have been studied via UV−vis-
and fluorescence spectroscopy. For brevity only the properties
of PTzDIBO will be discussed. In THF solution PTzDIBO
exhibits a longest wavelength absorption maximum (λmax) at
503 nm and an absorption onset at 568 nm. In absorption
spectra of thin films, spin coated from THF, the main absorption
maximum exhibits a marginal blueshift to 502 nm, and new maxi-
mum emerges at 533 nm along with a concurrent shift of the
absorption onset to 590 nm, corresponding to an optical band
gap of 2.10 eV. Annealing of the film of PTzDIBO at up to
120 °C did not alter the absorption spectrum, while upon
annealing above 140 °C the maximum at 533 nm is reduced to
a shoulder band, and a new shoulder centered on ca. 477 nm
emerges (see Figures S5 through S7 in the Supporting
Information). Overall, only a minor bathochromic shift of the
absorption onset is observed, when moving from solution to
the solid state. This is in contrast to the optical properties of
in oxidative homocoupling and formation of the head-to-head-
coupled 2,2′-dichloro-5,5′-bithiazole 8 (Scheme 1c). Yamamo-
to-polymerization of 8 yields the head-to-head−tail-
to-tail regioregular polybithiazole PBTzTIP (Mn = 5.9 kDa,
PDI = 2.06), which served as reference material to corroborate
the regioregularity of PTzTIP and PTzDIBO.
Polymerization of 7-Mga/b could be performed according
to different preparative protocols (methods A through C in the
Supporting Information) with Ni(dppe)- or Ni(dppp)-based
catalysts (dppe, 1,2-bis(diphenylphosphino)ethane; dppp, 1,3-
bis(diphenylphosphino)propane), which furnished the polymers
PTzTIP and PTzDIBO, respectively, as bright orange fluo-
rescent solids. However, the bulk of PTzTIP was found to be
soluble only in high boiling haloarenes such as hot 1,2-dichloro-
benzene (ODCB) or 1,2,4-trichlorobenzene. The chloroform-
soluble trace fractions of PTzTIP gave maximum number-
averaged molecular weight of Mn = 2.7 kDa (PDI = 1.30, DPn ≈
10−11), while the molecular weight of the insoluble bulk material
is presumed to be higher. PTzDIBO, on the other hand, is fully
soluble in common organic solvents, including hexane, and readily
gave molecular weights exceeding 100 kDa (DPn > 200), as deter-
mined via GPC relative to polystyrene standards.23−25 Unless
stated otherwise, analytical studies reported in the following have
been carried out with the insoluble bulk material of PTzTIP,
synthesized with a Ni(cod)2/dppp-catalyst system (method B in
the Supporting Information, cod =1,5-cyclooctadiene), and with
two batches of PTzDIBO with number-average molecular weights
of 111.6 kDa (PDI = 2.13), and 93.0 kDa (PDI = 2.19), that were
synthesized with Ni(dppp)Cl2 (method A in the Supporting
Information) and Ni(cod)2/dppp as catalyst, respectively. The
polymerization proceeds quickly, and was generally complete
within 40 min even when carried out at 0 °C (see Figures S3 and
S4 in the Supporting Information). The high reaction speed is
insofar surprising as a formally less reactive aryl chloride is
employed. The lower reactivity seems offset, however, by the
known high reactivity of the 2-position of the thiazole ring.26
Furthermore, nickel is generally more active in the cross-
coupling of aryl chlorides compared to palladium.27
Regiostructure. The head-to-tail structure of the polymers
can be inferred from the characteristic chemical shift of
the benzylic α-methylene group (TzCH2OSiR3, Figure 2A).28
1
In H NMR spectra of PTzDIBO and PTzTIP recorded in
C
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
rr-P3ATs2 and recently reported PTTz/PTTTz16 that exhibit
substantial bathochromic shifts in the film compared to spectra
recorded in solution. The bathochromic shift is associated with
π−π stacking of the conjugated polymer backbone, and is
generally more pronounced for regioregular polymers than for
random polymers containing regio-defects.2,31 In the present
case, however, the limited bathochromic shift is attributed to the
bulk of the side-chains preventing aggregation, rather than to the
presence of regio-defects. PTzDIBO fluoresces with a quantum
yield of 26% in THF solution; within the same range commonly
observed for regioregular polythiophenes.32 The emission
spectrum in solution revealed only a narrow Stokes shift and
well-defined vibronic structuring. In solution emission maxima
are observed at 550 and 590 nm along with two additional
shoulder bands. Fluorescence also persists in the thin film,
although the 550 nm transition is not observed and the vibronic
structure is less pronounced. The marginal Stokes shift and
the vibronic structuring indicate a rigid conformation of the
conjugated polymer backbone of PTzDIBO in solution. Indeed,
the vibronic structuring is more pronounced than what is
observed for rr-P3HT,33,32 but rather reassembles more rigid
conjugated π-systems that contain, e.g., fluorene34 or ladder-type
polymer structures.35 This observation may be explained by a
recent report by Bronstein and co-workers who demonstrated
that a coplanar conformation of head-to-tail-linked thienyl-
thiazole-dyads is stabilized through interaction of the lone pair
on nitrogen with the antibonding σ*-orbitals of the C−S-bonds
in the adjacent ring.16 In order to substantiate the presence of
this stabilizing interaction in thiazole-homopolymers, the above
calculation has been reproduced with in a head-to-tail-linked
bithiazole-dyad (see section 1.3 in the Supporting Information
for details). The calculations showed the rotational barrier in a
bithiazole-dyad to be very close in energy to the one previously
reported for thienyl-thiazole, and substantially greater what is
found for bithiophenes. Other researchers have reported O···S-
based weak interactions to also promote a coplanar conformation
of adjacent rings in conjugated polymers, and to thereby affect
the bulk morphology of the material.36 However, while the stabi-
lizing interaction clearly affects the electronic properties of
PTzDIBO in solution, a possible influence on the solid state
morphology of rr-PTzs still remains to be established.
Analyses of PTzTIP and PTzDIBO via cyclic voltammetry
showed the two polymers to have very similar electrochemical
properties (Figure 3b, Table 1). For reference purposes,
previously reported electrochemical data for rr-P3HT, PBTz,
and C9-PTz, recorded under similar experimental conditions,
are also included in Table 1.22 Both PTzTIP and PTzDIBO
undergo quasi-reversible reduction while oxidation was irrever-
sible with oxidation-onsets observed at +0.95 and +0.99 V
relative to the ferrocene/ferrocenium redox couple (Fc/Fc+).
These latter values are very close to those previously observed
for C9-PTz and PBTz, and correspond to energy levels for
the highest occupied molecular orbitals (HOMO) of −6.05 eV
for PTzTIP and −6.09 eV for PTzDIBO, based on the HOMO
of ferrocene (−5.10 eV).39 The onsets of the reduction waves
at −1.69 V and −1.74 V lead to electrochemical band gaps of
2.64 eV (PTzTIP) and 2.73 eV (PTzDIBO). The difference
between the electrochemical and optical band gaps of the
polymers reported herein (ca. 0.6 V) is significantly less than
what was observed for C9-PTz and PBTz (0.9−1.0 V).2 As a
consequence, the energy levels for the lowest unoccupied
molecular orbitals (LUMO) of PTzTIP and PTzDIBO derived
from the electrochemical and optical band gaps either appear
Figure 3. (a) UV−vis absorption- and fluorescence-spectra PTzDIBO
in THF solution and as thin film. Absorption spectrum in solution
recorded at 19.8 μg/mL, fluorescence spectrum recorded at 0.5 μg/mL.
(b) Cyclic voltammograms of PTzDIBO and PTzTIP. Recorded as
rub-coated films in acetonitrile, 0.1 M [NnBu4][PF6] at 50 mV/s. ∗ =
Fc/Fc+ standard.
to be stabilized (electrochemical, LUMOCV) or destabilized
(optical, LUMOopt), compared to C9-PTz and PBTz. In a study
on the properties of regioregular poly[3-(n-butyloxymethyl)-
thiophene] (P3MBT) Zoombelt and co-workers found that the
introction of alkoxymethyl-groups does not affect the frontier
orbital levels of the polymer compared to P3HT.37 In agreement
with this finding, the HOMO-levels of all reported polythiazoles
are virtually identical. Hence, the differences in LUMO-levels are
rather attributed to packing effects in the solid state and the
quasi-reversible nature of the electrochemical reductions
observed for PTzTIP and PTzDIBO.
Thermal Analyses and Solid State Properties. Thermal
analyses were carried out on PTzTIP and PTzDIBO, as well
as on the previously reported polymers C13-PTz and C9-PTz
(see Figures S8 and S9 in the Supporting Information).
Thermogravimetric analyses (TGA) showed C13-PTz and C9-
PTz to be equally thermally robust up to 440 °C, where rapid
degradation sets in. The silyloxy-substituted polymers were found
to be somewhat less durable and decomposed above 410 °C. In
differential scanning calorimetry (DSC) C9-PTz was found to
decompose without melting, while melting of PTzTIP set in at
ca. 425 °C but appeared irreversible due to concurrent decompo-
sition. In contrast, C13-PTz exhibited a melt endotherm at
386 °C upon heating, complemented by a crystallization exo-
therm at 362 °C in the cooling cycle, while for PTzDIBO a
reversible phase transition was observed with a melting endo-
therm at 145 °C upon heating and a sharp crystallization exo-
therm at 140 °C (scan rate 20 °C/min). No phase transitions
D
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Table 1. Electrochemical Potentials Given in V Relative to Fc/Fc+ with Orbital Energies Given in eV
a
b
b
b
LUMOopt
LUMOCV
red
onset
ox
onset
red
polymer
E
E
E
1/2
Eogpt
ECg V
HOMO
c
C9-PTz
−1.91
−1.92
−2.32
−1.69
−1.74
1.00
0.93
0.45
0.95
0.99
−2.09
−2.03
−2.34
d
1.90
1.90
1.90
2.09
2.10
2.91
2.85
2.77
2.64
2.73
−6.10
−6.03
−5.55
−6.05
−6.09
−4.20
−4.13
−3.65
−3.96
−3.99
−3.19
−3.18
−2.78
−3.41
−3.36
c
PBTz
c
rr-P3HT
PTzTIP
PTzDIBO
d
a
b
Derived from the absorption onset of the thin film UV−vis spectra. Derived from the oxidation onset and the HOMO-energy of ferrocene (−5.10 eV),
and the optical (LUMOopt) and electrochemical (LUMOCV) band gaps.38 Data adapted from ref 22. PTzTIP and PTzDIBO showed only quasi-
c
d
reversible reduction waves.
could be observed for PTzDIBO at higher temperatures. The
higher temperature melting events observed for PTzTIP and
C13-PTz are attributed to melting of the polymer main-chain,
while the reversible phase transition observed for PTzDIBO
is rather associated with melting of the side-chains.
In order to further elucidate the structures of the polymers
in the solid state, samples of C9-PTz, C13-PTz, PTzTIP, and
PTzDIBO have been investigated via wide-angle X-ray
scattering (WAXS). The refractograms of C9-PTz and C13-PTz
(Figure 4, A1/A2) are dominated by broad peaks centered on ca.
25° and 20°, corresponding to distances of ca. 3.7 and 4.7 Å,
attributed to the densely π-stacked polymer backbone,31,21b and
amorphous regions,21b respectively. PTzTIP shows a significantly
different refraction pattern that becomes better resolved upon
prolonged heating of a suspension of the polymer in chloro-
benzene (Figure 4, B1/B2). Maxima associated with π-stacking
at 23.2° and 24.8° (3.9 and 3.7 Å) are present. Still, the most
prominent features are maxima at 13.6°, 14.9°, and 16.5°
(6.6, 6.0, and 5.4 Å), that do not correspond to a readily identi-
fiable repeat-structure in the polymer. PTzDIBO exhibits an
again altered refraction pattern (Figure 4, C1/C2). In the refrac-
togram of a compacted pellet prominent peaks are visible at
14.5°, 20.7° and 21.5° (6.2, 4.4, and 4.2 Å), along with other
signals (Figure 4, C1). Heating of the polymer to 150 °C,
followed by slow cooling led to partial crystallization of the
sample and gave a better resolved refractogram (Figure 4, C2).
The signals observed in the original sample are still present at
14.6°, 20.7° and 21.7° (6.2, 4.4 and 4.2 Å). The peak at 14.6°
may be associated with the side-chain-repeat height,31 while the
peaks at 20.7° and 21.7° most likely correspond to densely
packed alkyl chains.38 A peak at 25.5° (3.6 Å), that may be
associated with π-stacking also emerges in the crystallized sample.
These findings indicate, that in the insoluble polymers C9-
PTz, C13-PTz extensive π-stacking is prevalent, while due to
the increased bulk of the side-chains in PTzTIP π-interactions
are less predominant. The solid state structure of PTzDIBO,
on the other hand, appears to be dominated by the packing of
the octadecyl-side-chains, which is corroborated by the low
melting point and the high solubility of the polymer.
Figure 4. WAXS refraction patterns of different polymer samples: (A1)
pellet of C9-PTz; (A2) pellet of C13-PTz; (B1) PTzTIP as precipitated;
(B2) PTzTIP after thermal treatment; (C1) pellet of PTzDIBO; (C2)
PTzDIBO cooled from 150 °C. For details on the sample preparation,
see the experimental section in the Supporting Information.
thiazolyl-Grignard species and Ni2+ or by oxidative addition
(OA) of nonmetalated monomer onto Ni0.22 This is a significant
difference to the polymerization of “reversed” thienyl-monomers,
wherein the necessity to form an initial head-to-head-linkage
reportedly hampers polymerization.6a,c,e Polymerization of 7-Mgb
could be performed with either dichloro nickel precatalysts
(Ni(L2)Cl2; L2 = dppp, dppe, method A), or with L2/Ni(cod)2
as a Ni(0) source (method B). Both methods reliably furnish
regioregular PTzDIBO, with either dppp or dppe as ligand. The
polydispersities achieved with dppp were comparatively high
(1.8−2.2 for Mn ≈ 100 kDa), while dppe-based catalysts
performed better under similar conditions (up to Mn = 99.3 kDa,
PDI = 1.51, method B). Still, a correlation between the
monomer/catalyst-ratio and the obtained molecular weights was
Evidence for Chain-Growth in the Polycondensation
Process. A key hurdle in our syntheses of polythiazoles is the
need to employ “reversed” thiazole-monomers (i.e., 7-Mga/b
)
that are metalated at the sterically hindered 5-position, since
“regular” metalation at the highly reactive 2-position leads to
rapid decomposition of the monomer.22 As a consequence,
initiation of the polymerization process is crucially different
from the initiation of regular monomers (Scheme 2a). According
to our current working hypothesis, initiation most likely proceeds
through the sterically unfavorable formation of a head-to-head-
dyad (10) via Yamamoto-coupling or disproportionation of an
intermediate aryl-nickel complex (9) generated from either a
E
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 2. Initiation Pathways and Model Compounds
not observed, and the molecular weight generally far exceeded
the value theoretically expected from the monomer/catalyst ratio
(see e.g. Figure S10 in the Supporting Information). While these
observations point toward the presence of a step-growth process,
another reason may be that due to the complex initiation-steps
and heterogeneous conditions (method A), initiation is sluggish
and only a fraction of the introduced catalyst is actually involved
in the polymerization. Furthermore, in method B formation of
catalytically inactive Ni(dppp)2/Ni(dppe)2 may inadvertently
lower the effective catalyst loading. In follow-up experiments
these issues could be alleviated, however, by the use of aryl-nickel
precatalysts that serve as external initiators (Scheme 2).
External initiation has been very successful in the synthesis of
poly(thiophene)s,6c,40 and poly(dialkoxyphenylene)s,10a,b,d
leading to essentially defect-free polymers, lower PDIs, and
better control over molecular weight and end-groups. Fur-
thermore, tailored precatalysts allow the in-depth study of the
polymerization mechanism,10a,b and the introduction of func-
tional end-groups.40b In the present case, external initiation
would allow to alleviate the steric hindrance in the first cross-
coupling step, and would make it possible to employ a well-
defined precatalyst in homogeneous solution.
Two aryl−nickel(dppe) complexes with o-methoxyphenyl
(o-anisyl, C1) and m-xylyl substituents (C2) have been
synthesized according to a modified procedure based on a
previous report by McNeil and co-workers (Scheme 2, see
Supporting Information for details).10d The o-anisyl-complex
C1 was chosen because the methoxy-substituent is sterically
less demanding than an alkyl-group, while still providing some
steric protection of the metal center.41 The m-xylyl-complex C2 is
less sterically encumbered and initiation should therefore be faster,
while the additional methyl groups improve solubility. C1 was
found to be chemically robust and could be completely
Figure 5. GPC chromatograms of batch-polymerization experiments
(method C) and monomer/catalyst ratios: (A) catalyst C1; (B) catalyst C2.
material with low polydispersities (<1.4 up to Mn > 100 kDa), in
accordance with a chain-growth process. C2 performed particularly
well with polydispersities below 1.2 up to molecular weights
around 80 kDa. (monomer/catalyst-ratio =50/1). Only at very
low catalyst loading (C2, monomer/catalyst ratio = 67/1 and
100/1) did the PDI begin to rise. The GPC-chromatograms
typically showed a bimodal mass-distribution with shoulder bands
and individual peaks that correspond to approximately twice the
molecular weight of the main peak. The bimodal mass-distribu-
tion may be attributed either to high molecular weight species
generated through chain−chain-coupling, as is commonly ob-
served in polythiophene syntheses,6b,25a,42 or possibly to competing
initiation pathways that lead do two different types of polymer.
The reaction mixtures were quenched with methanol acidified
with hydrochloric acid, which should prevent oxidative coupling
1
characterized by H and 31P NMR, and mass spectrometry. The
molecular structure of C1 could also be confirmed through single
crystal X-ray diffraction (crystallographic data included in the
Supporting Information). Catalyst C2 proved to be more sensitive
1
to decomposition and was characterized via H and 31P NMR.
Series of batch polymerizations were then carried out with both
C1 and C2, according to method C with different monomer-
to-catalyst-ratios (Figures 5 and 6). Both catalysts showed a linear
correlation between the molecular weight determined via GPC
and the monomer/catalyst ratio (Figures 6A and 6B) and furnished
F
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Figure 6. Plots of Mn and PDI vs monomer/catalyst to monomer ratio from batch polymerization experiments: (A) catalyst C1; (B) catalyst C2.
Part A includes Mn-values both determined via GPC (Mn,GPC) and derived from NMR-data (Mn,NMR).
of the polymer chains during the work-up.6b Chain-chain-
coupling via disproportionation after consumption of the
monomer may still have occurred. In order to further elucidate
this matter different polymer-fractions from a batch polymeri-
zation with catalyst C2 (catalyst/monomer ratio of 20:1; Figure 5B)
were separated via semipreparative GPC (see Figure S11 in the
Supporting Information). The individual polymer-fractions
exhibited number-average molecular weights of Mn = 20.5 kDa
(PDI = 1.06) and Mn = 42.8 kDa (PDI = 1.05), respectively, in
agreement with chain−chain-coupling after monomer consump-
tion. Notably, the very low PDIs of the individual batches would
indicate, that the polymerization process follows a well-controlled
chain-growth-process.
Attempts to further elucidate the polymerization process by
an analyses of the polymer-chain-end via mass spectrometry met
with mixed results. Polymeric species of up to m/z = 12 kDa
(batch: Mn,GPC = 8.6 kDa, catalyst C1, see Figure S12 in the
Supporting Information) could be observed at low resolution via
linear mode MALDI−ToF MS. The mass-spectra inadvertently
showed different types of polymeric species that could not be
assigned to specific end-groups due to the low resolution.
However, the incorporation of the precatalyst can be inferred
from NMR data, in combination with a model compound syn-
thesized via Negishi-coupling of two anisyl-moieties to monomer
1
1a (11, Scheme 2c). In H NMR spectra of o-anisyl-capped
polymers two characteristic singlets appear at 3.86 and 4.71 ppm,
that are attributed to the methoxy group of the anisyl end-group,
and the α-methylene group of the adjacent “head-to-head”-linked
thiazole ring (Figure 7a−c). The H NMR-spectrum of the
model compound (Figure 7d) shows two signals for the chemi-
Figure 7. 1H NMR spectra of batches of anisyl-capped PTzDIBO (a−c)
and model compound 11 (d).
1
cally inequivalent methoxy groups of the head-to-tail- and head-
to-head-linked anisole-rings at 4.01 and 3.86 ppm, respectively,
and a signal at 4.83 ppm assigned to the α-methylene group on
the thiazole ring. Using the signal of the methoxy group as
reference, the molecular weights of the respective polymer
samples were calculated (Figure 6A, see also Figure S13 in the
Supporting Information). The thus derived molecular weights for
low molecular weight fractions were in good agreement with the
ones determined via GPC, while at higher molecular weights
(>30 kDa) NMR gave higher molecular weights than GPC-
analyses. The good agreement of the 1H NMR-properties of the
model compound with the polymer samples clearly indicates
incorporation of the anisyl-moiety into the polymer. At this point,
we cannot confirm quantitative chain-end functionalization.
Indeed, small amounts of head-to-head-defects are clearly
present in low molecular weight batches (Figure 7c) that might
originate from initiation via the pathway outlined in Scheme 2a.
CONCLUSION
■
A synthetic access to reversed silyloxymethyl functionalized
thiazole-monomers has been developed, which can be poly-
merized via Kumada-coupling polycondensation to furnish
head-to-tail regioregular polythiazoles (rr-PTzs, PTzTIP,
PTzDIBO). Owing to the incorporation of highly solubilizing
diisobutyloctadecylsilyl-side-chains PTzDIBO is the first fully
soluble polythiazole, and readily gave number-average molec-
ular weights exceeding 100 kDa, corresponding to a degree of
polymerization greater than 200. The presence of the bulky
silyloxy side-chains affects the solid state structure of the polymers,
G
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(2) (a) Osaka, I.; McCullough, R. D. “Regioregular and
regiosymmetric polythiophenes. In Conjugated Polymer Synthesis;
Chujo, Y., Ed.; Wiley: New York, 2010, 59−90. (b) Osaka, I.;
McCullough, R. D. Advanced functional regioregular polythiophenes.
In Design and Synthesis of Conjugated Polymers; Leclerc, M.; Morin, J.-
F., Eds.; Wiley-VCH: Weinheim, Germany, 2010; pp 91−145.
(c) Perepichka, I. F.; Perepichka, D. F. Handbook of Thiophene-based
Materials: Applications in Organic Electronics and Photonics; Wiley:
Chichester, U.K., 2009. (d) Fichou, D. Handbook of Oligo- and
Polythiophenes; Wiley-VCH: Weinheim, Germany, 1999.
(3) (a) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. Rev.
2007, 107, 1339−1386. (b) McQuade, D. T.; Pullen, A. E.; Swager, T.
M. Chem. Rev. 2000, 100, 2537−2574.
(4) (a) Bryan, Z. J.; McNeil, A. J. Macromlecules 2013, 46, 8395−
8405. (b) Stefan, M. C.; Javier, A. E.; Osaka, I.; McCullough, R. D.
Macromolecules 2009, 42, 30−32. (c) Yokozawa, T.; Yokoyama, A.
Chem. Rev. 2009, 109, 5595−5619. (d) Osaka, I.; McCullough, R. D.
Acc. Chem. Res. 2008, 41, 1202−1214.
(5) (a) Grisorio, R.; Mastrorilli, P.; Suranna, G. P. Polym. Chem.
2014, DOI: 10.1039/C4PY00028E. (b) Yokozawa, T.; Suzuki, R.;
Nojima, M.; Ohta, Y.; Yokoyama, A. Macromol. Rapid Commun. 2011,
32, 801−806. (c) Elmalem, E.; Kiriy, A.; Huck, W. T. S.
Macromolecules 2011, 44, 9057−9061. (d) Yokoyama, A.; Suzuki, H.;
Kubota, Y.; Ohuchi, K.; Higashimura, H.; Yokozawa, T. J. Am. Chem.
Soc. 2007, 129, 7236−7237.
(6) (a) Tkachov, R.; Senkovskyy, V.; Komber, H.; Kiriy, A.
Macromolecules 2011, 44, 2006−2015. (b) Thelakkat, M.; Lohwasser,
R. H. Macromolecules 2011, 44, 3388−3397. (c) Senkovskyy, V.;
Sommer, M.; Tkachov, R.; Komber, H.; Huck, W. T. S.; Kiriy, A.
Macromolecules 2010, 43, 10157−10161. (d) Bronstein, H. A.;
Luscombe, C. K. J. Am. Chem. Soc. 2009, 131, 12894−12895.
(e) Boyd, S. D.; Jen, A. K.-Y.; Luscombe, C. K. Macromolecules 2009,
42, 9387−9389. (f) Loewe, R. S.; Ewbank, P. C.; Liu, J.; Zhai, L.;
McCullough, R. D. Macromolecules 2001, 34, 4324−4333.
and leads to a lesser prevalence of π-stacking and a widened
optical band gap, compared to 4-alkyl-substituted polythiazoles
(C9- and C13-PTz). Still, cyclic voltammetry indicates largely
similar electrochemical properties, in agreement with the
isoelectronic nature of the conjugated π-systems. The great
bulk of the side-chains required to render PTzDIBO soluble
is likely detrimental for the performance of the polymer in
organic electronic devices. Still, starting from the versatile
intermediate 6 other side-chains may be introduced that
furnish soluble PTzs better suited for device fabrication.
The investigation of the polymerization process through
batch polymerizations with externally initiating aryl-nickel
precatalyst indicated the presence of a chain-growth mecha-
nism, as evidenced by very low polydispersities and a linear
correlation between the obtained molecular weight and the
monomer/catalyst ratio. Furthermore, the incorporation of the
precatalyst-aryl moiety into the polymer chain could be proven
and the molecular weights could thereby be independently
derived via 1H NMR. The good correlation between molecular
weights derived from GPC and NMR corroborates both the
proposed initiation pathway and the presence of a chain-growth
mechanism. Given the very limited number of polyarenes that
can be accessed via quasi-living polycondensation, the likely
occurrence of chain-growth in the synthesis of head-to-tail
regioregular polythiazoles constitutes a significant progress in
the development of polymeric semiconductors.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details, additional analytical data, and crystallo-
graphic information. This material is available free of charge via
the Internet at http://pubs.acs.org.
(7) (a) Hollinger, J.; Jahnke, A. A.; Coombs, N.; Seferos, D. S. J. Am.
Chem. Soc. 2010, 132, 8546−8547. (b) Patra, A.; Wijsboom, Y. H.; Zade,
S. S.; Li, M.; Sheynin, Y.; Leitus, G.; Bendikov, M. J. Am. Chem. Soc. 2008,
130, 6734−6736. (c) Heeney, M.; Zhang, W.; Crouch, D. J.; Chabinyc, M.
L.; Gordeyev, S.; Hamilton, R.; Higgins, S. J.; McCulloch, I.; Skabara, P. J.;
Sparrowe, D.; Tierney, S. Chem. Commun. 2007, 5061−5063.
(8) Huang, L.; Wu, S.; Qu, Y.; Geng, Y.; Wang, F. Macromolecules
2008, 41, 8944−8947.
AUTHOR INFORMATION
■
Corresponding Author
*(F.P.) E-mail: frank.pammer@uni-ulm.de.
Notes
The authors declare no competing financial interest.
(9) Yokoyama, A.; Kato, A.; Miyakoshi, R.; Yokozawa, T.
Macromolecules 2008, 41, 7271−7273.
(10) (a) Lee, S. R.; Bloom, J. W. G.; Wheeler, S. E.; McNeil, A. J.
Dalton Trans. 2013, 42, 4218−4222. (b) Lee, S. R.; Bryan, Z. J.;
Wagner, A. M.; McNeil, A. J. Chem. Sci. 2012, 3, 1562−1566. (c) Lanni,
E. L.; Locke, J. R.; Gleave, C. M.; McNeil, A. J. Macromolecules 2011,
44, 5136−5145. (d) Lanni, E. L.; McNeil, A. J. Macromolecules 2010,
43, 8039−8044. (e) Miyakoshi, R.; Shimono, K.; Yokoyama, A.;
Yokozawa, T. J. Am. Chem. Soc. 2006, 128, 16012−16013.
(11) (a) Fukumoto, H.; Kimura, R.; Sasaki, S.; Kubota, K.;
Yamamoto, T. J. Polym. Sci., Part B: Polym. Phys. 2005, 43, 215−
222. (b) Yokozawa, T.; Nanashima, Y.; Ohta, Y. Macro Lett. 2012, 1,
862−866. (c) Nanashima, Y.; Yokoyama, A.; Yokozawa, T. J. Polym.
Sci. Part. A: Polym. Chem. 2012, 50, 1054−1061. (d) Nanashima, Y.;
Yokoyama, A.; Yokozawa, T. Macromolecules 2012, 45, 2609−2613.
(12) (a) Yokozawa, T.; Nanashima, Y.; Ohta, Y. ACS Macro Lett.
2012, 1, 862−866. (b) Senkovskyy, V.; Tkachov, R.; Komber, H.;
John, A.; Sommer, J.-U.; Kiriy, A. Macromolecules 2012, 45, 7770−
7777. (c) Senkovskyy, V.; Tkachov, R.; Komber, H.; John, A.;
Sommer, M.; Heuken, M.; Voit, B.; Huck, W. T. S.; Kataev, V.; Peter,
A.; Kiriy, A. J. Am. Chem. Soc. 2011, 133, 19966−19970.
ACKNOWLEDGMENTS
■
We thank Markus Lamla and Bettina Stockle for support with
̈
GPC measurements (THF), and Markus Wunderlin (Uni Ulm)
and Agnes Fizia (TU Kaiserslautern) for assistance with mass
spectrometry data collection. We also thank Harald Kelm and
Dirk Schaffner from the TU Kaiserslautern and Ullrich Ziegler
from Uni Ulm for support with NMR and CP-MAS NMR data
collection. This work was supported by the Alexander von
Humboldt foundation, the German Chemical Industry Fund
(FCI) (Feodor-Lynen research fellowship and Liebig Scholarship
to Frank Pammer), and the German Science Foundation (DFG).
REFERENCES
■
(1) (a) Inzelt, G. Conducting Polymers; Springer: Heidelberg,
Germany, 2008. (b) Freund, M. S.; Deore, B. Self-Doped Conducting
Polymers; Wiley: Chichester, U.K., 2007. (c) Skotheim, T. A.;
Reynolds, J. R. Handbook of Conducting Polymers, 3rd ed.; CRC
Press: Boca Raton, FL, 2007. (d) Hadziioannu, G.; Malliaras, G G.
Semiconducting Polymers; Wiley-VCH: Weinheim, Germany, 2007.
(e) Nalwa, H. S. Handbook of Conductive Organic Molecules and
Polymers; Wiley-VCH: Weinheim, Germany, 1997. (f) Kuzmany, H.;
Mehring, M.; Roth, S. Electronic Properties of Conjugated Polymers;
Springer: Berlin and Heidelberg, Germany, 1987.
(13) Bridges, C. R.; McCormick, T. M.; Gibson, G. L.; Hollinger, J.;
Seferos, D. S. J. Am. Chem. Soc. 2013, 135, 13212−13219.
(14) (a) Li, L.; Counts, K. E.; Kurosawa, S.; Teja, A. S.; Collard, D.
M. Adv. Mater. 2004, 16, 180−183. (b) Li, L.; Collard, D. M.
Macromolecules 2005, 38, 372−378. (c) Geng, Y.; Tajima, K.;
Hashimoto, K. Macromol. Rapid Commun. 2011, 32, 1478−1483.
H
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(15) Wen, L.; Duck, B. C.; Dastoor, P. C.; Rasmussen, S. C.
Macromolecules 2008, 41, 4576−4578.
(25) (a) Wong, M.; Hollinger, J.; Kozycz, L. M.; McCormick, T. M.;
Lu, Y.; Burns, D. C.; Seferos, D. S. ACS Macro Lett. 2012, 1, 1266−
1269. (b) Hiorns, R. C.; de Bettignies, R.; Leroy, J.; Bailly, S.; Firon,
M.; Sentein, C.; Khoukh, A.; Preud’homme, H.; Dagron-Lartigau, C.
Adv. Funct. Mater. 2006, 16, 2263−2273. (c) Liu, J.; Loewe, R. S.;
McCullough, R. D. Macromolecules 1999, 32, 5777−5785.
(26) Strotman, N. A.; Chobanian, H. R.; He, J.; Guo, Y.; Dormer, P.
G.; Jones, C. M.; Steves, J. E. J. Org. Chem. 2010, 75, 1733−1739.
(27) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176−
4211.
(28) PTzDIBO: 5.09 ppm at 25 °C and 5.11 ppm at 50 °C in
CDCl3; 5.27 ppm at 100 °C in ODCB-d4. PTzTIP: 5.28 ppm at 150
°C in ODCB-d4. PBTzTIP: 4.88 ppm at 25° in CDCl3; 5.00 ppm at
100 °C in ODCB-d4.
(16) Bronstein, H.; Hurhangee, M.; Fregoso, E. C.; Beatrup, D.; Soon,
Y. W.; Huang, Z.; Hadipour, A.; Tuladhar, P. S.; Rossbauer, S.; Sohn, E.;
Shoaee, S.; Dimitrov, S. D.; Frost, J. M.; Ashraf, R. S.; Kirchartz, T.;
Watkins, S. E.; Song, K.; Anthopoulos, T.; Nelson, J.; Rand, B. P.;
Durrant, J. R.; McCulloch, I. Chem. Mater. 2013, 25, 4239−4249.
(17) (a) Mamada, M.; Nishida, J.; Kumaki, D.; Tokito, S.; Yamashita,
Y. Chem. Mater. 2007, 19, 5404−5409. (b) Ando, S.; Murakami, R.;
Nishida, J.; Tada, H.; Inoue, Y.; Tokito, S.; Yamashita, Y. J. Am. Chem.
Soc. 2005, 127, 14996−14997. (c) Akhtaruzzaman, M.; Kamata, N.;
Nishida, J.; Ando, S.; Tada, H.; Tomurab, M.; Yamashita, Y. Chem.
Commun. 2005, 3183−3185.
(18) Lin, Y.; Fan, H.; Li, Y.; Zhan, X. Adv. Mater. 2012, 24, 3087−3106.
(19) Current examples: (a) Saeki, A.; Tsuji, M.; Yoshikawa, S.; Gopal,
A.; Seki, S. J. Mater. Chem. A 2014, 17, 6075−6080. (b) Osaka, I.;
Saito, M.; Koganezawa, T.; Takimiya, K. Adv. Mater. 2014, 26, 331−
338. (c) Ren, G.; Schlenker, C. W.; Ahmed, E.; Subramaniyan, S.;
Olthof, S.; Kahn, A.; Ginger, D. S.; Jenekhe, S. A. Adv. Funct. Mater.
2013, 23, 1238−1249. (d) Intemann, J. J.; Mike, J. F.; Cai, M.; Barnes,
C. A.; Xiao, T.; Roggers, R. A.; Shinar, J.; Shinar, R.; Jeffries-El, Ma. J.
Polym. Sci., Part A: Polym. Chem. 2013, 51, 916−923. (e) Itaru, O.;
Masahiko, S.; Hiroki, M.; Tomoyuki, K.; Kazuo, T. Adv. Mater. 2012,
24, 425−430. (f) Lu, W.; Kuwabara, J.; Kanbara, T. Polym. Chem.
2012, 3, 3217−3219. (g) Zhang, M.; Fan, H.; Guo, X.; Yang, Y.; Wang,
S.; Zhang, Z.-G.; Zhang, J.; Zhan, X.; Li, Y. J. Polym. Sci., Part A: Polym.
Chem. 2011, 49, 2746−2754. (h) Yamamoto, T.; Otsuka, S.-I.;
Fukumoto, H.; Sakai, Y.; Aramaki, S.; Fukudo, T.; Emoto, A.;
Ushijima, H. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 1508−1512.
(i) Allard, N.; Beaupre, S.; Badrou, R.; Najari, A.; Tao, Y.; Leclerc, M.
Macromolecules 2011, 44, 7184−7187. (j) Kudla, C. J.; Dolfen, D.;
Schottler, K. J.; Koenen, J.-M.; Breusov, D.; Allard, S.; Scherf, U.
Macromolecules 2010, 43, 7864−7867.
(20) (a) Mori, S.; Yamamoto, T.; Asakawa, N.; Yazawa, K.; Inoue, Y.
Polym. J. 2008, 40, 475−478. (b) Mori, S.; Inoue, Y.; Yamamoto, T.;
Asakawa, N. Phys. Rev. B 2005, 71, 054205−054205−11. (c) Yama-
moto, T.; Komarudin, D.; Arai, M.; Lee, B.; Suganuma, H.; Asakawa,
N.; Inoue, Y.; Kubota, K.; Sasaki, S.; Fukuda, T.; Matsuda, H. J. Am.
Chem. Soc. 1998, 120, 2047−2058. (d) Yamamoto, T.; Suganuma, H.;
Maruyama, T.; Inoue, T.; Muramatsu, Y.; Arai, M.; Komarudin, D.;
Ooba, N.; Tomaru, S.; Sasaki, S.; Kubota, K. Chem. Mater. 1997, 9,
1217−1225. (e) Yamamoto, T.; Suganuma, H.; Maruyama, T.;
Kubota, K. J. Chem. Soc., Chem. Commun. 1995, 1613−1614.
(29) Chen, T.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117,
233−244.
(30) Pammer, F.; Guo, F.; Lalancette, R. A.; Jakle, F. Macromolecules
̈
2012, 45, 6333−6343.
(31) Yamamoto, T.; Komarudin, D.; Arai, M.; Lee, B.-L.; Suganuma,
H.; Asakawa, N.; Inoue, Y.; Kubota, K.; Sasaki, S.; Fukuda, T.;
Matsuda, H. J. Am. Chem. Soc. 1998, 120, 2047−2058.
(32) (a) Cook, S.; Furube, A.; Katoh, R. Energy Environ. Sci. 2008, 1,
294−299. (b) Li, Y.; Vamvounis, G.; Holdcroft, S. Macromolecules
2002, 35, 6900−6906.
(33) (a) Panzer, F.; Bassler, H.; Lohwasser, R.; Thelakkat, M.;
̈
Kohler, A. J. Phys. Chem. Lett. 2014, 5 (15), 2742−2747. (b) Adachi,
̈
T.; Brazard, J.; Ono, R. J.; Hanson, B.; Traub, M. C.; Wu, Z.-Q.; Li, Z.;
Bolinger, J. C.; Ganesan, V.; Bielawski, C. W.; Vanden Bout, D. A.;
Barbara, P. F. J. Phys. Chem. Lett. 2011, 2, 1400−1404.
(34) Zhou, G.; Qian, G.; Ma, L.; Cheng, Y.; Xie, Z.; Wang, L.; Jing,
X.; Wang, F. Macromolecules 2005, 38, 5416−5424.
(35) Nehls, B. S.; Fuldner, S.; Preis, E.; Farrell, T.; Scherf, U.
̈
Macromolecules 2005, 38, 687−694.
(36) (a) Huang, H.; Zhou, N.; Ortiz, R. P.; Chen, Z.; Loser, S.;
́
Zhang, S.; Guo, X.; Casado, J.; Lopez Navarrete, J. T.; Yu, X.;
Facchetti, A.; Marks, T. J. Adv. Funct. Mater. 2014, 3016−3028.
(b) Guo, X.; Quinn, J.; Chen, Z.; Usta, H.; Zheng, Y.; Xia, Y.; Hennek,
J. W.; Ortiz, R. P.; Marks, T. J.; Facchetti, A. J. Am. Chem. Soc. 2013,
135, 1986−1996. (c) Guo, X.; Ortiz, R. P.; Zheng, Y.; Kim, M.-G.;
Zhang, S.; Hu, Y.; Lu, G.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc.
2011, 133, 13685−13697. (d) Guo, X.; Kim, F. S.; Jenekhe, S. A.;
Watson, M. D. J. Am. Chem. Soc. 2009, 131, 7206−7207. (e) Roncali,
J.; Blanchard, P.; Frere, P. J. Mater. Chem. 2005, 15, 1589−1610.
(37) Zoombelt, A. P.; Leenen, M. A. M.; Fonrodona, M.; Wienk, M.
M.; Janssen, R. A. J. Thin Solid Films 2008, 516, 7176−7180.
(38) Fontana, L.; Vinh, D. Q.; Santoro, M.; Scandolo, S.; Gorelli, F.
A.; Bini, R.; Hanfland, M. Phys. Rev. B 2007, 75, 174112 (1−11).
(39) (a) Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J.
R. J. Am. Chem. Soc. 2006, 128, 12714−12725. (b) Hansen, W. N.;
Hansen, G. J. Phys. Rev. A: At., Mol., Opt. Phys. 1987, 36, 1396−1402.
(c) Pavlishchuk, V. V.; Addison, A. W. Inorg. Chim. Acta 2000, 298,
97−102.
(21) (a) Politis, J. K.; Curtis, M. D.; Gonzal
́
ez-Ronda, L.; Martin, D.
ez-Ronda, L.;
C. Chem. Mater. 2000, 12, 2798−2804. (b) Gonzal
́
Martin, D. C.; Nanos, J. I.; Politis, J. K.; Curtis, M. D. Macromolecules
1999, 32, 4558−4565. (c) Politis, J. K.; Somoza, F. B., Jr.; Kampf, J.
́
W.; Curtis, M. D.; Gonzalez-Ronda, L.; Martin, D. C. Chem. Mater.
1999, 11, 2274−2284. (d) Politis, J. K.; Curtis, M. D.; He, Y.; Kanicki,
J. Macromolecules 1999, 32, 2484−2489. (e) Curtis, M. D.; Cheng, H.;
́
Johnson, J. A.; Nanos, J. I.; Kasim, R.; Elsenbaumer, R. L.; Gonzalez-
Ronda, L.; Martin, D. C. Chem. Mater. 1998, 10, 13−16. (f) Nanos, J.
I.; Kampf, J. W.; Curtis, M. D. Chem. Mater. 1995, 7, 2232−2234.
(22) Pammer, F.; Passlack, U. ACS Macro Lett. 2014, 3, 170−174.
(23) Molecular weights were determined via GPC in CHCl3 at 35 °C
relative to polystyrene standards. GPC-analyses of PTzDIBO with
THF as eluent gave higher molecular weights than GPC in CHCl3.
(e.g., batches polymerized with Ni(dppe)Cl2 gave Mn = 122.6 kDa,
(PDI = 1.43) and 97.8 kDa, (PDI = 1.26), when analyzed in THF,
while in CHCl3 Mn = 60.7 (PDI = 1.50) and 44.5 kDa (PDI = 1.52)
were measured for the same samples. For the soluble fraction of
PTzTIP the maximum Mn observed in THF was 3.5 kDa (PDI =
1.44), as compared to 2.7 kDa (PDI = 1.30) measured in CHCl3.
(24) Molecular weight determination of rod-like conjugated
polymers vs coil-like polystyrene standards leads to overestimation
of the apparent molecular weight (see literature included in ref 25 for
details). The authors are aware of this systemic deviation. However,
barring alternative means to determine the molecular weight,
uncorrected molecular weights are reported.
(40) (a) Chavez, C. A.; Choi, J.; Nesterov, E. E. Macromolecules 2014,
47, 506−516. (b) Smeets, A.; Willot, P.; De Winter, J.; Gerbaux, P.;
Verbiest, T.; Koeckelberghs, G. Macromolecules 2011, 44, 6017−6025.
(c) Komber, H.; Senkovskyy, V.; Tkachov, R.; Johnson, K.; Kiriy, A.;
Huck, W. T. S.; Sommer, M. Macromolecules 2011, 44, 9164−9172.
(d) Tkachov, R.; Senkovskyy, V.; Komber, H.; Sommer, J.-U.; Kiriy, A.
J. Am. Chem. Soc. 2010, 132, 7803−7810. (e) Doubina, N.; Stoddard,
M.; Bronstein, H. A.; Jen, A. K.-Y.; Luscombe, C. K. Macromol. Chem.
Phys. 2009, 210, 1966−1972. (f) Senkovskyy, V.; Khanduyeva, N.;
Komber, H.; Oertel, U.; Stamm, M.; Kuckling, D.; Kiriy, A. J. Am.
Chem. Soc. 2007, 129, 6626−6632.
(41) Ortho-substituted nickel−aryl complexes are generally found to
be more stable than unsubstituted derivatives. See also (a) Hidai, M.;
Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet. Chem. 1971, 30,
279−282. (b) Chatt, J.; Shaw, B. L. J. Chem. Soc. 1960, 1718−1729.
(42) Achord, B. C.; Rawlins, J. W. Macromolecules 2009, 42, 8634−
8639.
I
dx.doi.org/10.1021/ma501213g | Macromolecules XXXX, XXX, XXX−XXX