Design and synthesis of new polymeric materials for organic nonvolatile electrical bistable storage devices: Poly(biphenylmethylene)s

Article abstract of DOI:10.1021/ma049572k

The synthesis of new polymers, poly(biphenylmethylene)s, derived from bistriflates of bisphenol-type monomers, by Ni(0)-mediated polymerization has been presented. These polymers are interesting because of the nature of the polymer backbone that contains

Full text of DOI:10.1021/ma049572k

Macromolecules 2005, 38, 4147-4156
4147
Design and Synthesis of New Polymeric Materials for Organic
Nonvolatile Electrical Bistable Storage Devices:
Poly(biphenylmethylene)s
Matthias Beinhoff,† Luisa D. Bozano,† J. Campbell Scott,† and
Kenneth R. Carter*,‡
Polymer Science & Engineering Department, University of Massachusetts Amherst, Conte Center for
Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, and IBM Almaden Research
Center, NSF Center for Polymeric Interfaces and Macromolecular Assemblies, 650 Harry Road,
San Jose, California 95120-6099
Received March 3, 2004; Revised Manuscript Received December 9, 2004
ABSTRACT: The synthesis of new polymers, poly(biphenylmethylene)s, derived from bistriflates of
bisphenol-type monomers, by Ni(0)-mediated polymerization has been presented. These polymers are
interesting because of the nature of the polymer backbone that contains biphenyl units separated by
substituted methylene units. The solubility, mechanical properties, and electrical properties of the polymers
can be altered by proper selection of the methylene substituents. Polymers and oligomers had molecular
weights ranging from 2000 to 15 000 g/mol, as measured by calibrated gel permeation chromatography
(GPC), though light scattering and MALDI studies indicate that GPC tends to underestimate the molecular
weights of these polymers. The polymers have Tg’s between 230 and 300 °C and have thermal stabilities
ranging from 400 to 493 °C. Thermally cross-linkable, 4-phenylethenyl end-capped oligomers were
synthesized and fabricated into thin-film electronic devices, and preliminary results on their characteriza-
tion are discussed. The unique structure of the polymer backbone makes these materials potentially
interesting in electrical applications where large-band-gap polymers with good electron/hole mobility and
good thermal and oxidative stability are required.
Introduction
workers investigated Ni-catalyzed homo- and cross-
coupling reactions of various aromatic sulfonates, with
the triflate group as the most reactive leaving group.8
The optimized methodology was applied in Ni-catalyzed
step-growth polymerizations of selected bissulfonates of
hydroquinones.9-12
Another widely used protocol in the synthesis of PPPs
and related polymers, especially PFs, is the Ni-mediated
Yamamoto-type polycondensation of bishalogen mono-
mers.5,6 For the polymerization of dibromofluorenes,
polymers with a very high Mn of 30 000 up to 200 000
g/mol were reported.13 Conventional external heating14
and microwave-assisted15 procedures are readily avail-
able.
Both Ni-catalyzed and Ni-mediated reaction schemes
take advantage of the fact that only one monomer (AA-
type monomer) is needed, unlike the Suzuki polycon-
densation that requires either two monomers (AA- and
BB-type monomers) or a monomer carrying two differ-
ent leaving groups (AB-type monomer), which may
require application of precise stoichiometry and exten-
sive monomer synthesis and purification. However, one
reason Ni-based polycondensations are not applied more
often is the lower molecular weight sometimes obtained
when the leaving group carries an ortho substituent
other than hydrogen.8
Thermally cross-linkable semiconducting polymers
were introduced in recent years.16-18 Functionalized
with thermally polymerizable endgroups such as 4-phen-
ylethenyl, thin films of these materials were fashioned
into electronic devices by spin-coating. Thermal treat-
ment of these films renders them insoluble in common
organic solvents, allowing for coating of successive
polymer layers. This method of device fabrication can
have an advantageous effect on the properties of the
The modern electronics industry has an ever-increas-
ing demand for polymeric materials with new or fine-
tuned properties. Most research is devoted to conjugated
polymers that are, for example, applied as semiconduc-
tors1 or in electroluminescent devices,2 and the synthe-
sis of these materials is often a challenge for chemists.
Within the past decade, many polymers containing
conjugated phenyl groups such as poly(p-phenylene)s
(PPPs), polyfluorenes (PFs), and poly(phenylene-eth-
enylene)s (PPEs) have been synthesized. Various tran-
sition-metal-catalyzed step-growth polymerization tech-
niques (Suzuki,3,4 Yamamoto,5,6 Haghihara/Sonoga-
shira7) were utilized successfully. Monomers with aro-
matic bromides are utilized in most cases, less often aryl
iodides, chlorides, and sulfonates, and polymers with
Mn e 10 000 g/mol are generally obtained, which have
been found to be sufficient for most applications.
The use of halogenated aromatic monomers is limited
by their availability. Often their preparation by direct
halogenation of aryl substrates results in the formation
of several regioisomers, polyhalogenation, and purifica-
tion can be a tedious task. The leaving group ability
generally increases from chloride to bromide to iodide.
Sulfonates, however, are an attractive alternative to the
halides. They can conveniently be prepared from a
myriad of commercially available phenol derivatives,
and they show reactivity in the range of analogous
bromide and iodides. In model studies, Percec and co-
* Author to whom correspondence should be addressed.
Phone: 413-577-1416. Fax: 413-545-0082. E-mail: krcarter@
polysci.umass.edu.
† IBM Almaden Research Center.
‡ University of Massachusetts Amherst.
10.1021/ma049572k CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/09/2005

4148 Beinhoff et al.
Macromolecules, Vol. 38, No. 10, 2005
endcapping reactions, cross-linkable materials were also
prepared. The thermal, optical, and mechanical proper-
ties of representative examples were investigated. Se-
lected cross-linkable oligomers were fabricated into
electronic test devices, and preliminary results of their
characterization are presented.
Experimental Section
Materials. Phenol (1), cyclododecanone (2), bisphenol A
(3a), hexafluorobisphenol A (4,4′-hexafluoroisopropylidene)-
bisphenol (3b), bisphenol TP (4,4′-(diphenylmethylidene)-
bisphenol (3c), 4,4′-(9H-fluoren-9-ylidene)bisphenol (3d), bisphe-
nol Z (4,4′-cyclohexylidenebisphenol (3e), trifluoromethane
sulfonic anhydride (triflic anhydride), 4-bromostyrene (6), 2,2′-
bipyridyl, and 1,5-cyclooctadiene were purchased from Aldrich
or TCI and used without further purification. The active Ni-
(0) coupling reagent, bis(1,5-cyclooctadiene)nickel(0), was pur-
chased from Strem Chemicals and handled under inert
atmosphere. Pyridine was used as received. Anhydrous toluene
and dimethylformamide (DMF) were stored and used in a
glovebox. All nickel-mediated cross-coupling reactions were
carried out under oxygen-free conditions. 4,4′-Cyclodode-
cylidenebisphenol27 (3f) and bis-4-trifluoromethanesulfonyl-
oxyphenylsulfone (4g)28 are each mentioned in the literature,
though insufficient experimental and characterization data are
available; therefore, their preparation and characterization are
described in full detail. Poly{[1,1′-biphenyl]-4,4′-diyl-[2,2,2-
trifluoro-1-(trifluoromethyl)ethylidene]} (5b) was prepared in
a different way than in the reference.22 All other compounds
are new. Previously published protocols were utilized for Ni-
(0)-mediated polymerizations: both conventional heating14 and
microwave assisted.15
Microwave Reactor. The microwave heating was per-
formed in a SmithCreator single-mode microwave cavity
producing continuous radiation at a frequency of 2.45 GHz
(Personal Chemistry, Inc.). Reactions were conducted under
nitrogen in 9 mL, heavy-walled Pyrex glass reaction vials
sealed with aluminum crimp caps fitted with a silicone septum.
Reaction mixtures were stirred internally with a magnetic stir
bar during the irradiation. Reaction times and temperatures
are operator selectable. Reaction temperature is constantly
monitored by infrared thermometry on the outer surface of
the reaction vial, the pressure by a transducer on the top of
the vial’s septum, and the microwave output power is auto-
matically adjusted by the software algorithm to maintain
programmed temperature profiles. The instrument’s upper
operating limits are 250 °C and 25 bar. After the irradiation
period, the reaction vessel is cooled rapidly to ambient tem-
perature (and pressure) by compressed air (gas jet cooling).
Characterization. All NMR spectra were acquired at 22
°C on a Bruker AF 400 (400 MHz) spectrometer and internally
referenced via residual solvent signal (CHCl3: 1H, δ ) 7.24
ppm; 13C, δ ) 77.00 ppm; THF: 1H, δ ) 1.73; 3.58 ppm;
DMSO: 1H, δ ) 2.50 ppm). 19F NMR chemical shifts were
internally referenced to hexafluorobenzene (19F, δ ) -164.9
ppm). All chemical-shift values are given in ppm. 19F NMR
experiments were run with a relaxation delay time of 10 s per
pulse. Gas chromatography/mass spectrometry (GC-MS) was
performed using an Agilent 6890 Series GC (equipped with a
30 m HP-5MS column) interfaced with a HP 5973 mass-
selective detector. Gel permeation chromatography (GPC) was
performed on a Waters chromatograph (four Waters Styragel
HR columns HR1, HR2, HR4, and HR5E in series) connected
to a Waters 410 differential refractometer with THF as the
eluent. Molecular weight standards were narrow polydisper-
sity polystyrenes. Thermal gravimetric analysis was performed
using a Perkin-Elmer TGS-2, under nitrogen atmosphere with
a heating rate of 10 °C/min. A TA Instruments 2920 MDSC
was used to perform modulated differential scanning calori-
metric (MDSC) measurements. Samples were scanned under
nitrogen from -50 to 250 °C at a rate of 4 °C/min and a rate
modulation of 1 °C. Glass transition temperatures (Tg’s) were
determined by the inflection point of the complex heat capacity
Figure 1. Structural comparison of polyfluorene (above;
repeating unit length: 8.4 Å, bTb) and poly(biphenylmeth-
ylene) (below; repeating unit length: 10.3 Å, bTb).
resulting materials. Cross-linkable polyfluorenes, for
example, were found to exhibit less aggregation and
excimer emission compared to their un-cross-linked
analogues.16,17
In the development of nonvolatile organic memory,
which involves electrical characterization of thin-film
devices,19,20 wide-band-gap materials that possess good
electron/hole transport properties are needed. The
reason that well-known semiconducting polymers such
as polyfluorene and polythiophene do not work while
other wide band gap materials perform quite well is a
matter of current study.21 We therefore desired to
further explore a new class of processable oligomers and
polymers, namely poly(biphenylmethylene)s. This work
was inspired by a publication by Sheares and co-
workers22 who have reported hexafluoromethyl-substi-
tuted poly(biphenylmethylene)s. This class of macro-
molecules has a high content of aromatic units, consisting
of short, conjugated biphenyl segments bridged by
nonconjugated methylene units. Its structure is slightly
similar to polyphenylenes such as polyfluorene, as
depicted in Figure 1. One difference is the missing
carbon-carbon bond between two phenyl rings in the
fluorene five-membered ring. The second is the varying
substitution pattern of the methylene group. Whereas
in polyfluorene it occurs in the meta position the
methylene substituent (2,7 bond), in poly(biphenylm-
ethylene)s the para positions are connected (1,1′ bond).
In contrast to polyfluorene, the methylene group intro-
duces a kink into the backbone of an otherwise semirigid
poly(biphenylmethylene) backbone, increasing the de-
grees of freedom. Though a methylene unit interrupts
the conjugation between two biphenyl groups, such
polymeric material may have interesting electronic
properties. It has been suggested that 2,2-diphenylpro-
panes in the butterfly conformation have a spatial
overlap between the p atomic orbitals on the phenyl
carbon atoms adjacent to the bridge.23 These structural
characteristics should have a strong influence on the
material’s properties such as solubility, morphology, and
electronic behavior. Specifically, we were motivated to
explore these materials for the development of new
organic bistable devices where wide-band-gap materials
with low intrinsic electrical conduction perform best.24,25
To the best of our knowledge, such polymers have not
yet been reported in the literature with the exception
of the mentioned report,22 and the suggestion in a patent
of similar structures.26
Herein we report on the monomer and polymer
synthesis of a variety of poly(biphenylmethylene)s,
carrying different substituents, applying Yamamoto-
type polycondensation conditions. Through controlled

Macromolecules, Vol. 38, No. 10, 2005
Design and Synthesis of New Polymeric Materials 4149
(Cp). Thermal-mechanical analysis (DMA) was performed on
a DMA 983 from TA Instruments. Samples were scanned from
-50 to 250 °C at a rate of 5 °C/min under nitrogen. The Tg
was determined by the maximum of loss tangent (tan δ). UV/
vis absorption spectra were recorded using a Perkin-Elmer
UV-vis spectrometer Lambda 9 or HP 8452A diode array
spectrometer. Fluorescence was measured using a SA Instru-
ments FL3-11 fluorimeter. Spectra were taken from spun-cast
films on 1 in. quartz wafers. Polymer films were prepared on
precleaned quartz substrates, and spectroscopic measurements
were performed in air. Current voltage characteristics were
measured under a nitrogen atmosphere using a computer
interfaced Keithley Source-Measure Unit Model 238. The
devices were tested at room temperature for DC measurements
and in the pulse mode of the source-measure unit.
Device Fabrication and Characterization. Thin film
test devices were prepared using 1 in. square glass substrates
that were pre-patterned with indium tin oxide (ITO) (Thin
Solid Films, Inc., sputtered ITO, 1500 Å). Before the device
fabrication, the substrates were first washed with DI water,
then IPA, and finally dried for 10 min in an oven. The ITO
substrates were then treated with oxygen plasma for 45 min
to remove any additional organic residues. After the cleaning
process, the substrates were moved into a nitrogen atmosphere
drybox for all subsequent processing and electrical character-
ization. The polymer layers were prepared by spin-coating from
THF or p-xylene solutions of approximately 5-10 wt% solids.
Different spin speeds were used to control the thickness of the
films, which were measured independently by AFM. Solvent
removal and cross-linking of 4-phenylethenyl-encapped ma-
terials were induced by treatment at 150 °C for 1 h. All
subsequent metal-layer evaporations were carried out at a
pressure of 10-6 Torr. A calibrated crystal quartz monitor was
used to control the thickness of the layers. During the
deposition, the samples were rotated to ensure uniformity of
thickness. Each substrate holds six test areas that were 3.12
mm2 in size. All subsequent electrical characterization was
performed in a tandem drybox to avoid exposing the devices
to air.
Synthesis. 4,4′-Cyclododecylidenebisphenol (3f). Method (a).
Hydrogen chloride was bubbled through a stirred mixture of
phenol (1) (7.70 g, 81.82 mmol, 5.20 equiv), cyclododecanone
(2) (2.85 g, 15.63 mmol), and mercaptoacetic acid (0.20 mL,
2.88 mmol, 0.18 equiv) for 15 min at 40 °C. Upon being stirred
at room temperature, the reaction mixture solidified overnight.
Ethyl acetate (30 mL) was added, and the mixture was
neutralized by addition of diluted aqueous sodium hydroxide.
The phases were separated, the aqueous one was extracted
with ethyl acetate, the combined organic layers were dried over
MgSO4, filtered, and the solvent was evaporated. The residue
was purified by column chromatography on silica gel (hexanes/
ethyl acetate ) 5:1 f 2:1). The resulting oil was recrystallized
from methanol to yield 4.11 g (75%) of 3f as a colorless solid.
Method (b). To a stirred solution of acetic acid (3.0 mL),
sulfuric acid (96%, 2.5 mL) and mercaptoacetic acid (0.20 mL,
2.88 mmol, 0.19 equiv), phenol (7.3 g, 77.68 mmol, 5.01 equiv)
and cyclododecanone (2.83 g, 15.52 mmol) were added at 0 °C.
The reaction mixture solidified after 1.5 h and was let stand
overnight. After workup and purification (see Method (a)), 4.21
g of bisphenol 3f was obtained (77%). mp ) 206 °C (207-208.5
°C);27 Rf ) 0.16 (hexanes/EtOAc ) 4:1); 1H NMR (400 MHz) δ
7.00 (d, 3J ) 8.7 Hz, 4H), 6.69 (d, 3J ) 8.7 Hz, 4H), 4.48 (s, br,
1H, OH), 1.97 (m, br, 4H), 1.27-1.33 (m, 14H), 0.90 (m, br,
4H); 13C NMR (101 MHz) δ 152.9, 142.4, 128.7, 114.4, 47.2,
33.3, 26.5, 26.2, 22.2, 22.0, 20.0; Anal. Calcd for C24H32O2
(352.51): C, 81.77; H, 9.15. Found: C, 81.85; H, 9.06.
acid, dried over MgSO4, filtered, and the solvent was evapo-
rated. The residue was purified by column chromatography
on silica gel (hexanes/ethyl acetate ) 9:1). Recrystallization
from CH2Cl2/hexanes afforded 7.34 g (95%) of 4f. The GC-MS
spectrum showed a single peak with the mass 467 au, which
corresponds to [M-OSO2CF3]+. Colorless solid; mp ) 91 °C; Rf
1
) 0.86 (hexanes/EtOAc ) 10:1); H NMR (400 MHz) δ 7.20-
7.10 (m, 8H), 1.99 (m, br, 4H), 1.31 (m, br, 14H), 0.82 (m, br,
4H); 13C NMR (101 MHz) δ 149.3, 147.5, 129.3, 120.7, 118.9
(q, J {C,F} ) 321 Hz, CF3), 48.4, 33.2, 26.3, 26.0, 22.1, 21.8,
18.8; 19F NMR (376 MHz) δ -76.1; Anal. Calcd for C26H30F6O6S2
(616.64): C, 50.64; H, 4.90. Found: C, 50.36; H, 4.86.
2,2-Bis(4-trifluoromethanesulfonyloxyphenyl)propane (4a).
Yield: 93% (6.88 g); colorless solid; mp ) 57 °C (58-59 °C);29
3
3
1H NMR (400 MHz) δ 7.27 (d, J ) 8.9 Hz, 4H), 7.18 (d, J )
8.9 Hz, 4H), 1.68 (s, 6H); 13C NMR (101 MHz) δ 150.2, 147.7,
128.6, 121.0, 118.7 (q, J {C,F} ) 321 Hz, CF3), 42.8, 30.7; 19
NMR (376 MHz) δ -76.0; C20H18F6O6S2 (532.48).
F
2,2-Bis(4-trifluoromethanesulfonyloxyphenyl)hexafluoro-
propane (4b). Yield: 95% (7.99 g); colorless needles; mp ) 97-
98 °C (97.5-98.5 °C);30,31 Rf ) 0.80 (hexanes/EtOAc ) 10:1);
1H NMR (400 MHz) δ 7.47 (d, 4H), 7.32 (d, 4H); 13C NMR (101
MHz) δ 149.9, 133.1, 132.2, 123.6 (q, J {C,F} ) 286 Hz, C-CF3),
121.6, 118.7 (q, J {C,F} ) 322 Hz, SO2-CF3), 64.0 (septet, J
{C,F} ) 26 Hz, C-CF3); 19F NMR (376 MHz) δ -75.9 (s, 6F,
SO2-CF3), -67.0 (s, 6F, C-CF3); Anal. Calcd for C17H8F12O6S2
(600.36): C, 34.01; H, 1.34. Found: C, 34.14; H, 1.44.
Bis-4-trifluoromethanesulfonyloxyphenyl-bisphenylmeth-
ane (4c). Yield: 91% (4.68 g); recrystallyzed from CH2Cl2/
hexanes; colorless solid; mp ) 121 °C; Rf ) 0.72 (hexanes/
EtOAc ) 10:1); 1H NMR (400 MHz) δ 7.30-7.21 (m, 10H), 7.21
3
3
(d, J ) 8.8 Hz, 4H), 7.15 (d, J ) 8.8 Hz, 4H); 13C NMR (101
MHz) δ 147.8, 146.6, 145.2, 132.7, 130.8, 128.0, 126.7, 120.5,
118.7 (q, J {C,F} ) 321 Hz, CF3), 64.3; 19F NMR (376 MHz) δ
-76.0; Anal. Calcd for C27H18F6O6S2 (616.55): C, 52.60; H,
2.94. Found: C, 52.46; H, 2.99.
9,9-Bis(4-trifluoromethanesulfonyloxyphenyl)fluorene (4d).
Yield: 94% (16.65 g); colorless crystals; mp ) 154-155 °C; Rf
) 0.58 (hexanes/EtOAc ) 10:1); 1H NMR (400 MHz) δ 7.79 (d,
3J ) 7.6 Hz, 2H), 7.42-7.38 (m, 2H), 7.33-7.28 (m, 4H), 7.24
3
3
(d, J ) 8.9 Hz, 4H), 7.13 (d, J ) 8.9 Hz, 4H); 13C NMR (101
MHz) δ 149.6, 148.5, 145.8, 140.0, 129.8, 128.2, 125.9, 121.3,
120.7, 120.5 118.7 (q, J {C,F} ) 321 Hz, CF3), 64.4; 19F NMR
(376 MHz) δ -76.0; Anal. Calcd for C27H16F6O6S2 (614.54): C,
52.77; H, 2.62. Found: C, 52.79; H, 2.70.
1,1-Bis(4-trifluoromethanesulfonyloxyphenyl)cyclohexane (4e).
Yield: 96% (16.71 g); recrystallyzed from CH2Cl2/hexanes;
colorless needles; mp ) 70 °C; Rf ) 0.76 (hexanes/EtOAc )
10:1); 1H NMR (400 MHz) δ 7.30 (d, 3J ) 8.9 Hz, 4H), 7.17 (d,
3J ) 8.9 Hz, 4H), 2.24 (m, 4H), 1.51 (m, 6H); 13C NMR (101
MHz) δ 148.2, 147.5, 129.0, 121.2, 118.7 (q, J {C,F} ) 321 Hz,
CF3), 46.0, 37.2, 26.0, 22.0; 19F NMR (376 MHz) δ -76.0; Anal.
Calcd for C20H18F6O6S2 (532.48): C, 45.11; H, 3.41. Found: C,
45.34; H, 3.42.
Bis-4-trifluoromethanesulfonyloxyphenylsulfone (4g). Yield:
96% (7.38 g); recrystallized from CH2Cl2/hexanes; long, color-
less needles; mp ) 115 °C; Rf ) 0.57 (hexanes/EtOAc ) 4:1);
3
3
1H NMR (400 MHz) δ 8.05 (d, J ) 8.9 Hz, 4H), 7.43 (d, J )
8.9 Hz, 4H); 13C NMR (101 MHz) δ 152.7, 140.9, 130.4, 122.8,
118.6 (q, J {C,F} ) 321 Hz, CF3); 19F NMR (376 MHz) δ -76.0;
Anal. Calcd for C14H8F6O8S3 (514.40): C, 32.69; H, 1.59.
Found: C, 32.47; H, 1.56.
Typical Procedure for the Homopolymerization of Bistriflates
4a-g to Polymers 5a-g Carrying Triflate Endgroups (See
Table 1 for Yields, Mn, PDI, DP, Decomposition Temperatures,
and Tg). Poly{[1,1′-biphenyl]-4,4′-diyl-[2,2,2-trifluoro-1-(trif-
luoromethyl)ethylidene]} (5b).
Method (a): Conventional External Heating. A solution of
bis(1,5-cyclooctadiene)nickel(0) (894 mg, 3.3 mmol), 2,2′-bipy-
ridyl (528 mg, 3.4 mmol), and 1,5-cyclooctadiene (0.40 mL, 3.3
mmol) in degassed anhydrous toluene (10 mL) and DMF (10
mL) was stirred at 80 °C for 30 min. Via a cannula, a solution
of 4b (874 mg, 1.46 mmol) in degassed anhydrous toluene (40
mL) was then added. After the mixture was stirred for 24 h
at 80 °C, the resulting dispersion was poured into a vigorously
Typical Procedure for the Synthesis of Bistriflates 4a-g. 1,1′-
Bis(4-trifluoromethanesulfonyloxyphenyl)cyclododecane (4f).
To a solution of 4,4′-cyclododecylidenebisphenol (3g) (4.45 g,
12.60 mmol) in pyridine (40 mL) was added trifluoromethane-
sulfonic acid anhydride (6.40 mL, 37.91 mmol, 3.0 equiv)
within 30 min at 0 °C. The brownish solution was stirred at
room temperature overnight. Pyridine was distilled off under
reduced pressure, and the residue was dissolved in ethyl
acetate. The solution was washed with diluted hydrochloric

4150 Beinhoff et al.
Macromolecules, Vol. 38, No. 10, 2005
Table 1. Experimental Data of Homopolymers 5
methoda
monomerb
polymerc
yieldd (%)
Mne (g/mol)
PDIf
DPg
Tgh (°C)
decompi (°C)
a
4a
4b
4c
4d
4e
4f
4g
4a
4b
5a
5b
5c
5d
5e
5f
5g
5a
5b
1418
1.39
2.07
5
n.o.k
265
a
78
94
93
52
14855
49
495
a
oligomeric
6720
a
1.52
1.80
21
11
n.o.
287
>497
454
a
2610j
a
oligomeric
oligomeric
2259
a
b
50
69
40
72
87
59
25
67
43
1.53
1.44
1.33
1.54
12
36
38
14
n.o.
b, 250
10920
b, 200
11711
b, 150
4319
b
b
b
b
4c
4d
4e
4f
5c
5d
5e
5f
oligomeric
3322
1.64
10
oligomeric
oligomeric
2075j
b
4g
5g
oligomeric
a a: conventional heating, 16-24 h at 80 °C; b: microwave-assisted heating, 10 min at 200 °C, unless otherwise noted. b See Scheme
1 for structures. c See Scheme 2 for structures. d Isolated yield. Calculated by Mn/M(repeating unit); hence, in oligomers the triflate
endgroups tend to increase the value. e Values are for the THF-soluble fractions of the obtained polymers. f Polydipersity index, Mn/Mw.
g Degree of polymerization. h Glass transition tempearture. i Decomposition, 5% weight loss in TGA under nitrogen. j Sample contained
lower-molecular-weight fractions (multimodal distribution) that are not included in this value since they could not be quantified by GPC.
k Not observed.
stirred 1:1 mixture of methanol and concentrated hydrochloric
acid (100 mL). The phase-separated toluene layer was removed
with a pipet and dropped into methanol. The precipitated
material was centrifugated and dried in a vacuum to give the
title compound 5b as a colorless powder (345 mg, 78%). Mn
(GPC) ) 14.855, PDI ) 2.07, DP ) 49. There was found a
considerable loss of material due to fractionation. Oligomeric
4-Phenylethenyl Endgroups (See Table 2 for Yields, Mn, PDI,
DP, Decomposition Temperatures, and Tg). Poly{[1,1′-biphen-
yl]-4,4′-diyl-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]} (7b).
Method (a): Conventional External Heating. A solution of
bis(1,5-cyclooctadiene)nickel(0) (274 mg, 1.0 mmol), 2,2′-bipy-
ridyl (188 mg, 1.2 mmol), and 1,5-cyclooctadiene (1.2 mL, 1.0
mmol) in degassed anhydrous toluene (7 mL) and DMF (1 mL)
was stirred at 80 °C for 25 min. Via a cannula, a solution of
4b (301 mg, 0.50 mmol) and 4-bromostyrene (6) (17 mg, 0.09
mmol) in degassed anhydrous toluene (3 mL) was then added.
After the mixture was stirred for 24 h at 80 °C, the resulting
dispersion was poured into a vigorously stirred 1:1 mixture of
methanol and concentrated hydrochloric acid (25 mL). The
phase-separated toluene layer was removed with a pipet and
dropped into methanol, and the precipitated material was
centrifugated and dried in a vacuum to give the polymer 7b
as a colorless solid (97 mg, 63%). Mn (GPC) ) 8.580, PDI )
1.63, DP ) 28. There was found a considerable loss of material
due to fractionation. Oligomeric material of 7b was easily
soluble in methanol. 1H NMR (400 MHz, CDCl3) δ 7.60 (m,
1
material of 5b was easily soluble in methanol. H NMR (400
3
3
MHz, CDCl3) δ 7.61 (m, J {H,H} ) 8.1 Hz, 4H), 7.50 (m, J
{H,H} ) 8.1 Hz, 4H), 7.39 (m, Ph-OTf endgroup), 5.32 (m,
Ph-OTf endgroup); 19F NMR (376 MHz, CDCl3) δ -76.2 (SO2-
CF3), -67.0 (C-CF3).
Method (b): Microwave-Assisted Heating. To a freshly
prepared solution of bis(1,5-cyclooctadiene)nickel(0) (168 mg,
0.6 mmol), 2,2′-bipyridyl (77 mg, 0.5 mmol), and 1,5-cyclo-
octadiene (0.10 mL, 0.8 mmol) in anhydrous toluene (4 mL)
and DMF (1 mL) was added a solution of 4b (153 mg, 0.26
mmol) in anhydrous toluene (1 mL) via a cannula. Prior to
heating, the mixture was stirred in the sealed vial at room
temperature for 10 min then heated in the microwave reactor
at 200 °C for 10 min. The resulting dispersion was passed
through a 0.45 µm syringe filter and poured into a stirred
mixture of methanol and concentrated hydrochloric acid (1:1,
20 mL). The toluene used for washing the vial was added, and
the phase-separated toluene layer was removed with a pipet
and dropped under stirring into methanol. The precipitated
material was centrifugated and dried in a vacuum to give
polymer 5b as a colorless powder (46 mg, 60%). Mn (GPC) )
11.700, PDI ) 1.33, DP ) 38. There was found a considerable
loss of material due to fractionation. Oligomeric material of
5b was easily soluble in methanol.
3
4H), 7.51 (m, 4H), 6.74 (m, 1H), 5.79 (d, J {H,H} ) 17 Hz,
3
1H), 5.28 (d, J {H,H} ) 11 Hz, 1H); 13C NMR (101 MHz) δ
140.4, 132.9, 130.8, 126.9, 124.2 (q, J {C,F} ) 287 Hz, CF3),
64.3 (septett, J {C,F} ) 26 Hz, C-CF3); 19F NMR (376 MHz,
CDCl3) δ -66.7.
Method (b): Microwave-Assisted Heating Using a Catalyst
Stock Solution. In a glovebox, a 0.2727 mM catalyst stock
solution was prepared consisting of bis(1,5-cyclooctadiene)-
nickel(0) (1.50 g, 5.4 mmol), 2,2′-bipyridyl (850 mg, 5.4 mmol),
and 1,5-cyclooctadiene (0.68 mL, 5.5 mmol) in anhydrous
toluene (10 mL) and DMF (10 mL). Polymerization was
accomplished by adding 4.3 mL of the catalyst solution (1.17
mmol of the active Ni(0) complex) to a 10 mL reaction vial
already charged with 4b (339 mg, 0.57 mmol) and 4-bromosty-
rene (6) (10 mg, 0.06 mmol). The reaction vial was sealed and
placed in the microwave reactor and heated to 250 °C for 10
min. After cooling, the reaction solution was filtered (0.45 µm)
and precipitated into a stirred 1:1 mixture of methanol and
concentrated hydrochloric acid (35 mL). The separated toluene
phase was removed with a pipet and dropped into methanol,
and the precipitated material was centrifugated and dried in
a vacuum to give the title compound 7b as a colorless solid
(124 mg, 72%). Mn (GPC) ) 6.706, PDI ) 1.64, DP ) 22. There
was found a considerable loss of material due to fractionation.
Oligomeric material of 7b was easily soluble in methanol.
1
Polymer (5a). H NMR (400 MHz, CDCl3) δ 7.49 (d, 4H),
7.29 (d, 4H), 1.72 (s, 6H); 19F NMR (376 MHz, CDCl3) δ -76.0.
1
Polymer (5c). H NMR (400 MHz, CDCl3) δ 7.44 (m, 4H),
7.27-7.08 (m, 14H), 19F NMR (376 MHz, CDCl3) δ -76.0.
Polymer (5d). 1H NMR (400 MHz, d8-THF) δ 7.98 (m, 2H),
7.62-7.51 (m, 8H), 7.42 (m, 6H); 19F NMR (376 MHz, d8-THF)
δ -74.9.
1
Polymer (5e). H NMR (400 MHz, CDCl3) δ 7.48 (d, 4H),
7.31 (s, 4H), 2.30 (m, 4H), 1.55 (m, 6H); 19F NMR (376 MHz,
CDCl3) δ -75.9.
Polymer (5f). 1H NMR (400 MHz, CDCl3) δ 7.41 (s, br, 4H),
7.18 (s, 4H), 2.04 (s, br, 4H), 1.31 (s, br, 14H), 0.91 (s, br, 4H);
19F NMR (376 MHz, CDCl3) δ -76.2.
1
Polymer (5g). H NMR (400 MHz, CDCl3) δ 8.04 (m, 4H),
7.68 (m, 4H); 19F NMR (376 MHz, CDCl3) δ -76.0.
1
Polymer (7a). H NMR (400 MHz, CDCl3) δ 7.45 (d, 4H),
Typical Procedure for the Copolymerization of Bistriflates
4a-g and 4-Bromostyrene (6) to Polymers 7a-g Carrying
7.21 (d, 4H), 6.67 (m, 1H), 5.70 (m, 1H), 5.18 (m, 1H), 1.66 (s,
CH3).

Macromolecules, Vol. 38, No. 10, 2005
Design and Synthesis of New Polymeric Materials 4151
Table 2. Experimental Data of Homopolymers 7
methoda
monomersb
polymerc
yieldd (%)
Mne (g/mol)
PDIf
DPg
Tgh (°C)
decompi (°C)
a
4a, 6
4b, 6
4c, 6
4d, 6
4e, 6
4f, 6
4g, 6
4b, 6
4c, 6
4d, 6
4d, 6
4e, 6
4f, 6
4g, 6
7a
7b
7c
7d
7e
7f
61
63
98
74
60
81
85
72
62
79
93
47
58
76
2106
1.23
1.63
11
28
n.o.k
232
489
493
a
8580
a
oligomeric
3637
oligomeric
oligomeric
oligomeric
6706
a
1.82
11
297
430
a
a
a
7g
7b
7c
7d
7d
7e
7f
b, 250
1.64
22
250
n.o.
n.o.
n.o.
470
421
401
b
oligomeric
3107
b
1.67
1.66
10
11
b
3493
b, 250
3752j
b
b
oligomeric
oligomeric
7g
a a: conventional heating, 16-24 h at 80 °C; b: microwave assisted heating, 10 min at 200 °C, unless otherwise noted. b See Scheme
1 for structures. c See Scheme 2 for structures. d Isolated yield. Calculated by Mn/M(repeating unit); hence, in oligomers the triflate
endgroups tend to increase the value. e Values are for the THF-soluble fractions of the obtained polymers. f Polydipersity index, Mn/Mw.
g Degree of polymerization. h Glass transition tempearture. i Decomposition, 5% weight loss in TGA under nitrogen. j Sample contained
lower-molecular-weight fractions (multimodal distribution) that are not included in this value since they could not be quantified by GPC.
k Not observed.
Scheme 1. Synthesis of
4,4′-Cyclododecylidenebisphenol (3f)
Scheme 2. Monomer Synthesisa
1
Polymer (7c). H NMR (400 MHz, CDCl3) δ 7.50 (m, 4H),
7.28 (m, 14H), 6.78 (m, 1H), 5.80 (m, 1H), 5.25 (m, 1H).
1
Polymer (7d). H NMR (400 MHz, d8-THF) δ 7.96 (s, br,
2H), 7.68-7.31 (m, 14H), 6.89 (m, 1H), 5.93 (d, 3J {H,H} ) 18
3
Hz, 1H), 5.35 (d, J {H,H} ) 11 Hz, 1H).
1
Polymer (7e). H NMR (400 MHz, CDCl3) δ 7.49 (m, 4H),
7.34 (m, 4H), 6.73 (m, 1H), 5.76 (m, 1H), 5.24 (m, 1H), 2.32
(m, 4H), 1.59 (m, 6H).
a The symbol • indicates the point of connection.
1
Polymer (7f). H NMR (400 MHz, CDCl3) δ 7.41 (m, 4H),
Scheme 3. Polymer Synthesisa
7.17 (m, 4H), 6.67 (m, 1H), 5.70 (m, 1H), 5.18 (m, 1H), 2.04
(m, br, 4H), 1.30 (m, br, 14H), 0.90 (m, br, 4H);
Polymer (7g). 1H NMR (400 MHz, d6-DMSO) δ 8.08 (m,
4H), 7.92 (m, 4H), 6.80 (m, 1H), 5.92 (m, 1H), 5.33 (m, 1H).
Results and Discussion
a For a legend see Scheme 2.
Synthesis. Commercially available bisphenol A-type
compounds 3a-g served as starting materials for the
synthesis of the bistriflate monomers, with the exception
of the cyclododecyl derivative, which required the
synthesis of 4,4′-cyclododecylidenebisphenol (3f). The
monomer 3f was prepared by acid-catalyzed condensa-
tion of 2 equiv of phenol (1) and cyclododecanone (2) in
the presence of catalytic amounts of mercapto acetic acid
(Scheme 1).32 Two different protocols were successfully
applied toward the synthesis of 3f: (a) the mixture was
repeatedly saturated with gaseous hydrogen chloride
and stirred at room temperature or (b) the reaction
mixture was stirred in a 1:1 mixture of concentrated
sulfuric acid and glacial acetic acid. Both methods
afforded the bisphenol 3f in 75 and 77% yield, respec-
tively. The bistriflate monomers 4a-g were obtained
in yields >95% by reaction of their respective bisphenols
3a-g with trifluoromethane sulfonic acid anhydride in
pyridine (Scheme 2). Purification by column chroma-
tography on silica gel and recrystallization ensured
purities of virtually 100% (GC-MS).
ductive aryl-aryl coupling) of the bistriflates monomers
using a catalyst system consisting of bis(1,5-cycloocta-
diene)nickel(0), 2,2′-bipyridyl, and free 1,5-cyclooctadi-
ene (COD) in toluene or toluene/DMF mixtures (Scheme
3).33 Two series of poly(biphenylmethylene)s have been
synthesized for this study: homopolymers 5 from mono-
mers 4, carrying triflate endgroups (Scheme 3), and
homopolymers 7 from monomers 4 and 4-bromostyrene
(6, between 5 and 10 mol% vs triflate groups) leading
to 4-phenylethenyl end-capped polymers (Scheme 4).
The polymerization results are displayed in Tables 1
and 2. The end-capping procedure not only allows for
stoichiometric control of molecular weight but also
introduces thermally cross-linkable functionality into
the oligomer that can be used to produce polymeric
networks for application in electronic devices by spin-
coating (vide infra). Preparation of polymers 5 and 7
was carried out via two different routes: (a) conven-
tional external heating in a Schlenk flask at 85 °C for
16-24 h and (b) heating in a microwave reactor for 10
min at temperatures ranging from 150 to 250 °C. The
The macromolecular synthetic scheme involves the
Ni(0)-mediated Yamamoto-type polycondensation (re-

4152 Beinhoff et al.
Macromolecules, Vol. 38, No. 10, 2005
Scheme 4. 4-Phenylethenyl End-Capped Polymer
Synthesisa
methyl ether acetate (PGMEA); hence, the highest Mn
were observed for 5b. While the fluorenyl polymer 5d
is reasonably soluble, all other materials were only
sparingly soluble in organic solvents. Oligomer 5d with
a Mn of 3300 is readily soluble in THF, whereas material
with a Mn of 6700 (GPC values vs PS) did not dissolve
completely upon shaking the mixture for 16 h. Replace-
ment of the cyclohexyl group in polymer 5e by a
cyclododecyl group in polymer 5f did not result in a
distinct enhancement of the solubility. In the end, the
moderate molecular weights of these poly(biphenylm-
ethylene)s are not a setback for the targeted application
because generally the electronic properties of semicon-
ducting polymers level off with DPs of roughly 5-10
repeat units.14 Difficulties in preparing good, robust thin
films from low-molecular-weight polymers and oligo-
mers is overcome by synthesizing cross-linkable materi-
als.
The presence of residual triflate endgroups in poly-
mers 5 was determined by 19F NMR spectroscopy, which
proved to be a valuable sensitive tool for determining
the amount of fluorine-containing triflate groups. Tri-
flate endgroups in the homopolymers series 5 exhibited
a strong signal at about -76 ppm in the 19F NMR
spectra in chloroform, essentially the same value as
observed for the respective monomers. However, when
d8-THF was used as the solvent, the signal underwent
a downfield shift to -74.9 ppm. The amount of triflate
endgroups could be quantified by comparing their
signals with the signals from added hexafluorobenzene
of known concentration.37
Polymers 7a-f with 4-phenylethenyl endgroups were
prepared by copolymerization of bistriflate monomers
4a-g and 4-bromostyrene (6) (Scheme 4, Table 2). Using
essentially the same reaction conditions as outlined
above, the monofunctional endcapping agent 6 was used
in ratios of 5-10% vs triflate groups. As expected from
the calculated stoichiometric imbalance, DP 10 were
achieved. Surprisingly, 4-phenylethenyl end-capped
polymers 7 could conveniently be prepared in the high-
temperature microwave reactor as well. No noticeable
consumption of the vinyl group and hence no cross-
linkage was observed during polymerization, even at
temperatures as high as 250 °C for 10 min. This result
shows the utility of the efficiency of microwave-heated
reactions even when using functional organic sub-
strates. All GPC elution curves for the polymers from
these reactions were monomodal. As expected, thin films
prepared from these materials form insoluble cross-
linked networks when heated, dried, and cured at 150
°C for >1 h (see below).
There was no observed difference in solubility of
material of comparable molecular weight with either
triflate or 4-phenylethenyl endgroups. Polymer solubil-
ity plays a crucial role in the fabrication of electronic
devices by spin-coating. The poor solubility of some of
the polymers, even low-molecular-weight oligomers,
may be to some extent be due to the tendency toward
crystallization or the rigid nature of the polymer back-
bone. The lower reactivity of some of the monomers we
utilized is likely another cause of the low molecular
weights we observed in some cases. We attempted to
discern whether we were observing molecular-weight
limitations imposed by solubility versus reactivity by
attempting to synthesize random copolymers consisting
of two different triflate monomer. For example, combi-
nations of the fluorenyl-substituted monomer 4d with
a For a legend see Scheme 2.
utilization of microwaves has become a widespread tool
in organic synthesis in recent years, with the main
benefits of significant rate enhancements and higher
product yields with less occurrence of side reaction
pathways.34,35 Transition-metal-catalyzed or -mediated,
microwave-assisted reaction protocols both on the mo-
lecular35 and the macromolecular15 level are readily
available.
The synthesis of a first set of homopolymers 5
(Scheme 3, Table 1) by both heating methods gave low-
molecular-weight oligomers and higher-molecular-weight
polymers in typical yields ranging from 40 to 95%. The
materials had number average weights (Mn) up to 6.700
g/mol, polydispersity indexes (PDI) of 1.4-2.0 and
degrees of polymerizations (DP) up to 38 (THF soluble
fractions), as measured by GPC relative to polystyrene
(PS) standards.
Interestingly, Sheares and co-workers found that GPC
underestimates the molecular weight of a polymer
analogous to 5b by a factor of 1.4 when compared to
the more reliable data obtained by multiple-angle laser
light scattering (MALLS).22,36 Comparison of the mo-
lecular weight of polymer 5b made in this study
measured by GPC and quasi-elastic light scattering
(QELS) results in underestimation of the Mn value
measured by GPC by a factor of 1.6-1.8 (Figure 2). The
deviation from the theoretical PDI value of 2.0 and
comparably low yields of good soluble polymers are
consistent with other polymers prepared by transition-
metal-catalyzed or -mediated step-growth polymeriza-
tion methods, possibly due to the loss of some lower-
molecular-weight oligomeric material via fractionation
during workup. For material with low THF solubility,
GPC results may only reflect the lower-molecular-
weight fraction that is soluble. The predominant limit-
ing factor in obtaining high molecular weight appeared
to be the low solubility of a number of the polymers.
After the polymerization reaction, insoluble, precipitated
polymeric material is not clearly visible in the crude
reaction mixture since the crude slurry also contains
finely dispersed Ni black particles and Ni salts. Of all
the materials, only the hexafluoromethyl-substituted
polymer 5b showed very good solubility in a number of
common organic solvents such as toluene, chloroform,
THF, N-methylpyrrolidone (NMP), and propylene glycol
Figure 2. Comparison of GPC and quasi-elastic light scat-
tering (QELS) results on molecular-weight determination of
polymer 5b. GPC underestimates the Mn value by a factor of
1.6-1.8.

Macromolecules, Vol. 38, No. 10, 2005
Design and Synthesis of New Polymeric Materials 4153
Polymers 5 and 7 showed good thermal stability. Less
than 5% weight loss values well above 300 °C were
observed for most samples by TGA (10 °C/min, under
nitrogen), some were stable up to about 490 °C, e.g., the
hexafluoromethyl- and fluorenyl-substituted polymers
5b and 5d. MDSC data did not clearly reveal values
for Tg’s for most of the materials. This is likely due to
the high degree of crystallinity in the solid state, though
no melting transitions were noted. However, the ob-
served Tg’s were in the range of 220-300 °C, and the
thermal mechanical properties observed in DMA mea-
surements (see below) show that these materials possess
thermo-mechanical response and measurable Tg’s con-
sistent with the Tg’s observed by DSC for the other
samples. Polymer 5b forms thin, free-standing, non-
crosslinked films from a 20 wt% solution in PGMEA.
The Tg measured for this cast film was slightly lower
(255 °C) than that of the amorphous solid polymer
powder (265 °C), though both samples were taken from
the same batch.
Dynamic mechanical analysis (DMA) was performed
for polymers 5b and 7b (Figure 3). The observed Tg, as
measured by the large drop in the storage modulus and
the maximum of the loss modulus, increases from 263
°C for the linear polymer 5b to 292 °C for the cross-
linked polymer 7b. The linear polymer undergoes a
sharp seven-decade drop in modulus at Tg, whereas the
drop in modulus observed with the cross-linked system
is much less dramatic and at a much higher tempera-
ture. These data confirms that we have indeed incor-
porated better thermo-mechanical stability as a result
of the mild cross-linking introduced into the system (7b).
The loss of mechanical properties at nearly 300 °C is a
result of a failure of the cross-linked vinyl linkages at
that temperature with concurrent loss of mechanical
stability as the system reverts to a non-cross-linked,
low-molecular-weight, linear morphology.
Figure 3. Dynamic mechanical analysis (DMA). Storage and
Loss Modulus for 5b (--) and 7b (‚‚‚).
either the hexafluoromethyl compound 4b or the cy-
clododecyl monomer 4f were used in a 1:1 ratio to
synthesize random copolymers. No significant changes
in the molecular weight or solubility of the resulting
copolymers were observed. This led us to believe that
low reactivity of the cyclododecyl monomer is the
primary reason that it fails to give high-molecular-
weight polymerswhile we note that the oligomeric
copolymers also have extremely low solubility. No
crystallinty was observed by DSC measurements. At the
time of the study, WAXD facilities were not available;
however, future collaborative WAXD studies have been
proposed.
The 4-phenylethenyl end-capped polymers, series 7,
showed the expected resonances of the vinyl protons in
the 1H NMR spectra at 5.32 (d), 5.90 (d), and 6.85 ppm
(m), respectively. However, some of the 19F NMR spectra
of the 4-phenylethenyl end-capped polymers still showed
a trace of the triflate signal at -76 ppm. This indicates
that the end-capping with 4-bromostyrene (6) did not
reach 100% completion in these cases. It was possible
to quantitatively replace all of the triflate endgroups
in a secondary, follow-up Ni(0)-meditated cross-coupling
reaction of these materials with an excess of 4-bro-
mostyrene (6).
The absorption and photoluminescence behavior for
selected polymers 5 and 7 were measured on spun-cast
thin films on quartz substrates. Typical spectra are
displayed in Figure 4 (polymers 5d and 7d). The
absorption spectra all show two broad bands with λmax
ranging from 210 to 225 nm and 270 to 290 nm,
respectively, and a weak shoulder at 310 nm. Since the
backbones of the two polymers are identical, the absorp-
Characterization. Selected materials were exam-
ined by TGA and MDSC, (see Tables 1 and 2 for details).
Figure 4. Absorption and photoluminescence spectra of polymers 5d (‚‚‚) and 7d (--).

4154 Beinhoff et al.
Macromolecules, Vol. 38, No. 10, 2005
Figure 5. Schematic representation of the formation of a cross-linked film.
tion spectra are very similar. The 4-phenylethenyl
endgroups of polymer 7 do not noticeably alter the
absorption spectra since 4-vinylbiphenyl absorbs (in
solution) at 274 nm.38 The emission spectra exhibit also
broad bands with varying intensities and λmax ranging
from 315 to 325 nm for polymers 5 with triflate
endgroups and at about 405 nm for polymers 7 with
4-vinylbiphenyl endgroups. The latter one has clear
shoulders on both the high- and low-wavelength sides
which look like a vibronic progression, with 0-1 stron-
ger than 0-0. Moreover, the emission is much stronger
than of polymers 5. The large red-shift in the emission
band of 7 results from rapid exciton transfer to the
4-vinylbiphenyl endgroups. These have more-extended
conjugation and, therefore, lower exciton energy than
the biphenyl units in the chain. Thus, backbone units
Figure 6. UV absorbance spectra of 7d after thermal curing
(1 h, 150 °C) and after curing and solvent rinsing (THF).
dominate the absorption, but the endgroups are respon-
sible for the emission.
Electronic Devices. The cross-linkable, 4-phenyleth-
enyl end-capped oligomers 7b and 7d were successfully
utilized in electronic device fabrication. To prepare thin
film samples for UV/vis and photoluminescence char-
acterization, the polymers were spin-cast on a 1 in.
quartz wafers from 5 to 10 wt% THF or p-xylene
solutions and subsequently baked at 150 °C under N2
for 1 h to effect solvent removal and curing. This curing
involves the thermally initiated cross-linking of the
oligomer 4-phenylethenyl endgroups. The cross-linking
process is represented in Figure 5. The resulting net-
work films have decreased solubility in organic process-
ing solvents and are more robust than analogous non-
cross-linked films. The advantages of these types of
curable systems have been explored previously.16,17 To
demonstrate the increased solvent resistance of the
cured oligomers, the absorption spectra of the cured film
before and after rinsing the substrate with THF solvent
are shown in Figure 6. Though a slight reduction of
absorption after rinsing is noted, the UV-vis data
suggests that greater than 80% of the polymer remains
after rinsing. When non-cross-linked films are subjected
to the same procedure, the film is completely removed,
precluding their use in processes where multilayer films
are prepared by successive solvent coating techniques.
The solvent resistance imparted in 7b and 7d allows
for their use in multilayer thin film devices.
Figure 7. Device structure of the fabricated devices.
thermal and electronic stability and that are cross-
linkable are preferable. Polymers such as x-DHF (poly
(9, 9-di-n-hexylfluorene)), and x-HTPA (poly-[(4-n-hexyl-
triphenyl)amine]), where “x-” denotes “cross-linkablity”,
are conjugated materials that have been extensively
studied for electronic applications41 but are sensitive to
both electrical and photooxidative degradation.
In Table 3, four interesting cross-linkable materials,
x-DHF, x-HTPA, and the newly synthesized polymers
7b and 7d are compared. Their structure, electrical
performances, and energy band gap are also indicated.
The band-gap values for x-DHF and x-HTPA are re-
ported in the literature,41 while an estimation of the
optical band gap of 7b and 7d can be derived from their
absorption spectra.42 From the comparison, we observe
that the polymer 7b and 7d have a wider band gap than
that of x-DHF and x-HTPA; this has important implica-
tions in the electrical properties, as explained below.
Applying a voltage to the polymer layer when config-
ured between two electrodes as depicted in Figure 7 and
measuring the current output, one can study the electri-
cal properties of the different polymers. The current
density is plotted as a function of applied voltage in
Figure 8 using a semilogarithmic scale. Since the I-V
characteristic of 7b had similar low current behavior
to the 7d material, only three of the four materials
considered are compared for clarity, x-DHF, x-HTPA,
and 7d. The thickness of the polymer layer was different
A schematic representation of the structure of the
diodes-type devices that were prepared and character-
ized is shown in Figure 7. Devices 3.12 mm × 1 mm in
area were prepared on ITO substrates (see Experimen-
tal Section). The aluminum layer was thermally evapo-
rated at 10-6 Torr in a vacuum chamber. A shadow
mask was used to define the size of the top electrode
contact and, therefore, the device’s operational area.
For electronic applications such as bistable memory
devices,21,39,40 wide band-gap polymers that possess high

Macromolecules, Vol. 38, No. 10, 2005
Design and Synthesis of New Polymeric Materials 4155
Table 3. Summary of Materials Used to Fabricate Electrical Devices
for the various materials, ranging from 50 to 100 nm
(7b, 7d).
match the metal work function of the ITO (x-HTPA) and
Al (x-DHF) electrodes, explaining the respective good
hole- and electron-injection properties of these materi-
als. The HOMO and LUMO levels of 7b and 7d have
not yet been determined, making it difficult to interpret
the low current density observed from the I-V mea-
surements in terms of whether it is due to intrinsically
low conduction or poor injection properties.
The three devices were tested for other electrical
properties, such as lifetime and temperature depen-
dence, and the poly(biphenylmethylene) materials dem-
onstrated more stability than the x-DHF- and x-HTPA-
based devices. Therefore, they are perhaps the best
candidates so far for application as semiconducting
polymers for the fabrication of memory devices where
stabilty and long operational lifetimes are important.
Reports on their operations in bistable organic memory
devices are forthcoming.40
There is a large observable difference between the
polymers. At 4 V, the current density of the polymer
7d (and 7b) is 6 orders of magnitude smaller than the
current observed for x-DHF and x-HTPA. Furthermore,
while x-DHF and x-HTPA show rectifying properties,
the polybiphenylmethylene materials show no rectifica-
tion and a symmetrical I-V characteristic with respect
of the voltage polarity (positive or negative). This
indicates that the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital
(LUMO) probably have similar barrier heights to the
work functions of the metal electrodes. In the case of
x-DHF and x-HTPA, the energy levels tend to well
Summary
The synthesis of new polymers, poly(biphenylmeth-
ylene)s, derived from bistriflates of bisphenol-type
monomers by Ni(0)-mediated polymerization has been
presented. These polymers are interesting because of
the nature of the polymer backbone that contains
biphenyl units separated by substituted methylene
units. The unique structure of the polymer backbone
makes these materials potentially interesting in electri-
cal applications where large-band-gap polymers with
low current density and good thermal and oxidative
stability are required. The solubility, mechanical prop-
erties, optical properties, and electrical properties of the
polymers can be altered by proper selection of the
Figure 8. Comparison of the electrical properties of devices
based on different polymer films for ITO/polymer/Al structure.

4156 Beinhoff et al.
Macromolecules, Vol. 38, No. 10, 2005
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methylenesubstituents.Thermallycross-linkable,4-phen-
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fabricated into thin-film electronic devices, and prelimi-
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Acknowledgment. Financial support from both the
MRSEC Program of the National Science Foundation,
under Award No. DMR-9808677 for the Center for
Polymeric Interfaces and Macromolecular Assemblies,
and the IBM Corporation are gratefully acknowledged.
We thank Teddie Magbitang for help with the GPC and
light scattering and Lucy Lu for thermal analysis.
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