Templated ceramic microstructures by using the breath-figure method

Article abstract of DOI:10.1002/chem.200400921

We describe the synthesis of two cyclobutadiene(cyclopentadienyl)-cobalt- containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies

Full text of DOI:10.1002/chem.200400921

FULL PAPER
Templated Ceramic Microstructures by Using the Breath-Figure Method
Brian C. Englert,[a] Stefan Scholz,[a] Peter J. Leech,[a] Mohan Srinivasarao,[a, b] and
Uwe H. F. Bunz*[a]
Abstract: We describe the synthesis of
two cyclobutadiene(cyclopentadienyl)-
washed away with an appropriate sol-
vent. Upon pyrolysis at 5008C under
either nitrogen or air, the bubble
arrays persist as ceramics and are in-
soluble in organic solvents or water.
The formed pyrolyzed bubble arrays
were analyzed by optical and scanning
electron microscopy, as well as energy
dispersive X-ray microanalysis (EDX).
The composition of the ceramic materi-
als is discussed based on EDX and IR
data.
cobalt-containing
poly(p-phenylene
ethynylene)s (PPEs) and their use as
precursors for stable ceramic surface
coatings. Organometallic PPEs were
shaped into hexagonally ordered as-
semblies by using the breath-figure
method. Such breath figures can be
Keywords: breath figures · bubble
arrays · ceramics · organometallic
polymers · self-assembly
Introduction
templating methods instead. A common approach is to infil-
trate a colloidal crystal, made from polystyrene spheres,
with a soluble inorganic precursor. The precursor is process-
ed into a highly cross-linked preceramic from which the poly-
styrene particles are burned off at temperatures above
4808C. Alternatively, arrays of silica nanospheres can be
backfilled and the spheres removed later by hydrofluoric
acid. Impressive three-dimensional structures have been ob-
tained by both methods, but the dimensions of the skeletal
structures are fixed and dependent upon the size of the tem-
plates, that is, the polystyrene or silica mesospheres.[5,6]
Condensing water vapor forms small droplets on cold sur-
faces. An example of this process is the fogging of glass or
metal, first investigated by Lord Rayleigh.[7] Water droplets
form patterns, “breath figures” on solid and liquid sur-
faces.[8] If moist air is blown over a dilute solution of
polystyrene in a volatile solvent, breath figures can be
“fossilized” as hexagonally ordered polymeric bubble
arrays.[9] This effect was harnessed to imprint micron-sized
bubble arrays onto polymers of widely different struc-
ture.[10–13] Srinivasarao et al.[14] investigated the mecha-
nism of bubble-array formation and fabricated polymeric
arrays in which the size of the monodisperse bubbles
varied in the range of 0.2–20 microns. The generation of
bubble arrays is simple yet dynamic with respect to the
size of the bubbles, and can be dependent on polymer struc-
ture. We report bubble arrays of silicon-containing organo-
metallic polymers[15] that change into microstructured
ceramic materials at temperatures above 5008C. The origi-
nally interconnected bubble arrays turn into a mesh of
À À
We report on hexagonally microstructured Si C Co and
À
À
Si Co O ceramics produced from precursor polymers that
form self-assembled bubble arrays using the breath-figure
method.
À
Non-oxide Si C ceramics are inorganic materials that are
hard, resistant to high temperatures, oxidizing and reducing
agents, and insoluble in organic solvents. Ceramic materials
can be shaped by using a precursor polymer that is cast into
a mould, cross-linked, and thermolyzed.[1–3] Polysilanes and
polycarbosilanes are utilized towards this end. High unsatu-
ration and good processability of the precursor polymers are
prerequisites. Microstructured ceramics have potential use
in photonic crystals, as support for vertebrate cell growth,
and as dirt-repellent coatings showing the “lotus leaf”
effect,[4] while backfilling ceramic arrays with organic semi-
conductors would provide access to novel device architec-
tures.
It would be tedious to scratch microstructures into thin
ceramic films. There have been widespread efforts to utilize
[a] B. C. Englert, Dr. S. Scholz, P. J. Leech, Prof. M. Srinivasarao,
Prof. U. H. F. Bunz
School of Chemistry and Biochemistry
Georgia Institute of Technology, Atlanta, GA 30332 (USA)
Fax : (+1)404-385-1795
E-mail: uwe.bunz@chemistry.gatech.edu
[b] Prof. M. Srinivasarao
School of Polymer, Textile and Fiber Engineering
Center of Advanced Research on Optical Microscopy (CAROM)
Georgia Institute of Technology, Atlanta, GA 30332 (USA)
Chem. Eur. J. 2005, 11, 995 – 1000
DOI: 10.1002/chem.200400921
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self-assembled ceramic “picoliter beakers”[10a] after pyroly-
sis.
with a PDI of 4.54. Polymers 3, 8, and 10 were characterized
by their NMR and IR spectra.
We attempted to cast bubbles from 3 but only badly mis-
shapen arrays formed. Upon co-dissolution of 3 with a 3.2-
fold excess of carboxy-terminated polystyrene, well-devel-
oped bubble arrays were obtained from a carbon disulfide/
pentane mixture (2:1 v/v, Figure 1). The bubbles change size
from domain to domain. Single domains, however, show per-
fectly monodisperse patches of hexagonally arranged bubble
arrays. Upon heating to 5308C,
Results and Discussion
Reaction of the cobalt–cyclobutadiene complex 1[16] with
diiodide 2 and a Pd/Cu catalyst[17,18] furnished polymer 3[15]
(Scheme 1) in a yield of 88%, a molecular weight (Mn) of
most of the polymeric sub-
stance has been removed by py-
rolysis and only a small amount
of material is left (Figure 1,
right). The hexagonal ordering,
nevertheless, is still visible in
the remaining ridges (Figure 1,
right).
Small changes in the polymer
structure can lead to better
bubble arrays when using the
breath-figure method. Some
silyl-substituted PPEs formed
bubble arrays easily.[19] Howev-
er, polymer 10 did not give any
useful bubble arrays and its
oligomer (Pn =5; Pn =degree of
polymerization) showed defec-
tive arrays. When polymer 8
was subjected to the conditions
of breath-figure formation,
bubble arrays of excellent qual-
ity resulted in the first experi-
ments when using CS2 and
forced airflow. It is not clear
what determines the successful
Scheme 1. Syntheses of polymers 3, 8, and 10. a) [PdCl2(Ph3P)2], CuI/THF, piperidine; b) Lithium diisopropyl-
amide (LDA), triisopropylsilylchloride (TIPSCl), THF; c) DMF, K2CO3. Abbreviations: Ethex=(2-ethyl)hex-
yl, Cp=cyclopentadienyl, Dodec=dodecyl.
formation of bubble arrays
from specific polymers but we
think that it is the compounded
2.7ꢁ104, and a polydispersity index (PDI) of 9.1 (bimodal).
Compound 3 is deep yellow, of fibrous appearance, and
soluble in chloroform, THF, and dichloromethane. The sily-
lated monomer 7 was prepared by reacting 6-chlorohexyne
4 with lithiumdiisopropylamide (LDA) and quenching the
resulting anion with chlorotriisopropylsilane (TIPSCl) to
give 5. A base-catalyzed reaction of 5 with the hydroqui-
none derivative 6 provided monomer 7. Coupling of the cy-
clobutadiene complex 1 with 7 under standard Pd catalysis
conditions furnished polymer 8 in an 84% yield as a flaky,
deep yellow, and nonfluorescent material after aqueous
workup and precipitation into methanol; 8 was isolated with
a Mn of 1.3ꢁ104 and a PDI of 1.6. To access a cobalt-free
polymer, the diiodide 7 was coupled to 1,4-diethynyl-2,5-bis-
dodecylbenzene 9. The resulting PPE 10 was obtained in an
89% yield as a highly fluorescent, yellow solid, soluble in
common organic solvents. According to gel permeation
chromatography, the molecular weight of 10 is 30.4ꢁ103
effects of molecular structure, molecular weight, and poly-
dispersity. At the moment we are investigating the molecu-
Figure 1. Left: SEM image of a bubble array formed from a mixture of
polystyrene (65%) and polymer
20.00 kV, WD=21 mm). Right: Same material, pyrolyzed at 5308C,
viewed under conventional light microscope. All polystyrene has
burned off as seen in this optical micrograph.
3 at ambient temperature (EHT=
a
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Chem. Eur. J. 2005, 11, 995 – 1000

Templated Ceramic Microstructures
FULL PAPER
lar-weight dependency upon the propensity of bubble for-
mation.
Figure 2 displays an optical micrograph of the bubble
arrays formed from 8 (Pn =15). The bubbles are uniform
and approximately 5 mm in diameter. The inset shows the
mass loss is small. That is not surprising as the degree of un-
saturation in 8 is high. Polystyrene on the other hand depo-
lymerizes above 4808C and that explains why mixed bubbles
formed from 3 and polystyrene are greatly reduced upon py-
rolysis.
To quantify the mass loss, thermogravimetric analyses
(TGA) of 8 were performed under nitrogen and under air
(Figure 4). Under nitrogen (Figure 4, right) there was a
weight loss of 5.6% up to 2648C and a combined weight
loss of 12.8% at 4508C. The pyrolyzed material was amor-
phous according to powder X-ray diffraction analysis. The
À
IR spectrum showed the total absence of any C H stretch-
ing bands or organic functional-group bands, ascertaining
that 8 was converted into an amorphous ceramic. To gain in-
sight into which organic fragments might be lost upon pyrol-
ysis, high-temperature mass spectrometry was performed on
grains of 8. Mass spectra run at 200 and 2068C did not show
any common or specific degradation patterns. At 4518C, sig-
nals at 189 and 207 amu were observed. These peaks cannot
be attributed to specific fragments stemming from the origi-
nal polymer structure. The combined results suggest that
Figure 2. Optical micrograph (conventional light microscope) of the
bubble arrays of 8 at ambient temperature. The black rings are due to
the lack of depth of focus in light microscopy. The bubbles are approxi-
mately 5 microns in diameter. The inset is a diffraction pattern of the
bubble array taken with a Bertrand lens. The width of the picture is
65 microns.
diffraction pattern of this
bubble array taken through a
Bertrand lens, confirming the
hexagonal ordering. Bubble
arrays of
8 remained intact
upon heating to >5008C, con-
sistent with earlier experiments
performed upon organometallic
PPEs. It was shown that poly-
mers of the same type as 8 at-
tained a nematic liquid crystal-
line phase but did not melt.[15]
The bubble arrays were heated
to 5308C under nitrogen and
collapsed from open intercon-
Figure 4. Right: TGA of 8 under nitrogen. Up to 2658C, 5.6% of weight is lost. Up to 4508C, 12.8% weight is
lost. Left: TGA of 8 in air. Up to 6008C, 2.8% weight is lost. The vertical axis is weight (%) for both graphs.
nected structures into more compact honeycomb-like arrays
of picoliter-sized holes. Figure 3 displays a scanning electron
micrograph (SEM) image of the arrays after pyrolysis. Most
of the material survived the pyrolysis conditions, and the
mostly hydrogen is lost and that cross-linking occurs, but
without cleavage of any specific molecular fragments during
pyrolysis. The loss of small molecules is not uncommon in
the pyrolysis of carbon-rich organometallic materials as
shown by Vollhardt et al. for the pyrolysis of dicobalt–octa-
carbonyl complexes of tolanes and similar systems.[20] Scan-
ning electron microscopy allowed us to determine the ele-
mental composition of the ceramic formed from 8 by using
energy dispersive X-ray microanalysis (EDX).[21] The N2-py-
rolyzed ceramic formed from 8 contains 69.08% carbon,
12.49% oxygen, 8.30% silicon, and 10.13% cobalt according
to EDX. Upon pyrolysis, only loss of hydrogen would be ex-
pected. Loss of methane was not evidenced by mass spec-
trometry, so all of the heavier elements should be conserved
in the ceramic. Within the experimental error margins of
EDX, the recorded data support a stoichiometry of approxi-
mately C49CoO2Si2 (elemental analysis calcd (%): C 80.0, O
4.36, Si 7.63, Co 7.96). The deviation of the obtained values
(up to 10%) from the calculated values is common in the
Figure 3. Left: SEM image of the bubble array of polymer 8 after a pyrol-
ysis under nitrogen up to 5308C (1000-fold magnification). Right: Same
material at higher magnification (8000-fold).
Chem. Eur. J. 2005, 11, 995 – 1000
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U. H. F. Bunz et al.
EDX measurement of lighter elements such as carbon and
oxygen, while higher elements are determined with greater
accuracy. The increased value for the oxygen content, how-
ever, could either be an artifact or might occur as a conse-
quence of trace oxidation of 8 during pyrolysis. Due to the
relatively large error margin in EDX measurements it is dif-
ficult to strictly exclude other, similar stoichiometries. We
conclude that the pyrolysis of 8 under nitrogen leads to an
amorphous ceramic containing C, Si, Co, and some oxygen.
Within experimental error margins, these results are sugges-
tive of a preservation of the starting stoichiometry for all el-
ements except hydrogen.
Conclusion
By using the breath-figure method it is easy to make micro-
structured oxide and non-oxide ceramics from conjugated
precursor polymers. The organometallic cyclobutadiene(cy-
clopentadienyl)cobalt-containing polymer 8 is an excellent
choice for the fabrication of self-assembled bubble arrays.
Upon heating, under nitrogen or air, to temperatures above
5008C, the microscopic ordering of the bubble arrays is pre-
À À
served. Under nitrogen
a Si C Co ceramic with low
amounts of oxygen is obtained, while in air all of the carbo-
À
À
naceous matter is burned off and instead a Si Co O ceram-
ic of the approximate composition Co2Si4O11 is formed. In
the future we plan to investigate these cobalt silicate ceram-
ics for catalytic purposes[22] and expand this facile fabrica-
tion method to ferrocene-containing polymers. These should
produce magnetite and ferrosilicate microstructures that
could be utilized as magnetic and electronic materials.[3]
The ceramic bubbles are conserved in air at elevated tem-
peratures. Heating of the bubble array, which is shown in
Figure 3, to 5308C in air led to a slightly altered array with
thinner but sharper walls (see Figure 5), suggesting that
Experimental Section
1
General: The H and 13C NMR spectra were taken with a Varian Mercu-
ry 300 MHz or a Bruker AMX 400 MHz spectrometer using broadband
probe heads. Proton chemical shifts are referenced to the residual peaks
of CDCl3 at d=7.24 ppm (vs TMS). The 13C{1H} resonances are refer-
enced to the central peak of CDCl3 at d=77.0 ppm (vs TMS) or [D4]di-
chloroethane at d=74.0 ppm. Compounds 1, 2, and 9 were prepared in
accordance with published procedures. SEM images were taken and
EDX was performed on a LEO 1530 thermally-assisted FEG SEM,
equipped with an EDX unit by Oxford Instruments. Additional SEM
images were taken on a Hitachi S800 thermally assisted FEG SEM.
Figure 5. SEM image of the bubble array of polymer 8 after a second py-
rolysis in air at two different magnifications.
some more material is burned off during this process. The
ligaments that connect the inorganic picoliter holes are re-
duced from 1 micron to approximately 0.5 microns. Howev-
er, the overall microscopic structure persists and is actually
increased in sharpness.
The molecular weights of the obtained polymers were determined by gel
permeation chromatography (GPC) on a Shimadzu SCL-SPD-LC-10 AT
system with an integral UV/Vis detector. The samples were run on stan-
dard cross-linked polystyrene Waters GPC columns with polystyrene
standards using chloroform as the solvent.
The TGA trace of the pyrolysis of 8 in air is shown in
Figure 4 (left). Upon heating to 6008C, a weight loss of only
2.8% was observed; this was curious. The concomitant
EDX data showed that there is no carbon left in the ceram-
ic, but the oxygen content is increased. A composite of the
stoichiometry Co2Si4O11 is formed (elemental analysis calcd
(%): Co 29.02, Si 27.66, O 43.33; found: Co 23.71, Si 22.13,
O 54.18; EDX). The oxygen values deviate by the greatest
percentage, but, as mentioned earlier, determination of
lighter elements is prone to some error in EDX measure-
ments.[20] The oxide ceramic is amorphous and does not
show any X-ray diffraction pattern. Under these conditions
we have probably formed a cobalt silicate or a mixed SiO2/
Co2O3 ceramic. We speculate that the pyrolysis in air has
burned out the carbon, but at the same time has oxidized
the silicon and the cobalt, so that the oxidative removal of
carbon is compensated for by the uptake of oxygen under
formation of the ceramic oxide. This process explains the
very low weight loss upon pyrolysis of 8 in air.
Bubble preparation: The bubbles were cast from a solution of 3 mg poly-
mer per mL of carbon disulfide, and prepared at a temperature of 238C,
a
humidity of 84%, and an airspeed varying between 150 and
[10,14]
300 mminÀ1
.
Bubbles of polymer 3 were cast from a solution of 1 mg
polymer and 3.5 mg polystyrene (Mr =25ꢁ103) in a CS2/pentane mixture
(800/400 mL, v/v). Air speed and moisture were as stated above.
Bubble pyrolysis under nitrogen: The samples were pyrolyzed under ni-
trogen in a tube furnace with the following setup: The samples were
placed in a quartz tube sealed at one side with nitrogen flowing through
it. The probe container was placed into a tube furnace equipped with a
second quartz tube of a wider diameter. The ends of the latter tube were
capped with glass-fiber wool. Samples were heated to 1008C and held for
1 h, then heated to 2008C and held for another hour, and finally heated
to 6008C and held for 3 h. The samples remained under nitrogen during
cooling to around 3008C. At this point, the color had changed from
orange to slate gray.
Bubble pyrolysis in air: Samples subjected to pyrolysis under nitrogen
were cooled to room temperature; the sample was then heated overnight
to 8008C in air using the same setup as described above.
Synthesis of polymer 3: In a flame-dried Schlenk flask 1,3-diethynylcyclo-
butadiene(cyclopentadienyl)cobalt 1 (300 mg, 1.35 mmol) and 1,4-bis(2-
ethyl)hexyl-2,5-diiodobenzene 2 (749 mg, 1.35 mmol) were dissolved in a
mixture of piperidine (3.5 mL) and THF (1.5 mL). The solution was de-
gassed by three pump–freeze cycles. Bis(triphenylphosphine)palladium(ii)
chloride (23.5 mg, 33.5 mmol, 2.5 mol%) and copper(i) iodide (6.4 mg,
34 mmol, 2.5 mol%) were added in a stream of nitrogen. The mixture was
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Chem. Eur. J. 2005, 11, 995 – 1000

Templated Ceramic Microstructures
FULL PAPER
heated up to 408C for 48 h. The highly viscous reaction mixture was al-
lowed to cool to room temperature, taken up in chloroform, and washed
with water (25 mL), 10% aqueous ammonia solution (25 mL), and 25%
aqueous hydrochloric acid (25 mL). The chloroform solution was concen-
trated in vacuo to 25 mL, and then added to methanol (1 L). The sand-
like yellow polymer that precipitated was filtered off, washed with meth-
anol, and dried in vacuo using an oil pump (622 mg, 88%). 1H NMR
(300 MHz, CDCl3, 258C): d=7.10 (s, 2H), 5.02 (s, 5H), 4.62 (s, 2H), 2.58
(s, 4H), 1.60 (m, 2H), 1.28 (brs, 16H), 0.89 ppm (m, 12H); 13C{1H} NMR
(100 MHz, CDCl3, 408C): d=140.60, 132.78, 122.79, 91.12, 89.63, 81.13,
68.13, 64.10, 50.63, 47.64, 32.57, 25.69, 23.04, 14.00, 9.80 ppm; IR (KBr):
n˜ =2954, 2927, 2920, 2911, 2892, 2869, 2856, 2178, 1455, 1434, 1412, 1378,
1107, 1001, 811 cmÀ1; UV/Vis (CHCl3): lmax (e)=369 nm (0.507ꢁ106);
GPC (polystyrene standard): Mn =26976, PDI=9.1 (bimodal).
methane was added, and the solution was washed with 1n HCl, 1n
NH4OH, and water. The organic layer was dried over MgSO4 and the sol-
vent concentrated. The resulting polymer was dissolved in dichlorome-
thane and precipitated out of methanol three times to yield 10 as a
yellow solid (0.556 g, 89%). 1H NMR (300 MHz, CDCl3, 258C): d=7.38
(m, 2H), 6.92 (m, 2H), 4.11 (m, 4H), 2.87 (m, 4H), 2.38 (m, 4H), 2.03
(m, 4H), 1.82 (m, 4H), 1.16 (m, 46H), 1.07 (m, 36H), 0.88 ppm (m, 6H);
13C{1H} NMR (75 MHz, [D4]dichloroethane, 258C): d=153.30, 142.00,
132.24, 122.77, 116.68, 114.12, 108.52, 94.09, 90.56, 80.70, 69.43, 35.19,
31.92, 30.60, 29.72, 29.67, 29.50, 29.37, 28.34, 25.35, 22.69, 19.55, 18.61,
14.10, 11.55, 11.40, 11.26 ppm; IR (KBr): n˜ =677, 798, 816, 858, 1013,
1265, 2172, 2332, 2359, 2866, 2926, 2959 cmÀ1; GPC (polystyrene stand-
ards): Mn =30.4ꢁ103, PDI=4.54.
TGA measurements: These measurements were taken on a Shimadzu
TGA-50 Thermogravimetric Analyzer. The samples were weighed into a
40 mL alumina crucible and the lid was punctured. Each sample was
heated from 25–6008C at a rate of 258CminÀ1 under nitrogen.
Synthesis of 5: Under nitrogen, 6-chlorohexyne 4 (10.0 g, 85.8 mmol) was
dissolved in dry THF (100 mL). The mixture was cooled to À788C. Lithi-
um diisopropylamide (2n solution in heptane, 42.9 mL, 85.8 mmol) was
added dropwise. The mixture was stirred for 10 min and allowed to warm
to À108C and stirred for a further 30 minutes. It was then cooled to
À788C and triisopropylsilylchloride (16.5 g, 85.8 mmol) was added drop-
wise. The mixture was stirred for 24 h, then slowly poured into water and
extracted with chloroform. The organic solution was washed with 0.5n
HCl. The organic layer was separated and dried over MgSO4 and the sol-
vent was removed. The remaining oil was distilled using an oil pump
vacuum (808C) to yield 5 as a light-brown oil (21.6 g, 92%). 1H NMR
(300 MHz, CDCl3, 258C): d=3.58 (t, 2H), 2.32 (t, 2H), 1.92 (m, 2H),
1.70 (m, 2H), 1.07 ppm (s, 21H); 13C{1H} NMR (75 MHz, CDCl3, 258C):
d=108.18, 81.16, 44.76, 31.73, 26.24, 18.95, 11.64 ppm; IR (KBr): n˜ =678,
879, 968, 1015, 1251, 1297, 1446, 2131, 2167, 2243, 2522, 2562, 2622, 2684,
2716, 2721, 2804, 2834, 2853, 3024 cmÀ1; MS: m/z calcd for [C15H29ClSi]:
272.93; found: fragmentation.
Acknowledgement
We thank the National Science Foundation (PI UB, CHE 0138659) for
generous support and the Georgia Institute of Technology for Startup
funds for U. B.; S. S. thanks the Deutsche Forschungsgemeinschaft for a
Postdoctoral fellowship.
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Synthesis of 7: 1,4-Hydroxy-2,5-diiodo benzene 6 (3.00 g, 8.29 mmol), po-
tassium carbonate (11.5 g, 82.9 mmol), and 5 (9.05 g, 33.5 mmol) were
dissolved in dimethylformamide (200 mL). The mixture was heated to
reflux for 48 h, allowed to cool to room temperature, diluted with di-
chloromethane and washed with 1n HCl (2ꢁ150 mL). The solvent was
removed in vacuo and the crude solid was purified by chromatography
on silica gel (1:1, dichloromethane/hexane) to yield 7 as a colorless, crys-
talline solid (2.99 g, 43%). M.p. 488C; 1H NMR (300 MHz, CDCl3,
258C): d=7.17 (s, 2H), 3.99 (t, 2H), 2.38 (t, 2H), 1.97 (m, 2H), 1.80 (m,
2H), 1.10 ppm (s, 42H); 13C{1H} NMR (75 MHz, CDCl3, 258C): d=
152.89, 122.90, 108.69, 86.56, 80.99, 69.94, 28.56, 25.85, 19.94, 19.08,
11.68 ppm; IR (KBr): n˜ =658, 961, 1046, 1210, 1250, 1346, 1385, 1463,
1682, 2166, 2359, 2722, 2866, 2944, 3086 cmÀ1
[C36H60I2O2Si2]: 834.84; found: 834.4.
; MS: m/z calcd for
Synthesis of polymer 8: Diiodo monomer 7 (0.738 g, 0.883 mmol) and di-
ethynyl monomer 1 (0.196 g, 0.875 mmol) were dissolved in THF (2 mL)
and piperidine (1.5 mL) in an oven-dried Schlenk flask. The flask was
frozen, evacuated, and flushed with nitrogen four times after which
[PdCl2(Ph3P)2] (6.2 mg, 8.8 mmol) and CuI (1.7 mg, 8.8 mmol) were added.
The mixture was allowed to stir at room temperature for 48 h. The sol-
vent was removed and the mixture dissolved in dichloromethane, washed
with 1n HCl, 1n NH4OH, and water. The organic layer was dried over
MgSO4 and the solvent removed. The resulting polymer was dissolved in
dichloromethane and precipitated out of methanol three times to yield 8
as an orange solid (0.599 g, 84%). 1H NMR (300 MHz, CDCl3, 258C):
d=6.81 (m, 2H), 5.04 (m, 5H), 4.68 (m, 4H), 1.95 (m, 4H), 1.79 (m,
4H), 1.07 ppm (m, 42H); 13C{1H} NMR (75 MHz, CDCl3, 258C): d=
153.90, 116.73, 108.54, 69.04, 64.48, 56.11, 28.33, 25.49, 19.50, 18.63,
11.33 ppm; IR (KBr): n˜ =677, 791, 881, 1003, 1034, 1067, 1263, 1377,
1462, 1502, 1649, 2166, 2361, 2723, 2754, 2849, 2926, 2962, 3111,
3389 cmÀ1; GPC (polystyrene standards): Mn =13.4ꢁ103, PDI=1.59.
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Received: September 8, 2004
Published online: December 21, 2004
1000
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www.chemeurj.org
Chem. Eur. J. 2005, 11, 995 – 1000