Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

Article abstract of DOI:10.1021/acs.macromol.8b02754

A dibromo derivative of Dewar benzene, trans-5,6-dibromobicyclo[2.2.0]hex-1-ene, was polymerized using ring-opening metathesis polymerization (ROMP). The reaction proceeded in a controlled manner as changing the initial monomer-to-catalyst ratio afforded monodispersed polymers with tunable molecular weights and growing polymer chains were extended upon subsequent exposure to additional monomer. Treatment of the halogenated polymers with an alkyllithium reagent resulted in elimination followed by isomerization to afford trans-poly(acetylene). Based on a series of mechanistic and spectroscopic studies, the transformation was proposed to proceed through a cyclobutenyl intermediate that undergoes rearrangement. The methodology was found to be versatile as triblock copolymers containing the halogenated homopolymer were prepared and converted to their poly(acetylene)-containing derivatives. The polymers were characterized using gel permeation chromatography as well as a range of spectroscopic (NMR, FT-IR, UV-vis, and Raman) and analytical techniques.

Full text of DOI:10.1021/acs.macromol.8b02754

Article
pubs.acs.org/Macromolecules
Cite This: Macromolecules XXXX, XXX, XXX−XXX
Unveiling a Masked Polymer of Dewar Benzene Reveals trans-
Poly(acetylene)
Jinwon Seo,†,‡ Stanfield Y. Lee,† and Christopher W. Bielawski*,†,‡,§
†Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
‡Department of Chemistry and §Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST),
Ulsan 44919, Republic of Korea
S
* Supporting Information
ABSTRACT: A dibromo derivative of Dewar benzene, trans-
5,6-dibromobicyclo[2.2.0]hex-1-ene, was polymerized using
ring-opening metathesis polymerization (ROMP). The
reaction proceeded in a controlled manner as changing the
initial monomer-to-catalyst ratio afforded monodispersed
polymers with tunable molecular weights and growing
polymer chains were extended upon subsequent exposure to
additional monomer. Treatment of the halogenated polymers
with an alkyllithium reagent resulted in elimination followed
by isomerization to afford trans-poly(acetylene). Based on a
series of mechanistic and spectroscopic studies, the trans-
formation was proposed to proceed through a cyclobutenyl intermediate that undergoes rearrangement. The methodology was
found to be versatile as triblock copolymers containing the halogenated homopolymer were prepared and converted to their
poly(acetylene)-containing derivatives. The polymers were characterized using gel permeation chromatography as well as a
range of spectroscopic (NMR, FT-IR, UV−vis, and Raman) and analytical techniques.
multifold: (1) poly(acetylene) typically becomes insoluble
when the chain length exceeds 10 repeat units,22 and (2)
catalysts that enable the direct polymerization of acetylene in a
manner that is controlled and facilitates access to high polymer
remain elusive.23−26 Moreover, few methods are available for
accessing stereopure cis- or trans-poly(acetylene), and
relatively sophisticated conditions are often required.20,27 For
example, Shibahara reported that the latter is obtained by
polymerizing pressurized acetylene (ca. 1.0 kPa) on a liquid
crystalline substrate under a magnetic field.28 Exposure of
stereorandom poly(acetylene) to elevated temperatures or
isomerization catalysts over extended periods of time also
facilitates access to derivatives with high contents of trans
repeat units; however, side reactions (e.g., cross-linking) are
often observed.29,30
To address the aforementioned challenges, a number of
indirect methods to access poly(acetylene) have been
developed (see Scheme 1). Feast demonstrated that 7,8-
bis(trifluoromethyl)tricyclo[4,2,2,02,5]deca-3,7,9-triene, also
known as the “Durham precursor”,31−33 can be polymerized
using ring-opening metathesis polymerization (ROMP) and
then transformed to poly(acetylene) via a retro [4 + 2]
cycloaddition.34,35 Grubbs also reported different methods for
accessing poly(acetylene) through the ROMP of cyclo-
INTRODUCTION
■
Because of their potential uses in contemporary electronic
devices, including light-emitting diodes,1,2 solid-state lasers,3
photovoltaics,4,5 and chemical sensors,6,7 polymers containing
π-conjugated backbones have attracted significant atten-
tion.8−13 The prototypical example is poly(acetylene), which
was synthesized from its constituent monomer by Natta in the
1950s.14 The polymer is comprised only of carbon and
hydrogen and represents one of the first organic materials
shown by Shirakawa, MacDiarmid, and Heeger to exhibit
markedly enhanced electrical conductivities upon exposure to
halogen vapor.15−17 Because poly(acetylene) contains alkenes
along the backbone, it can exist in multiple isomeric forms,18
each of which displays a different set of properties. For
example, cis- and trans-poly(acetylene) exhibit unique
decomposition temperatures (cf. 467 vs 412 °C, respectively),
glass transition temperatures (357 vs 337 °C), oxidation
potentials (−5.49 vs −5.19 eV), and infrared signatures (ν =
740 vs 1015 cm−1).19 Moreover, trans-poly(acetylene) has
been reported to display a higher electrical conductivity value
than its cis isomer (10−5 vs 10−9 Ω−1 cm−1)20 as well as a
higher polarizability due to the differential projection lengths
of the corresponding repeating units (2.425 Å vs 2.125 Å).21
As such, trans-poly(acetylene) features characteristics that may
be relatively attractive for use in certain electronic applications.
Aside from the intrinsic differences between its geometric
isomers, the synthesis of well-defined forms of poly(acetylene)
remains challenging. The reasons for the limitation are
Received: January 1, 2019
Revised: March 10, 2019
© XXXX American Chemical Society
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Scheme 1. Selected Examples of Routes That Have Been Used To Synthesize Poly(acetylene)
Scheme 2. Synthesis of trans-5,6-Dibromobicyclo[2.2.0]hex-1-ene (1)
octatetraene (COT)19 or benzvalene.29 Although inclusion of
chain transfer agents in the former facilitated access to
telechelic derivatives,36 yields of <50% were reported due to
backbiting and competitive formation of benzene as a side-
product.19,36 Benzvalene, on the other hand, features the same
empirical formula as acetylene, and the corresponding polymer
can be rearranged to poly(acetylene) without significant mass
loss.29 However, cross-linking (ca. 19%) occurs upon isomer-
ization, which was attributed to the electrophilic nature of the
requisite catalyst (HgCl2). In all these approaches, the
poly(acetylene) products consisted of mixtures of cis and
trans isomers.
benzene (t1/2 = 2 days),37 and features two cyclobutenyl units
which may lead to network formation during polymerization.38
To circumvent these fundamental and practical drawbacks,
efforts were recentered on a halogenated derivative, trans-5,6-
dibromobicyclo[2.2.0]hex-1-ene (1). Compound 1 is a
known39 liquid that features vicinal dihalides capable of
elimination. As will be described below, high molecular weight
polymers were successfully polymerized in a controlled manner
and even incorporated into multiblock derivatives. Dehaloge-
nation of these polymers resulted in spontaneous isomerization
to poly(acetylene). Surprisingly, the trans form of poly-
(acetylene) was obtained as the exclusive product.
To mitigate the issues outlined above, we envisioned a
synthetic route to poly(acetylene) that entailed the ROMP of
Dewar benzene followed by isomerization of the correspond-
ing intermediate. Although Dewar benzene is strained and thus
could afford well-defined polymers using contemporary
catalysts, the monomer is volatile,37 facilely isomerizes to
RESULTS AND DISCUSSION
■
The route used to synthesize 1 was modified from previously
reported procedures40,41 and is summarized in Scheme 2. After
reducing phthalic acid (2) with a sodium mercury amalgam,
the resulting 1,3-cyclohexadiene derivative 3 was purified by
B
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Figure 1. (a) Plot of Mn (red) and Đ (blue) values versus the [1]0 to [G3]0 feed ratio. Conditions: [1]0 = 0.21 M, CH2Cl2, 30 min. Isolated yields
were typically >90%. (b) Representative gel permeation chromatograms recorded for poly(1) (blue) and its chain extended polymer (red).
Conditions and data: [1]0/[Ru]0 = 21, CH2Cl2; Mn = 3.0 kDa, Đ = 1.25 (blue); additional 1 was added after 30 min: ([1]0 + [1]1)/[Ru]0 = 42,
CH2Cl2, Mn = 7.4 kDa, Đ = 1.13 (red).
Scheme 3. Synthesis of trans-Poly(acetylene) through a Polymerization−Elimination−Isomerization Sequence
recrystallization from aqueous sulfuric acid and isolated in 74%
yield. Dehydration afforded the corresponding anhydride 4,
which was purified by sublimation and collected in 93% yield
as a white, crystalline product. Subsequent photochemical
isomerization was conducted in diethyl ether at room
temperature and monitored over time using 1H NMR
spectroscopy. Removal of the residual solvent after the reaction
was determined to be complete (ca. 27 h) afforded crude 5.
While it was previously reported that the anhydride can be
purified via sublimation,40 the technique was inefficient in our
hands due to the presence of unidentified byproducts that
formed during the photoisomerization reaction. Likewise,
other purification techniques, including column chromatog-
raphy and extraction, were also unsuccessful. To overcome
these challenges, 5 was first esterified with methanol in the
presence of a catalytic amount of acid to afford 6, which
facilitated purification. Subsequent hydrolysis of the purified
product resulted in the desired bis(acid) 7. The addition of
bromine to a suspension of 7 in CH2Cl2 afforded the vicinal
dibromide 8 as a white solid in 97% yield. Finally, electrolytic
decarboxylation followed by column chromatography afforded
1 as a colorless liquid.42,43
With monomer 1 in hand, polymerization efforts com-
menced using the third-generation Grubbs catalyst (G3). A
CH2Cl2 solution of the monomer ([1]0 = 0.21 M) was treated
with the catalyst ([1]0/[G3]0 = 42) for 30 min at ambient
temperature followed by excess ethyl vinyl ether to quench the
reaction. The mixture was then poured into cold hexane which
resulted in the precipitation of a solid that was collected in 90%
yield based on the assumed structure for poly(1). Gel
permeation chromatography (GPC) revealed that the material
produced was monodispersed (Đ = 1.14) and exhibited a
number-average molecular weight (Mn) that was in relatively
good agreement (16.4 kDa) with the theoretical value (15.0
kDa). Further support for a successful polymerization was
obtained by inspecting the 1H NMR spectrum recorded for the
polymer to that of the monomer. For example, the signals
attributed to the cyclobutenyl ring of the monomer (δ 6.4
ppm; CDCl3) shifted upfield and became broad (5.3−6.1 ppm;
CDCl3) upon polymerization (see Figure S24).
To determine whether the polymerization of 1 proceeded
via a controlled, chain-growth mechanism, an iterative series of
experiments were performed. As summarized in Figure 1a, a
linear relationship between the initial monomer-to-catalyst
feed ratio and the measured molecular weights of the polymers
produced was observed. Moreover, as shown in Figure 1b,
increases in molecular weights were seen when additional
monomer was introduced to the reaction mixture after
consumption of the initial monomer feed, consistent with
chain extension. Collectively, these results suggested to us that
the polymerization methodology was controlled and afforded
well-defined polymers with tunable molecular weights.
As summarized in Scheme 3, subsequent efforts were
directed toward eliminating the vicinal dibromides from the
aforementioned polymers.44−46 Adding methyllithium dis-
solved in diethyl ether to a THF solution of poly(1) (2.0
equiv of CH3Li per polymer repeat unit; [1]0 = 0.05 M) at
−78 °C resulted in a color change from pale brown to red as
the mixture warmed to room temperature.47 The color of the
solution darkened over time, and an insoluble black material
was observed after 30 min. In addition, the formation of
CH3Br, an expected elimination byproduct, was observed by
1
mass spectrometry as well as H NMR spectroscopy (see
Figure S15).48 After quenching the reaction through the
dropwise addition of methanol, the precipitate was collected
via filtration, washed with methanol, and then dried under
vacuum to afford 9 in >99% yield. Conducting the reaction in
the dark and under an atmosphere of nitrogen afforded a
quantitative yield, presumably due to minimization of photo-
chemical side reactions.
The product of the aforementioned reaction (9) was
characterized using a range of spectroscopic techniques. For
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Figure 2. Raman spectra recorded for (a) 9 and (b) the polymer obtained from the ROMP of COT. Infrared spectra recorded for (c) 9 and (d) the
polymer obtained from the ROMP of COT. (e) A solid-state CP-MAS 13C NMR spectrum recorded for 9. Note: the asterisks (∗) denote spinning
side bands. (f) A picture of a film of 9 (1.8 cm × 1.8 cm × 13 μm) as prepared on a glass substrate prior to exposure to iodine.
a
Scheme 4. Proposed Isomerization Pathways
a
Starting with 10, the pathway to the left involves intermediates that undergo thermally induced, electrocyclic ring-opening and therefore should
afford a mixture of polymers that feature cis- and trans-alkenes. The pathway to the right involves radical intermediates that isomerize to trans-
poly(acetylene) (9).
comparison purposes, poly(acetylene) was independently
prepared from COT using a method reported in the
literature.19 As shown in Figures 2a and 2b, the Raman
spectra recorded for the polymers prepared using both
methods were similar and featured signals consistent with
the presence of C−C (ca. 1117 cm−1) and CC (ca. 1507
cm−1) bonds. IR spectroscopy has been used to distinguish cis-
and trans-poly(acetylene) since the respective isomers exhibit
distinctive C−H out-of-plane vibrational modes.28 As shown in
Figure 2c, a signal at 999 cm−1, which was attributed to the C−
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Scheme 5. Synthetic Methodology Used To Prepare Different Triblock Copolymers
H stretching frequency of trans-poly(acetylene), was measured
for 9. For comparison, signals at 746 and 931−992 cm−1 were
recorded upon analyzing the poly(acetylene) obtained from
the ROMP of COT (see Figure 2d) and assigned to the cis and
trans isomers, respectively, in accord with literature reports.19
Likewise, a single signal (δ 135 ppm) was observed upon
analyzing 9 using solid-state cross-polarization magic angle
spinning (CP-MAS) 13C NMR spectroscopy (see Figure 2e).
13C NMR signals assigned to trans-alkenes in poly(acetylene)
have been reported (136−139 ppm) and can be distinguished
from their corresponding geometric isomers (126−129
ppm).27 Electrical conductivities were measured (10−4 Ω−1
cm−1) by applying contacts to films of 9 (see Figure 2f) and
found to be in agreement with values reported for trans-
poly(acetylene).20 The conductivity values increased (30 Ω−1
cm−1) upon exposure of the polymer films to iodine vapor.
Collectively, the spectroscopic data indicated that trans-
poly(acetylene) was obtained as the only detectable product
from the methodology described above, which was a surprising
result and prompted us to postulate potential mechanisms (see
Scheme 4). Although previous reports have shown that certain
cyclobutenes and related polyladderenes can undergo selective
electrocyclic ring-opening,49−52 mixtures of cis and trans
products may result when the precursors feature assorted
stereoisomers.53,54 Because the spectroscopic data recorded for
9 indicated that the material was composed of a single
stereoisomer, an alternative route wherein ring-opening
proceeds through a radical intermediate that isomerizes to
the thermodynamically favored (trans) polymer product was
considered.
To probe the underlying mechanism, efforts were first
directed toward identifying potential intermediates. Precursor
poly(1) was subjected to a solution of CH3Li in THF-d8 at
−50 °C and then monitored by 1H NMR spectroscopy. Signals
assigned to the hydrogens bonded to the brominated carbons
(δ 4.4−4.8 ppm) disappeared over time and were accompanied
by the formation of new signals that were consistent with those
expected from the cyclobutenyl moieties in 10 (6.0−6.2 ppm)
(see Figure S13).55,56 Next, the isomerization reaction was
conducted in the presence of a radical trap.57 A THF-d8
solution of poly(1) was charged with CH3Li (2.0 equiv per
repeat unit) at −50 °C followed by (2,2,6,6-tetramethyl-
piperidin-1-yl)oxyl (TEMPO) (3.0 equiv per repeat unit) and
then warmed to room temperature.58 At the conclusion of the
reaction, a black precipitate was collected and found to display
spectroscopic signatures that were similar to the trans-
poly(acetylene) described above (see Figure S3). Moreover,
the trap was not detected in the product via elemental analysis
or other analytical techniques. Collectively, these results
indicated that the isomerization may have proceeded through
radical intermediates that rapidly isomerize to the thermody-
namically favored, conjugated polymer product before reacting
with a trap.
Because the poly(acetylene) described above was found to
be insoluble, subsequent efforts were directed toward capital-
izing on the advantages of the polymerization methodology to
access soluble derivatives. On the basis of previous reports,59,60
we hypothesized that connecting a poly(acetylene) block to
nonconjugated segments would render the entire copolymer
processable. exo,exo-5,6-Bis(methoxymethyl)bicyclo[2.2.1]-
hept-2-ene (11)61 was chosen as a comonomer due to its
high solubility in common organic solvents, lack of acidic
functional groups, and high ring strain. The polymerization of
11 was found to proceed in a controlled manner62 and afforded
monodispersed products with molecular weights that agreed
with their theoretical values (see Figure S9).
As summarized in Scheme 5, a triblock copolymer derived
from 11 and 1 was prepared and then explored as a precursor
to poly(acetylene). Exposure of a CH2Cl2 solution of 11 to G3
([11]0/[Ru]0 = 63) followed by stirring at −15 °C initiated a
polymerization reaction. To monitor the formation of polymer
over time, an aliquot was removed from the solution after 15
min and poured into a mixture of CH3OH and ethyl vinyl
ether to quench the reaction. The precipitate that formed was
collected and analyzed by GPC (Mn = 19.3 kDa, Đ = 1.08). A
CH2Cl2 solution of 1 was then introduced to the residual
catalyst solution (([11]0 + [1]0)/[Ru]0 = 126). After stirring
for an additional 15 min, an aliquot was removed and worked
up as described above (Mn = 32.3 kDa, Đ = 1.10). Finally,
additional 11 (([11]0 + [1]0 + [11]1)/[Ru]0 = 189) was
added. After quenching the reaction, triblock copolymer 12
was isolated in 73% overall yield. GPC analysis revealed that
the material exhibited a Mn of 51.4 kDa (Đ = 1.18) (cf. the
theoretical Mn value of the copolymer based on quantitative
monomer conversions was 38.0 kDa), and the number of
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used as a light source. Electrolysis was conducted using a GW Instek
GPR-11H300 instrument and platinum plates (4 cm × 4 cm, 0.2
mm). Solvents were dried and degassed using a Vac Atmospheres
repeat units in the segment of poly(1) was calculated to be 55
from its deduced Mn value (13.0 kDa).63
Adding methyllithium to a THF solution of the triblock
copolymer 12 (2 equiv of CH3Li per polymer repeat unit) at
room temperature resulted in the formation of a dark red color,
consistent with the formation of 13 followed by isomerization
to 14.64,65 Pouring the treated solution into cold methanol
afforded a precipitate, which was collected and characterized.
1H NMR spectroscopic analysis of the product revealed that
signals assigned to the halogenated methines found in the
segment of poly(1) disappeared and a new signal (δ 6.0−7.0
ppm; THF-d8), consistent with the repeat unit of poly-
(acetylene), had formed. A solution of 14 in THF exhibited a
λmax value near 500 nm and an irreversible oxidation at 0.5 V
(vs ferrocene in CH3CN), in agreement with values expected
for poly(acetylene) (see Figures S1 and S2).66 Data recorded
in the solid state were also in agreement with the structural
assignment. For example, 14 exhibited Raman signals at 1110
and 1492 cm−1 as well as an IR absorption band at 1012 cm−1.
Likewise, a 13C NMR signal (δ 134 ppm) consistent with that
expected for trans-poly(acetylene) was measured (see Figure
S27).67 Although iodine doping was found to significantly
enhance the conductivity displayed by a film of the copolymer
by more than 2 orders of magnitude (5 × 10−3 vs 2 × 10−5 Ω−1
cm−1), the change was less significant than that observed with
poly(acetylene), presumably due to the presence of the
insulating segments of poly(11). Regardless, these data
suggested to us that the aforementioned methodology afforded
well-defined triblock copolymers wherein poly(norbornene)-
based homopolymers were connected to a poly(acetylene)
core.68
1
solvent purification system. H NMR and 13C NMR spectra were
recorded in acetone-d6 (1H: 2.05 ppm; 13C: 29.8 ppm), THF-d8 (1H:
3.58 ppm), methylene chloride-d2 (1H: 5.32 ppm; 13C: 54.0 ppm), or
chloroform-d1 (1H: 7.26 ppm; 13C: 77.2 ppm) using Bruker 400 and
100 MHz spectrometers, respectively. Solid-state CP-MAS 13C NMR
spectra were recorded using a Bruker 125 MHz spectrometer.
Coupling constants (J) are expressed in hertz (Hz). Splitting patterns
are indicated as follows: br, broad; bd, broad doublet; bt, broad
triplet; bm, broad multiplet; s, singlet; d, doublet; t, triplet; m,
multiplet. High-resolution mass spectra (HR-MS) were obtained from
a JMS-T100LP AccuTOF LC-plus 4G atmospheric pressure
ionization high resolution time-of-flight mass spectrometer (Waters
Inc.) Gel permeation chromatography (GPC) was performed on a
Malvern GPCmax solvent/sample module. THF was used as the
eluent at a flow rate of 0.8 mL min−1. Infrared (IR) spectra were
recorded on an Agilent Cary-630 FT-IR spectrometer. Raman spectra
were recorded on a WITec alpha 300M confocal Raman microscope.
Thermogravimetric analyses (TGA) were performed on a Thermal
Advantages (TA) Q500 at a heating rate of 10 °C min−1 under an
atmosphere of nitrogen. Differential scanning calorimetry (DSC) was
performed under an atmosphere of nitrogen on a Thermal Advantages
Q2000 at a heating or cooling rate of 20 °C min−1. Electrochemical
measurements were conducted using a rotating ring−disk electrode
(Pine Research Instrumentation, Durham, NC) that was connected to
an Echochemie Inc. PGSTAT302N bipotentiostat running the NOVA
version 1.1 software program (Metrohm Autolab, Utrecht, Nether-
lands). Elemental analyses were performed using a ThermoScientific
Flash 2000 organic elemental analyzer that was calibrated with 2,5-
bis(5-tert-butylbenzoxazol-2-yl)thiophene. Conductivity values were
acquired on an Advanced Instrument Technology CMT-SR200N
sheet resistance/resistivity measurement system. Melting points were
determined with a MPA 100 Optimelt automated melting point
system and are uncorrected. Atomic force microscopy measurements
were conducted with a Multimode 8 nanoscope V (Bruker). X-ray
photoelectron spectroscopy experiments were performed using
an Escalab 250Xi (Thermo Fisher Scientific, Waltham, MA) equipped
with a monochromated aluminum Kα source (1486.6 eV). UV−vis
spectroscopy data were recorded on an Agilent Cary 100 UV−vis
spectrometer outfitted with a Peltier multicell temperature controller.
Synthesis of Poly(1). 5,6-Dibromobicyclo[2.2.0]hex-1-ene (0.10
g, 0.42 mmol) and CH2Cl2 (1.5 mL) were added to an air-free
reaction flask (10 mL) at room temperature under a positive flow of
nitrogen. A solution of the G3 dissolved in anhydrous CH2Cl2 (4.4
mg in 0.5 mL) was injected, and the mixture was gently stirred for 30
min at room temperature. The reaction was quenched upon the
addition of ethyl vinyl ether (0.1 mL), and the resulting mixture was
poured into cold hexane (ca. 100 mL). A dark pink precipitate formed
CONCLUSIONS
■
Ring-opening metathesis polymerization (ROMP) of a
dihalogenated derivative of Dewar benzene led to the
formation of a poly(acetylene) precursor in a controlled
manner. Subjecting the polymer to an alkyllithium agent
resulted in elimination to form an intermediate that was
consistent with a ring-opened, polymeric form of Dewar
benzene. Rapid isomerization ensued and afforded trans-
poly(acetylene), as determined using a range of spectroscopic
and analytical techniques as well as through comparison with
independently prepared samples. The methodology was also
successfully adapted to prepare triblock copolymers containing
segments of poly(acetylene). The copolymers were found to be
soluble in common solvents and formed films that exhibited
increased electrical conductivities upon doping. The method
described herein is an effective tool for preparing poly-
(acetylene) with a high trans-olefin content and well-defined
copolymers thereof and thus can be expected to find utility in
the growing number of applications that require the use of
conjugated polymeric materials.
1
and was subsequently collected in 90% yield. H NMR (400 MHz,
CDCl3): δ 5.30−6.10 (br, 2H), 4.25−4.75 (br, 2H), 3.21−4.0 (br,
2H).
Synthesis of Poly(11). exo,exo-5,6-Bis(methoxymethyl)bicyclo-
[2.2.1]hept-2-ene (0.20 g, 1.09 mmol) and CH2Cl2 (1.6 mL) were
added to an air-free reaction flask (10 mL) at room temperature
under a positive flow of nitrogen. A solution of G3 dissolved in
anhydrous CH2Cl2 (4.4 mg of catalyst in 0.5 mL of solvent) was
injected, and the mixture was gently stirred for 30 min at room
temperature. The polymerization was then quenched upon the
addition of ethyl vinyl ether (0.1 mL), and the resulting mixture was
poured into cold methanol (ca. 100 mL) to induce precipitation. The
product was collected and dried under vacuum (83% yield). 1H NMR
(400 MHz, CDCl3): δ 5.10−5.46 (br, 2H), 3.22−3.65 (br, 10H),
1.78−2.80 (br, 5H), 1.01−1.37 (br, 1H).
Preparation of trans-Poly(acetylene) (9). A solution of
methyllithium (1.6 M in diethyl ether) was added dropwise (0.53
mL total volume) to a THF solution containing poly(1) (0.10 g
polymer/8.3 mL THF) at room temperature. The formation of an
insoluble black material was observed after 30 min. The material was
EXPERIMENTAL SECTION
■
General Methodology. Unless otherwise noted, all manipu-
lations were performed under an atmosphere of nitrogen using
standard Schlenk techniques. Phthalic acid, sodium acetate, and acetic
anhydride were purchased from Sigma-Aldrich. Bromine was
purchased from Junsei Chemical. Hydrochloric acid (35 wt %) was
purchased from Daejung Chemicals & Metals. cis-5-Norbornene-exo-
2,3-dicarboxylic anhydride was purchased from Alfa Aesar. A sodium
mercury amalgam was prepared according to literature procedures.69
An Ace photochemical reactor (medium pressure Hg, 450 W) was
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subsequently collected and dried under reduced pressure (quantita-
tive yield).
(2) Dai, L. M.; Winkler, B.; Dong, L. M.; Tong, L.; Mau, A. W. H.
Conjugated Polymers for Light-Emitting Applications. Adv. Mater.
2001, 13, 915−925.
Film Preparation. A solution of poly(1) (prepared by mixing 5.0
mg of polymer and 1 mL of THF) was drop-casted on a glass
substrate (1.8 cm × 1.8 cm). A solution of CH3Li (1.6 M in diethyl
ether) was added dropwise (26 μL total volume), and the resulting
mixture was agitated for 10 s using a glass rod. The resulting film was
washed with absolute ethanol and then dried under nitrogen for 24 h
at room temperature.
Iodine Doping. Iodine (10 g) was placed at the bottom of a
chamber subjacent to a glass substrate supporting a polymer film.
Evacuation of the chamber (0.05 Torr) facilitated iodine sublimation
at room temperature. After 17 h, the chamber was entombed in a
glovebag filled with nitrogen, and the conductivity of the sample was
measured.
Triblock Copolymer Preparation. Monomer 11 was dissolved
in anhydrous CH2Cl2 (0.8 mL). Subsequent injection of predeter-
mined quantities of G3 dissolved in 0.6 mL of anhydrous CH2Cl2
followed by stirring at −15 °C for 15 min facilitated the consumption
of the monomer. A solution of monomer 1 dissolved in 0.8 mL of
anhydrous CH2Cl2 was then injected, and the mixture was stirred for
an additional 15 min. Similarly, a solution of monomer 11 dissolved in
0.8 mL of anhydrous CH2Cl2 was added, and the resulting solution
was stirred for 15 min. Excess ethyl vinyl ether was added to quench
the reaction, and then the resulting mixture was poured into cold
methanol to induce precipitation. The product was collected via
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.8b02754.
Additional synthetic details, additional electrochemical
measurement details and data, UV−vis spectra, infrared
and Raman spectra, an XPS survey spectrum, elemental
analysis data, AFM data, DSC and TGA data, GPC data,
1
isomerization kinetics details and data, and H and 13C
NMR spectra (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail bielawski@unist.ac.kr; Tel +82-52-217-2952.
(19) Klavetter, F. L.; Grubbs, R. H. Polycyclooctatetraene
(Polyacetylene): Synthesis and Properties. J. Am. Chem. Soc. 1988,
110, 7807−7813.
ORCID
Stanfield Y. Lee: 0000-0001-6955-2573
Christopher W. Bielawski: 0000-0002-0520-1982
Notes
(20) MacDiarmid, A. G.; Heeger, A. J. Organic Metals and
Semiconductors: The Chemistry of Polyacetylene, (CH)x and its
Derivatives. Synth. Met. 1980, 1, 101−118.
The authors declare no competing financial interest.
(21) Huang, Z. H.; Jelski, D. A.; Wang, R. S.; Xie, D. M.; Zhao, C.
D.; Xia, X. F.; George, T. F. Polarizabilities of trans and cis
Polyacetylene and Interactions Among Chains in Crystalline
Polyacetylene. Can. J. Chem. 1992, 70, 372−376.
(22) Knoll, K.; Schrock, R. R. Preparation of tert-Butyl-Capped
Polyenes Containing up to 15 Double Bonds. J. Am. Chem. Soc. 1989,
111, 7989−8004.
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Synthesis, Doping and Structure. Prog. Polym. Sci. 1985, 11, 57−89.
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of Acetylene with a Ruthenium Olefin Metathesis Catalyst. Macro-
molecules 2004, 37, 6255−6257.
(25) Munardi, A.; Aznar, R.; Theophilou, N.; Sledz, J.; Schue, F.;
Naarmann, H. Morphology of Polyacetylene Produced in the
Presence of the Soluble Catalyst Ti(OnBu)4-n-BuLi. Eur. Polym. J.
1987, 23, 11−14.
ACKNOWLEDGMENTS
■
The Institute for Basic Science (IBS-R019) and the BK21 Plus
Program as funded by the Ministry of Education and the
National Research Foundation of Korea are acknowledged for
support. We thank Dr. Karel Goossens and Dr. Sibanarayan
Tripathy for their assistance with the solid-state NMR
measurements. We are grateful to Ms. Younghye Park for
creating the graphical abstract.
REFERENCES
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analysis (see Figure S5 and Table S1).
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isomerization of 13 to 14 was measured to be 20.4 1.0 kcal/mol.
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