Folded H-stacking polymers by conformational control with 2-substituted trimethylene tethers

Article abstract of DOI:10.1021/ma1011057

Oligomers and polymers of type [-CH₂CHRCH₂-(π)-] _n comprising aryl units tethered by 2-substituted trimethylene were found to exist as a folding H-stacking structure in polar solvents such as CH₃CN and in film,

Full text of DOI:10.1021/ma1011057

6562 Macromolecules 2010, 43, 6562–6569
DOI: 10.1021/ma1011057
Folded H-Stacking Polymers by Conformational Control with
2-Substituted Trimethylene Tethers
Jun-ichi Watanabe, Tohru Hoshino, Yu-suke Nakamura, Edo Sakai, and Sentaro Okamoto*
Department of Material & Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku,
Yokohama 221-8686, Japan
Received May 18, 2010; Revised Manuscript Received July 11, 2010
ABSTRACT: Oligomers and polymers of type [-CH2CHRCH2-(π)-]n comprising aryl units tethered by
2-substituted trimethylene were found to exist as a folding H-stacking structure in polar solvents such as
CH3CN and in film, which was evidenced by their blue-shifted UV absorption compared to that of the parent
aryl compounds, and exhibited predominantly excimer-like emission. In addition, annealing of the films
resulted in a unique layered structure, which may arise from the folded polymer form.
Introduction
Controlled spatial arrangement of planar π-conjugate groups
or molecules is of great importance in organic material develop-
ment. Spatial interaction between π-conjugate moieties affects
their photophysical, electronic and electrochemical properties
such as excimer emission and charge transfer in solution or in the
solid state. Their ordered assembly involving two-dimensional
orientation (J- and H-aggregations) and higher dimensional
assembly of π molecules enables us to obtain the desired proper-
ties. In this context, molecular design and synthesis for ordering
fabrication modulated by molecular crystalline properties, self-
assembly, and supramolecular chemistry have been intensively
studied;1 however, control of molecular self-association behavior
and orientations remains a challenge.
Two-dimensional orientation of π molecules, i.e., J- and
H-aggregations, gives distinct photophysical, electronic and
photoelectronic properties. For instance, Dautel and Moreau
have prepared films comprising J- or H-aggregates of the same
π unit and have demonstrated that the type of aggregation
significantly affects the electronic properties of the material;2
the film with the J-aggregates exhibited high brightness of emis-
sion and low photoconductivity suitable for OLED (organic
light-emitting diode) devices, while the film with H-aggregates
displayed no brightness and higher photocurrents promising for
devices of photovoltaic cell.
Figure 1. Ordering orientation of planar π-molecules (or -moieties).
derivatives 1 by molecular mechanics calculation (MM2) and by
the NMR and fluorescence measurements of the corresponding
synthetic samples. The results are summarized in Table 1. The
table illustrates three conformations [open (O), half-open (H-O),
and closed (C)], simplified for each 2-substituted 1,3-diphenyl-
propane derivative 1, based on the energy differences calculated
by molecular mechanics (MM2) (the effect of solvent was not
considered). The populations of these conformations (O:H-O:C)
at 300 K were estimated according to a Boltzmann distribution.
Although the ultraviolet (UV) absorption spectra of synthetic
1,3-diphenylpropanes 1a-h did not have remarkable difference,
their emission showed distinct behavior (vide infra). The fluores-
cence (FL) spectra showed emission peaks at 285 and 333 nm,
which may be considered as emissions from single benzene rings
and benzene excimers, respectively.6 The ratio of the intensities of
these peaks, which were calculated by using a height of each peak,
is summarized in Table 1, and the representative fluorescence
spectra are shown in Figure 2.
The results of the calculation suggest that a closed (stacked)
structure is a superior conformation for compounds 1b-f; in
fact, these compounds predominantly exhibited excimer-type
emissions (Figure 2 and SI: S-06). For instance, 1c, 1d, and 1f
have the λem,max around 330 nm in a region of benzene excimer
emission with much weaker emission from a single benzene ring
(around 285 nm) (Figure 2a). Meanwhile, the calculation results
suggest that the open and half-open conformations were major
for 2,2-disubstituted trimethylene-tethered compound 1a, and
indeed, 1a emitted more strongly at 280 nm than at 330 nm
(Figure 2a). The steric effect of the substituent at the 2-position
of the trimethylene tether was observed. Emission from single
benzene ring (∼285 nm) decreased in order of bulkiness of the
2-substituent (Figure 2b). Thus, an increase in substituent
bulkiness enhanced the presence of the stacked conformation.
Also ordering assemblies of π-moieties in polymeric molecules
is of interest because of the low processing costs and the desirable
mechanical properties of electronically active polymers;3 in this
process, folded polymers A and B including π-units in a chain
backbone3,4 and polymers C having π-units as pendants5 can be
designed (Figure 1). Here, we introduce a new approach for
spatial orientation of chromophores in simple, linear polymer
structures of type A,4 which are folded via conformational
control with 2-substituted trimethylene tethering moieties.
Results and Discussion
1. Design of 2-Substituted Trimethylene Tethering Group. First,
to design the folding π-stacking polymer, we carried out confor-
mational analysis of 2-substituted trimethylene-tethered6 biaryl
*Corresponding author. E-mail: okamos10@kanagawa-u.ac.jp.
pubs.acs.org/Macromolecules
Published on Web 07/28/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 16, 2010 6563
Table 1. Conformational Analysis and Fluorescent (FL) and 1H NMR Data of 2-Substituted 1,3-Diphenylpropanes 1
a Based on energy differences calculated by MM2 (Quantum CAChe 4.9), estimated according to a Boltzmann distribution at 300 K. b Fluorescence of
a 10-4 M solution in CH2Cl2 at room temperature. c 1H NMR (CDCl3, 500 MHz, 20 °C) chemical shift of o-protons of Ph moieties. d Ratio of FL
intensity at 282 and 333 nm.
1H NMR analyses of 1 (500 MHz, CDCl3) also supported
the stability of the closed conformation for compounds 1b-g
(Table 1 and Figure 3a). In comparison to toluene spectra,
compounds 1b-g displayed an upfield shift of proton
peaks at the ortho-position of Ph moieties in the range of
0.13-0.23 ppm because of a shielding effect along with the
stacking structure. Although MM2 calculation (nonsolvent
conditions), fluorescence (in CH2Cl2), and NMR (in CDCl3)
measurements were conducted under different conditions, it
is noteworthy that a plot of the intensity of excimer emission
to the chemical shifts (O) shown in Figure 3b is in very good
agreement with a plot of the calculated population of closed
form to the chemical shifts ([). Regarding m- and p-protons,
similar relations were observed (SI: S-04). Figure 3c,d
shows the calculated closed structure of 1d by MM2, in
which two benzene rings are nearly parallel and the distances
of C1-C10 and C4-C40 were estimated to be 2.93 and
determined by gel-permeation chromatography (GPC) anal-
ysis (eluent: THF; calibration: polystyrene standards)] and
4b [π = (E,E)-CHdCH-C6H4-CHdCH, Mn = 7.14 ꢀ
103, Mw/Mn = 1.68] were synthesized by the Suzuki-
Miyaura coupling reaction7 with bis(boronic ester)s 38 as a
polymerization reaction. The polymers were obtained by
reprecipitation from CHCl3 by addition of ethyl acetate (for
4a) or methanol (for 4b), and their GPC analysis showed
unimodal fraction profiles (SI: S-02, S-03). The reaction of 2
and 3a in the absence of (n-Oct)3MeNCl resulted in the
formation of the shorter polymer 4a0 (Mn = 2.08 ꢀ 103,
Mw/Mn = 1.33). Although these Mn and Mw were estimated
by GPC analyses with calculation against polystyrene stan-
dards, the synthesized polymers 4 and flexible polystyrene
may be much different in hydrodynamic volume, in parti-
cular if 4 would present in a folded structure. Therefore, the
actual number-average molecular weights of polymers 4 may
be higher than those by GPC, although, unfortunately, end-
group analysis of these polymers could not be carried out due
to their undefined terminal structure.
˚
3.66 A, respectively.
2. Synthesis of Polymers 4 with 2-Substituted Trimethylene
Tethers. With these results, we designed polymers 4 having
a 2-substituted 1,3-diphenylpropane tether of type of 1d,
expecting folded H-stacking structure A for the resulting
polymers (Scheme 1). 1,3-Diphenylpropane tether unit 2
was readily prepared in a high yield from diethyl malonate
through four steps involving dialkylation, decarboxylation,
formation of tertiary alcohol, and silylation reactions. With
use of the resulting tether unit 2, both polymers 4a [π = 2,20-
bithiophen-5,50-diyl, Mn = 7.03 ꢀ 103, Mw/Mn = 1.44,
To compare the photophysical properties of polymers 4
with those of the corresponding single π unit, model com-
pounds 5,50-bis(4-methylphenyl)-2,20-bithiophene (diMe-
P2T)9 and 1,4-bis(4-methylstyryl)benzene (BStB)10 were
prepared by the Pd-catalyzed coupling reaction of 3a or 3b,
respectively, with 4-iodotoluene.
3. Optical Properties of Polymers 4. In general, the mole-
cular aggregates in the solid state show distinct changes in

6564 Macromolecules, Vol. 43, No. 16, 2010
Watanabe et al.
fluorescence spectra of 4a shown in Figure 4b, 4a in CH2Cl2
showed a broad red-shifted emission to diMe-P2T. A CH3CN
solution and film of 4a exhibited similar spectra, only emitting in
the excimer emission region (λem,max = 512 nm). The emission
intensity of the solutions was decreased along with their red shift
at the same concentration (considering the repeat unit for the
polymer) (Figure 4c). The shorter polymer (oligomer) 4a0
showed a similar but moderate photophysical trend. These
results clearly demonstrate that π-units, p-C6H4-Th-Th-
p-C6H4, in polymers 4a were successfully assembled into the
H-type stacking form in a CH3CN solution and in film.12 In
contrast to these results on polymer 4a, it has been reported that
a solution of 5,50-diphenyl-2,20-bithiophene (P2T) shows 376 nm
of λabs,max, 433 and 455 nm of λem,max, and376nmofλex,max in its
UV absorption, fluorescence, and excitation spectra, respec-
tively, and its aggregate in thin film exhibits red-shifted absorp-
tion and emission (λabs,max = 440 nm, λem,max = 515, 550 nm).9b
These indicate that P2T may aggregate in thin film with an
orientation(s) other than that involving H-type stacking form.
Similarly, broad blue-shifted excitation and broad red-
shifted emission spectra were recorded for a film of polymer
4b compared with those of the parent π-unit BStB, where an
emission was again observed predominantly in the excimer
region (Figure 5). The results again demonstrate that π-units,
p-C6H4-CHdCH-p-C6H4-CHdCH-p-C6H4, in poly-
mers 4b were assembled into the H-type stacking form in
a CH3CN solution and in film.12 Thus, a blue-shifted UV-
absorption against that of BStB was recorded for a solution
of 4b in CH3CN (Figure 5a). Red-shifted fluorescence
against BStB was observed for a CH3CN solution and film
of 4b with 10 and 52 nm differences, respectively (Figure 5b).
As revealed from Figure 5b, excitation spectra for these
maximum emissions of 4b in a CH3CN solution and in
film were shifted with 38 and 45 nm differences to higher
energy region, respectively. It has been reported that 1,4-
bis(styryl)benzene (Ph-CHdCH-p-C6H4-CHdCH-Ph)
are arranged layer by layer in the herringbone structure
involving the H-type stacking orientation of the molecules
in crystalline, and its neat film exhibits blue-shifted absorp-
tion (∼300 nm) and red-shifted emission (460 and 488 nm)
against those of the solution.10b The films of 4b and the
known 1,4-bis(styryl)benzene closely resemble each other in
their spectra.
In conclusion, the spectroscopic behavior observed for a
solution and film of 4a and 4b (blue-shifted absorption, red-
shifted and quenched emission) can be attributed to their
H-stacking structure. Regarding solvent effects, it can be
explained that, in solution of relatively less polar solvents
such as cyclohexane and CH2Cl2, the solvation to both less-
polar polymers may disturb their ordering arrangement to
make the array of π units irregular, whereas the polymer
chain can be packed down intramolecularly in polar solvents
such as CH3CN and in film.
4. Thermal Analyses and Morphology of Polymers 4 in
Film. From a thermogravimetry (TG) curve of polymer 4a
[SI: S-27a(b)], 5% and 10% weight loss were observed at 261
and 268 °C, respectively, where two phases of decomposition
occurred. A constant weight loss (24%) observed at a range
of 300-400 °C could be considered as decomposition by
elimination of silanol (HOSiEt3) from the silyl ether struc-
ture of tertiary alcohol in the polymer, since HOSiEt3 is 24 wt
% in the repeat unit structure for the polymer. Similar
phenomena were recorded for polymer 4b (SI: S-27b).
On the basis of the results of TG analysis of 4a, two peaks
at 192 °C and around 260 °C observed in differential thermal
analysis (DTA) [SI: S-27a(a)] may be assigned to be for
melting and decomposition by the elimination of silanol,
Figure 2. Representative fluorescence spectra of a CH2Cl2 solution of 1
(excited at 260 or 262 nm): (a) 1a (blue: 10-4 M), 1c (red: 10-4 M), 1d
(black: 10-4 M), 1f (green: 10-4 M), toluene (dotted: 2 ꢀ 10-5 M). (b) 1c
(red:10-4 M), 1d (black: 10-4 M), 1g (pink: 10-4 M), 1h (aqua: 10-4 M).
their absorption band as compared to their monomeric state
(Figure 1). J-aggregates by a head-to-tail arrangement of the
π-molecules display the bathochromically shifted J-bands,
whereas a sandwich-type arrangement (H-aggregates) by a
plane-to-plane stacking exhibits the hypsochromically shifted
H-bands and also much weaker, quenched fluorescence
spectra.11 Therefore, to determine the orientation of π
moieties in the synthesized polymers, ultraviolet-visible
(UV-vis) absorption, fluorescence, and excitation spectra
of polymers 4a, 4a0, and 4b thus prepared were measured,
and the results are shown in Figures 4 and 5. The con-
centrations (M) of polymer solutions in the figures are
indicated as an amount (mol) of the repeat unit for the
polymer per a volume of solution (L). The film was
prepared simply by applying a CH2Cl2 solution of poly-
mers to quartz glass and removing the solvent, where a
thickness of the film was not determined. The UV absorp-
tions of solutions of 4a, 4a0, and 4b at different concent-
rations were measured (SI: S-08, S-11, S-13). The results
that the intensity of absorbance was proportional to the
concentration in a range of 10-6-10-4 M suggested that
the effect of polymer aggregation in a solution on optical
properties can be excluded at e10-4 M.
In a CH2Cl2 solution, a small blue shift (9 nm) of the
absorption maximum (λabs,max) of 4a (λabs,max = 367 nm)
from that of diMe-P2T (λabs,max = 376 nm) was observed,
and a CH3CN solution (λabs,max = 340 nm) and film
(λabs,max = 344 nm) of 4a exhibited a large blue shift from
that of diMe-P2T (Figure 4a). Similarly, excitation spectra of
4a (λex,max = 336 nm) for an emission maximum (λem,max
=
512 nm) showed a significant blue shift (38 nm) compared
with that of diMe-P2T (λex,max =374nmforλem,max =463nm),
and the excitation spectra were much weaker than that of diMe-
P2T at the same concentration (considering the repeat unit
for the polymer) (Figure 4c). As revealed from normalized

Article
Macromolecules, Vol. 43, No. 16, 2010 6565
Figure 3. (a) 1H NMR spectra of 1f and toluene (CDCl3, 500 MHz, 20 °C). (b) Relation between chemical shifts of o-protons of 1 and distribution of
the closed conformation estimated by fluorescence (O) or MM2 calculation ([). (c) Top view and (d) side view of the MM2-optimized structure for 1d
(gray: C; red: O; purple: Si).
respectively. The DTA chart of 4b and optical microscopic
observation suggested that the melting started around
210 °C, the temperature of which was close to the tempera-
ture for beginning decomposition (∼230 °C) (SI: S-27b).
The differential scanning calorimetry (DSC) profile for the
first heating of 4a to 220 °C (10 °C/min) showed three peaks,
which can respectively be considered as temperatures for
glass transition (115.5 °C), crystallization (around 144 °C),
and melting (around 180 °C) (SI: S-28a). But in the chart for
a second heating, the peaks became less clear and the third
heating exhibited only a peak around 125 °C. The DSC
profiles obtained for polymer 4b had a similar trend (SI:
S-28b). Although rationalization of the behavior of enthalpy
changes for these peculiar polymers is unclear at this time
and must await further study, based on these DTA, TG, and
DSC data along with optical microscopic observation, we set
an annealing procedure of films of 4a and 4b (vide infra).
A film of polymer 4a, which was prepared by spin-coating
on a silicon substrate through the use of its CH2Cl2 solution
and solvent removal, provided only a flat surface image in
atomic force microscope (AFM) analysis. However, an
interesting AFM images were obtained after annealing
(heated to melt at 210 °C for 1 min, cooled to 160 °C for
2 min and then to rt) (Figure 6a). The observed film surface
had craterlike holes that displayed an inner layered structure
of the film. Each of the layers had a thickness of 3 nm, the
length of which is in good agreement with that calculated for
the width of the expected folded structure of polymer 4a as
illustrated in Figure 7.
X-ray diffraction (XRD) analyses of polymer powder
peeled from the film, prepared by spin-coating on a silicon
substrate and removing the solvent, were carried out for the
samples before and after annealing treatment mentioned
above (Figure 6b,c). Observed XRD patterns were nearly
identical before and after annealing, and both showed a
sharp peak at 2.96 nm, the length of which is again in good
agreement with the calculated width of the expected folded
structure of 4a (Figure 7). A polymer powder just after
precipitation from the CHCl3 solution also showed almost
the same reflection profile (data not shown). From these
observations, we assume that a polymer molecule of 4a
may have an ordered aggregate morphology with its folded

6566 Macromolecules, Vol. 43, No. 16, 2010
Watanabe et al.
Scheme 1
structure in the solid state of precipitates and cast-film, and
then annealing of its film produces a layered structure as
illustrated in Figure 7. Similarly, the XRD profile for an
annealed film of polymer 4b had a sharp peak of 3.02 nm
(Figure 6d), the value of which is somewhat larger than that
of 4a. It is in good agreement with the fact that a π-unit of 4b,
˚
bis(styryl)benzene, is ∼1 A longer than that of 4a, diphenyl-
bithiophene (Figure 7). The assignment of other peaks
observed by XRD analyses must await further study.
Conclusion
We have demonstrated that, in simple linear skipped π poly-
mers, conformational control via 2-substituted trimethylene
tethering groups makes the polymer fold, which stabilizes the
H-type stacking form in solution as well as in solids. The XRD
patterns of the pristine film before annealing and the annealed film
of 4a were nearly identical, both of which had a sharp peak at 3 nm,
nearly identical to the width of the expected folded polymer
structures. Thus, we have synthesized and designed a new polymer
programmed to fold in H-stacking. This may be important for
charge transport as requested on solar cell. In addition, we have
also obtained nanostructured morphologies by annealing the films
while keeping the layered structure, the nanostructure of which
may be also of importance as requested on photovoltaic cell. The
present approach for controlling the spatial arrangement might be
expected to become a novel motif for the development of new soft
materials, and further investigation on the possible application by
changing the structure of π unit included is underway.
Figure 4. UV-vis absorption and fluorescence spectra of polymer 4a
and oligomer 4a0: (a) UV-vis absorption (normalized): 10-6 M for
diMe-P2T (black), 10-5 M for 4a in CH2Cl2 (orange), 10-5 M for 4a in
CH3CN (pink), and film of 4a (green). (b) Fluorescence (normalized):
10-6 M. Excited at 375 nm for diMe-P2T (black), 367 nm for 4a in
CH2Cl2 (orange), 336 nmfor 4a in CH3CN (pink), and 344 nm for a film
of 4a (green). (c) Fluorescence: 10-6 M solution in CH3CN, excited at
374 nm for diMe-P2T (black), 336 nm for 4a (pink), and 364 nm for 4a0
(blue).
for 13C, respectively, on JEOL JNM-ECA600, 500 and -EX270
and HITACHI R-1900 spectrometers. Chemical shifts are re-
ported in parts per million (ppm, δ) relative to Me4Si (δ 0.00),
residual CHCl3 (δ 7.26 for 1H NMR), or a center peak of CDCl3
(δ 77.0 for 13C NMR). IR spectra were recorded on an FT-IR
spectrometer (JASCO FT/IR-4100). All reactions sensitive to
oxygen and/or moisture were performed under an argon atmo-
sphere. The Mn and Mw/Mn of polymers were measured with
a TOSOH HLC-8020 gel-permeation chromatography (GPC)
Experimental Section
General Data. NMR spectra were recorded in CDCl3 at 600,
500, 270, and 90 MHz for 1H and 150, 125, 67.5, and 22.5 MHz

Article
Macromolecules, Vol. 43, No. 16, 2010 6567
Figure 5. UV absorption, fluorescence, and excitation spectra of poly-
mer 4b and BStB. (a) UV absorption: BStB (gray, 10-7 M in CH2Cl2),
4b (green, 10-6 M in CH2Cl2), 4b (peach, 10-6 M in CH3CN).
(b) Fluorescence: BStB (black, 10-7 M in CH2Cl2), 4b (peach, 10-6 M in
CH3CN), 4b (blue, film). Excitation: BStB (black, 10-7 M in CH2Cl2),
4b (peach, 10-6 M in CH3CN), 4b (blue, film).
Figure 6. AFM images and XRD spectrum of 4a and 4b. (a) AFM
images of 4a film (spin-coated on silicon substrate, heated at 210 °C for
1 min, cooled to 160 °C for 2 min, and then cooled to rt). (b) XRD chart
of 4a (after spin-coating and removing solvent and before annealing,
film was removed from the substrate, and the resulting powder was
analyzed). (c) XRD chart of 4a (after annealing on a silicon substrate,
film was removed from the substrate, and the resulting powder was
analyzed). (d) XRD chart of 4b (after annealing on a silicon substrate,
film was removed from the substrate, and the resulting powder was
analyzed).
unit (eluent: THF; calibration: polystyrene standards) using two
TSK-gel columns (2 ꢀ Multipore HXL-M). High-resolution
mass spectra (HR-MS) were measured on JEOL Accu TOF
T-100 equipped with ESI ionization. UV-vis absorption spec-
tra were recorded on a Shimadzu UV-2450 spectrometer. Ex-
citation and fluorescence spectra were measured on a Shimadzu
RF-5300PC spectrometer. Thermogravimetry/differential ther-
mal analysis (TG/DTA) was carried out with Seiko Instruments
Inc. EXSTAR6000 TG/DTA6200 under nitrogen (heating rate:
10 °C/min). Differential scanning calorimetry (DSC) measure-
ment was carried out with Seiko Instruments Inc. EXSTAR6000
DSC6220 under nitrogen (heating rate: 10/min; cooling rate:
5 °C/min). AFM images were recorded under ambient condi-
tions using a Digital Instrument Nanoscope V operating in the
tapping mode. X-ray diffraction (XRD) patterns were obtained
using a Rigaku RINT-UltimaIII diffractometer with Cu KR
radiation. Molecular mechanics (MM2) calculations were per-
formed using Quantum CAChe 4.9 program package. On the
basis of the energy differences calculated by MM2, the popula-
tions of these conformations (O:H-O:C) were estimated ac-
cording to a Boltzmann distribution. 1,3-Diphenylpropane
derivatives 1b-h were prepared from 1a, which was obtained by
the reaction of diethyl malonate and benzyl bromide with NaH
in DMF, by the conventional reactions according to the pro-
cedure (see SI: S-01). Dry solvents (THF and ether) were pur-
chased from Kanto Chemical Co., Inc., and used as received
without any additional purification and degassing procedure.
The structures of synthesized diMe-P2T9 and BStB10 were
confirmed by comparison of their spectral data with those
reported.
Ethyl 2-(4-Bromobenzyl)-3-(4-bromophenyl)propanoate. To a
mixture of NaH (55% in oil, 2.95 g, 67.5 mmol) and DMF
(60 mL) was added diethyl malonate (4.53 mL, 30.0 mmol) at
0 °C. After being stirred for 30 min at 0 °C, to the mixture was

6568 Macromolecules, Vol. 43, No. 16, 2010
Watanabe et al.
1.21 (s, 6H, (CH3)2C), 0.97 (t, 9H, J = 7.8 Hz, (CH3CH2)3Si),
0.61 (q, 6H, J = 8.0 Hz, (CH3CH2)3Si). 13C NMR (150 MHz,
CDCl3): δ 141.4, 131.1, 130.6, 119.1, 76.1, 54.9, 36.2, 28.2,
7.2, 6.9. IR (neat): 2954, 2874, 1591, 1488, 1459, 1404, 1383,
1365, 1236, 1178, 1143, 1102, 1072, 1012, 798.4, 724.1 cm-1
.
:
þ
HR-MS: m/z = calcd for C24H34 Br2KOSi [M þ K]
563.0383; found 563.0352.
Polymers 4a and 4a0. To a solution of 2 (2.11 g, 4.0 mmol), 3a
(1.67 g, 4.0 mmol), (n-Oct)3MeNCl (330 mg, 0.82 mmol) in 2 M
aqueous Na2CO3 (8.0 mL), and THF (22 mL) which had been
deaerated for 1 h was added a solution of Pd(PPh3)4 (185 mg,
0.16 mmol) in THF (5.0 mL). The reaction mixture was stirred
for 12 h (polymer 4a0) or 3 days (polymer 4a) at 80 °C, and then it
was cooled to room temperature. The resulting mixture was
added into a saturated aqueous NaHCO3, and the product was
extracted with CHCl3 three times. The combined organic layers
were washed with water and dried over anhydrous Na2SO4.
After filtration and evaporation, the residue was dissolved in
CHCl3 and poured into a large amount of MeOH. The
resulting residue was dissolved in CHCl3 and poured into a
large amount of AcOEt. The obtained polymer was washed
with AcOEt several times and dried under reduced pressure.
A brown solid polymer 4a was obtained. Polymer 4a. Yield:
1.68 g, 3.16 mmol, 79%. GPC: Mn = 7.03 ꢀ 103, Mw =1.01ꢀ 104,
Mw/Mn = 1.44. 1H NMR (CDCl3, 600 MHz): δ 7.42-6.70 (br
m, overlap with CHCl3 peak, 12H in one unit, Ar), 3.08-2.89
(br, 2H in one unit, CH2Ar), 2.43-2.24 (br, 2H in one
unit, CH2Ar), 2.19-2.08 (br, 1H in one unit, CHCH2Ar),
1.36-1.13 (br, 6H in one unit, (CH3)2C), 1.07-0.86 (br, 9H
in one unit, (CH3CH2)3Si), 0.73-0.47 (br, 6H in one
unit, (CH3CH2)3Si). 13C NMR (CDCl3, 150 MHz): δ 142.9,
141.9, 136.2, 135.7, 131.2, 129.4, 127.7, 125.5, 125.1, 124.2,
123.2, 76.1, 54.9, 36.7, 34.2, 30.3, 29.4, 28.1, 7.3, 6.9. IR (film):
2954, 2875, 1497, 1445, 1415, 1382, 1364, 1215, 1177, 1144, 1112,
1040, 790.7, 740.5 cm-1. Polymer 4a0. Yield: 0.319 g, 0.60 mmol,
15%. GPC: Mn = 2.08 ꢀ 103, Mw = 2.77 ꢀ 103, Mw/Mn = 1.33.
Polymer 4b. To a solution of 2 (790 mg, 1.50 mmol), 3b (573
mg, 1.50 mmol), (n-Bu)4NBr (484 mg, 1.50 mmol) in 2 M
aqueous K2CO3 (3.0 mL), and THF (8.0 mL) which had been
deaerated for 1 h was added a solution of Pd(PPh3)4 (69 mg,
0.060 mmol) in THF (2.0 mL). The reaction mixture was stirred
for 3 days at 80 °C, and then it was cooled to room temperature.
The resulting mixture was added into a saturated aqueous
NaHCO3, and the product was extracted with CHCl3 three
times. The combined organic layers were washed with water and
dried over anhydrous Na2SO4. After filtration and evaporation,
the residue was dissolved in CHCl3 and poured into a large
amount of MeOH. The obtained polymer was washed with
Et2O several times and dried under reduced pressure. The
polymer 4a (371 mg, 0.751 mmol) was obtained in 50% yield
as a yellow-brown solid. GPC: Mn = 7.14 ꢀ 103, Mw = 1.20 ꢀ
Figure 7. Illustration of postulated layer structure for annealed films of
4a and 4b.
added 4-bromobenzyl bromide (15.7 g, 63.0 mmol), and the
reaction mixture was stirred for 2 h at room temperature. After
checking completion of the reaction by TLC analysis, the
mixture was quenched with saturated aqueous NH4Cl, and the
aqueous layer was extracted with AcOEt. The combined organic
layers were washed with brine, dried over anhydrous MgSO4,
filtered through a pad of Celite, and concentrated in vacuo. To
the resulting residue were added LiCl (5.09 g, 120 mmol), H2O
(1.08 mL, 60.0 mmol), and DMF (100 mL) at room temperature,
and the reaction mixture was stirred for 7 h at 160 °C. After
checking completion of the reaction by TLC analysis, the
mixture was quenched with water, and the aqueous layer was
extracted with AcOEt. The organic layers were washed with
brine, dried over anhydrous MgSO4, filtered through a pad of
Celite, and concentrated in vacuo. The residue was chromato-
graphed on silica gel (hexane:AcOEt = 30:1) to give ethyl 2-(4-
bromobenzyl)-3-(4-bromophenyl)propanoate (11.5 g, 27.0 mmol)
in 90% yield as a yellow oil. 1H NMR (600MHz, CDCl3) δ7.39 (d,
4H, J = 8.4 Hz, Ar), 7.02 (d, 4H, J = 7.8 Hz, Ar), 3.96 (q, 2H, J =
7.4 Hz, CO2CH2CH3), 2.92-2.85 (m, 3H, CHCH2Ar and
CHCH2Ar), 2.73 (dd, 2H, J = 4.8, 12.6 Hz, CH2Ar), 1.03 (t,
3H, J = 7.2 Hz, CO2CH2CH3). 13C NMR (150 MHz, CDCl3): δ
174.3, 137.8, 131.5, 130.6, 120.4, 60.5, 49.2, 37.6, 14.0. IR (neat):
2962, 1731, 1592, 1488, 1445, 1405, 1375, 1259, 1214, 1160, 1103,
1072, 1012, 806.1 cm-1. HR-MS:m/z=calcdforC18H18 Br2NaO2
[M þ Na]þ: 446.9571; found 446.9586.
(3-(4-Bromobenzyl)-4-(4-bromophenyl)-2-methylbutan-2-yloxy)-
triethylsilane (2). To a mixture of CeCl3 (4.44 g, 18.0 mmol) and
THF (48 mL) which had been stirred for 12 h at room temperature
was added MeLi (in Et2O 1.6 M, 11.3 mL, 18.0 mmol) at -78 °C.
After being stirred for 1 h at -78 °C, to the mixture was added a
solution of ethyl 2-(4-bromobenzyl)-3-(4-bromophenyl)propano-
ate (2.56 g, 6.00 mmol) in THF (6.0 mL), and the reaction mixture
was stirred for 2 h at -78 °C. After checking completion of the
reaction by TLC analysis, the mixture was quenched with 0.1 M
aqueous CH3COOH, and the aqueous layer was extracted with
AcOEt. The combined organic layers were washed with water,
dried over Na2SO4, filtered through a pad of Celite, and con-
centrated in vacuo. To the resulting residue was added pyridine
(12 mL) and triethylsilyl chloride (1.3 mL, 7.5 mmol) at room
temperature, and the reaction mixture was stirred for 20 h at 60 °C.
After checking completion of the reaction by TLC analysis, the
mixture was quenched with saturated aqueous NH4Cl, and the
aqueous layer was extracted with hexane. The combined organic
layers were washed with water, dried over anhydrous MgSO4,
filtered through a pad of Celite, and concentrated in vacuo. The
residue was chromatographed on silica gel (hexane only) to give 2
1
104, Mw/Mn = 1.68. H NMR (CDCl3, 600 MHz): δ 7.44-
6.81 (br m, overlap with CHCl3 peak, 16H, Ar and CHdCH),
3.13-2.77 (br, 2H, CH2Ar), 2.48-2.23 (br, 2H, CH2Ar),
2.16-2.00 (br, 1H, CH2Ar), 1.35-1.04 (br, 6H, (CH3)2C),
1.04-0.83 (br, 9H, (CH3CH2)3Si), 0.71-0.48 (br, 6H,
(CH3CH2)3Si). 13C NMR (CDCl3, 150 MHz): δ 142.3,
136.6, 134.5, 129.3, 128.7, 128.4, 127.3, 126.7, 126.5, 126.2,
76,2, 54.9, 36.6, 28.3, 7.3, 6.9. IR (film): 3021, 2954, 2875,
1600, 1516, 1459, 1419, 1383, 1364, 1212, 1177, 1144, 1110,
1040, 960.4, 825.4, 724.1, 549.6 cm-1
.
Acknowledgment. We thank the Scientific Frontier Research
Project from the Ministry of Education, Culture, Sports, Science and
Technology, Japan for financial support. We thank Prof. T. Ikehara
and Dr. T. Kataoka, Kanagawa University for AFM analysis.
1
(3.00 g, 5.7 mmol) in 95% yield as colorless oil. H NMR (600
MHz, CDCl3): δ 7.25 (d, 4H, J = 8.4 Hz, Ar), 6.81 (d, 4H, J =
8.4 Hz, Ar), 2.92 (dd, 2H, J = 4.8, 14.4 Hz, CH2Ar), 2.30 (dd, 2H,
J= 8.1, 14.1 Hz, CH2Ar), 2.00(tt, 1H,J=4.3, 8.4Hz, CHCH2Ar),
Supporting Information Available: Experimental and ana-
lytical details and spectroscopic data. This material is available
free of charge via the Internet at at http://pubs.acs.org.

Article
Macromolecules, Vol. 43, No. 16, 2010 6569
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