Synthesis of dendronized polymers through bergman cyclization of enediyne-containing Frechet-type dendrimers

Article abstract of DOI:10.1002/pola.24556

In this article, dendronized polymers with rigid backbones were synthesized from enediyne-containing Frechet-type dendrimers. Two generations of dendrimers were conically incorporated with 3-(2-(2-(trimethylsilyl)ethynyl)phenyl)prop-2- yn-1-ol. The trimethylsilyl protection groups of enediyne units were subsequently removed, and two types of brush polymers with rigid conjugated backbone were prepared through Bergman cyclization polymerization at elevated temperature under vacuum. The dendronized polymers were characterized with GPC, IR, UV-vis, and NMR spectroscopy. Furthermore, the morphology of the dendronized polymer was revealed by atomic force microscopy.

Full text of DOI:10.1002/pola.24556

Synthesis of Dendronized Polymers Through Bergman Cyclization
of Enediyne-Containing Frechet-Type Dendrimers
JIANGUO MA,1,2 XIAOWEI MA,1 SHENG DENG,1 FEI LI,1 AIGUO HU1
1Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering,
East China University of Science and Technology, Shanghai 200237, China
2Faculty of Chemistry Biology and Materials Science, East China Institute of Technology, Jiangxi 344000, China
Received 1 December 2010; accepted 21 December 2010
DOI: 10.1002/pola.24556
Published online 18 January 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: In this article, dendronized polymers with rigid
backbones were synthesized from enediyne-containing Fre-
chet-type dendrimers. Two generations of dendrimers were
conically incorporated with 3-(2-(2-(trimethylsilyl)ethynyl)phe-
nyl)prop-2-yn-1-ol. The trimethylsilyl protection groups of
enediyne units were subsequently removed, and two types
of brush polymers with rigid conjugated backbone were pre-
pared through Bergman cyclization polymerization at elevated
temperature under vacuum. The dendronized polymers were
characterized with GPC, IR, UV–vis, and NMR spectroscopy.
Furthermore, the morphology of the dendronized polymer
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was revealed by atomic force microscopy.
2011 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1368–
1375, 2011
KEYWORDS: Bergman cyclization; degree of polymerization;
dendrimer; dendronized polymers; enediyne; gel permeation
chromatography; graft copolymers; grafting through
INTRODUCTION Dendronized polymers have attracted enor-
mous interest in many fields because of their unique proper-
ties in self-assembly into condensed soft matter and great
potentials in a wide range of applications1–21 such as sen-
sor,22,23 drug delivery,24–26 stimuli-responsive materials,27–29
and microelectronics.30–32 Dendronized polymers are formed
through dendritic wedges attached by their cores to linear
backbones with such a high grafting density that the den-
drons may forced to stretch away to form rigid structures.
With the increase of generation of dendrons, dendronized
polymers tend to extend from random coils to shaped nano-
structures because of the increasing of repulsions between
dendritic side chains.1 Numerous synthetic methods have
been developed for the synthesis of well-defined dendron-
ized polymers in recent years. They can be classified in three
categories based on how the dendritic moieties are attached
on the linear backbones, namely, ‘‘grafting from,’’22,33–37
‘‘grafting onto,’’38–41 and ‘‘grafting through’’23–25,28,30,42–56 as
the most popular strategy. Beneficial from lately developed
synthetic organic methods, like ‘‘click chemistry’’42 and living
radical polymerizations, dendritic polymers with various
architectures, like gradient, block, alternative copolymers,
and functionalities, have been explored. Furthermore, these
giant structures–related self-assembly properties and their
potential applications in a variety of fields have also been
investigated. Among all these dendronized polymers, the
polymers with conjugated backbone57 have drawn special
attentions because of their unique optical and electrical
properties. Proper functionalizations allow conjugated poly-
mers to be competitive candidates for transistors, solar cells,
and sensors.58–65 Furthermore, the conjugated dendronized
polymers are architecturally interesting for chemists because
of the possibility of forming extended chain conformations.
The optoelectrical properties of conjugated polymers depend
strongly on the organization of the side chains, and the solu-
bility of conjugated polymers plays a key role in application
in the number of areas. As a result, development of some
new synthetic strategies for conjugated polymers is of great
importance. Recently, we have reported the preparation
of conjugated brushed polymers with polycaprolactone as
flexible side chains via Bergman cyclization.66 Herein, we
extended our work by choosing Frechet-type dendrons
as side chains to construct dendronized polymers with
conjugated backbones through Bergman cyclization.
The Bergman cyclization (Scheme 1) is described as a ther-
mally allowed rearrangement of 3-ene-1,5-diynes to generate
aryl 1,4-diradicals.67 In last 3 decades, Bergman cyclization
has been extensively investigated both theoretically and
experimentally owing to its relevance to the biological activ-
ities of enediyne antitumor antibiotics.68–73 The exploration
of Bergman cyclization in polymer and material science was
reported in a few cases. Moore et al.74,75 used the diradicals
generated from Bergman cyclization of macrocyclic ene-
diynes to investigate their behaviors in initiating free radical
polymerizations of various functionalized olefines. Smith
Correspondence to: A. Hu (E-mail: hagmhsn@ecust.edu.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 1368–1375 (2011) 2011 Wiley Periodicals, Inc.
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SCHEME 1 Bergman cyclization
and related polymerization.
et al.76,77 reported preparation of a prenetwork polyarylene
via Bergman cyclization polymerization of bis-ortho-diynylar-
ene (BODA) monomers. The cured BODA network polymers
can serve as excellent precursors for glassy carbonous mate-
rials. Tolbert and coworkers78 synthesized crosslinked
poly(3,4-bis(phenylethynyl) styrene) utilizing Bergman cycli-
zation, the highly aromatic polymers showed potential appli-
cations in lithographic materials. In addition, some novel
polymers with special architectures have been reported
recently through Bergman cyclization.79–83 Despite of these
efforts, the synthesis of conjugated polymers through Berg-
man cyclization has been rarely addressed. In this research,
we report the synthesis of dendronized conjugated polymers
utilizing Bergman cyclization with enediyne-containing den-
drimer as macromonomers through ‘‘grafting through’’ strat-
egy. First, two generations of dendrimers were prepared and
attached with enediyne-containing molecules. After removal
of protection groups on enediyne moiety, dendronized poly-
mers were obtained through thermal Bergman cyclization at
high temperature and characterized accordingly (Scheme 2).
group as periphery were introduced onto compound 1.
Trimethylsilyl group (TMS) is a key terminal group in this
enediyne-containing compound, which can inhibit unwanted
Bergman cyclization or oxidative coupling of terminal alkyne
during preparation and storage because of its steric
hindrance effect. On the other hand, TMS groups could be
easily removed under mild conditions. The dendritic parts
were synthesized following the procedure developed by
Frechet et al. All the synthesis took place smoothly to give
desired products in high yields.
Synthesis of Dendronized Conjugated Polymers
Bergman cyclization reaction of dendrimer 5 and 11 was
conducted in bulk. These reactions were run under vacuum
to exclude any species that could quench the active diradi-
cals. According to our previous work,66 Bergman cyclization
of model compound which is structurally similar to com-
pound 5 and 11 could be triggered at medium temperature.
The formation of brush polymers can be even faster at
higher temperature. The absolute molecular weight of brush
polymer 12 and 13 was determined by gel permeation
chromatography (GPC) equipped with wide-angle laser light
scattering photometer and laser differential refractive
photometer. The results revealed broad molecular weight
dispersion (Table 1), which was due to the step-growth
nature of coupling reaction of diradicals generated via
Bergman cyclization.79 The molecular weights obtained
RESULTS AND DISCUSSION
Synthesis of Dendrimers
We have reported that compound 1 was chosen as conical
group for the synthesis of enediyne-containing derivatives
because of its structural feature and facial preparation.66 In
this article, two generation of dendrimers with benzyloxy
SCHEME 2 Synthetic route for enediyne-containing dendrimers and dendronized polymers.
SYNTHESIS OF DENDRONIZED POLYMERS, MA ET AL.
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TABLE 1 Enediyne-Containing Dendrimers and
Characterization with Ultraviolet–Vision Spectroscopy
The UV–vis spectra of dendrimers 5, 11 and dendronized
polymers 12, 13 are shown in Figure 2. The adsorption
spectra of dendrimer showed well-defined peaks at 256,
270, and 311 nm in spectrum a and 256, 270, 285, and 311
nm in spectrum c, which are assigned to benzyl group of
compound 5 and 11. However, all aforementioned features
in UV–vis spectra disappeared after Bergman cyclization,
while an intensive, broad peak showed up in spectrum b
and two broad peaks appeared in spectrum d, respectively.
All these polymers showed strong adsorption deep into visi-
ble region, which confirmed the formation of longer conju-
gated system after Bergman Cyclization.
Dendronized Polymers
Dendronized
Polymers
Mn
Mw
PDI
12
13
1.762 ꢁ 106
7.579 ꢁ 104
3.318 ꢁ 106
1.313 ꢁ 105
1.88
1.73
through calibration with polystyrene standards are much
lower than that obtained from laser light scattering because
of the highly branched nature40 and rigid structure of these
dendronized polymers. Based on the molecular weight of
dendronized monomers 5 and 11, the degrees of polymeriza-
tion (DPs) for 12 and 13 are thus calculated to be 3624 and
83, respectively. It is obvious that with increase of genera-
tion of dendritic wedges, the polymerization of diradicals
generated from Bergman cyclization is suppressed.
1
Characterization with H NMR Spectroscopy
The formation of dendronized ‘‘polynaphthalene’’ through
Bergman cyclization polymerization was confirmed by 1H
NMR spectroscopy as shown in Figure 3. After Bergman
cyclization, peaks of 2.9 and 3.2 ppm corresponding to ter-
minal alkyne of compound 5 in spectra of a and compound
11 in spectra of c were disappeared. A new peak appeared
around 7.8–8.0 ppm in spectra of b and d, which can be
assigned to naphthalene subunits of ‘‘polynaphthalene.’’
Recently, Matzger and coworkers investigated the structure
of ‘‘polynaphthalene’’ synthesized from Bergman cycliza-
tion.81 It was found that polymers prepared by Kumada cou-
pling of 1,4-dibromonaphthalene and Bergman cyclization of
ortho-diethynylbenzene are structurally different. According
to various structural analysis results, it was shown that poly-
naphthalene prepared from Bergman cyclization consisted of
not only naphthalene but also indene subunits. A radical
chain growth mechanism was thus proposed for the forma-
tion of indene moiety besides step-growth mechanism for
Bergman cyclization polymerization. In our previous work,66
we have identified both of these moieties thanks to the high
solubility of brushed polymer in common organic solvents.
In spectra c and d, the peaks corresponding to indenyl
Characterization with IR Spectroscopy
IR spectra of compounds 5, 11, 12, and 13 are shown in
Figure 1. The CAH stretching vibrations at 3270 cmꢀ1 in the
spectrum of a and 3290 cmꢀ1 in the spectrum of b were
assigned to terminal triple bonds of the compound 5 and
11, respectively. After thermal Bergman Cyclization, both
of these peaks were completely gone as shown in c and d,
which indicated that both triple bonds in enediyne moieties
were disappeared. The CAH stretching vibrations at
2920 and 2850 cmꢀ1, which are corresponding to the benzy-
lene groups, in the spectra c and d were strengthened,
respectively. The peak around 2235 cmꢀ1 in spectrum a is
corresponding to stretching vibration of triple bonds in
compound 5. For compound 11, this peak is barely seen
probably due to low enediyne fraction in the molecule.
Nevertheless, this peak was disappeared in spectra c and d,
indicative of the occurrence of Bergman cyclizations.
FIGURE 2 UV–vis spectra of 5 (a), 12 (b), 11 (c), and 13 (d) in
FIGURE 1 FTIR spectra of 5 (a), 11 (b), 12 (c), and 13 (d).
CHCl3.
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FIGURE 3 1H NMR spectra of 5 (a), 12 (b), 11 (c), 13 (d) in CDCl3.
moieties appear between 6.0 and 6.5 ppm. Thus, the back-
bone of these dendronized polymers can be rationalized
as random conjugated copolymers of naphthalene and
indenylenemethylene.
In our system, the packing arrangement caused by p–p
stacking interactions between benzyl ring units and hydro-
phobic interaction between the nonpolar hydrocarbon
dendrons86 are both probably responsible for the formation
of ellipsoid-shaped structures.
Characterization with AFM
AFM images were used to visualize the morphologies of
dendronized polymers on a flat substrate. First, the polymer
12 was dissolved in N,N-dimethylformamide at low con-
centration (1.5 ꢁ 10ꢀ6g/mL), and the solution of polymer
was then spin coated onto silicon wafer and visualized by
tapping-mode AFM. ‘‘Rod-like’’ objects were seen in AFM
images as shown in Figure 4. However, either dimension of
these objects is much shorter than the theoretical length of
main chain of 12 calculated from DP. It was reported that
dendronized polymers with low generations of dendritic
wedges may pose as spherical objects on a flat surface as
the steric repulsions of dendrons are not high enough to
elongate the persistent length of main chain.84 Dendronized
polymers may also bundling together and round shaped.85
EXPERIMENTAL
Materials
Tetrahydrofuran (THF) and Triethylamine (Et3N) were dried
with sodium and calcium hydride under an atmosphere of
nitrogen before use, respectively. All other chemicals were
analytical grade and used as received without further purifi-
cation. All reactions were performed with dried Schlenk
techniques under an atmosphere of nitrogen unless other-
wise noted. 4-(2-(2-(trimethylsilyl)ethynyl)phenyl)but-3-yn-
1-ol (1) was synthesized according to literature procedure,87
detailed information could also be found in our recently
published paper.66
FIGURE 4 Tapping-mode AFM
images of polymer 12 on silicon
wafer.
SYNTHESIS OF DENDRONIZED POLYMERS, MA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Characterization
24 h under nitrogen at room temperature and then filtered
and concentrated. The residue was purified on a silica-gel
column (ethyl acetate/petroleum ether ¼ 1/5, Rf ¼ 0.8) to
give pure product as a yellow oil (0.2 g, 90%).1H NMR
(CDCl3, d, ppm): 7.41–7.44 (PhAH, 2H), 7.34–7.40 (PhAH,
10H), 7.33 (PhAH, 2H), 7.21 (PhAH, 2H), 6.80 (PhAH, 1H),
5.05 (PhAOACH2A, 4H), 4.51 (ACCACH2ACH2A, 2H), 2.93
(ACCACH2A, 2H), 0.26 (s, SiACH3, 9H). 13C NMR (CDCl3, d,
ppm): 165.4, 159.3, 136.0, 131.6, 131.4, 128.1, 127.6, 127.1,
125.7, 125.1, 108.0, 106.9, 103.2, 97.8, 89.1, 80.4, 69.7, 62.4,
19.7, 13.7. ꢀ0.2. MS (ESIþ): m/z calcd. for C36H34O4Si:
559.2305 [(M þ H)þ], found: 559.2307 [(M þ H)þ].
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
recorded in chloroform-d (CDCl3) on an Ultra Shield 400
spectrometer (Bruker BioSpin AG, Magnet System 400 MHz/
54 mm). The absolute Mn, Mw, and PDI were determined by
GPC on a WATERS 515 equipped with wide angle laser light
scattering photometer (DAWN HELEOS) (laser wavelength
is 658.0 nm) and 1aser differential refrative photometer
(Optilab rEX), using THF as an eluent at 40 ꢂC with a PS
calibration. Fourier transform infrared analysis (FTIR) was
recorded from film coated on KBr pelltes on a Nicolet Magna
5700 FTIR spectrometer. UV analyses were performed on a
UV-2550PC spectrometer from CHCl3 solutions at room
temperature. The AFM images of the polymers were
recorded on a Digital Instruments Nanoscope V atomic force
microscope (VEECO).
4-(2-Ethynylphenyl)but-3-ynyl 3,5-bis(benzyloxy)
Benzoate (5)
To a solution of compound 4 (0.17 g, 0.3mmol) in THF
(10 mL) was added tetrabutylammonium fluoride (TBAF)
(0.39 g, 5 equiv. to TMS group). After stirring for 5 min at
room temperature under nitrogen, the solution was passed
through a short silica gel column, and filtrate was con-
centrated in vacuo, a pale yellow oil was obtained without
further purification (0.14 g, 98%). Note: This reaction
was run in dark environment. 1H NMR (CDCl3, d, ppm):
7.40–7.43 (PhAH, 2H), 7.33–7.40 (PhAH, 10H), 7.25–7.30
(PhAH, 2H), 7.23 (PhAH, 2H), 6.80 (PhAH, 1H), 5.05
(PhAOACH2A, 4H), 4.51 (ACCACH2ACH2A, 2H), 3.24
(ACCAH, 1H), 2.94 (ACCACH2A, 2H). 13C NMR (CDCl3, d,
ppm): 165.6, 159.3, 136.0, 132.1, 131.6, 128.2, 127.8, 127.2,
125.9, 124.1, 108.1, 106.8, 89.6, 81.8, 80.6, 81.2, 69.9, 62.6,
19.8. MS (ESIþ): Anal. Calcd. for C17H20O2Si: 509.1729 [(M þ
Na)þ], found: 509.1726.
Synthesis
3,5-Bis (benzyloxy)methyl Benzoate (2)
This compound was synthesized according to literature pro-
cedure with minor modification.88,89 Methyl 3,5-dihydroxy-
benzoate (4.2 g, 25 mmol), benzyl bromide (9.41 g, 55
mmol), and 18-crown-6 (1.46 g, 5.5 mmol) were dissolved in
dry acetone. After three cycles vacuum-nitrogen operation,
K2CO3 (10.37 g, 75 mmol) was added. The mixture was
refluxed for 48 h under nitrogen. After cooled to room tem-
perature, the crude product was filtered and washed with
dichloromethane, the filtrate was concentrated, the residue
was purified by silica column chromatography using petro-
leum ether/dichloromethane (4/1) and dichloromethane/
diethyl ether (12/1) (Rf ¼ 0.85) as elutes to give the final
product as a white powder (8.25 g, 95%). 1H NMR (CDCl3,
d, ppm): 7.33–7.44 (PhAH, 10H), 7.30 (PhAH, 2H), 6.80
(PhAH, 1H), 5.08 (PhAOACH2A, 4H), 3.90 (PhACOOCH3,
3H).
(3,5-Bis(benzyloxy)phenyl)methanol (6)
Compound 2 (4.62 g, 13.3 mmol) was dissolved in dry tetra-
hydrofuran and added dropwisely to a slurry of LiAlH4
(0.76 g, 20 mmol) in dry tetrahydrofuran at 0 ꢂC; the mix-
ture was stirred overnight at room temperature under nitro-
gen, and then the reaction mixture was quenched with a
small amount of water and filtered. The filtrate was concen-
trated by rotary evaporation, the crude product was
extracted with dichloromethane and washed with brine,
dried over anhydrous MgSO4, then filtered and concentrated.
The product was obtained as a white solid without further
3,5-Bis(benzyloxy)benzoic Acid (3)
To a solution of compound 2 (1.74 g, 5 mmol) in THF (15
mL) and methanol (2.5 mL), a saturated aqueous solution of
KOH (1.12 g, 20 mmol) was added. The reaction mixture
was refluxed overnight. After cooled to room temperature, 1
M HCl was added and the pH of solution was adjusted to 3–
5, the mixture was concentrated in vacuo, and then the resi-
due was extracted with dichloromethane and washed with
brine. The organic layer was dried over anhydrous MgSO4,
filtered, the solvent was removed under reduce pressure and
a white solid was obtained without further purification (1.62
g, 97%). 1H NMR (CDCl3, d, ppm): 12.50 (PhACOOH, 1H),
7.37–7.44 (PhAH, 10H), 7.30 (PhAH, 2H), 6.85 (PhAH, 1H),
5.08 (PhAOACH2A, 4H).
1
purification (4.16 g, 98%). H NMR (CDCl3, d, d, ppm): 7.32–
7.43 (PhAH, 10H), 6.63 (PhAH, 2H), 6.55 (PhAH, 1H),
5.04 (PhAOACH2A, 4H), 4.64 (PhACH2AOH, 2H), 2.40
(PhACH2AOH, 2H).
1,3-Bis(benzyloxy)-5-(bromomethyl)benzene (7)
To a dry tetrahydrofuran solution of a mixture of compound
6 (3.2 g, 10 mmol) and CBr4 (4.15 g, 12.5 mmol) was slowly
added PPh3 (3.28 g, 12.5 mmol) under nitrogen, then the
mixture was stirred at room temperature for 15 min under
nitrogen and then quenched with deionized water. The
mixture was extracted with dichloromethane and washed
with brine. The organic phase was dried over anhydrous
MgSO4, filtered and concentrated in vacuo, and the crude
product was purified by column chromatography using
4-(2-(2-(Trimethylsilyl)ethynyl)phenyl)but-3-ynyl
3,5-bis (benzyloxy)benzoate (4)
To a mixture of 1 (0.09 g, 0.4 mmol), 3 (0.2 g, 0.6 mmol),
and 4-dimethylaminopyridine (0.01 g, 0.08 mmol) dissolved
in dry dichloromethane (4 mL), a solution of N,N0-dicyclohex-
ylcarbodiimide (0.116 g, 0.56 mmol) in dry dichloromethane
(2 mL) was added dropwisely. This mixture was stirred for
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petroleum ether, dichloromethane/petroleum ether(1/4), and
dichloromethane/petroleum ether (4/1) as elute (Rf ¼ 0.7),
respectively. The final product was obtained as a pale yellow
solid (3.14 g, 82%). 1H NMR (CDCl3, d, ppm): 7.33–7.43
(PhAH, 10H), 6.64 (PhAH, 2H), 6.55 (PhAH, 1H), 5.03
(PhAOACH2A, 4H), 4.42 (PhACH2ABr, 2H).
4-(2-Ethynylphenyl)but-3-ynyl 3,5-bis(3,5-bis(benzyloxy)-
benzyloxy)benzoate (11)
To a solution of 10 (0.147 g, 0.15 mmol) in THF (8 mL) was
added TBAF (0.31 g, 8 equivalent to TMS group). After
stirring for 1 h at room temperature under nitrogen, the so-
lution was passed through a short silica gel column and
eluted with ethyl acetate, the crude product was purified by
column chromatography using ethyl acetate/petroleum ether
(1/2) as elute (Rf ¼ 0.7) and get a yellow oily product
(0.13 g, 96%). Note: This reaction was run in dark environ-
Methyl 3,5-bis(3,5-bis(benzyloxy)benzyloxy)benzoate (8)
To a solution of compound 7 (3.0 g, 7.8 mmol), 3,5-dihydr-
oxybenzoate (0.6 g, 3.54 mmol), and 18-crown-6 ether (0.19
g, 0.71 mmol) in dry acetone, potassium carbonate (1.47 g,
10.62 mmol) was added. The mixture was refluxed for 48 h
under nitrogen and then the solvent was removed in vacuo;
the residue was extracted with dichloromethane and washed
with brine. The organic phase was dried over anhydrous
MgSO4, filtered and concentrated under reduced pressure.
The residue was purified successively by silica column
chromatography using petroleum ether/dichloromethane (4/
1) and dichloromethane /diethyl ether (12/1) (Rf ¼ 0.8) as
elutes to give pure product as a white solid (2.57 g, 94%).
1H NMR (CDCl3, d, ppm): 7.34–7.43 (PhAH, 20H), 7.30–7.33
(PhAH, 2H), 6.77 (PhAH, 1H), 6.68 (PhAH, 4H), 6.58
(PhAH, 2H), 5.04 (PhAOACH2A, 12H), 3.91 (PhACOOACH3,
3H).
1
ment. H NMR (CDCl3, d, ppm): 7.42–7.44 (PhAH, 2H), 7.32–
7.42 (PhAH, 20H), 7.28–7.32 (PhAH, 2H), 7.18–7.24 (PhAH,
2H), 6.73 (PhAH, 1H), 6.63 (PhAH, 4H), 6.54 (PhAH, 2H),
5.00 (PhAOACH2A, 12H), 4.48 (ACCACH2ACH2A, 2H), 3.20
(ACCAH, 1H), 2.91 (ACCACH2A, 2H). 13C NMR (CDCl3, d,
ppm): 165.5, 159.7, 159.2, 138.3, 136.2, 132.1, 131.5, 128.1,
127.6, 127.1, 125.8, 125.1, 108.1, 106.6, 105.9, 101.6, 89.5,
81.7, 80.6, 80.1, 69.6, 69.5, 62.5, 19.8. MS (ESIþ): Anal.
Calcd. for C61H50O8: 933.3413 [(M þ Na)þ], found: 933.3403
[(M þ Na)þ].
Synthesis Dendronized Polymers
Compound 5 was added into a tube and sealed under vac-
uum. Then, the tube was embedded in a refluxing dimethyl-
o-phthalate bath. After 8 h of heating, a brownish oil was
obtained inside the tube, which was proven to be brush
polymer with high polydispersity. The high-molecular-weight
fraction was obtained either by repeat precipitation in a
mixture solvent of THF and methanol or dialysis via THF.
3,5-Bis(3,5-bis(benzyloxy)benzyloxy)benzoic Acid (9)
To a solution of compound 8 (0.93 g, 1.2 mmol) in THF (10
mL) and methanol (2 mL), a saturated solution of KOH (0.27
g, 4.8 mmol) was added. The reaction mixture was refluxed
overnight at 55 ꢂC. The resulting mixture was treated same
as compound 3, and a white solid was obtained without fur-
ther purification (0.87 g, 95%). 1H NMR (CDCl3, d, ppm):
12.50 (PhACOOH, 1H), 7.33–7.43 (PhAH, 20H), 7.30–7.32
(PhAH, 2H), 6.81 (PhAH, 1H), 6.68 (PhAH, 4H), 6.58
(PhAH, 2H), 5.04 (PhAOACH2A, 12H).
CONCLUSIONS
We have successfully synthesized dendronized polymers
with rigid conjugated backbone through a thermal polymer-
ization of two enediyne-containing dendronized monomers
via Bergman Cyclization. The dendronized polymers with DP
of 3624 and 83 were obtained starting from 5 and 11,
respectively. IR, 1H NMR, and UV–vis spectra showed disap-
pearance of acetylene groups and formation of conjugated
backbone after Bergman cyclization. And the ‘‘rod-like’’
morphology of the conjugated polymer was further visual-
ized by AFM. The two dendronized polymers are readily
soluble in common organic solvents. The exploration of
thermal and optoelectronic properties of these polymers are
under further investigation.
4-(2-(2-(Trimethylsilyl)ethynyl)phenyl)but-3-ynyl
3,5-bis(3,5-bis(benzyloxy) benzyloxy)benzoate (10)
1 (0.072 g, 0.3 mmol), 9 (0.34 g, 0.45 mmol), and 4-dimethy-
laminopyridine (0.007 g, 0.06 mmol) were dissolved in dry
dichloromethane (5 mL), and a solution of N,N0-dicyclohexyl-
carbodiimide (DCC) (0.086 g, 0.42 mmol) in 1 mL dry
dichloromethane was added dropwisely to the above mixture
and stirred for 24 h under nitrogen at room temperature.
Then, the reaction mixture was filtered and the filtrate was
concentrated, the residue was purified by column chroma-
tography using ethyl acetate/petroleum ether (1/2) as elute
(Rf ¼ 0.85) and a pale yellow oil was obtained (0.27 g,
The support of National Natural Science Foundation of China
(20874026, 20704013), Shanghai Shuguang Project (07SG33),
New Century Excellent Talents in University, and Shanghai
Leading Academic Discipline Project (B502) is gratefully
acknowledged. A. Hu thank Shouwu Guo of Shanghai Jiaotong
University for his kindly help in AFM.
1
92%). H NMR (CDCl3, d, ppm): 7.42–7.44 (PhAH, 2H), 7.33–
7.42 (PhAH, 20H), 7.31–7.33 (PhAH, 2H), 7.18 (PhAH, 2H),
6.78 (PhAH, 1H), 6.67 (PhAH, 4H), 6.58 (PhAH, 2H), 5.03
(PhAOACH2A, 12H), 4.52 (ACCACH2ACH2A, 2H), 2.94
(ACCACH2A, 2H), 0.25 (s, SiACH3, 9H). 13C NMR (CDCl3, d,
ppm): 165.8, 160.1, 159.6, 138.8, 136.7, 132.0, 131.8, 128.5,
127.9, 127.5, 126.0, 125.5, 108.5, 107.1, 106.3, 103.5, 101.6,
98.2, 89.4, 80.8, 70.0, 69.8, 62.9, 20.1, 0.0. MS (ESIþ): Anal.
REFERENCES AND NOTES
1 Chen, Y. M.; Xiong, X. Q. Chem Commun 2010, 46, 5049–
5060.
Calcd. for
C
61H50O8: 1005.3799 [(M
þ
Na)þ], found:
2 Rosen, B. M.; Wilson, C. J.; Wilson, D. A.; Peterca, M.; Imam,
1005.3798 [(M þ Na)þ].
M. R.; Percec, V. Chem Rev 2009, 109, 6275–6540.
SYNTHESIS OF DENDRONIZED POLYMERS, MA ET AL.
1373

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
3 Percec, V. Philos Trans R Soc A 2006, 364, 2709–2719.
27 Ge, Z. S.; Luo, S. Z.; Liu, S. Y. J Polym Sci Polym Chem
2006, 44, 1357–1371.
4 Rudick, J. G.; Percec, V. Acc Chem Res 2008, 41, 1641–1652.
28 Kwon, Y. K.; Chvalun, S. N.; Blackwell, J.; Percec, V.; Heck,
5 Karakaya, B.; Claussen, W.; Gessler, K.; Saenger, W.;
J. A. Macromolecules 1995, 28, 1552–1558.
Schluter, A. D. J Am Chem Soc 1997, 119, 3296–3301.
29 Percec, V.; Heck, J. A.; Tomazos, D.; Ungar, G. J Chem Soc
6 Li, C. X.; Schluter, A. D.; Zhang, A.; Mezzenga, R. Adv Mater
Perkin Trans 2 1993, 2381–2388.
2008, 20, 4530–4534.
30 Fei, Z. P.; Han, Y.; Bo, Z. S. J Polym Sci Polym Chem 2008,
7 Popa, I.; Zhang, B. Z.; Maroni, P.; Schluter, A. D.; Borkovec,
46, 4030–4037.
M. Angew Chem Int Ed 2010, 49, 4250–4253.
31 Tang, R. P.; Chuai, Y. T.; Cheng, C. X.; Xi, F.; Zou, D. C.
8 Schluter, A. D.; Rabe, J. P. Angew Chem Int Ed 2000, 39,
J Polym Sci Polym Chem 2005, 43, 3126–3140.
864–883.
32 Percec, V.; Glodde, M.; Bera, T. K.; Miura, Y.; Shiyanov-
skaya, I.; Singer, K. D.; Balagurusamy, V. S. K.; Heiney, P. A.;
Schnell, I.; Rapp, A.; Spiess, H. W.; Hudson, S. D.; Duan, H.
Nature 2002, 419, 384–387.
9 Rapp, A.; Schnell, I.; Sebastiani, D.; Brown, S. P.; Percec, V.;
Spiess, H. W. J Am Chem Soc 2003, 125, 13284–13297.
10 Prokhorova, S. A.; Sheiko, S. S.; Mourran, A.; Azumi, R.;
Beginn, U.; Zipp, G.; Ahn, C.-H.; Holerca, M. N.; Percec, V.;
Moller, M. Langmuir 2000, 16, 6862–6867.
33 Moingeon, F.; Roeser, J.; Masson, P.; Arnaud, F.; Mery, S.
Chem Commun 2008, 1341–1343.
11 Prokhorova, S. A.; Sheiko, S. S.; Mo¨ ller, M.; Ahn, C.-H.;
34 Zhang, Y. H.; Xu, Z. Z.; Li, X. K.; Chen, Y. M. J Polym Sci
Percec, V. Macromol Rapid Commun 1998, 19, 359–366.
Polym Chem 2007, 45, 3994–4001.
12 Percec, V.; Ahn, C. H.; Ungar, G.; Yeardley, D. J. P.; Moller,
35 Yoshida, M.; Fresco, Z. M.; Ohnishi, S.; Frechet, J. M. J.
M.; Sheiko, S. S. Nature 1998, 391, 161–164.
Macromolecules 2005, 38, 334–344.
13 Percec, V.; Ahn, C. H.; Cho, W. D.; Jamieson, A. M.; Kim, J.;
Leman, T.; Schmidt, M.; Gerle, M.; Moller, M.; Prokhorova, S.
A.; Sheiko, S. S.; Cheng, S. Z. D.; Zhang, A.; Ungar, G.; Yeard-
ley, D. J. P. J Am Chem Soc 1998, 120, 8619–8631.
36 Malkoch, M.; Carlmark, A.; Woldegiorgis, A.; Hult, A.;
Malmstrom, E. E. Macromolecules 2004, 37, 322–329.
37 Shu, L. J.; Schluter, A. D.; Ecker, C.; Severin, N.; Rabe, J. P.
Angew Chem Int Ed 2001, 40, 4666–4669.
14 Percec, V.; Ahn, C. H.; Barboiu, B. J Am Chem Soc 1997,
119, 12978–12979.
38 Leung, K. C. F.; Mendes, P. M.; Magonov, S. N.; Northrop,
B. H.; Kim, S.; Patel, K.; Flood, A. H.; Tseng, H. R.; Stoddart,
J. F. J Am Chem Soc 2006, 128, 10707–10715.
15 Percec, V.; Heck, J.; Johansson, G.; Tomazos, D.; Ungar, G.
Macromol Symp 1994, 77, 237–265.
39 Zhang, Y. H.; Huang, J.; Chen, Y. M. Macromolecules 2005,
16 Fouquey, C.; Lehn, J.-M.; Levelut, A.-M. Adv Mater 1990, 2,
38, 5069–5077.
254–257.
40 Mynar, J. L.; Choi, T. L.; Yoshida, M.; Kim, V.; Hawker, C. J.;
17 Percec, V.; Heck, J.; Lee, M.; Ungar, G.; Alvarez-Castillo, A.
Frechet, J. M. J. Chem Commun 2005, 5169–5171.
J Mater Chem 1992, 2, 1033–1039.
41 Desai, A.; Atkinson, N.; Rivera, F.; Devonport, W.; Rees, I.;
Branz, S. E.; Hawker, C. J. J Polym Sci Polym Chem 2000, 38,
1033–1044.
18 Percec, V.; Heck, J.; Tomazos, D.; Falkenberg, F.; Blackwell,
H.; Ungar, G. J Chem Soc Perkin Trans 1 1993, 2799–2811.
19 Percec, V.; Tomazos, D.; Heck, J.; Blackwell, H.; Ungar, G.
42 Lau, K. N.; Chow, H. F.; Chan, M. C.; Wong, K. W. Angew
J Chem Soc Perkin Trans 2 1994, 31–44.
Chem Int Ed 2008, 47, 6912–6916.
20 Percec, V.; Lee, M.; Heck, J.; Blackwell, H. E.; Ungar, G.;
43 Zhang, Y. H.; Xu, Z. Z.; Li, X. K.; Chen, Y. M. J Polym Sci
Alvarez-Castillo, A. J Mater Chem 1992, 2, 931–938.
Polym Chem 2007, 45, 3303–3310.
21 Percec, V.; Heck, J.; Johansson, G.; Tomazos, D.; Kawasumi,
M.; Ungar, G. J Macromol Sci Pure Appl Chem 1994, 31,
1031–1070.
44 Xiong, X. Q.; Chen, Y. M.; Feng, S.; Wang, W. Macromole-
cules 2007, 40, 9084–9093.
45 Zhang, Y.; Li, X. K.; Deng, G. H.; Chen, Y. M. Macromol
22 Zhu, B.; Han, Y.; Sun, M.; Bo, Z. Macromolecules 2007, 40,
Chem Phys 2006, 207, 1394–1403.
4494–4500.
46 Percec, V.; Rudick, J. G.; Wagner, M.; Obata, M.; Mitchell, C. M.;
23 Kim, H. J.; Jung, E. Y.; Jin, L. Y.; Lee, M. Macromolecules
Cho, W. D.; Magonov, S. N. Macromolecules 2006, 39, 7342–7351.
2008, 41, 6066–6072.
47 Nystrom, A.; Malkoch, M.; Furo, I.; Nystrom, D.; Unal, K.;
Antoni, P.; Vamvounis, G.; Hawker, C.; Wooley, K.; Malmstrom,
E.; Hult, A. Macromolecules 2006, 39, 7241–7249.
24 Li, W.; Zhang, A.; Schluter, A. D. Chem Commun 2008,
5523–5525.
25 Jiao, Q.; Yi, Z.; Chen, Y. M.; Xi, F. J Polym Sci Polym Chem
48 Kasemi, E.; Zhuang, W.; Rabe, J. P.; Fischer, K.; Schmidt,
M.; Colussi, M.; Keul, H.; Yi, D.; Colfen, H.; Schluter, A. D. J Am
Chem Soc 2006, 128, 5091–5099.
2008, 46, 4564–4574.
26 Percec, V.; Dulcey, A. E.; Balagurusamy, V. S. K.; Miura, Y.;
Smidrkal, J.; Peterca, M.; Nummelin, S.; Edlund, U.; Hudson, S.
D.; Heiney, P. A.; Hu, D. A.; Magonov, S. N.; Vinogradov, S. A.
Nature 2004, 430, 764–768.
49 Ecker, C.; Severin, N.; Shu, L.; Schluter, A. D.; Rabe, J. P.
Macromolecules 2004, 37, 2484–2489.
1374
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
50 Zhang, A. F.; Zhang, B.; Wachtersbach, E.; Schmidt, M.;
71 Joshi, M. C.; Bisht, G. S.; Rawat, D. S. Bioorg Med Chem
Schluter, A. D. Chem Eur J 2003, 9, 6083–6092.
Lett 2007, 17, 3226–3230.
51 Percec, V.; Holerca, M. N. Biomacromolecules 2000, 1, 6–16.
72 Usuki, T.; Nakanishi, K.; Ellestad, G. A. Org Lett 2006, 8,
5461–5463.
52 Percec, V.; Schlueter, D.; Ungar, G.; Cheng, S. Z. D.; Zhang,
A. Macromolecules 1998, 31, 1745–1762.
73 Zeidan, T. A.; Kovalenko, S. V.; Manoharan, M.; Alabugin, I.
V. J Org Chem 2006, 71, 962–975.
53 Percec, V.; Schlueter, D. Macromolecules 1997, 30, 5783–
5790.
74 Rule, J. D.; Moore, J. S. Macromolecules 2005, 38, 7266–
7273.
54 Percec, V.; Schlueter, D.; Ronda, J. C.; Johansson, G.; Ungar,
G.; Zhou, J. P. Macromolecules 1996, 29, 1464–1472.
75 Rule, J. D.; Wilson, S. R.; Moore, J. S. J Am Chem Soc 2003,
125, 12992–12993.
55 Kwon, Y. K.; Chvalun, S.; Schneider, A.-I.; Blackwell, J.;
Percec, V.; Heck, J. A. Macromolecules 1994, 27, 6129–6132.
76 Perpall, M. W.; Perera, K. P. U.; DiMaio, J.; Ballato, J.; Foulger,
S. H.; Smith, D. W. Langmuir 2003, 19, 7153–7156.
56 Percec, V.; Schlueter, D.; Kwon, Y. K.; Blackwell, J.; Moeller,
M.; Slangen, P. J. Macromolecules 1995, 28, 8807–8818.
77 Smith, D. W.; Shah, H. V.; Perera, K. P. U.; Perpall, M. W.;
Babb, D. A.; Martin, S. J. Adv Funct Mater 2007, 17, 1237–1246.
57 McNeill, C. R.; Greenham, N. C. Adv Mater 2009, 21, 3840–
3850.
78 Chen, X. H.; Tolbert, L. M.; Hess, D. W.; Henderson, C.
Macromolecules 2001, 34, 4104–4108.
58 Gunes, S.; Neugebauer, H.; Sariciftci, N. S. Chem Rev 2007,
107, 1324–1338.
79 John, J. A.; Tour, J. M. J Am Chem Soc 1994, 116, 5011–
5012.
59 Smith, R. C.; Tennyson, A. G.; Lim, M. H.; Lippard, S. J. Org
Lett 2005, 7, 3573–3575.
80 Smith, D. W.; Babb, D. A.; Snelgrove, R. V.; Townsend, P. H.;
Martin, S. J. J Am Chem Soc 1998, 120, 9078–9079.
60 McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem Rev
2000, 100, 2537–2574.
81 Johnson, J. P.; Bringley, D. A.; Wilson, E. E.; Lewis, K. D.;
Beck, L. W.; Matzger, A. J. J Am Chem Soc 2003, 125, 14708–
14709.
61 Alcazar, D.; Wang, F.; Swager, T. M.; Thomas, E. L. Macro-
molecules 2008, 41, 9863–9868.
82 Lewis, K. D.; Rowe, M. P.; Matzger, A. J. Tetrahedron 2004,
62 Hu, Y. F.; Gao, J. J Am Chem Soc 2009, 131, 18236–18237.
63 Ho, H. A.; Leclerc, M. J Am Chem Soc 2004, 126, 1384–1387.
60, 7191–7196.
83 Prasanna, K.; Perera, U.; Krawiec, M.; Smith, D. W. Tetrahedron
64 Percec, V.; Rudick, J. G.; Peterca, M.; Wagner, M.; Obata,
M.; Mitchell, C. M.; Cho, W. D.; Balagurusamy, V. S. K.; Heiney,
P. A. J Am Chem Soc 2005, 127, 15257–15264.
2002, 58, 10197–10203.
84 Guo, Y. F.; van Beek, J. D.; Zhang, B. Z.; Colussi, M.; Walde,
P.; Zhang, A.; Kroger, M.; Halperin, A.; Schluter, A. D. J Am
Chem Soc 2009, 131, 11841–11854.
65 Percec, V.; Obata, M.; Rudick, J. G.; De, B. B.; Glodde, M.;
Bera, T. K.; Magonov, S. N.; Balagurusamy, V. S. K.; Heiney, P.
A. J Polym Sci Polym Chem 2002, 40, 3509–3533.
85 Wang, M.; Zou, S.; Guerin, G.; Shen, L.; Deng, K.; Jones, M.;
Walker, G. C.; Scholes, G. D.; Winnik, M. A. Macromolecules
2008, 41, 6993–7002.
66 Cheng, X.; Ma, J.; Zhi, J.; Yang, X.; Hu, A. Macromolecules
2010, 43, 909–913.
86 Wong, C. H.; Chan, W. S.; Lo, C. M.; Chow, H. F.; Ngai, T.;
67 Bergman, R. G. Acc Chem Res 1973, 6, 25–31.
Wong, K. W. Macromolecules 2010, 43, 8389–8399.
68 Alabugin, I. V.; Manoharan, M. J Phys Chem A 2003, 107,
87 Scott, E. E.; Donnelly, E. T.; Welker, M. E. J Organomet
3363–3371.
Chem 2003, 673, 67–76.
69 Basak, A.; Mandal, S.; Das, A. K.; Bertolasi, V. Bioorg Med
88 Ke, G.; Guan, W. C.; Tang, C. Y.; Guan, W. J.; Deng, F. Bio-
Chem 2002, 12, 873–877.
macromolecules 2007, 8, 322–326.
70 Basak, A.; Bag, S. S.; Das, A. K. Eur J Org Chem 2005,
89 Hawker, C. J.; Frechet, J. M. J. J Am Chem Soc 1990, 112,
1239–1245.
7638–7647.
SYNTHESIS OF DENDRONIZED POLYMERS, MA ET AL.
1375