A new route to hyperbranched macromolecules: Syntheses of photosensitive poly(aroylarylene)s via 1,3,5-regioselective polycyclotrimerization of bis(aroylacetylene)s

Article abstract of DOI:10.1021/ma050342v

A new synthetic route to hyperbranched polymers is developed. Polycyclotrimerizations of functional diynes 1-3 initiated by a simple base of piperidine lead to the formation of hyperbranched poly(aroylarylene)s P1-P3 with perfect 1,3,5-regioregularity and

Full text of DOI:10.1021/ma050342v

6382
Macromolecules 2005, 38, 6382-6391
A New Route to Hyperbranched Macromolecules: Syntheses of
Photosensitive Poly(aroylarylene)s via 1,3,5-Regioselective
Polycyclotrimerization of Bis(aroylacetylene)s
Hongchen Dong,† Ronghua Zheng,† Jacky W. Y. Lam,† Matthias Ha1ussler,†
Anjun Qin,† and Ben Zhong Tang*,†,‡
Department of Chemistry, The Hong Kong University of Science & Technology, Clear Water Bay,
Kowloon, Hong Kong, China, and Department of Polymer Science and Engineering, Zhejiang
University, Hangzhou 310027, China
Received February 17, 2005; Revised Manuscript Received May 28, 2005
ABSTRACT: A new synthetic route to hyperbranched polymers is developed. Polycyclotrimerizations of
functional diynes 1-3 initiated by a simple base of piperidine lead to the formation of hyperbranched
poly(aroylarylene)s P1-P3 with perfect 1,3,5-regioregularity and high degree of branching (up to 100%)
in high yields (up to 99%). The polymers show high photosensitivities and can be readily photo-cross-
linked to give photoresist patterns with nanometer resolutions.
were estimated by a Waters Associates gel permeation chro-
matograph (GPC) system, using a set of monodisperse poly-
styrenes as calibration standards and THF as eluent at a flow
rate of 1.0 mL/min. IR spectra were recorded on a Perkin-
Elmer 16 PC FTIR spectrophotometer. 1H and 13C NMR
spectra were measured on a Bruker ARX 300 NMR spectrom-
eter using dichloromethane-d2 or chloroform-d as solvents and
tetramethylsilane (TMS) as internal reference (δ ) 0). UV
spectra were recorded on a Milton Roy Spectronic 3000 Array
spectrophotometer. Mass spectra were recorded on a Finnigan
TSQ 7000 triple quadrupole spectrometer operating in a
chemical ionization (CI) mode using methane as carrier gas.
Thermal transitions of the polymers were investigated by
differential scanning calorimetry (DSC) using a Setaram DSC
92 at a heating rate of 10 °C /min. Thermal stability was
evaluated on a Perkin-Elmer thermogravimetric analyzer TGA
7 at a heating rate of 20 °C/min under nitrogen.
Introduction
Because of their unique molecular architecture, hy-
perbranched polymers (hb-Ps) are envisioned to exhibit
novel properties and to serve as advanced functional
materials.1 Realization of the full potential of hb-Ps calls
for the exploration of new, versatile methods for their
syntheses. We recently developed a facile approach to
conjugated hb-polyarylenes (hb-PAs) through the diyne
polycyclotrimerizations catalyzed by transition-metal
complexes (Scheme 1).2 The hb-PAs show excellent
optical properties such as high light-emitting efficiency
and superb optical-limiting performance.3
The transition-metal-mediated reaction is, however,
intolerant of functionality and thus cannot be used for
the syntheses of hb-PAs bearing functional groups. The
cyclization produces random mixtures of 1,2,4- and
1,3,5-trisubstituted benzenes, making the structures of
the hb-PAs irregular. In this work, we succeeded in
exploring a new route to hb-PAs that is functionality-
tolerant and regioselective. Using base-catalyzed alkyne
polycyclization, hb-PAs with carbonyl functionality,
namely poly(aroylarylene)s (hb-PAAs), were synthesized
in perfect 1,3,5-regioregular fashion and high degree of
branching (Scheme 2). The hb-PAAs exhibit high photo-
sensitivity and generate photopatterns with nanometer
resolutions.
Monomer Preparation. All the bis(aryl ethynyl ketone)s
(1-3) were prepared by etherifications of m- and p-hydroxyl-
benzaldehydes, followed by two-step Grignard addition and
alcohol oxidation of the resultant dialdehydes (Scheme 3). The
experimental procedures for the preparation of 3,3′-(1,6-
hexylenedioxy)bis(benzoylacetylene) 1(m) are given below as
an example.
To a 100 mL flask were added 3-hydroxybenzaldehyde [4(m);
1.68 g, 13.7 mmol], K2CO3 (3.16 g, 22.8 mmol), and 50 mL of
acetonitrile. After the mixture was stirred at room temperature
for 20 min, 0.49 mL of 1,6-dibromohexane (5; 6.1 mmol) was
slowly added. The reaction mixture was refluxed for 24 h.
Acetonitrile was evaporated in a vacuum, and the residue was
extracted with diethyl ether three times. The organic layer
was further washed with water and brine and was then dried
over anhydrous magnesium sulfate overnight. After removing
the solvent, a yellow crude product was obtained. Recrystal-
lization in ethanol afforded 1.31 g of a white needle crystal of
3,3′-(1,6-hexylenedioxy)dibenzaldehyde 6(m) (67% yield).
Experimental Section
General Information. All the chemicals used in this study
were purchased from Aldrich unless otherwise specified. 1,4-
Dioxane, dimethylformamide (DMF), tetrahydrofuran (THF),
diphenylamine, diethylamine, piperidine, toluene, and tetralin
were distilled over sodium benzophenone ketyl or calcium
hydride prior to use. Ethynylmagnesium bromide, 3-hydroxy-
benzaldehyde, 4-hydroxybenzaldehyde, 1,6-dibromohexane,
and 1,12-dodecane were used as received without further
purification.
Part of the dialdehyde (1.20 g, 3.68 mmol) was dissolved in
40 mL of THF, and the solution was cooled to 0 °C in an ice
bath. Ethynylmagnesium bromide (0.5 M in THF, 20 mL, 10
mmol) was added dropwise. The reaction mixture was stirred
at room temperature for 12 h, and the reaction was then
quenched by 40 mL of saturated aqueous ammonium chloride
solution. The mixture was extracted with dichloromethane
several times and dried over anhydrous magnesium sulfate.
Evaporation of the solvent gave a yellow crude diol product
7(m) in 80% yield (1.11 g).
Weight-average (Mw) and number-average molecular weights
(Mn) of the polymers and their polydispersity indexes (Mw/Mn)
† The Hong Kong University of Science & Technology.
‡ Zhejiang University.
* Corresponding author: Ph +852-2358-7375; Fax +852-2358-
1594; e-mail tangbenz@ust.hk.
10.1021/ma050342v CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/30/2005

Macromolecules, Vol. 38, No. 15, 2005
Regioselective Polycyclotrimerizations of Diynes 6383
Scheme 1. Transition-Metal-Catalyzed Monoyne Cyclization and Diyne Polycyclotrimerization
Scheme 2. Nonmetallic Base-Catalyzed
1,3,5-Regioselective Polycyclotrimerization of
Bis(aroylacetylene)
Scheme 4. Regioselective 1,3,5-Cyclotrimerization of
Aryl Ethynyl Ketone and Synthesis of Model
Compound 9 by Benzannulation of 3-Butoxyphenyl
Ethynyl Ketone 8
became red. The reaction was quenched by 2-propanol and was
filtered. The filtrate was evaporated, and the resultant solid
was dissolved in 150 mL of dichloromethane. The mixture was
washed sequentially with saturated aqueous sodium bicarbon-
ate solution and water. The solution was dried over anhydrous
magnesium sulfate. The crude product was purified by flash
column chromatography using chloroform as eluent. A white
solid of 1(m) was obtained in 70% yield (0.77 g).
Characterization Data of 3,3′-(1,6-Hexylenedioxy)bis(benzoyl-
acetylene) 1(m). IR (thin film), ν (cm-1): 3210 (tC-H stretch-
ing), 2945, 2910, 2872, 2858 (CH2 stretching), 2094 (CtC
stretching), 1633 (CdO stretching), 1590, 1440, 1268, 873. 1H
NMR (300 MHz, CDCl3), δ (ppm): 7.79 (d, 2H), 7.62 (s, 2H),
7.40 (t, 2H), 7.18 (d, 2H), 4.04 (t, 4H), 3.44 (s, 2H), 1.87-1.83
(m, 4H), 1.59-1.54 (m, 4H). 13C NMR (75 MHz, CDCl3), δ
(ppm): 177.17, 159.26, 137.40, 129.68, 122.82, 121.81, 113.46,
80.60, 80.30, 68.05, 29.01, 25.76. MS (CI): m/e 375.11 [(M +
1)+, calcd for C24H22O4: 374.15].
Scheme 3. Preparation of Bis(aryl ethynyl ketone)
Monomers 1-3
4,4′-(1,6-Hexylenedioxy) bis(benzoylacetylene) 1(p). White
solid, yield 50%. IR (thin film), ν (cm-1): 3195 (tC-H
stretching), 2939, 2867 (CH2 stretching), 2091 (CtC stretch-
1
ing), 1630 (CdO stretching), 1593, 1258, 1163, 844. H NMR
(300 MHz, CDCl3), δ (ppm): 8.13 (d, 4H), 6.96 (d, 4H), 4.06 (t,
4H), 3.39 (s, 2H), 1.86 (m, 4H), 1.57 (m, 4H). 13C NMR (75
MHz, CDCl3), δ (ppm): 175.90, 164.30, 132.13, 129.39, 114.32,
80.37, 80.00, 68.16, 28.91, 25.71. MS (CI): m/e 375.11 [(M +
1)+, calcd for C24H22O4: 374.15].
Without further purification, the diol (1.11 g, 2.95 mmol)
was dissolved in 50 mL of acetone. A solution of Jones reagent
(a mixture of 2.6 g of CrO3 in 2.3 mL of concentrated sulfuric
acid and 10 mL of water) was added dropwise until the solution

6384 Dong et al.
Macromolecules, Vol. 38, No. 15, 2005
Table 1. Polycyclotrimerizations of Diynes 1-3 in the
Presence of in Situ Generated Catalyst from DMFa
b
b
no. monomer
solvent
yield (%)
Mw
Mw/Mn
1
2
3
4
5
6
7
1(m)
1(m)
1(m)
1(m)
2(m)
2(m)
3(m)
DMFc
53
41
9400
12300
12800
3.4
3.0
3.5
DMF/toluenec,d
DMF/teralinc,d
DMF/dioxanec,d
DMFc
71
tracee
44
67
73
5900
5400
10800
2.6
2.7
3.8
DMF/teralinc,d
DMF/teralinc,d
a Refluxed under nitrogen for 72 h. [M]0 ) 0.14 M. b Determined
by GPC in THF on the basis of a polystyrene calibration. c DMF
) dimethylformamide. d Volume ratio ) 1:1. e Oligomeric product
that does not precipitate out from methanol.
Table 2. Polycyclotrimerization of Diyne 1(m) in the
Presence of Externally Added Catalysta
Figure 1. Effect of catalyst concentration [cat.] on the
polycyclotrimerization of 1(m) catalyzed by piperidine in
dioxane under reflux for 24 h; [M]0 ) 0.14 M.
b
b
no.
catalyst
[cat.] (mM) yield (%)
Mw
Mw/Mn
1
2
3
4
5
diethylamine
diethylamine
diethylamine
diphenylamine
diphenylamine
7
14
21
7
tracec
27
27
0
12 200
14 000
4.2
4.3
14
0
a Refluxed in toluene under nitrogen for 72 h. [M]0 ) 0.14 M.
b Determined by GPC in THF on the basis of a polystyrene
calibration. c Oligomeric species that do not precipitate out from
methanol.
Table 3. Piperidine-Catalyzed
1,3,5-Polycyclotrimerization of 1-3a
solventb
yield (%)
Mw
Mw/Mn
c
c
no.
monomer
1
2
3
4
5
6
7
1(m)
1(m)
1(m)
1(p)
2(m)
3(m)
3(p)
dioxane
CB
tetralin
CB
dioxane
dioxane
tetralin
79
99
93
60
85
75
95
19 200
14 500
31 000
10 000
15 000
gel (insoluble)
24 300 6.0
4.5
5.3
4.9
5.0
4.0
Figure 2. TGA thermograms of hyperbranched poly(aroyl-
arylene)s P1-P3 recorded under nitrogen at a heating rate of
20 °C/min.
a Refluxed for 24 h under nitrogen, [M]0 ) 0.14 M, [peperidine]
) 42 mM. b CB ) chlorobenzene. c Determined by GPC in THF
on the basis of a polystyrene calibration.
technique. A typical procedure for the polymerization of 1(m)
is given below as an example.
In a 15 mL Schlenk tube with a three-way stopcock on the
sidearm was placed 100 mg of 1(m) (0.267 mmol) under
nitrogen in a glovebox. Distilled dioxane (1.9 mL) was injected
into the tube using a hypodermic syringe, followed by the
addition of a solution of piperidine (0.267 mM) in dioxane (0.30
mL). The mixture was stirred under reflux for 24 h. Afterward,
the polymerization mixture was added dropwise to ∼300 mL
of methanol through a cotton filter under stirring. The
precipitate of the polymer [P1(m)] was allowed to stand
overnight and was then collected by filtration. The isolated
polymer was washed with methanol and dried under vacuum
at room temperature to a constant weight.
Characterization Data of P1(m). Brown power, yield 79%.
Mw ) 19 200, Mw/Mn ) 4.5 (GPC, polystyrene calibration). IR
(thin film), ν (cm-1): 3243 (tC-H stretching), 3067 (Ar-H
stretching), 2940, 2867 (CH2 stretching), 2095 (CtC stretch-
ing), 1667 (CdO stretching), 1580, 1485 (CdC ring stretching).
1H NMR (300 MHz, CD2Cl2), δ (ppm): 8.43, 8.33, 7.91, 7.72,
7.59, 7.40, 6.92, 4.00, 3.50, 1.78, 1.52. 13C NMR (75 MHz,
CDCl3), δ (ppm): 195.39, 194.93, 165.52, 159.75, 159.07,
156.18, 138.45, 134.33, 133.84, 133.34, 130.58, 129.84, 122.95,
121.89, 121.26, 120.14, 117.58, 115.84, 114.01, 107.97, 81.36,
68.58, 29.45, 28.10, 26.55, 24.83, 20.69.
3,3′-(1,4-Phenylenedimethoxy)bis(benzoylacetylene) 2(m). Pale
yellow solid, yield 82%. IR (thin film), ν (cm-1): 3259 (tC-H
stretching), 2877 (CH2 stretching), 2095 (CtC stretching),
1638 (CdO stretching), 1578, 1276. 1H NMR (300 MHz,
CDCl3), δ (ppm): 7.82 (d, 2H), 7.72 (s, 2H), 7.48 (s, 4H), 7.42
(t, 2H), 7.24 (d, 2H), 5.13 (s, 4H), 3.43 (s, 2H). 13C NMR (75
MHz, CDCl3), δ (ppm): 176.99, 158.84, 137.48, 136.32, 129.82,
127.85, 123.20, 122.04, 114.03, 80.70, 80.26, 69.88. MS (CI):
m/e 395.08 [(M + 1)+, calcd for C26H18O4: 394.12].
3,3′-(1,12-Dodecylenedioxy)bis(benzoylacetylene) 3(m). White
solid, yield 61%. IR (thin film), ν (cm-1): 3216 (tC-H
stretching), 2917, 2852 (CH2 stretching), 2096 (CtC stretch-
1
ing), 1631 (CdO stretching), 1597, 1270. H NMR (300 MHz,
CDCl3), δ (ppm): 7.78 (d, 2H), 7.76 (s, 2H), 7.39 (t, 4H), 7.16
(d, 2H), 4.00 (t, 4H), 3.43 (s, 2H), 1.84-1.75 (m, 4H), 1.46-
1.30 (m, 16H). 13C NMR (75 MHz, CDCl3), δ (ppm): 177.19,
159.35, 137.40, 129.64, 122.73, 121.82, 113.50, 80.56, 80.33,
68.28, 29.50, 29.31, 29.09, 25.95. MS (CI): m/e 459.20 [(M +
1)+, calcd for C30H34O4: 458.25].
4,4′-(1,12-Dodecylenedioxy)bis(benzoylacetylene) 3(p). White
solid, yield 74%. IR (thin film), ν (cm-1): 3201 (tC-H
stretching), 2924, 2853 (CH2 stretching), 2094 (CtC stretch-
1
ing), 1633 (CdO stretching), 1595, 1259. H NMR (300 MHz,
P1(p). Yellow power, yield 65%. Mw ) 9100, Mw/Mn ) 4.0
(GPC, polystyrene calibration). IR (thin film), ν (cm-1): 3066
(Ar-H stretching), 2941, 2867 (CH2 stretching), 1661 (CdO
CDCl3), δ (ppm): 8.12 (d, 4H), 6.93 (d, 4H), 4.03 (t, 4H), 3.38
(s, 2H), 1.83-1.76 (m, 4H), 1.46-1.30 (m, 16H). 13C NMR (75
MHz, CDCl3), δ (ppm): 185.59, 145.46, 142.00, 123.39, 81.22,
80.63, 66.33, 17.95, 17.71, 17.34, 13.51. MS (CI): m/e 459.18
[(M + 1)+, calcd for C30H34O4: 458.25].
1
stretching), 1600, 1574 (CdC ring stretching). H NMR (300
MHz, CD2Cl2), δ (ppm): 8.47, 8.31, 8.22, 7.80, 6.94, 4.00, 1.80,
1.51. 13C NMR (75 MHz, CDCl3), δ (ppm): 193.97, 163.70,
162.65, 139.07, 137.75, 133.66, 132.88, 132.39, 129.45, 114.87,
68.66, 67.89, 29.37, 27.99, 26.09, 24.88.
Polymer Synthesis. All polymerization reactions were
carried out in a nitrogen atmosphere using a standard Schlenk

Macromolecules, Vol. 38, No. 15, 2005
Regioselective Polycyclotrimerizations of Diynes 6385
Table 4. Thermal Properties of Hyperbranched
Poly(1,3,5-aroylarylene)s
polymer
Tda (°C)
Wrb (%)
Tgc (°C)
P1(m)
P1(p)
P2(m)
P3(p)
453
438
454
443
36
24
64
23
91.1
103.3
ndd
79.2
a Temperature for 5% weight loss. b Weight residue at 800 °C.
c Measured by DSC under nitrogen at a heating rate of 10 °C /min
(recorded during the first heating scan). d Not detectable.
P2(m). Yellow power, yield 85%. Mw ) 15 000, Mw/Mn ) 4.0
(GPC, polystyrene calibration). IR (thin film), ν (cm-1): 3064
(Ar-H stretching), 2927, 2872 (CH2 stretching), 1667 (CdO
1
stretching), 1581, 1485 (CdC ring stretching). H NMR (300
Figure 3. IR spectra of (A) monomer 1(m) and (B) its polymer
P1(m) (sample from Table 3, no. 1).
MHz, CD2Cl2), δ (ppm): 8.32, 8.27, 7.34, 7.17, 5.04. 13C NMR
(75 MHz, CDCl3), δ (ppm): 194.65, 159.23, 158.26, 138.90,
138.20, 137.17, 134.34, 132.65, 130.09, 128.06, 123.32, 122.05,
120.35, 117.99, 115.82, 71.51, 70.16.
P3(m). Brown power, yield 75% (GPC and NMR data not
available because of its insolubility in common organic solvents
such as THF, chloroform, and DMF.) IR (thin film), ν (cm-1):
3068 (Ar-H stretching), 2924, 2852 (CH2 stretching), 1664
(CdO stretching), 1578, 1484 (CdC ring stretching).
P3(p). Brown power, yield 95%. Mw ) 24 300, Mw/Mn ) 6.0
(GPC, polystyrene calibration). IR (thin film), ν (cm-1): 3068
(Ar-H stretching), 2925, 2852 (CH2 stretching), 1657 (CdO
stretching), 1600, 1508 (CdC ring stretching). (NMR data not
available because the polymer became insoluble in common
organic solvents after it had been dried in the vacuum oven.)
Preparation of Model Compound. 1,3,5-Tris(4-butyloxy-
benzoyl)benzene (9), the model compound, was synthesized by
the 1,3,5-regioselective alkyne cyclotrimerization reaction
shown in Scheme 4. The starting material, 3-(butyloxy)-
benzoylacetylene (8), was prepared by the procedures similar
to those for the synthesis of monomer 1(m). Characterization
data of 8: Yellow liquid, yield 93%. IR (thin film), ν (cm-1):
3200 (tC-H stretching), 2924, 2853 (CH2 stretching), 2094
(CtC stretching), 1633 (CdO stretching), 1595, 1568, 1259,
1
849. H NMR (300 MHz, CDCl3), δ (ppm): 7.77 (d, 1H), 7.62
(s, 1H), 7.38 (t, 1H), 7.17 (d, 1H), 4.00 (t, 2H), 3.48 (s, 1H),
1.82-1.73 (m, 2H), 1.56-1.43 (m, 2H), 1.00-0.95 (t, 3H). 13C
NMR (75 MHz, CDCl3), δ (ppm): 177.15, 159.24, 137.30,
129.56, 122.56, 121.63, 113.48, 80.62, 80.23, 67.84, 31.03,
19.07, 13.69.
Figure 4. 1H NMR spectra of (A) monomer 1(m), (B) its
polymer P1(m) (sample taken from Table 3, no. 1), and (C)
model compound 9. The solvent peaks are marked with
asterisks (/).
1,3,5-Tris(4-butyloxybenzoyl)benzene was synthesized under
conditions similar to those used in the polycyclotrimerizations
of bis(aryl ethynyl ketone)s 1-3 as described above. The
reaction was carried out in dioxane (2.0 mL) with 0.2 g (0.99
mmol) of 8 and 0.556 mL of piperidine solution in dioxane
(0.267 mM). The product (9) was purified by silica gel chro-
matography using an ethyl acetate/hexane mixture (1:3 by
volume) as eluent. Pale yellow oil; yield 78%. IR (thin film), ν
(cm-1): 3071 (Ar-H stretching), 2956, 2873 (CH2 stretching),
1667 (CdO stretching), 1594, 1486 (CdC ring stretching). 1H
NMR (300 MHz, CDCl3), δ (ppm): 8.38 (s, 3H), 7.38-7.34 (m,
9H), 7.16 (d, 3H), 4.02 (t, 6H), 1.81-1.76 (m, 6H), 1.54-1.46
(m, 6H), 1.00-0.95 (t, 9H). 13C NMR (75 MHz, CDCl3), δ
(ppm): 194.59, 159.23, 138.11, 137.57, 133.88, 129.39, 122.61,
120.05, 114.80, 68.00, 31.25, 19.30, 13.92. MS (CI): m/e 607.22
[(M + 1)+, calcd for C39H42O6: 606.30].
Photo-Cross-Linking and Photopatterning. Photo-cross-
linking reactions of the polymer films were conducted using
the 365 nm light obtained from a Spectroline ENF-280C/F UV
lamp in air at a distance of 1 cm from the light source. The
incident light intensity was ∼1 mW/cm2. The polymer films
for UV measurements were prepared by spin-coating the
polymer solutions (∼2 wt % in dichloroethane) at 2000 rpm
for 1 min on quartz plates. Photosensitivity of the polymer
(D0.5) was evaluated by the energy needed to obtain a gel
fraction of 0.5 (or 50%).4 Dichloroethane solutions of the
polymers (10% w/w) were coated onto thin glass plates to give
films of ∼1-2 µm in thickness. The films were dried in a
vacuum at 40 °C for 3 h. After exposure to the UV light, the
films were developed in dichloroethane for 60 s at room
temperature and then dried for 3 h at 40 °C under reduced
pressure. The weights of the films were measured by a Perkin-
Elmer AD-6 autobalance with accuracy of (0.01 mg. The gel
fraction of films was plotted against the log of the exposure
dose, and the photosensitivity (D0.5) and the contrast at 0.5
gel fraction (γ0.5) were determined from the curve.
The photoresist patterns were prepared on silicon wafer
using a Cu-negative mask (for microscale patterns) or an
ASML 5000/55A stepper (for nanoscale patterns). The polymer
solution was coated and prebaked following the standard
experimental procedures for the photosensitivity study.4,5 The
films were exposed to a 365 nm UV light for an exposure dose
of ∼1 J/cm2. The films were then developed in dichloroethane
for 2 min. After the films were heated at 80 °C for 2 h, the
resist patterns were evaluated on a Digital Instrument Nano
IIIa atomic force microscopy (AFM; Digital Instrument Co.).
Results and Discussion
Regioselective Diyne Polycyclotrimerization.
The alkyne monomers containing carbonyl moieties, i.e.,
bis(aroylacetylene)s 1-3, were prepared by etherifica-
tion of m- or p-hydroxybenzaldehyde 4 with alkyl/aryl

6386 Dong et al.
Macromolecules, Vol. 38, No. 15, 2005
Chart 1. Partial Molecular Structure of Hyperbranched Poly(aroylarylene) P1(m) with a Labeling Scheme for
Figure 4B
Scheme 5. Termination of a Propagating Branch (10) by the Formation of Cyclophane 11 through
Cyclodimerization of 10 with a Diyne Monomer (1 or 2 or 3)
dibromide 5, followed by Grignard addition and alcohol
oxidation (cf. Scheme 3). All the monomers were char-
acterized spectroscopically, from which satisfactory
analysis data were obtained (see Experimental Section
for details). It is known that an aroylacetylene (monoyne)
cyclotrimerizes when refluxed in DMF or in the presence
of diethylamine.6 We tried to polymerize bis(aroyl-
acetylene)s 1-3 (diynes) under these conditions. Poly-
mers were formed in relatively low yields after the
diynes were refluxed in DMF or its mixtures for a long
time (72 h; Table 1). When the polymerization of 1(m)
was carried out in the presence of diethylamine, poly-
mers were obtained in even lower yields (7-21%; Table
2). We tried to shorten the reaction time and increase
the polymer yield by using other bases as catalysts.
Disappointedly, when diphenylamine was used, no
polymerization occurred at all.
in common solvents such as THF, chloroform, and DMF.
The polymers are thermally stable, losing merely 5% of
Delightfully, however, when piperidine was used, a
shorter reaction time (24 h) converted 1(m) into poly-
mers in higher yields (up to 99%; Table 3, no. 2). The
effect of catalyst concentration ([cat.]) was studied, and
it was found that the best results were obtained at [cat.]
∼ 42 mM (Figure 1). At this [cat.], 1(p), 2(m), and 3 were
all polymerized, demonstrative of the usefulness of
piperidine as a catalyst for diyne polycyclotrimerization.
All the polymers except for P3(m) are completely soluble
Figure 5. 13C NMR spectra of (A) monomer 1(m), (B) its poly-
mer P1(m) (sample taken from Table 3, no. 1), and (C) model
compound 9. The solvent peaks are marked with asterisks (/).

Macromolecules, Vol. 38, No. 15, 2005
Regioselective Polycyclotrimerizations of Diynes 6387
Scheme 6. Molecular Structures of Dendritic (D), Linear (L), and Terminal (T) Units of P1(m)
their weights when heated to temperatures as high as
438-454 °C (Figure 2). They undergo glass transitions
at ∼79-103 °C (Table 4) and can be quantitatively
converted into thermosets by heating to ∼200 °C.
manner. To collect direct structure information, we
characterized the polymers by spectroscopic methods.
Examples of the IR spectra of P1(m) and its monomer
1(m) are given in Figure 3. The diyne monomer [1(m)]
shows absorption bands at 3211 and 2093 cm-1 due to
tC-H and CtC stretchings, respectively. These bands
are still observable in the spectrum of its polymer
[P1(m)] at similar wavenumbers but in lower intensities
because most of the triple bonds have been converted
to the benzene rings by the diyne polycyclotrimerization.
Molecular Structure Characterization. To verify
that the diynes (1-3) have been polymerized by piperi-
dine through an alkyne polycyclotrimerization mecha-
nism, we conducted a model reaction using m-(butoxy)-
benzoylacetylene (8), a monoyne, as a model compound
for diyne 1(m). When 8 was reacted under similar
conditions (cf. Table 3, no. 1), 1,3,5-tris[3-(butoxy)-
benzoyl]benzene (9) was isolated as the sole cyclic
product in high yield (Scheme 4). This proves that 1(m)
must have been polycyclotrimerized in a regioselective
1
The H NMR spectrum of P1(m) well corresponds to
its expected molecular structure, with no peaks un-
assignable (Figure 4B and Chart 1). The acetylene
proton of its monomer 1(m) absorbs at δ 3.50 (a), which

6388 Dong et al.
Macromolecules, Vol. 38, No. 15, 2005
Degree of Branching (DB). As illustrated in Scheme
6 using P1(m) as an example, there exist four kinds of
structural units in a hyperbranched poly(1,3,5-triaroyl-
benzene): one kind of dendritic unit (D), one kind of
linear unit (L), and two kinds of terminal units (T). The
terminals can be the unreacted ethynyl triple bonds (Tt)
and the cyclophane rings formed by the cyclization of
one ethynyl group of a propagation branch with two
ethynyl groups of a diyne monomer (Tc; cf. Scheme 5).
The following relationships hold among the contents or
fractions (f) of these four units (fD, fL, fTt, and fTc):
(3fD + 3fL + 3fTt)/(fL + 2fTt) ) Ai/Aa
(fL + 2fTt)/fTc ) Aa/Aj
(1)
(2)
where Ai, Aa, and Aj are the integrated areas of the
resonance peaks i, a, and j, whose ratios can be readily
1
determined from the H spectrum shown in Figure 4:
Ai/Aa ) 1.046/0.118
Aa/Aj ) 0.118/0.168
(3)
(4)
Figure 6. (A) 1H and (B) 13C NMR spectra of P1(m) prepared
in tetralin (Table 3, no. 3). The solvent peaks are marked with
asterisks (/).
Obviously, according to definition
becomes much weaker after polymerization. The polym-
erization shifts the resonances of the phenyl protons of
1(m) at δ 7.76 (g) and 7.63 (h) to δ 7.40, with the phenyl
protons on the periphery of P1(m) resonated at δ 7.72
(g′) and 7.59 (h′). By comparison with the spectrum of
model compound 9, the peak of P1(m) at δ ∼8.33 (i) is
readily assigned to the protons of the new benzene rings
formed in the polymerization. The peaks at δ 8.43 (k)
and 7.91 (j) arise from the resonance of tribenzoylphenyl
protons of the cyclophane formed by the end-capping of
a triple bond in a polymer branch by two triple bonds
in a monomer (Scheme 5).6c The 13C spectrum of P1(m)
shows a weak peak of the triple bond at δ 81.4 and a
largely downfield shifted carbonyl resonance at δ 195.4
(Figure 5B) due to the conversion of the triple bonds of
1(m) to the benzene rings of P1(m).
fD + fL + fTt + fTc ) 1
(5)
From the equations given above, the content of cyclic
terminal (fTc) is determined to be fTc ) 0.33. In other
words, the degree of cyclic termination via cyclophane
formation (DC) is DC ) 33%. From the spectrum given
in Figure 3, it can be seen that fTt g 0. It is therefore
estimated that fD g 0.45 and fL e 0.22. According to
definition [DB ) (fD + fTt + fTc)/(fD + fL + fTt + fTc)],7,8
DB of P1(m) is estimated to be DB g 78%. This value
is much higher than those of “conventional” hb-Ps
(commonly ∼50%).1c The hb-PAAs with higher DBs can
be synthesized by varying the reaction conditions: for
example, a P1(m) with a DB of 100% is prepared in
Scheme 7. Proposed Mechanism for Regioselective 1,3,5-Polycyclotrimerization of Aroylethyne

Macromolecules, Vol. 38, No. 15, 2005
Regioselective Polycyclotrimerizations of Diynes 6389
Scheme 8. Proposed Mechanism for Photo-Cross-Linking in P2(m)
tetralin, as verified by the absence of triple-bond
resonances in its NMR spectra (Figure 6).
Mechanism of Polycyclotrimerization. As proven
by the spectroscopic analyses, the diynes have been
regioselectively polycyclotrimerized into hb-PAAs by
piperidine. This regioselectivity stems from the ionic,
instead of coordination,2,3 mechanism of the base-
catalyzed cyclotrimerization.6b Piperidine may have
reacted with an aroylethynyl group to form a keto-
enamine (13), which further reacts with two more
aroylethynyl groups to give a dihydrobenzene (16;
Scheme 7). The piperidine moiety of 16 is removed by
its reaction with another aroylethynyl group and aro-
matization gives a 1,3,5-trisubstituted benzene ring
Figure 7. (A) Plots of gel fractions (Fg) of P1(m) and P2(m) films vs exposure doses (D). AFM images of (B) microscale and (C,
D) nanoscale patterns obtained from P2(m) films exposed to 1 J/cm2 of UV irradiation.

6390 Dong et al.
Macromolecules, Vol. 38, No. 15, 2005
cross-linking efficiencies. This is indeed the case: for
example, a thin film of P2(m) on a glass plate can be
readily cross-linked by the irradiation with a hand-held
UV lamp at room temperature. The cross-linking may
have proceeded via a well-established radical mecha-
nism:9,10 the triplet tAB unit in one P2(m) abstracts
hydrogen from the benzyl unit of another P2(m), and
subsequent coupling of the radicals so formed leads to
the gel formation (Scheme 8).
Figure 7 depicts the dose effect on the gel formation
of P1(m) and P2(m) films after they have been exposed
to a weak UV light (∼1 mW/cm2). Although the photo-
cross-linking conditions have not been optimized, both
the hb-PAAs already exhibit sensitivities (D0.5 ) 50-
180 mJ/cm2) better than those of some commercial
negative resists (NRs) such as NR1-3000RY and NR9-
3000P (both 190 mJ/cm2) and NR7-1000PY (390 mJ/
cm2).11 Compared to P1(m), P2(m) shows lower D0.5 and
higher γ0.5 (contrast).11 This is possibly due to the more
rapid reduction of the ketone group in P2(m), thanks
to the ease in abstracting hydrogen from its benzyl unit.
This hypothesis is supported by the fact that the K band
of the tAB units of P2(m) drops much faster than that
of P1(m) (Figures 8 and 9).
Well-resolved patterns with line widths of 1.0 and 1.5
µm are readily obtained when a film of P2(m) has
been exposed to a UV dose of 1 J/cm2 (Figure 7B).
Patterns with submicron resolutions (line width down
to 500 nm) are also achievable, as demonstrated by
the examples given in Figure 7 (panels C and D) and
Figure 9. Clearly, P2(m) is an excellent photoresist
material.
Conclusion
Figure 8. Changes in the UV spectra of the films of (A) P2(m)
and (B) P1(m) with exposure times; irradiation wavelength λ
) 365 nm; ∆A ) (A - A0) × 100%, where A0 is the absorption
of the original (unirradiated) polymer film. Data for the P2(m)
film are shown in the inset of panel B for comparison.
In this work, we found a new synthetic route to
regioregular hb-Ps. The diyne polycyclotrimerization
initiated by a simple base of piperidine give new hb-
PAAs with high Mws (up to 31 000) and DBs (up to
100%) in high yields (up to 99%). The polycyclization is
strictly regioselective and highly tolerant to functional
groups. The hb-PAAs are readily cross-linkable by UV
irradiation to give photopatterns with nanometer reso-
lution. The unique molecular structures of the hb-PAAs
may endow them with optical nonlinearity and redox
activity12 and enable them to serve as polymer precur-
sors to organic spintronics and magnets.6b
(17). Repetition of this cycle results in the formation of
an hb-PAA of high molecular weight.
Photo-Cross-Linking and Photopatterning. Ben-
zophenone has been introduced into natural (e.g.,
protein) and synthetic polymers (e.g., polyimide) to serve
as a photo-cross-linker.9 The hb-PAAs contain many
triaroylbenzene (tAB) units and may exhibit high photo-
Figure 9. (A) Two- and (B) three-dimensional AFM images of the nanometer-sized photoresist pattern generated by a P2(m)
film irradiated by a 365 nm UV light with an exposure dose of 1 J/cm2.

Macromolecules, Vol. 38, No. 15, 2005
Regioselective Polycyclotrimerizations of Diynes 6391
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Acknowledgment. The work described in this paper
was partially supported by the Research Grants Council
of Hong Kong (603304, 604903, N_HKUSR606_03,
HKUST6085/02P and 6121/01P), the University Grants
Committee of Hong Kong through an Area of Excellence
(AoE) Scheme (AoE/P-10/01-1A), and High Impact Area
(HIA) Grants of our University (HIA02/03.SC06). We
also thank the financial support from the National
Science Foundation of China and the Cao Guangbiao
Foundation of Zhejiang University.
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