Multi-armed, TEMPO-functionalized unimolecular initiators for starburst dendrimer synthesis via stable free radical polymerization. 1. Tri azo-functionalized unimer

Article abstract of DOI:10.1139/v04-107

The synthesis of azobenzene-functionalized multi-armed unimolecular initiators or "unimers" that can be polymerized using styrene or styrenic derivatives via TEMPO (2,2,6,6-tetramethylpiperidenyl-1-oxyl) mediated stable free radical polymerization (SFRP) is described. The unimers are composed of an azobenzene-functionalized core and a TEMPO-modified unit. Homopolymers and copolymers of styrene and acetoxystyrene were synthesized using the mono-and trifunctionalized unimers as initiators under bulk conditions with average molecular weights and polydispersities reported. The studies lay the groundwork for further investigations involving SFRP towards building a light harvesting system by introducing chromophores onto the polymer chains for capturing light and thence transferring it to the azobenzene core.

Full text of DOI:10.1139/v04-107

1393
Multi-armed, TEMPO-functionalized unimolecular
initiators for starburst dendrimer synthesis via
stable free radical polymerization. 1. Tri azo-
functionalized unimer
Dalia Abdallah, Mohmad Asri Abd Ghani, Michael F. Cunningham,
Peter M. Kazmaier, Barkev Keoshkerian, and Erwin Buncel
Abstract: The synthesis of azobenzene-functionalized multi-armed unimolecular initiators or “unimers” that can be
polymerized using styrene or styrenic derivatives via TEMPO (2,2,6,6-tetramethylpiperidenyl-1-oxyl) mediated stable
free radical polymerization (SFRP) is described. The unimers are composed of an azobenzene-functionalized core and a
TEMPO-modified unit. Homopolymers and copolymers of styrene and acetoxystyrene were synthesized using the
mono-and trifunctionalized unimers as initiators under bulk conditions with average molecular weights and
polydispersities reported. The studies lay the groundwork for further investigations involving SFRP towards building a
light harvesting system by introducing chromophores onto the polymer chains for capturing light and thence transfer-
ring it to the azobenzene core.
Key words: azo-functionalized unimolecular initiator, stable free radical polymerization, starburst dendrimer.
Résumé : On décrit la synthèse d’initiateurs unimoléculaires tentaculaires à base d’azobenzènes, dénommés unimères,
qui peuvent être polymérisés à l’aide de styrène ou de ses dérivés par le biais d’une polymérisation avec un radical
libre stable catalysée par le 2,2,6,6-tétraméthylpipéridinyl-1-oxyle (TEMPO). Les unimères sont formés d’un noyau
azobenzène fonctionnalisé et d’une unité TEMPO modifiée. On a synthétisé des homopolymères et des copolymères du
styrène et de l’acétoxystyrène en utilisant des unimères mono- et trifonctionnalisés comme initiateurs, dans des condi-
tions globales, et on rapporte des poids moléculaires et des polydispersités moyennes. Les études posent les fondements
pour des études ultérieures, impliquant des polymérisations avec un radical libre stable, dans l’élaboration d’un système
permettant de recueillir la lumière en introduisant sur les chaînes de polymère des chromophores qui pourraient capter
la lumière et par la suite la transmettre au noyau azobenzène.
Mots clés : initiateur unimoléculaire à base d’azobenzène fonctionnalisé, polymérisation avec un radical libre stable,
dendrimère en « éclatement d’étoile ».
[Traduit par la Rédaction] Abdallah et al. 1402
Introduction
ple these two categories of complexity in a single system to
enable the investigation of the unique properties of this sys-
tem.
The synthesis of macromolecules with “complex” and
controlled architecture is becoming increasingly important in
the field of polymer chemistry (1). There are two categories
of complexity that one can introduce: functional complexity
and architectural complexity. Azo moieties are an example
of functional complexity since they can operate as optical
transducers, i.e., through light absorption, energy transfer,
and cis/trans isomerism. The second category, architectural
complexity, can be achieved by introducing branches into
the polymer backbone, which leads to the formation of graft
or star polymer systems. In our study, we would like to cou-
Traditional methods of synthesizing well-defined macro-
molecular architectures involve living polymerization tech-
niques such as anionic (2), cationic (3), group transfer
polymerization (4), and transition-metal catalysis (5). How-
ever, as a result of work over the past decade living free rad-
ical polymerization is now possible where there is control
over the molecular weight, the end group, and the ability to
synthesize block copolymers.
Georges et al. (6) were the first to report the synthesis of
low polydispersity polystyrene using free radical polymer-
Received 2 February 2004. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 9 November 2004.
D. Abdallah, M.A.A. Ghani, and E. Buncel.1 Department of Chemistry, Queen’s University, Kingston, ON K7L 3N6, Canada.
M.F. Cunningham. Department of Chemical Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada.
P.M. Kazmaier and B. Keoshkerian. The Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, ON L5K 2L1,
Canada.
1Corresponding author (e-mail: buncele@chem.queensu.ca).
Can. J. Chem. 82: 1393–1402 (2004)
doi: 10.1139/V04-107
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Scheme 1.
ization, based on use of the stable nitroxide radical 2,2,6,6-
tatramethylpiperdinyloxy (TEMPO) in combination with
benzoyl peroxide (BPO) as a bimolecular initiating system.
The TEMPO unit acts as a “capping” agent for the growing
polymer chain and controls the polymerization (7). The use
of stable nitroxides to control free radical polymerization
was originally stimulated by the work of Moad and Rizzardo
(8) who employed TEMPO to reversibly terminate a grow-
ing polymer chain.
The work described in this paper focuses on the synthesis
of multiazofunctionalized azo unimolecular initiators, which
we call “unimers”, for stable free radical polymerization
(SFRP). The structures of the unimers are shown below,
where 6 and 7 are used in the synthesis of 8, 9, and 10, i.e.,
monoazofunctionalized, diazofunctionalized, and triazofunc-
tionalized unimers, respectively. The mono- and trifunction-
alized unimers were used in the polymerization of styrene
and acetoxystyrene to form homopolymers, block copoly-
mers, and random copolymers, where we report the average
molecular weights and polydispersities based on GPC analy-
sis.
We are specifically interested in azobenzene-modified
polymers to study and compare cis/trans isomerization of the
azobenzene units of the mono-, di-, and trifunctionalized
polymers upon irradiation. It is anticipated that cis/trans
isomerism of the azo core should have a profound effect on
the overall tertiary structure of the molecules.
The present work continues our studies with azo, azoxy,
and hydrazo arenes, encompassing various structure reactiv-
ity studies, such as rearrangements (Wallach, benzidine),
spiropyran-merocyanine interconversion systems, and
periphery-modified dendrimers, with applications in optical
data storage, holography and drug delivery, as well as light
harvesting properties (11).
During the past decade much work has been done on de-
signing and synthesizing functionalized unimolecular initia-
tors that contain the TEMPO unit. Some examples of
unimolecular initiators synthesized by Hawker and co-
workers (9, 10) are shown below. Compounds 1, 2, 3, and 4
are monofunctionalized unimolecular initiators that form lin-
ear polymers upon polymerization, while compound 5 is a
trifunctionalized unimolecular initiator that forms a star
polymer upon polymerization, where T stands for the
TEMPO moiety.
Results and discussion
Our strategy is to develop the chemistry on a monoazo-
functionalized unimer 8 and then extend this chemistry to
the more complex difunctionalized 9 and trifunctionalized
GEN 0 unimer systems.
Monoazofunctionalized unimolecular initiator 8
The monoazofunctionalized unimer 8 is composed of two
parts, the core, p-hydroxyazobenzene 14 and the TEMPO-
containing unit, TEMPO modified 4-ethylbenzyl iodide 7.
Scheme 1 shows the preparation of TEMPO-modified 4-
ethylbenzyl iodide 7 starting from commercially available 4-
ethylbenzaldehyde 11.
To introduce a TEMPO unit and form the TEMPO-
modified derivative of compound 13, a carbon-centered radi-
cal must be generated in the presence of TEMPO. Hawker et
al. (9) used di-tert-butyl peroxide to generate the carbon-
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Abdallah et al.
1395
centered radicals at ca. 125 °C. We used di-tert-butyl
peroxyoxalate instead since it undergoes facile decomposi-
tion in solvents such as benzene below 50 °C to give tert-
butoxy radicals.
Diazofunctionalized unimolecular initiator 9
The difunctionalized azobenzene unimer 9 is composed of
a core containing two azobenzene units and two TEMPO-
modified units attached to the ends of the core. The synthe-
sis of 9 was accomplished in 62% yield as shown in
Scheme 2.
Coupling of the TEMPO units onto bis(4-aminophenyl)-
1,2-ethane 16 to form the difunctionalized azobenzene-
modified unimer was effected by reaction with 7 (Scheme 1)
(18% yield).
Coupling of the azobenzene core with the TEMPO-
containing unit was first attempted using the bromo derivative
6 with poor yield (9%) (12). To optimize the yield, the iodo
derivative 7 was synthesized using the Finkelstein reaction.
The monofunctionalized azobenzene unimer was synthe-
sized as shown in Scheme 1 in 75% yield (16). The proton
NMR spectrum confirms that the azobenzene core became
attached to the TEMPO-containing unit. The aromatic pro-
tons on the azobenzene unit appear at 7 to 8 ppm and the
TEMPO unit protons at 0.5–0.6 ppm.
Triazofunctionalized unimolecular initiator 10, GEN 0
The trifunctionalized unimer is the zeroth generation of a
dendrimer, i.e., GEN 0, a star-shaped unimer composed of a
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Can. J. Chem. Vol. 82, 2004
Scheme 2.
Scheme 3.
core with three azobenzene units and three TEMPO-
modified units attached to the ends of the core.
The preparation of GEN 0 (Scheme 3) involved first the
synthesis of the core 21 in three steps:
Controlled free radical polymerizations
We now describe polymerization studies that have been
performed towards synthesis of polymers having an azoben-
zene unit at the core. The studies entailed the mono- and
trifunctionalized azobenzene unimers that were used in the
polymerization of styrene and acetoxystyrene, to give
homopolymers, block and random copolymers.
(1)
(2)
(3)
Nucleophilic aromatic substitution yielded 19.
Reduction of 19 gave 20 in 94% yield.
Diazotization and coupling gave 21 in 73% yield.
Controlled free radical polymerization of monoazo-
functionalized unimer
Introduction of the TEMPO units to form GEN 0 was ef-
fected by Williamson ether coupling between the azoben-
zene core and the TEMPO-modified 4-ethylbenzyl iodide 7
(Scheme 1) in 22% yield (12). Gen 0 is readily soluble in
halogenated solvents such as dichloromethane or chloro-
form, and can be distinguished from the starting compound
Monoazo-functionalized polystyrene MAz-PS-T
Polymerization of styrene with monofunctionalized azo-
benzene unimer 8 was effected under bulk conditions
(Scheme 4) at 135 °C. The polymerization was stopped after
2 h by cooling to room temperature. The polymer MAz-PS-
T was dissolved in THF and precipitated from methanol to
give a yellow powder (26%) with an average molecular
weight of 13 500 g/mol and a narrow polydispersity of 1.26
1
21, which dissolves only in acetone or DMSO. H NMR
shows the TEMPO moiety between 0.7 and 1.7 ppm and the
aromatic protons between 7 and 8 ppm.
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Abdallah et al.
1397
Scheme 4.
Scheme 5.
Scheme 6.
1
based on GPC analysis. The H NMR shows broad peaks at
1.4 and 1.8 ppm representing the aliphatic hydrogens of the
polystyrene, the methylene and methine protons, respec-
tively. Aromatic hydrogens of polystyrene appear as broad
peaks between 6.4 and 7.2 ppm. The 13C NMR shows a peak
at 145.6 ppm for the quaternary carbon of the aromatic moi-
ety of polystyrene while the other carbons of the aromatic
moiety appear at 128.4, 128.1, and 126.1 ppm. Aliphatic
carbons appear at 44.3 and 40.7 ppm. The UV–vis absorp-
tion spectrum of MAz-PS-T in THF showed distinct π–π*
and n–π* absorption bands of azobenzene appearing at ca.
350 and 450 nm, respectively, confirming that the polymer
sample contains the azobenzene unit.
methyl protons of the acetoxy group appear as a singlet at
2.3 ppm. The 13C NMR shows a peak at 169.5 ppm repre-
senting the carbonyl carbon of the acetate group. Peaks at
149.1 and 142.6 ppm represent the quaternary carbons of the
aromatic moiety of the polyacetoxystyrene while peaks at
128.8, 127.6, 122.0, and 121.5 represent the rest of the aro-
matic carbons. Aliphatic carbons of polyacetoxystyrene ap-
pear at 44.1 and 40.5 ppm representing the methylene and
methine protons, respectively. The methyl carbon of the ace-
tate group appears at 21.6 ppm.
Monoazofunctionalized block (acetoxystyrene–styrene) co-
polymer MAz-PAS-PS-T
Chain extension of MAz-PAS-T with styrene under bulk
conditions yielded MAz-PAS-PS-T, a block copolymer of
acetoxystyrene and styrene, as illustrated in Scheme 6. The
polymerization was stopped after 2 h and the reaction mix-
ture was dissolved in THF and precipitated from methanol to
give an off-white – yellow powder with an average molecu-
Monoazofunctionalized polyacetoxystyrene MAz-PAS-T
The polymerization of acetoxystyrene with 8 was effected
under the same conditions as for MAz-PS-T, in bulk, under
nitrogen and heating at 135 °C as illustrated in Scheme 5.
The polymerization was stopped after 75 min at which point
the mixture became too viscous for stirring. A yellow pow-
der (MAz-PAS-T) with an average molecular weight of
35 300 g/mol and a polydispersity of 1.34 formed upon dis-
solving the reaction mixture in THF and precipitating from
1
lar weight of 40 400 g/mol and 1.54 polydispersity. The H
NMR shows the aliphatic protons of the polymer chain be-
tween 1.2 and 2.2 ppm and the aromatic protons between 6.2
and 7.5 ppm. The methyl protons of the acetate group appear
as a singlet at 2.3 ppm. The 13C NMR shows the carbonyl
carbon of the acetate group at 169.5 ppm, the quaternary ar-
omatic carbons of the polyacetoxystyrene at 149.1 and
142.6 ppm and the quaternary aromatic carbon of polysty-
1
methanol (49%). The H NMR shows two broad peaks be-
tween 1.2 and 2.0 ppm representing the aliphatic protons of
polyacetoxystyrene and a broad peak between 6.2 and
6.9 ppm for the aromatic protons of polyacetoxystyrene. The
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Can. J. Chem. Vol. 82, 2004
Scheme 7.
Scheme 8.
rene at 145.7 ppm. The rest of the aromatic carbons of the
polymer chain appear at 128.4, 128.1, 126.0, and 121.5 ppm.
The aliphatic carbons appear at 46.2, 44.0, 43.2, and
40.8 ppm. The methyl carbon of the acetoxy group appears
at 21.6 ppm consistent with the block copolymer structure.
heating the reaction mixture at 135 °C as illustrated in
Scheme 9. The polymerization was stopped after 75 min.
The polymer was dissolved in THF and precipitated from
methanol, filtered and dried to give a yellow powder (TAz-
PAS-3T) a star polymer, with an average molecular weight
of 74 400 g/mol and a polydispersity of 1.49 based on light
scattering detector analysis.
Monoazofunctionalized random (acetoxystyrene–styrene)
copolymer MAz-PAS/PS-T
Contrasting with the design for block copolymer MAz-
PAS-PS-T, where the strategy is to begin with polymer
MAz-PAS-T and under SFRP react that with acetoxystyrene,
the second monomer was reacted simultaneously to give a
random copolymer.
Thus, polymerization of acetoxystyrene, styrene (1:2 vol-
ume ratio), and monofunctionalized azobenzene unimer 8
under bulk conditions yielded the random copolymer MAz-
PAS/PS-T as shown in Scheme 7. The polymer was dis-
solved in THF and precipitated from methanol, filtered and
dried to give a yellow solid with an average molecular
weight of 16 400 g/mol and a polydispersity of 1.24.
Starburst block (acetoxystyrene–styrene) azo dendrimer
TAz-PAS-PS-3T
The block copolymer TAz-PAS-PS-3T was synthesized
by polymerizing TAz-PAS-3T with styrene under bulk con-
ditions at 135 °C, as shown in Scheme 10. The polymeriza-
tion was stopped after 45 min and the reaction mixture was
dissolved in THF and precipitated from methanol, filtered
and dried to give an off-white – yellow solid with an average
molecular weight of 126 000 g/mol and a polydispersity of
1.64 based on light scattering detector analysis.
Conclusions
Monoazofunctionalized poly(4-hydroxystyrene) MAz-PHS-T
The hydrolysis of MAz-PAS-T was effected by adding
ammonium hydroxide to a solution of MAz-PAS-T in meth-
anol under reflux conditions as shown in Scheme 8. The
polymer was precipitated from water, filtered and dried to
give yellow crystals in 40% yield. The absence of a 13C car-
bonyl peak at 165.9 ppm confirms that the hydrolysis is
complete. The aromatic quaternary carbon attached directly
to the hydroxy group appears at 155.3 ppm while the other
aromatic quaternary carbon appears at 137.0 ppm. The other
aromatic carbons of the polymer chain appear at 128.8 and
115.1 ppm. Aliphatic carbons of the polymer chain appear
between 28.6 and 39.7 ppm.
In conclusion, it has been shown in this work that func-
tionally and architecturally dendritic structures with azo cores
can be synthesized using controlled radical polymerization.
The synthesis of mono-, di-, and triazofunctionalized
unimers was accomplished by coupling of the azobenzene
cores, 14, 16, and 21, with TEMPO-modified 4-ethylbenzene
1
7. A combination of H and 13C NMR and mass spectra was
used for full characterization of the unimers.
The mono- and trifunctionalized unimers were used in
polymerization reactions with styrene and acetoxystyrene.
Structures of the azobenzene-modified polymers were char-
1
acterized by means of a combination of H and 13C NMR
and UV–vis spectra. The monoazofunctionalized unimer 8
was polymerized with styrene to form a homopolymer,
MAz-PS-T, with Mn value 13 500 and PD 1.26. Polymeriza-
tion with acetoxystyrene yielded a polymer, MAz-PAS-T,
with Mn 35 300 and PD 1.34. Copolymers of styrene and
acetoxystyrene were also synthesized, where a block copoly-
mer, MAz-PAS-PS-T, with Mn 40 400 and a PD 1.54 and a
Controlled free radical polymerization of a triazo-
functionalized unimer
Polyacetoxystyrene starburst azo dendrimer TAz-PAS-3T
Polymerization of acetoxystyrene with triazofunction-
alized unimer GEN 0 was done under bulk conditions by
© 2004 NRC Canada

Abdallah et al.
1399
Scheme 9.
recorded on Bruker AM300 spectrophotometer (1H
300.1 MHz, 13C 75.5 MHz). Chemical shifts are reported in
parts per million (ppm) relative to the peaks for residual
CHCl3 in CDCl3 (δ 7.28 ppm) and acetone-d5H in acetone-d6
(δ 2.05 ppm). Mass spectrometry results were recorded on a
Fisons VG Quattro (triple-quadropole MS–MS). Several
techniques were used to identify the mass of the parent ion,
such as electron ionization (EI), chemical ionization (CI),
fast atom bombardment (FAB), and electrospray (ES). High-
resolution mass spectrometry (HR-MS) to establish molecu-
lar weights of new compounds was performed by the
University of Ottawa Mass Spectrometry Service and Uni-
versity of Alberta Mass Spectrometry Service. Melting
points were determined on a Mel-Temp capillary melting
point apparatus and were not corrected.
Scheme 10.
4-Ethylbenzyl alcohol 12 (13)
12 was prepared by reduction of 11 as outlined in
Scheme 1. To a stirred solution of 11 (13.1 g, 97.8 mmol) in
methanol (100 mL) was added a solution of sodium
borohydride (1.4 g, 37.0 mmol) in sodium hydroxide (2 mL,
2 mol/L) and water (18 mL) dropwise while maintaining the
temperature at 23 °C. After removing the solvent on a rotary
evaporator, the residue was dissolved in water (200 mL) and
extracted with CH2Cl2 (3 × 100 mL). Drying (MgSO4), fil-
tration, and solvent removal on a rotary evaporator followed
by column chromatography using hexanes – ethyl acetate
(2:1) as the eluant yielded 12 as a pale yellow oil (10.0 g,
82%). IR (KBr disk, cm–1): 3340, 2969, 2933, 2868, 1417,
random copolymer, MAz-PAS/PS-T, with Mn 16 400 and
PD 1.24 were obtained.
The trifunctionalized unimer, GEN 0, was also polymer-
ized with acetoxystyrene to yield a polymer, TAz-PAS-3T,
with Mn 74 400 and PD 1.49. This polymer was co-
polymerized with styrene to give a block copolymer, TAz-
PAS-PS-3T, with an Mn value of 126 000 and a PD of 1.64.
It is anticipated that the present polymers would have to
be modified at the periphery to achieve light harvesting
properties by functionalization with naphthyl moieties. The
studies predict the formation of an on/off molecular switch
through trans to cis isomerization of the azobenzene unit by
irradiation of the naphthyl moieties and then energy transfer
to the azo core.
1
1032, 813. H NMR (CDCl3) δ: 7.28 (4H, dd), 4.61 (2H, s),
1.06 (1H, d), 2.73 (2H, q), 1.33 (3H, t). 13C NMR (CDCl3) δ:
143.34, 138.03, 127.75, 127.00, 64.57, 28.39, 15.48.
4-Ethylbenzyl bromide 13 (12)
Triphenyl phosphine (11.8 g, 45.0 mmol) was added in
two parts to a mixture of 12 (5.0 g, 36.8 mmol) and CBr4
(14.8 g, 44.6 mmol) in dry THF (75 mL) and stirred under
argon for 2 h. After removing the solvent by rotary evapora-
tion, the residue was dissolved in water (100 mL) and ex-
tracted with CH2Cl2 (3 × 50 mL), dried over MgSO4,
Experimental section
IR spectra were recorded on a Bomen MB-120 spectro-
1
photometer as KBr disks. H and 13C NMR spectra were
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Can. J. Chem. Vol. 82, 2004
filtered, and the solvent was evaporated on a rotary evapora-
tor. Column chromatography using CH2Cl2 as the eluant
yielded a pale yellow oil (7.0 g, 95%). IR (KBr disk, cm–1):
3062, 2962, 2926, 2868, 1898, 1618, 1510, 1438, 1222, 827.
1H NMR (CDCl3) δ: 7.40, 7.26 (4H, dd), 4.58 (2H, s), 2.74
(2H, q), 1.34 (3H, t). 13C NMR (CDCl3) δ: 144.72, 135.08,
129.11, 128.36, 33.81, 28.66, 15.49. EI-MS m/z: 198.4 and
199.9 (calcd. for C9H11Br: 198.0 and 200.0).
of 7 (1.0 g, 2.49 mmol), 14 (0.60 g, 3.03 mmol), anhyd.
K2CO3 (0.54 g, 3.91 mmol), and crown ether (0.24 g,
0.91 mmol) in dry acetone (50 mL) was refluxed (60 °C) un-
der argon for 48 h. After removal of the solvent by rotary
evaporation, the residue was dissolved in CH2Cl2 (50 mL)
and extracted with water (3 × 50 mL). The organic layer was
dried over MgSO4, filtered, and the solvent was removed by
rotary evaporation. Column chromatography using CH2Cl2
as the eluant yielded an orange solid 7 (0.75 g, 75%), mp
125 to 126 °C. IR (KBr disk, cm–1): 3064, 2968, 1497, 1457,
Di-tert-butylperoxyoxalate (14)
1
1251, 1145, 930, 836, 687. H NMR (CDCl3) δ: 7.94 (2H,
A solution of oxalyl chloride (2.5 mL) in petroleum ether
(25 mL) was added slowly to a stirred cold solution of anhy-
drous pyridine (4 mL) and 5.5 mol/L solution of tert-butyl
hydroperoxide (5 mL) in petroleum ether (50 mL) over
20 min while maintaining the temperature at –4 °C. The re-
action mixture was then warmed to 15 °C where the white
precipitate formed was filtered and the filtrate was cooled
for 15 min in dry ice – acetone (–78 °C) to allow crystalliza-
tion of peroxyoxalate as fine white crystals. The solvent was
decanted and the peroxyoxalate crystals, 4.01 g (69%), dried
under argon and stored in the refrigerator.
d), 7.90 (2H, d), 7.55–7.32 (3H, m), 7.40 (4H, d), 7.12 (2H,
d), 5.16 (2H, s), 4.83 (1H, q), 1.51 (3H, d), 1.58–1.26
(6H, m), 1.26, 1.19, 1.06, 0.70 (12H, each br s). 13C NMR
(CDCl3) δ: 160.10, 158.30, 145.92, 130.77, 129.44, 127.75,
127.29, 125.14, 122.97, 115.53, 83.21, 70.70, 59.97, 40.76,
30.83, 23.60, 20.44, 17.26. CI-MS m/z: 472.294 317 (calcd.
for C30H37N3O2: 471.2885).
Diazofunctionalized core 16 (16)
16 was synthesized from 4,4′-ethylenedianiline 15 via
diazotization and coupling as shown in Scheme 2. The
diazonium salt solution resulting when a solution of stirred
sodium nitrite (4.16 g, 60.3 mmol) in water (5 mL) was
added slowly to a solution of 15 (5.0 g, 23.6 mmol) in aq.
HCl (17 mL of HCl in 5 mL of water) cooled below 2 °C in
an ice-water bath, was coupled with phenol as follows. The
diazonium salt solution was added slowly with stirring to a
solution of phenol (5.6 g, 59.6 mmol) in 10% sodium hy-
droxide (12.8 g NaOH in 120 mL water) while maintaining
the reaction temperature below 2 °C and was allowed to
stand in an ice-water bath for 1 h with stirring. After the so-
lution was acidified slowly with concd. HCl, the resultant
precipitate was filtered, washed with cold water several
times, recrystalized from ethanol, and precipitated with ice
to give a diazofunctionalized core 16 as a light orange solid
TEMPO-modified 4-ethylbenzyl bromide 6 (15)
As outlined in Scheme 1, a mixture of 13 (5 g,
25.1 mmol), TEMPO (3 g, 19.2 mmol) and di-tert-butyl-
peroxyoxalate (4 g, 1.59 mmol) in benzene (40 mL) was
stirred and heated to 35 °C under argon for 24 h. After re-
moving the solvent by rotary evaporation the product was
purified by column chromatography using hexanes–dichloro-
methane (1:1) as the eluant to give the TEMPO modified 4-
ethylbenzyl bromide 6 as a white solid (1.78 g, 20%), mp 63
to 64 °C. IR (KBr disk, cm–1): 3013, 2969, 1509, 1442,
1
1227, 1056, 842, 697. H NMR (CDCl3) δ: 7.36 (4H, dd),
4.80 (1H, q), 4.52 (2H, s), 1.50 (3H, d), 1.41–1.11 (6H, m),
1.31, 1.27, 1.09, 1.05 (18H, each br s). 13C NMR (CDCl3) δ:
146.20, 136.17, 128.79, 126.98, 82.71, 59.69, 40.35, 34.19,
33.72, 23.51, 20.36, 17.22. CI-MS m/z: 354.144 548 and
356.141 660 (1:1) (calcd. for C18H28NOBr: 353.135 41 and
355.133 54).
1
(6.2 g, 62%), mp 245 to 246 °C. H NMR (acetone-d6) δ:
9.10 (2H, s), 7.84 (4H, d), 7.79 (4H, d), 7.41 (4H, d), 7.01
(4H, d), 3.08 (4H, s). 13C NMR (acetone-d6) δ: 37.60,
116.14, 122.73, 125.09, 129.72. EI-MS m/z: 422.174 20
(calcd. for C26H22N4O2 422.174 28).
TEMPO-modified 4-ethylbenzyl iodide 7 (16)
Following the Finkelstein reaction outlined in Scheme 1, 6
(0.90 g, 2.91 mmol) was added to a stirred solution of so-
dium iodide (7.5 g, 50 mmol) in dry acetone (20 mL), which
was refluxed under argon for 3 h. After filtering and removal
of the solvent by rotary evaporation, the solid was dissolved
in CH2Cl2 (50 mL) and extracted with water (50 mL) and
CH2Cl2 (2 × 50 mL) where the extracts were dried over
MgSO4, filtered and the solvent evaporated to yield a white
solid (7) (1.1 g, 94%), mp 72 °C. IR (KBr disk, cm–1): 3004,
2922, 1506, 1446, 1280, 1055, 874, 836, 699. 1H NMR
(CDCl3) δ: 7.36, 7.27 (4H, dd,), 4.77 (1H, q), 4.49 (2H, s),
1.61–1.18 (6H, m), 1.47 (3H, d), 1.23, 1.18, 1.04, 0.68 (12H,
each br s). 13C NMR (CDCl3) δ: 145.51, 137.51, 128.35,
126.92, 82.55, 59.57, 40.23, 34.33, 23.26, 20.30, 17.10,
5.96. CI-MS m/z: 402.131 155 (calcd. for C18H28NOI:
401.121 6).
Diazofunctionalized unimer 9 (12)
9 was synthesized by the coupling of 7 with 16 as illus-
trated in Scheme 2. A mixture of 7 (0.50 g, 1.41 mmol),
diazofunctionalized core 16 (0.24 g, 0.57 mmol), anhyd.
K2CO3 (0.040 g, 0.30 mmol), and crown-ether (0.030 g,
0.11 mmol) in dry acetone (20 mL) was refluxed (60 °C) un-
der argon for 48 h. After removal of solvent by rotary evapo-
ration, the residue was dissolved in CH2Cl2 (50 mL) and
extracted with water (3 × 50 mL), dried over MgSO4, fil-
tered, and the solvent was removed by rotary evaporation.
Column chromatography using hexanes – ethyl acetate (3:2)
1
as the eluent yielded an orange solid 9 (0.1 g, 18%). H
NMR (CDCl3) δ: 7.90 (4H, d), 7.80 (4H, d),
7.38 (8H, d),
7.29 (4H, d), 7.09 (4H, d), 5.13 (4H, s), 4.82 (2H, q), 3.04
(4H, s), 1.48 (6H, d), 1.60–0.60 (12H, m), 1.29, 1.18, 1.03,
0.68 (24H, each br s). 13C NMR (CDCl3) δ: 124.47, 122.49,
127.59, 126.87, 126.87, 114.88, 82.67, 69.74, 37.39, 23.38,
34.06, 29.51, 28.44, 20.77, 20.23, 20.20. EI-MS m/z:
969.600 22 (calcd. for C62H76N6O4: 969.600 08).
Monoazofunctionalized unimer 8 (12)
8 was synthesized by the coupling of 7 and para-
hydroxyazobenzene 14 as illustrated in Scheme 1. A mixture
© 2004 NRC Canada

Abdallah et al.
1401
160.85, 159.55, 158.52, 149.35, 146.54, 125.17, 124.60,
119.72, 116.10, 105.45. EI-MS: 714.222 683 (calcd. for
C42H31N6O6 714.222 7).
1,3,5-Tris(4′-nitrophenoxy)benzene 19 (17)
1,3,5-Tris(4′-nitrophenoxy)benzene was prepared via SNAr
displacement as outlined in Scheme 3. A mixture of 1,3,5-
trihydroxybenzene dihydrate (phloroglucinol) 17 (12.40 g,
76.50 mmol), 4-fluoronitrobenzene 18 (24.4 mL,
230 mmol), potassium fluoride (26.70 g, 460.0 mmol), and
150 mL of DMSO was heated to reflux temperature for
30 min. The reaction mixture was then cooled to room tem-
perature (r.t.), and the precipitate was filtered, washed with
water (150 mL), and allowed to dry to give a crude product
as a tan flaky solid, which was recrystallized from ethyl ace-
tate – charcoal and followed by chloroform–hexanes to give
1,3,5-tris(4′-nitrophenoxy)benzene 19 as a creamy white
solid (25.0 g, 50%), mp 203 to 204 °C (lit. value (7) 203.5–
205.5 °C). IR (KBr disk, cm–1): 3091, 2840, 2448, 1918,
1591, 1561, 1468, 1340, 1230, 1114, 994, 848, 741, 632.
1H NMR (CDCl3) δ: 8.27 (6H, d), 7.15 (6H, d), 6.67 (3H, s).
13C NMR (CDCl3) δ: 161.30, 157.77, 143.60, 126.09,
118.21, 107.60. EI-MS m/z: 489.081 9 (calcd. for
C24H15N3O9 489.080 1).
Triazofunctionalized unimer 10 (GEN 0) (12)
GEN 0 was synthesized by coupling of 7 with 21 as illus-
trated in Scheme 3. A mixture of 7 (0.15 g, 0.37 mmol), the
azo core 21 (0.11 g, 0.15 mmol), and anhyd. K2CO3
(0.050 g, 0.58 mmol) in dry acetone (20 mL) was heated at
reflux (60 °C) under argon for 48 h. After removal of the
solvent by rotary evaporation, the residue was purified by
column chromatography using CH2Cl2 as the eluant to give
GEN 0 (0.05 g, 22%) as an orange thick oil. IR (KBr
disk, cm–1): 2968, 2926, 2868, 2362, 2335, 1584, 1496,
1
1455, 1370, 1225, 1095, 1005, 838. H NMR (CDCl3) δ:
7.91 (12H, d), 7.40 (12H, d), 7.18 (12H, d), 7.10 (2H, d),
6.58 (3H, s), 5.15 (6H, s), 4.84 (3H, apparent d), 1.51 (9H,
d), 1.66–1.00 (18H, m), 1.32, 1.20, 1.07, 0.71 (36H, each
br s). 13C NMR (CDCl3) δ: 161.28, 159.07, 158.13, 149.12,
145.95, 134.85, 127.39, 126.93, 124.69, 124.47, 119.33,
115.18, 105.09, 82.86, 70.34, 59.76, 40.41, 34.50, 23.64,
20.37, 17.28. ES-MS: (M + H)+ 1535.2 (calcd. for
C96H111N9O9 1533.85).
1,3,5-Tris(4′-aminophenoxy)benzene 20 (18)
The synthesis of 20 is outlined in Scheme 3. To a stirred
solution of 19 (8.0 g, 16 mmol) and Fe powder (8.10 g,
145 mmol) in 50% ethanol (100 mL) was added slowly HCl
(0.6 mL concd. HCl in 10 mL of 50% ethanol) and the reac-
tion mixture was refluxed for 2 h. After the reaction mixture
was made alkaline by addition of 15% KOH, the iron was
filtered quickly and washed with 95% ethanol (2 × 50 mL).
The solvent was removed by rotary evaporation and the resi-
due was dissolved in chloroform (100 mL) and extracted
with water (3 × 500 mL). The organic layer was dried over
MgSO4, filtered, and the solvent was evaporated on a rotary
evaporator. The residue was dried under vacuum for 48 h to
give 1,3,5-tris(4′-aminophenoxy)benzene 20 as a light purple
solid (6.10 g, 94%), mp 88–90 °C (lit. value (8) 88 to
89 °C). IR (KBr disk, cm–1): 3424, 3352, 3212, 1606, 1503,
Polymerization of styrene with monoazofunctionalized
unimer (MAz-PS-T)
MAz-PS-T was synthesized by polymerizing styrene with
8 under bulk conditions as illustrated in Scheme 4. A mix-
ture of monofunctionalized unimer 8 (0.10 g, 0.20 mmol)
and styrene (18.2 g, 17 5mmol) was heated at 135 °C under
nitrogen for 3 h. The polymerization mixture was dissolved
in 50 mL of THF and precipitated from 750 mL of metha-
nol, filtered and dried in a vacuum oven at 70 °C resulting in
a yellow powder (4.69 g, 26%). Mn = 13 500, Mw/Mn = 1.26.
Polymerization of acetoxystyrene with
monoazofunctionalized unimer (MAz-PAS-T)
1
1451, 1214, 1113, 1003, 8.31. H NMR (CDCl3) δ: 6.86
MAz-PAS-T was synthesized by polymerizing
acetoxystyrene with 8 under bulk conditions as illustrated in
Scheme 5. A mixture of monofunctionalized unimer 8
(0.10 g, 0.20 mmol) and acetoxystyrene (26.6 g, 164 mmol)
was heated at 135 °C under nitrogen for 75 min. The poly-
merization mixture was dissolved in 50 mL of THF and pre-
cipitated from 750 mL of methanol, filtered and dried in a
vacuum oven at 70 °C resulting in a yellow powder (12.9 g,
49%). Mn = 35 300, Mw/Mn = 1.34.
(6H, d), 6.65 (6H, d), 6.18 (3H, s), 3.67 (6H, br s). 13C NMR
(CDCl3) δ: 160.77, 147.84, 142.90, 121.23, 116.17, 99.97.
EI-MS m/z: 399.157 3 (calcd. for C24H21N3O3 399.158 4).
Triazofunctionalized core 21 (13)
The trifunctionalized core 21 was synthesized from 20 via
diazotization and coupling as illustrated in Scheme 3. A
diazonium salt solution resulted when sodium nitrite (1.56 g,
22.6 mmol) in water (12 mL) was added slowly with stirring
to a solution of 20 (3 g, 7.52 mmol) in aq. HCl (5 mL of
HCl in 12 mL of water) cooled below 2 °C in an ice-water
bath. The diazonium salt was added slowly with stirring to
phenol (2.1 g, 22.3 mmol) in 10% sodium hydroxide
(48 mL) while maintaining the reaction temperature below
2 °C and was allowed to stand in an ice-water bath for 1 h
with stirring. After the solution was acidified with HCl the
resultant precipitate was filtered, washed with cold water
several times, and air-dried for a few days to give the
trifunctionalized azobenzene core (21) as a dark red solid
(4.50 g, 84%), mp 190 °C. IR (KBr disk, cm–1): 3405, 3168,
Block copolymer of acetoxystyrene–styrene with
monoazofunctionalized unimer (MAz-PAS-PS-T)
MAz-PAS-PS-T was synthesized by polymerizing MAz-
PAS-T with styrene under bulk conditions as illustrated in
Scheme 6. A mixture of MAz-PAS-T (3.00 g) and styrene
(18.2 g, 175 mmol) was heated at 135 °C under nitrogen for
2 h. The polymerization mixture was dissolved in 50 mL of
THF and precipitated from 750 mL of methanol, filtered and
dried in a vacuum oven at 70 °C resulting in an off-white –
yellow powder (5.49 g). Mn = 40 400, Mw/Mn = 1.54.
1
1451, 1312, 1225, 1146, 999, 685. 638. H NMR (acetone-
Random copolymer of acetoxystyrene–styrene with
monoazofunctionalized unimer (MAz-PAS/PS-T)
MAz-PAS/PS-T was synthesized by polymerizing
d6) δ: 7.89 (6H, d), 7.81 (6H, d), 7.24 (6H, d), 6.99 (6H, d),
6.63 (3H, br s), 6.62 (3H, s). 13C NMR (acetone-d6) δ:
© 2004 NRC Canada

1402
Can. J. Chem. Vol. 82, 2004
Chem 82, 551 (2004); (c) K.S. Cheon, Y.S. Park, P.M.
Kazmaier, and E. Buncel. Dyes Pigm. 53, 3 (2002).
2. P.J. Lutz, G. Beinert, and P.F. Rempp. Macromol. Chem. (Ox-
ford), 183, 2787 (1982).
3. H.A. Nguyen and J.P. Kennedy. Polym. Bull. 10, 74 (1983).
4. D.Y. Sogah, W.R. Hertler, O.W. Webster, and G.M. Cohen.
Macromolecules, 20, 1473 (1987).
acetoxystyrene and styrene with monofunctionalized unimer
8 under bulk conditions as illustrated in Scheme 7. A mix-
ture of 8 (0.1 g, 0.20 mmol), styrene (12.7 g, 123 mmol) and
acetoxystyrene (7.45 g, 45.0 mmol) was heated at 135 °C
under nitrogen for 2 h. The polymerization mixture was dis-
solved in 50 mL of THF and precipitated from 750 mL of
methanol, filtered and dried in a vacuum oven at 70 °C re-
sulting in a yellow powder (4.36 g). Mn = 16 400 g/mol,
Mw/Mn = 1.24.
5. C.B. Gorman, E.J. Ginsburg, and R.H. Grubbs. J. Am. Chem.
Soc. 115, 1397 (1993).
6. M.K. Georges, R.P.N. Veregin, P.M. Kazmaier, and G.K.
Hamer. Macromolecules, 26, 2987 (1993).
7. C.J. Hawker. J. Am. Chem. Soc. 116, 11 185 (1994).
8. G. Moad and E. Rizzardo. Macromolecules, 28, 8722 (1995),
references therein.
9. C.J. Hawker, G.G. Barclay, A. Orellana, J. Dao, and W.
Devenport. Macromolecules, 29, 16 (1996).
Synthesis of monofunctionalized azobenzene poly(4-
hydroxystyrene) (MAz-PHS-T) (19)
MAz-PHS-T was synthesized by hydrolysis of MAz-
PAS-T as illustrated in Scheme 8. Concd. ammonium hy-
droxide (1.5 mL) in 5 mL of water was added dropwise to a
0.5 g solution of MAz-PAS-T in 20 mL of methanol. The
reaction mixture was refluxed at 65 °C under nitrogen and
was stopped after 24 h and was left to cool at room tempera-
ture. The polymer was precipitated from 200 mL of water,
filtered and dried in an oven at 50 °C to yield yellow crystals
(0.20 g, 40%).
10. C.J. Hawker. Angew. Chem. Int. Ed. Engl. 34, 1456 (1995).
11. (a) E. Buncel. Can. J. Chem. 78, 1251 (2000); (b) S.
Swansberg, E. Buncel, and R.P. Lemieux. J. Am. Chem. Soc.
122, 6594 (2000); (c) J.T.C Wojtyk, P.M. Kazmaier, and E.
Buncel. J. Chem. Soc. Chem. Commun. 1703 (1998); (d) E.
Buncel and K.S. Cheon. J. Chem. Soc. Perkin Trans. 2, 1241
(1998); (e) R.A. Cox, E. Buncel, and S. Patai (Editors). The
chemistry of hydrazo, azo, and azoxy groups. Vol. 2. Wiley
Interscience, New York. 1997; (f) S.-R. Keum, K.-B. Lee, P.M.
Kazmaier, and E. Buncel. Tetrahedron Lett. 35, 1015 (1994);
(g) R.A. Cox, I. Onyido, and E. Buncel. J. Am. Chem. Soc.
114, 1358 (1992); (h) E. Buncel and S. Rajagopal. Acc. Chem.
Res. 23, 226 (1990); (i) D.L.H. Williams and E. Buncel. In
Isotopes in organic chemistry. Vol. 5. Edited by E. Buncel and
C.C. Lee. Elsevier, Amsterdam. 1980. pp. 184–197; (j) R.A.
Cox and E. Buncel. In The chemistry of the hydrazo, azo, and
azoxy groups. Edited by S. Patai. Wiley, London. 1975.
pp. 775–859; (k) A.J. Dolenko and E. Buncel. In The chemis-
try of the hydrazo, azo, and azoxy groups. Edited by S. Patai.
Wiley, London. 1975. pp. 725–773; (l) E. Buncel. Acc. Chem.
Res. 8, 132 (1975); (m) E. Buncel. In Mechanisms of molecu-
lar migrations. Vol. 1. Edited by B.S. Thyagarajan. Wiley, New
York. 1968. pp. 61–119.
Polymerization of acetoxystyrene with
triazofunctionalized unimer (TAz-PAS-3T)
TAz-PAS-3T was synthesized by polymerizing
acetoxystyrene with 10 under bulk conditions as illustrated
in Scheme 9. A mixture of trifunctionalized unimer 10
(0.10 g, 0.07 mmol) and acetoxystyrene (26.6 g, 164 mmol)
was heated at 135 °C under nitrogen for 75 min. The poly-
merization mixture was dissolved in 50 mL of THF and pre-
cipitated from 750 mL of methanol, filtered and dried in a
vacuum oven at 70 °C resulting in a yellow powder (13.66 g,
51%). Mn = 74 400, Mw/Mn = 1.49.
Block copolymer of acetoxystyrene–styrene with
triazofunctionalized unimer (TAz-PAS-PS-3T)
TAz-PAS-PS-3T was synthesized by polymerizing TAz-
PAS-3T with styrene under bulk conditions as illustrated in
Scheme 10. A mixture of TAz-PAS-3T (3.00 g) and styrene
(18.2 g, 175 mmol) was heated at 135 °C under nitrogen for
45 min. The polymerization mixture was dissolved in 50 mL
of THF and precipitated from 750 mL of methanol, filtered
and dried in a vacuum oven at 70 °C resulting in an off-
white – yellow powder (6.13 g). Mn = 126 000, Mw/Mn =
1.64.
12. C.J. Hawker and J.M.J. Fréchet. J. Am. Chem. Soc. 112, 7638
(1990).
13. B.S. Furniss, A.J. Hannaford, P.W.G. Smith, and A.R. Tatchell.
Vogel’s textbook of practical organic chemistry. 5th ed. 1996.
14. P.D. Bartlett, E.P. Benzing, and R.E. Pincock. J. Am. Chem.
Soc. 82, 1762 (1960).
15. Y. Miura, K. Hirota, H. Moto, and B. Yamada. Macro-
molecules, 18, 4659 (1998).
16. B.S. Furniss, A.J. Hannaford, P.W.G. Smith, and A.R. Tatchell.
Vogel’s textbook of practical organic chemistry. 5th ed. 1996.
p. 572.
Acknowledgements
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support.
17. T. Takeichi and J.K. Stille. Macromolecules, 19, 2093 (1986).
18. S.A. Mahood and P.V.L. Schaffner. Org. Synth. Coll. Vol. II,
160 (1967).
19. G.G. Barclay, C.J. Hawker, H. Ito, A. Orellana, P.R.L.
Malenfant, and R.F. Sinta. Macromolecules, 31, 1024 (1998).
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© 2004 NRC Canada