Multi-armed, TEMPO-functionalized unimolecular initiators for starburst dendrimer synthesis via stable free radical polymerisation. 2. Tris (1,3,5)benzyloxy unimers

Article abstract of DOI:10.1139/v04-106

The synthesis of the trifunctionalized TEMPO-modified unimolecular initiators, unimers I, II, and III is described. Unimer I was prepared via an S_N2 type Williamson ether coupling of 1,3,5-tris(iodomethyl)benzene with a TEMPO-containing ethylbenzene hydroxy derivative. The synthesis of unimer II, however, was accomplished through S_N1 reaction of 1,3,5-tris(bromomethyl)benzene with the hydroxy-ethylbenzene TEMPO derivative in the presence of silver triflate. Synthesis of unimer III started from phloroglucinol and an S_NAr reaction with 1-fluoro-4-nitrobenzene, followed by reduction to the amino compound and Schiff base formation with the TEMPO-derivatized aromatic aldehyde. Stable free radical polymerisation (SFRP) of styrene and acetoxystyrene with unimer I are also described with molecular weights and polydispersities reported. It is concluded that the SFRP of styrene with a triradical initiator meets the requirements of a living system.

Full text of DOI:10.1139/v04-106

1403
Multi-armed, TEMPO-functionalized unimolecular
initiators for starburst dendrimer synthesis via
stable free radical polymerisation. 2. Tris
(1,3,5)benzyloxy unimers1
Mohmad Asri Abd Ghani, Dalia Abdallah, Peter M. Kazmaier,
Barkev Keoshkerian, and Erwin Buncel
Abstract: The synthesis of the trifunctionalized TEMPO-modified unimolecular initiators, unimers I, II, and III is de-
scribed. Unimer I was prepared via an SN2 type Williamson ether coupling of 1,3,5-tris(iodomethyl)benzene with a
TEMPO-containing ethylbenzene hydroxy derivative. The synthesis of unimer II, however, was accomplished through
SN1 reaction of 1,3,5-tris(bromomethyl)benzene with the hydroxy-ethylbenzene TEMPO derivative in the presence of
silver triflate. Synthesis of unimer III started from phloroglucinol and an SNAr reaction with 1-fluoro-4-nitrobenzene,
followed by reduction to the amino compound and Schiff base formation with the TEMPO-derivatized aromatic alde-
hyde. Stable free radical polymerisation (SFRP) of styrene and acetoxystyrene with unimer I are also described with
molecular weights and polydispersities reported. It is concluded that the SFRP of styrene with a triradical initiator
meets the requirements of a living system.
Key words: stable free radical polymerisation, starburst dendrimer, multi-armed unimolecular initiators.
Résumé : On décrit la synthèse d’initiateurs unimoléculaires trifonctionnalisés à base de 2,2,6,6-tétraméthylpipéridinyl-
oxyle (TEMPO), les unimères I, II et III. L’unimère I a été préparé par le biais d’une réaction SN2, de type formation
d’éther de Williamson, par le couplage du 1,3,5-tris(iodométhyl)benzène avec un dérivé hydroxylé de l’éthylbenzène
portant le radical TEMPO. Toutefois, la synthèse de l’unimère II a été réalisée par le biais d’une réaction SN1 du
1,3,5-tris(iodométhyl)benzène avec le dérivé hydroxylé de l’éthylbenzène portant le radical TEMPO, en présence de tri-
flate d’argent. La synthèse de l’unimère III a été réalisée à partir du phloroglucinol et une réaction SNAr avec le 1-
fluoro-4-nitrobenzène, suivie d’une réduction en dérivé amino et de la formation d’une base de Schiff avec un aldéhyde
aromatique portant le radical TEMPO. On décrit aussi la polymérisation avec un radical libre stable du styrène et de
l’acétoxystyrène catalysée par l’unimère I et on rapporte les poids moléculaires et les polydispersités moyennes. On
conclut que la polymérisation avec un radical libre stable du styrène catalysée par un initiateur triradicalaire satisfait
les besoins d’un système vivant.
Mots clés : polymérisation avec un radical libre stable, dendrimère en « éclatement d’étoile », initiateur unimoléculaire
tentaculaire.
[Traduit par la Rédaction] Ghani et al. 1412
Introduction
where controlled architecture in a star polymer is achieved
through stable free radical polymerisation (SFRP) using the
stable nitroxide radical 2,2,6,6-tetramethylpiperidinyloxy
(TEMPO) (1). Our approach is to synthesize unimolecular
initiators containing the TEMPO unit, termed unimers, which
are then employed in synthesis of star polymers and copoly-
mers. We describe here the synthesis of three trifunction-
alized unimers (I, II, III). The polymerisations of styrene and
acetoxystyrene with unimer I to form homopolymers and co-
The achieving of controlled architecture in macromole-
cules is at the forefront in the synthesis of novel materials
with improved properties. In the realm of polymers, pro-
found changes in properties accompany the introduction of
branches into the polymer backbone, which leads to the for-
mation of graft or star polymer systems.
The present work forms part of a series of investigations
Received 2 February 2004. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 9 November 2004.
M.A.A. Ghani, D. Abdallah, and E. Buncel.2. Department of Chemistry, 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.
1Part 1, ref. 1.
2Corresponding author (e-mail: buncele@chem.queensu.ca).
Can. J. Chem. 82: 1403–1412 (2004)
doi: 10.1139/V04-106
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Can. J. Chem. Vol. 82, 2004
polymers are also described. This work is a continuation of
our structure-property studies of functionalized dendrimers
(2).
in THF under reflux (24 h) in the presence of sodium hy-
dride, after flash chromatographic separation, gave unimer I
as a light yellow thick syrup (97%).
Unimolecular initiator II synthesis
Results and discussion
The unimer II was prepared by the following sequence
(Scheme 2): (a) Initially the benzyloxamine derivatives 3
(X = H, CH2Cl, CH2Br, CH2I, CH2OH) were synthesized
starting with commercially available ethylbenzene deriva-
tives and using modifications of the methods of Georges and
co-workers (7), Hawker et al. (8), Priddy and co-workers (9),
and Miura et al. (10). In our hands the highest yield of 3
(X = H), 93% after crystallization from ethanol, was ob-
tained by reacting ethylbenzene with tert-butyl peroxyoxa-
late and TEMPO (10); (b) in an alternative method, use of
Jacobson’s catalyst (Salem (10, 11)) with the ethylbenzene
derivatives in the presence of di-tert-butyl peroxide, sodium
Unimolecular initiator I synthesis
The synthesis of unimer I consisted of a three-step se-
quence (Scheme 1): (i) The benzyloxyamine ester 1 was first
prepared by a modification of the method reported by
Veregin (3), Hawker (4), Kobatake (5), and their co-workers,
by heating benzoyl peroxide and TEMPO with excess sty-
rene at 80 °C for 30 min (82% yield after recrystallization
from 2-propanol). (ii) Saponification of 1 (4, 6) by heating at
reflux with 2 mol L–1 KOH in ethanol and flash chromatogra-
phy gave the alcohol 2 as a light yellow oil (97%). (iii) Wil-
liamson ether coupling of 2 with 1,3,5-tris(iodomethyl)benzene
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Ghani et al.
1405
Scheme 1.
Scheme 2.
Controlled free radical polymerisation of unimolecular
initiator I
borohydride, and TEMPO (12) gave alkoxyamines 3 in
yields ranging over 20% (X = CH2Cl), 41% (X = H), and
51% (X = CH2OH). Attempted formation of unimer II
through SN2 Williamson ether coupling of 3 (X = CH2OH)
with 1,3,5-tris(iodomethyl)benzene as in the case of unimer
I, was unsuccessful in our hands. The preparation of unimer
II was then accomplished via an SN1 type reaction of 1,3,5-
tris(bromomethyl)benzene with 3 (X = CH2OH) in the pres-
ence of silver triflate (17% after column chromatographic
separation).
Polystyrene starburst dendrimer I
Two polymerisations of styrene were performed with
Unimer I under bulk conditions at 135 °C, SFRP 1 and
SFRP 2. The progress of the SFRP processes was monitored
by withdrawal of aliquots from the reaction mixture at dif-
ferent times for % conversion and molecular weight determi-
nations.
In the first polymerisation (SFRP 1), 1200 equiv. of sty-
rene to 1 equiv. of unimer I were used under the above con-
ditions for 3 h. The polymer was precipitated from methanol
to give star polystyrene with terminal TEMPO end groups
(PS-3T1), as a white solid (15 g), average molecular weight
(Mn) 34 200 and polydespersity (PD) 1.29.
Unimolecular initiator III synthesis
The reaction scheme followed the sequence shown in
Scheme 3.
(1) The triamine core 4 was obtained in two steps: an SNAr
reaction between 1,3,5-trihydroxy-benzene and 1-
fluoro-4-nitrobenzene in the presence of KF in DMSO
produced the 1,3,5-tris(4-nitrophenyl)benzene derivative
4-NO2 in 50% yield. The triamino core 4-NH2 was then
obtained through Fe–HCl reduction in 94% yield after
purification.
(2) Unimer III was obtained as the Schiff base adduct on re-
action of the triamino core compound 4-NH2 with the
benzyloxyamine derivative 3 (X = CHO) (85% yield af-
ter column chromatographic purification).
The second polymerisation (SFRP 2) was performed us-
ing 400 equiv. of styrene to 1 equiv. of unimer I for 4 h to
give PS-3T2 (8.70 g) after precipitation from methanol. The
polystyrene had a Mn value of 12 700 and a PD of 1.34.
1
The H NMR for both polymer samples showed broad
peaks between 1.50 and 1.87 ppm representing the methy-
lene and methine protons. Aromatic protons of polystyrene
appear as a broad multiplet between 6.49 and 7.10 ppm.
The polymerisation results are shown in Table 1. The
conversion-time relationship is plotted for the formation of
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Can. J. Chem. Vol. 82, 2004
Scheme 3.
Table 1. Polymerisation results with unimer I.
Conversiona (%)
Mn (Theo.)
Mn (Exptl., GPC)
PDd (GPC)
b
c
Method
Time
SFRP 1
30
60
120
180
10
18
45
51
12 320
21 290
54 180
60 760
12 390
21 040
28 080
34 150
1.20
1.17
1.28
1.29
SFRP 2
30
60
120
180
240
12
24
38
48
53
4 800
9 600
15 200
19 200
21 200
5 685
8 951
11 690
14 350
12 710
1.25
1.23
1.27
1.27
1.34
aBased on TGA.
bCalculation of Mn (Theo.): (i) for SFRP 1: Mn (Theo.) = conversion (%) × molecular weight (monomer) × 1200
(ratio of styrene to unimer I); (ii) for SFRP 2: Mn (Theo.) = conversion (%) × molecular weight (monomer) × 400
(ratio of styrene to unimer I).
cEstimated by GPC based on polystyrene standards.
dPD = Mn/Mw estimated by polystyrene standards.
Fig. 1. Plot of % conversion vs. time for SFRP 1 and SFRP 2
with unimer I.
PS-3T1 and PS-3T2 in Fig. 1. As the polymerisation time
increases, monomer conversion also increases. Even though
the ratio of styrene : unimer I for SFRP 1 and SFRP 2 is
3:1, the rate of conversion is almost constant for the two
polymerisations. Thus, the polymerisation rate is independ-
ent of unimer I concentration.
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Ghani et al.
1407
Fig. 2. Semilogarithmic plot of conversion with reaction time for
the SFRP processes with varying initial concentration for SFRP
1 and SFRP 2.
Fig. 3. Theoretical and experimental molecular weights for
SFRP 1 plotted against % conversion.
A kinetic plot in semilogarithmic coordinates showing the
variation of monomer consumption with time is presented in
Fig. 2. Mo represents the initial monomer concentration
while Mt is the concentration after time t. Thus, the SFRP of
styrene at 135 °C with a triradical initiator (unimer I) meets
the requirement of a living system.
Fig. 4. Theoretical and experimental molecular weights for
SFRP 2 plotted against % conversion.
Number average molecular weights (Mn) and poly-
dispersities were determined by GPC with polystyrene stan-
dards. The plot of the theoretical and experimental Mn data
against % conversion are shown in Figs. 3 and 4 for SFRP 1
and SFRP 2, respectively. The experimental Mn data are
very close to the calculated theoretical values at the early
stages of the polymerisation, which indicates that the formed
styryl radicals initiated all growing chains at the same time.
There are large deviations of Mn compared with the theoreti-
cal values after 40% conversion, which suggests that deter-
mination of molecular weight using polystyrene standards
(linear chains) is not suitable for star polystyrene. At higher
molecular weights the multi-armed polystyrene has a totally
different structure and properties compared to the linear ana-
log and will have less hydrodynamic volume. In a related
SFRP study with a trifunctionalized unimer, Hawker (13)
found that the experimental Mn = 16 500 of the star polymer
was lower than the theoretical value (Mn = 21 000). How-
ever, when the star polymer was hydrolyzed and the molecu-
lar weight of the individual arms measured it was fully
consistent with the proposed structure and that each arm of
the initiator can actively initiate the monomer similar to the
monoinitiator system.
Hydrolysis of polyacetoxystyrene starburst dendrimer I
Removal of the acetyl group from PAS-3T was carried
out in methanol by treatment with ammonium hydroxide
(15) to give a light yellow solid with an average molecular
weight of 16 500 and a PD of 1.23. The decrease in average
molecular weight in comparison to PAS-3T (Mn = 21 100) is
in good agreement with calculated values for deacetylation.
The 1H NMR shows the disappearance of the singlet at
2.81 ppm for the methyl protons of the acetoxy group; also,
the disappearance of the carbonyl carbon and the methyl
group carbon peaks at 196.2 and 21.23 ppm, respectively,
confirming that the hydrolysis is complete.
Starburst block copolymer (styrene–acetoxystyrene)
dendrimer I
The synthesis of block copolymer was undertaken from
PS-3T1. A diblock copolymer was obtained via the SFRP
technique using 4-acetoxystyrene (25 mL) as the feed mono-
mer at 135 °C for 4 h. A white powder precipitated from
Polyacetoxystyrene starburst dendrimer I
The polymerisation of acetoxystyrene (400 equiv. to
1 equiv. of unimer I) was effected under bulk conditions at
135 °C for 3 h. The polymer was precipitated from methanol
to give 5.0 g of a white solid (PAS-3T) with an average mo-
1
methanol (26 g, Mn 95 500, and PD 1.23). The H NMR
shows two broad peaks at 7.10 and 6.25 ppm corresponding
to the protons of the aromatic rings of polystyrene and
polyacetoxystyrene, while an intense peak at 2.25 ppm rep-
resents the methyl protons of the acetyl group.
1
lecular weight of 21 100 and a PD of 1.30. The H NMR
shows broad peaks between 1.78 and 1.40 ppm representing
the aliphatic protons and a broad multiplet between 7.08 and
6.33 ppm for the aromatic protons of polyacetoxystyrene.
The methyl protons of the acetoxy group appear as a singlet
at 2.81 ppm. The 13C NMR shows a peak at 169.2 ppm for
the carbonyl carbon and 21.23 ppm for the methyl carbon of
the acetate group.
Conclusions
The synthesis of unimers I, II, and III was accomplished
by reaction sequences outlined in Schemes 1, 2, and 3. Each
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Can. J. Chem. Vol. 82, 2004
unimer contains one stereogenic center at the TEMPO junc-
tion and the products are obtained as complex diastereo-
meric mixtures.
The polymerisation of styrene and acetoxystyrene was ef-
fected with unimer I to form homopolymers and copoly-
mers. For styrene, two polymerisations (SFRP 1 and SFRP
2) were done using different ratios of unimer I to styrene. A
polymer with a Mn of 34 200 and a PD of 1.29 was produced
from SFRP 1 while SFRP 2 yielded a polymer with a Mn of
12 700 and a PD of 1.34. Conversion-time relationships for
SFRP 1 and SFRP 2 were plotted and an equivalent rate of
polymerisation in both cases was obtained, i.e., the rate is
independent of unimer I concentration. Linear semilogarith-
mic kinetic plots of monomer consumption vs. time were
obtained, which meets the requirements of a living system.
On plotting the theoretical and experimental Mn data against
% conversion, the experimental data correlate with theoreti-
cal at low Mn while a variance at higher Mn values is in ac-
cord with the star-shaped structure of the polymer.
With acetoxystyrene, unimer I gave a polymer (PAS-3T)
with a Mn of 21 100 and a PD of 1.30. This was hydrolyzed
to yield the hydroxystyrene polymer (PHS-3T) with a Mn of
16 500 and a PD of 1.23.
A star block copolymer of styrene and acetoxystyrene was
obtained from polymerisation of PS-3T with acetoxystyrene
to give a polymer with a Mn of 95 500 and of PD 1.23.
anhyd. MgSO4. After removal of the solvent, the product
was purified by flash column chromatography using CH2Cl2
as the eluant to give 2 as a light yellow oil (2.70 g, yield
97%). IR (neat, cm–1): 3421–3302, 2930, 1739; 1721, 1606,
1458, 1360, 1248, 1125, 1027, 920, 762, 703. 1H NMR
(CDCl3) δ: 7.43–7.32 (5H, m, Haryl), 5.92 (1H, br s, HOH),
1.64–1.46 (6H, m, H8,9,10), 1.58, 1.39, 1.30, 1.22 (12H, br s,
H
12,13,14,15). The signals for H1a, H1b, and H2 could not be
fully resolved, however, the 13C NMR signals were in satis-
factory agreement with the reported data (15) and the MS is
also satisfactory. 13C NMR (CDCl3) δ: 138.31 (C3), 127.72
(C5), 127.27 (C6), 126.17 (C4), 83.02 (C2), 69.05 (C1), 61.04
(C7 or C11), 59.76 (C7 or C11), 39.78, 39.60 (C8,10), 33.99,
32.45 (C12,13 or C14,15), 20.11, 19.79 (C14,15 or C12,13), 16.53
(C9). CI-MS m/z: 278.2 (calcd. for C17H27NO2 277.20).
Experimental section
Unimer I
Phenethyloxy(2,2,6,6-tetramethylpiperidino)benzoate 1
A solution of TEMPO (3.43 g, 22.0 mmol) and BPO
(8.0 g, 33.0 mmol) in repurified styrene (150 mL) in a
round-bottomed (RB) flask was heated under argon at 80 °C
for 30 min while stirring, during which period the solution
changed from red to light yellow. After cooling, excess sty-
rene was removed under reduced pressure at ca. 50 °C and
the residue was purified by flash column chromatography
using CH2Cl2 as the eluant to give a pale yellow oil.
Recrystallization from 2-propanol yielded 1 as a white solid
(7.0 g, 82%), mp 72 °C (lit. value (5) mp 72.2–72.6 °C). IR
(KBr disk, cm–1): 2928, 1713, 1460, 1371, 1264, 1129,
1100, 997, 700. 1H NMR (CDCl3) δ: 7.95 (2H, d, JH-H
ortho = 6.9, H3), 7.57–7.26 (8H, m, Haryl, H1,2), 5.09 (1H,
app. t (overlapping d, d), J6b7 = 6.3, J6a7 = 5.1, H7), 4.85
(1H, d, d, J6a6b = 11.1, J6a7 = 5.1, H6a), 4.55 (1H, d, d,
J6a6b = 11.1, J6b7 = 6.3, H6b), 1.66–1.02 (6H, m, H13,14,15),
1.39, 1.23, 1.09, 0.78 (12H, br s, H17,18,19,20). 13C NMR
(CDCl3) δ: 166.38 (C5), 140.76 (C8), 132.88 (C9), 130.24
(C4), 129.63 (C3), 128.33, 128.10 (C1,11), 127.68 (C2,10),
84.01 (C7), 66.83 (C6), 60.16 (C12,16), 40.48 (C13,15), 34.11
(C17,18 or C19,20), 20.37 (C19,20 or C17,18), 17.21 (C14). CI-MS
m/z: 382.3 (calcd. for C24H31NO3 381.2).
Williamson ether coupling of 2 and 1,3,5-tris(iodo-
methyl)benzene
A solution of alcohol 2 (2.50 g, 10 mmol) in dry THF
(50 mL) in a RB flask fitted with a reflux condenser was
treated with dry sodium hydride (1.10 g, 5 mmol) and the re-
action mixture was stirred under argon at room temperature
for 4 h. The iodo compound (1.25 g, 2.50 mmol) in dry THF
(20 mL) was added slowly to the reaction mixture that was
then heated at reflux for 24 h. On cooling, the resultant pre-
cipitate was filtered and the filtrate was evaporated to dry-
ness. The residue in CH2Cl2 (100 mL), was washed with
water (3 × 100 mL), and purified by flash column chroma-
tography using ethyl acetate – hexanes – CH2Cl2 (1:3:6) as
Benzyloxyamine of styrenic alcohol 2
The reaction mixture consisting of ester 1 (4.0 g,
10 mmol) in ethanol (ca. 150 mL) and 2 mol L–1 KOH
(25 mL) was heated under reflux for 3 h. After removal of
ethanol on a rotary evaporator, the residue was dissolved in
CH2Cl2 (100 mL), which was extracted with water (3 ×
100 mL). The residual CH2Cl2 solution was dried over
© 2004 NRC Canada

Ghani et al.
1409
the eluant to give unimer I as a light yellow thick syrup
(2.30 g, 97%). IR (neat, cm–1): 2925, 2854, 1605, 1458,
1
1376, 1242, 1183, 957, 858, 761. H NMR (CDCl3) δ: 7.33–
7.25 (15H, m, Haryl), 6.78 (3H, s, H1), 4.85 (3H, app t (over-
lapping d, d), J4b5 = 6.6, J4a5 = 5.1, H5), 4.31 (6H, q, JH-H
=
12.3, H3), 3.94 (3H, d, d, J4a4b = 9.6, J4a5 = 5.1, H4a), 3.64
(3H, d, d, J4a4b = 9.6, J4b5 = 6.6, H4b), 1.61–1.13 (18H, m,
H
11,12,13), 1.33, 1.19, 1.05, 0.66 (36H, each br s, H15,16,17,18).
13C NMR (CDCl3) δ: 141.91 (C2), 138.28 (C6), 127.80,
127.72 (C7,8), 127.15 (C9), 125.21 (C1), 85.36 (C5), 72.72
(C3,4), 60.03 (C10,14), 40.40 (C11,13), 33.82 (C15,16 or C17,18),
20.26 (C17,18 or C15,16), 17.09 (C12). HR-MS (FAB+) calcd.
for C60H88N3O6: 946.667 7; found: 946.692 7. Anal. calcd.
for C60H87N3O6 (%): C 76.15, H 9.27, N 4.44; found: C
76.47, H 9.27, N 4.47.
23 mmol), [salen]MnCl (1.90 g, 3 mmol), di-tert-butyl per-
oxide (2.20 g, 15 mmol), sodium borohydride (1.14 g,
30 mmol) in toluene–ethanol (1:1) (300 mL) medium at r.t.
for 30 h. Removal of solvent under vacuo, extraction
(CH2Cl2), H2O wash, drying (MgSO4), followed by flash
column chromatography (CH2Cl2 eluant) yielded 3 (X =
CH2OH) as a light yellow solid (2.20 g., 51%), mp 40 °C.
IR (neat, cm–1): 3326 (broad), 2932, 1457, 1365, 1250,
1
1199, 1128, 1055, 944, 829, 732. H NMR (CDCl3) δ: 7.33
(4H, s, H3,4), 4.81 (1H, q, JH-H = 6.6, H5), 4.70 (2H, s, H1),
2.20 (1H, br s, HOH), 1.49 (3H, d, JH-H = 6.9, H7), 1.48–1.10
(6H, m, H9,10,11), 1.33, 1.21, 1.07, 0.71 (12H, each br s,
H
13,14,15,16). 13C NMR (CDCl3) δ: 144.95 (C5), 138.99 (C2),
126.45, 126.35 (C3,4), 82.52 (C6), 64.80 (C1), 59.32(C8,12),
39.94 (C9,11), 34.08, 33.84 (C13,14 or C15,16), 23.34 (C7),
19.99 (C15,16 or C13,14), 16.84 (C10). CI-MS m/z: 292.3
(calcd. for C18H29NO2 291.2).
Unimer II
Illustrative synthesis of the benzyloxyamine of
ethylbenzene (3 (X = H)) via the peroxyoxalate method
Di-tert-butylperoxyoxalate (2.21 g, 9.6 mmol), prepared
by a modification of Bartlett’s method (16) in 25 mL of
ethylbenzene was treated with TEMPO (1.0 g, 6.4 mmol)
and the mixture was stirred under argon at 35 °C. The red
colour of the solution disappeared to give a light yellow
solution within 30 min. Excess ethylbenzene was removed
under reduced pressure at r.t. to give a viscous oil that solidi-
fied on standing in the refrigerator. The solid was repeatedly
recrystallized from ethanol to provide the benzyloxyamine
of 4-ethylbenzene (3 (X = H)) (1.55 g, 93%) as colourless
needles, mp 44 °C (lit. value (16) mp 44–46 °C). IR (KBr
disk, cm–1): 2977, 2936, 1461, 1366, 1283, 1244, 1218,
Silver-assisted SN1 reaction for the formation of unimer
II
–
Silver trifluoromethanesulfonate (silver triflate, CF3SO3
Ag+) was employed for the etherification of 3 (X = CH2OH)
with the core (1,3,5-tris(bromoethyl)benzene).
A solution of the alcohol 3 (X = CH2OH) (0.47 g,
1.60 mmol) and silver triflate (0.33 g, 1.60 mmol) in di-
chloromethane (10 mL) at 0 °C was stirred for 1 h following
which the tris bromide (0.15 g, 0.42 mmol) was added and
stirring was continued for another 6 h. The solution was then
diluted with CH2Cl2 (20 mL), filtered through a plug of
Celite, and the filtrate was washed with 1 mol L–1 HCl
(50 mL), then satd. NaHCO3 (50 mL), brine (50 mL), dried
(MgSO4), and finally concentrated by rotary evaporation.
The crude product was purified by flash column chromatog-
raphy using hexanes – ethyl acetate (3:1) as the eluant to
give unimer II as a light yellow thick syrup (70 mg, 17%)
and other complex by-products that could not be assigned.
IR (neat): 2972, 2930, 2869, 1449, 1360, 1259, 1209, 1131,
1
1126, 1064, 980, 927, 778, 699. H NMR (CDCl3) δ: 7.36–
7.25 (5H, m, Haryl), 4.82 (1H, q, JH-H = 6.6, H5), 1.52 (3H, d,
JH-H = 6.6 H6), 1.42–1.28 (6H, m, H8,9,10), 1.36, 1.21, 1.07,
0.700 (12H, each br s, H12,13,14,15). 13C NMR (CDCl3) δ:
145.86 (C4), 128.02 (C2), 126.77 (C1), 126.61 (C3), 83.13
(C5), 59.67 (C7,11), 40.39 (C8,10), 34.19 (C12,13 or C14,15),
23.58 (C6), 20.32 (C14,15 or C12,13), 17.25 (C9). CI-MS m/z:
262.3 (calcd. for C17H27NO 261.2).
Illustrative synthesis of the benzyloxyamine of 4-ethyl-
benzyl alcohol (3 (X = CH2OH)) via Jacobson’s method
The Jacobson reaction (11, 12) was carried out with 4-
vinylbenzyl alcohol (2.0 g, 15 mmol), TEMPO (3.51 g,
1
1064, 1019, 935, 821, 680 cm–1. H NMR (CDCl3) δ: 7.33
© 2004 NRC Canada

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Can. J. Chem. Vol. 82, 2004
(12H, s, H6,7 and H1), 4.80 (3H, q, JH-H = 6.6, H9), 4.58
(12H, app. d, d, H3,4), 1.70–1.30 (18H, m, H12,13,14), 1.49
(12H, d, JH-H = 7.2, H10), 1.32, 1.19, 1.05, 0.70 (36H, each
br s, H16,17,18,19). 13C NMR (CDCl3) δ: 145.29 (C8), 138.73
(C5), 136.53 (C2), 128.00 (C6,7), 126.60 (C1), 82.87 (C9),
72.17, 71.92 (C3,4), 59.63 (C11,15), 40.32 (C12,14), 34.20
(C16,17 or C18,19), 23.57 (C10), 20.31 (C18,19 or C16,17), 17.19
(C13). FAB-HR-MS: (M + H)+ calcd. for C63H94N3O6:
988.7143; found: 988.7141.
out allowing the mixture to cool, the iron was filtered
quickly and washed with 95% ethanol (2 × 50 mL). The sol-
vent was removed by rotary evaporation and the residue was
redissolved in chloroform (100 mL) and extracted with wa-
ter (3 × 500 mL). The organic layer was dried (MgSO4),
filtered from the desiccant, evaporated to dryness, and fur-
ther dried in vacuo for 48 h to give 1,3,5-tris(4′-amino-
phenoxy)benzene (4-NH2) as a light purple solid (6.10 g,
94%), mp 88–90 °C (lit. value (18) mp 88 to 89 °C). IR
(KBr disk, cm–1): 3424, 3352, 3212 (NH2), 1606, 1503,
1451, 1214 (C-O), 1113, 1003, 8.31 (C-N). 1H NMR
(CDCl3) δ: 6.86 (6H, d, JH-H ortho = 8.7, H3), 6.65 (6H, d,
JH-H ortho = 8.7, H2), 6.18 (3H, s, H6), 3.67 (6H, br s,
(Hamino)). 13C NMR (CDCl3) δ: 160.77 (C5), 147.84 (C4),
142.90 (C1), 121.23 (C3), 116.17 (C2), 99.97 (C6). HR-MS
(EI) m/z calcd. for C24H21N3O3: 399.1584; found: 399.1573.
Unimer III
1,3,5-Tris(4′-nitrophenoxy)benzene (4-NO2)
1,3,5-Tris(4′-nitrophenoxy)benzene (4-NO2) was prepared
via SNAr displacement according to the method of Takeichi
and Stille (17).
A mixture of 1,3,5-trihydroxybenzene dihydrate (phloro-
glucinol) (12.40 g, 76.50 mmol), 4-fluoronitrobenzene
(24.4 mL, 230 mmol), potassium fluoride (26.70 g,
460.0 mmol), and 150 mL of DMSO was heated under re-
flux for 30 min. After cooling the precipitate that formed
was filtered, washed with water (150 mL), and allowed to
dry to give a crude product as a tan flaky solid. The super-
natant of the initial filtrate on adding water (100 mL) gave
more precipitate, which was filtered, washed with water
(400 mL), and allowed to dry to give additional crude prod-
uct. The combined crude products were recrystallized from
ethyl acetate – charcoal and followed by chloroform–
hexanes to give 1,3,5-tris(4′-nitrophenoxy)benzene (4-NO2)
as a creamy white solid (25.0 g, 50%), mp 203 to 204 °C
(lit. value (17) mp 203.5–205.5 °C). IR (KBr disk, cm–1):
3091, 2840, 2448, 1918, 1591, 1561, 1468, 1340, 1230,
1
Synthesis of the Schiff base adduct (unimer III)
1114, 994, 848, 741, 632. H NMR (CDCl3) δ: 8.27 (6H, d,
Unimer III was prepared by the reaction of aldehyde 3
(X = CHO) with amine 4-NH2 via a method modified from
Furniss et al. (19).
JH-H ortho = 9.3, H2), 7.15 (6H, d, JH-H ortho = 7.2, H3),
6.67 (3H, s, H6). 13C NMR (CDCl3) δ: 161.30 (C4), 157.77
(C5), 143.60 (C1), 126.09 (C2), 118.21 (C3), 107.60 (C6).
HR-MS (EI) m/z calcd. for C24H15N3O9: 489.0801; found:
489.0819.
A solution of 3 (X = CHO) (0.60 g, 2.10 mmol) and 4-
NH2 (0.25 g, 0.63 mmol) in 95% ethanol (10 mL) was
stirred at reflux for 30 min after which water (3 mL) was
added until cloudy and the solution was allowed to cool and
induced to crystallize. The product was filtered, rinsed with
cold aqueous ethanol, and purified by flash column chroma-
tography using CH2Cl2 as the eluant to give unimer III, as a
light yellow rubber-like solid (0.675 g, 85%). IR (KBr
disk, cm–1): 3435, 2969, 2928, 2869, 1614, 1497, 1453,
1366, 1218, 1121, 1064, 1003, 937, 836, 700. 1H NMR
(CDCl3) δ: 8.47 (3H, s, H7), 7.86 (6H, d, JH-H ortho = 8.1,
H9), 7.43 (6H, d, JH-H ortho = 8.1, H10), 7.23 (6H, d, JH-H
1,3,5-Tris(4′-aminophenoxy)benzene (4-NH2)
Reduction of 4-NO2 was performed according to an ex-
perimental procedure adapted from the synthesis of 2,4-
toluenediamine as described by Mahood and Schaffner (18).
To a stirred solution of 4-NO2 (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% eth-
anol). The reaction mixture was heated at reflux for 2 h and
was then made alkaline to litmus with 15% aq. KOH. With-
© 2004 NRC Canada

Ghani et al.
1411
ortho = 8.7, H5), 7.09 (6H, JH-H ortho = 8.7, H4), 6.43
(3H, s, H1), 4.85 (3H, q, JH-H = 6.6, H12), 1.68–1.39
(18H, m, H15,16,17), 1.52 (9H, d, JH-H = 6.6, H13), 1.32, 1.20,
1.06, 0.69 (36H, each br s, H19,20,21,22). 13C NMR (CDCl3) δ:
159.92 (C7), 159.84 (C2), 154.28 (C8), 149.63 (C11), 148.25
(C6), 134.84 (C3), 128.69 (C9), 127.00 (C10), 122.35 (C5),
120.18 (C4), 102.99 (C1), 83.17 (C12), 59.76 (C14,18), 40.39
(C15,17), 34.50 (C19,20 or C21,22), 23.64 (C13), 20.37 (C21,22 or
C
19,20), 17.23 (C16). ES-MS m/z calcd. for C78H96N6O6:
1213.7: found: 1214.3.
PAS-3T was obtained as a white powder (5.0 g). Mn
=
21 100, Mn/Mw = 1.30.
Synthesis of PS-3T1
SFRP 1 polymerisation of styrene (50 mL, 0.44 mol) us-
ing unimer I (0.36 g, 0.38 mmol) was carried out at 135 °C
under nitrogen via bulk polymerisation (no solvent added)
for 4 h. As the reaction proceeded, the clear solution became
viscous over time. Intermediate samples (0.5 mL) were with-
drawn at times 0.5 h, 1 h, 2 h, 3 h, and 4 h to follow the
progress of polymerisation. Each intermediate sample was
transferred into two small vials for thermal gravimetric anal-
ysis (TGA) and gel permeation chromatography (GPC) pur-
poses. To determine conversion, the sample was transferred
directly from the vial to the TGA apparatus. The second vial
was evaporated to remove the excess styrene, diluted with
THF (ca. 1 mL), and analyzed by GPC. Polymerisation was
stopped after 4 h. The polymer was precipitated from metha-
nol (500 mL), redissolved in dichloromethane (100 mL), and
finally polystyrene with a terminal TEMPO group (PS-3T1)
was isolated as a white powder, after drying in a vacuum
oven at 50 °C for 12 h, yield 15.0 g. Mn = 34 200, Mn/Mw =
1.29.
Synthesis of PHS-3T
To a solution of PAS-3T (0.50 g) in methanol (20 mL) at
reflux under nitrogen was added dropwise ammonium hy-
droxide (1.5 mL in 5 mL water). After the addition, heating
of the reaction mixture was continued at reflux for 24 h. The
reaction mixture was then cooled to room temperature, the
polymer was isolated by precipitation in water (200 mL), fil-
tered, and washed several times with water. The polymer
was dried in a vacuum oven at 50 °C for 12 h to give star
polyhydroxystyrene (PHS-3T) as a light yellow solid
(0.3 g). Molecular weights and polydispersities of PHS-3T
were estimated by GPC. Mn = 16 400, Mn/Mw = 1.23.
Synthesis of PS-3T2
SFRP 2 polymerisation of styrene (25 mL, 0.22 mol) us-
ing unimer I (0.418 g, 0.500 0 mmol) was repeated in the
identical manner as described above, forming PS-3T2 as a
white solid, 8.70 g. Mn = 12 700, Mn/Mw = 1.34.
Synthesis of PAS-3T
Bulk polymerisation of acetoxystyrene (25 mL, 0.164 mol)
using unimer I (0.18 g, 0.38 mmol) was performed in an
identical manner to the synthesis of PS-3T1. The product
Synthesis of block copolymer PS-PAS-3T
To a solution of acetoxystyrene (25.00 mL, 0.164 mmol)
was added PS-3T1 (10.0 g) and the reaction mixture was de-
© 2004 NRC Canada

1412
Can. J. Chem. Vol. 82, 2004
2. K.S. Cheon, Y.S. Park, P.M. Kazmaier, and E. Buncel. Dyes
Pigm. 53, 3 (2002).
3. R.P.N. Veregin, M.K. Georges, G.K. Hamer, and P.M. Kazmaier.
gassed under nitrogen for 30 min. The reaction mixture was
then stirred and heated at 135 °C for 4 h. During this time
the polymerisation mixture became progressively more vis-
cous. The reaction mixture was cooled to room temperature,
redissolved in dichloromethane (200 mL), and precipitated
with methanol (1000 mL). The product was dried in a vac-
uum oven at 60 °C for 12 h to give PS-PAS-3T as a white
powder (26.0 g). Molecular weights and polydispersities of
PS-PAS-3T were estimated by GPC. Mn = 95 500, Mn/Mw =
1.21.
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Acknowledgements
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support.
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© 2004 NRC Canada