Efficient Synthesis of High Molar Mass, First- to Fourth-Generation Distributed Dendronized Polymers by the Macromonomer Approach

Article abstract of DOI:10.1002/chem.200305142

A homologous series of first- to fourth-generation (G1-G4) dendronized macromonomers, 5, 7, 10, and 12, was synthesized, and their polymerization behavior under radical conditions investigated. These conditions were thermally induced radical polymerizatio

Full text of DOI:10.1002/chem.200305142

FULL PAPER
Efficient Synthesis of High Molar Mass, First- to Fourth-Generation
Distributed Dendronized Polymers by the Macromonomer Approach
Afang Zhang,[a] Bin Zhang,[b] Eva W‰chtersbach,[b] Manfred Schmidt,*[b] and
A. Dieter Schl¸ter*[a]
Abstract: A homologous series of first-
to fourth-generation (G1 G4)
thousands for PG2 and PG3, and to
the oligomeric regime for PG4. ATRP
was applied only to the G1 and G2
monomers 5 and 7. Kinetic studies on
monomer 5 provide evidence that its
polymerization proceeds in a control-
led fashion. The highest monomer-to-
initiator ratios which still gave mono-
modal molar mass distributions were
300:1 (for 5) and 100:1 (for 7), which
correspond to achievable molar mass
regime for PG1 and PG2 of approxi-
mately Mn =100000 (DPcalcd(PG1)=
200, DPcalcd(PG2)=90). The polydis-
persities lie in the usual range (PDI=
1.1 1.2). The molar masses were deter-
mined by GPC in DMF with calibra-
tion against absolute molar masses of
PG1 determined by light scattering.
dendronized macromonomers, 5, 7, 10,
and 12, was synthesized, and their poly-
merization behavior under radical con-
ditions investigated. These conditions
were thermally induced radical poly-
merization (TRP) and atom-transfer
radical poymerization (ATRP). TRP
was applied to all monomers and gave
polymers PG1 PG4, whose molar
masses range from several millions for
PG1 to estimated several hundreds of
Keywords: dendrimers ¥ dendron-
ized polymers ¥ macromonomers ¥
polymerization
polymerization
¥
radical
Introduction
dendronized macromonomers followed by generation-by-
generation buildup with G1 dendrons until the final, fourth
generation was reached. Because of this mode of synthesis
the representatives of this series had virtually the same
degree of polymerization and distribution, whereby the
latter was relatively broad. Controlled radical polymeriza-
tions were recently developed to the point where narrowly
distributed materials are now available for a number of
monomers, most of which are simple styrenes and acryl-
ates.[5] A good example of this is so-called atom-transfer rad-
ical polymerization (ATRP), in which transition-metal hal-
ides are used to activate the carbon atom of a carbonꢀ hal-
ogen bond long enough for radical attack on a monomer
and short enough to undergo termination.[5,6]
To investigate the broader potential, including areas
where commercial polymers are mostly used instead, easy
synthetic access to high molar mass and reasonably narrowly
distributed dendronized polymers was needed. Such a goal
included avoidance of the relatively laborious attach-to
buildup procedure, irrespective of its remarkably high
degree of structure control. We describe here novel and op-
timized routes to methacrylate-based G1 G4 dendronized
macromonomers without spacers between the polymerizable
group and dendron that involve only a few high-yield steps
which give analytically pure materials on 20 30 g (G1 and
G2) and 2 4 g scales (G3 and G4). The ™spontaneous∫ (ther-
mally induced) polymerization (TRP) and ATRP of the G1
The dendronization of polymer chains at each repeat unit
with increasingly voluminous dendrons has led to new comb
macromolecules which are referred to as dendronized poly-
mers.[1] The unusual structure of these polymers with their
tight and highly branched layer around the backbone has
raised fundamental questions in polymer science, which all
have their origin in the influence of the layer on the confor-
mation and rigidity of the backbone.[2] It has also opened
the way to unprecedented applications of certain representa-
tives in relation to the bottom-up approach to nanosciences,
in which dendronized polymers are used as individual nano-
objects.[3] A quasihomologous series of first- to fourth-gener-
ation (G1 G4) polymers proved to be specifically successful
here, because it allowed systematic, generation-dependent
study of certain phenomena. This series was made available
on a 0.5 1 g scale per representative.[4] It was obtained by
conventional free-radical polymerization of G1 and G2
[a] Prof. Dr. A. D. Schl¸ter, Dr. A. Zhang
Freie Universit‰t Berlin, Institut f¸r Chemie
Takustrasse 3, 14195 Berlin (Germany)
E-mail: adschlue@chemie.fu-berlin.de
[b] Prof. M. Schmidt, B. Zhang, E. W‰chtersbach
Johannes Gutenberg-Universit‰t, Institut f¸r Physikalische Chemie
Jakob-Welder-Weg 11, 55128 Mainz (Germany)
E-mail: mschmidt@mail.uni-mainz.de
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DOI: 10.1002/chem.200305142
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FULL PAPER
monomer to the correspond-
ing polymer PG1 are delineat-
ed in detail, and respective ad-
vantages and disadvantages of
these methods are compared.
Polymerizations of other mon-
omers under TRP conditions
provide a comprehensive pic-
ture of what can be achieved
with such monomers in de-
pendence on their generation.
A few experiments were also
conducted with the radical ini-
tiator bis(tert-butylcyclohexyl)
peroxocarbonate (BCPC). Fi-
nally an in-depth molar mass
determination of PG1 is pre-
sented.
Scheme 1. Reagents and conditions: a) 1. 2, 9-borabicyclo[3.3.1]nonane, toluene, 08C, 12h (96%); 2. 1 m KOH,
1, ]Pd(PPh3)4], 1008C, 10 h (86%); b) 3a, KOH, 558C, 10 h (92%); c) 3a, LAH, THF, 08C, 16 h (93%); d) 4a,
25% HCl, THF, 08C, 4 h (96%); e) 4a, MAC, DMAP, TEA, THF, 08C, 12h (94%); f) 1. 3b, HOBt, EDC,
DCM, ꢀ308C, 3 h; 2) 4b, TEA, DCM, MeOH, ꢀ208C, 14 h (65% for both steps); g) 6a, 25% HCl, THF, 08C,
4 h (97%); h) 6a, MAC, DMAP, THF, RT, 12h (96%).
Results and Discussion
Monomers: The spacerless[7]
G1 G4 macromonomers 5, 7,
10, and 12 were selected for
this study. Given the experience with structurally related
monomers[8] they ought to be easily and reasonably accessi-
ble. Additionally, they carry functional groups at the den-
dron termini, which at a later stage allows the ™surfaces∫ of
the resulting polymers to be engineered for various applica-
tions. Synthesis of 5 and 7 starts with the known step[8] from
dibromobenzoic ester 1 to branching unit 3a (Scheme 1),
which was scaled up here to the degree that 3a is now avail-
able on a 100 g scale. Reduction of 3a with lithium alumi-
num hydride (LAH) in THF afforded alcohol 4a in 93%
yield. In diethyl ether the yield dropped to 35%.[9] Com-
pound 4a represents a dividing point on the route to two
monomers. Monomer 5 was obtained directly by treating 4a
with freshly distilled methacrylic acid chloride (MAC). For
monomer 7, 4a was first deprotected with hydrochloric acid
to give 4b, the free amino groups of which were coupled to
acid 3b with standard peptide methods involving hydroxy-
benzotriazole (HOBt) and N-(3-dimethylaminopropyl)-N’-
ethylcarbodiimide hydrochloride (EDC) to give G2alcohol
6, which was treated with MAC to yield 7. Here the use of
freshly distilled MAC proved important as far as maximum
molar masses of the corresponding polymers was concerned.
Both syntheses were carried out several times and can be
considered optimized. Their efficiency is illustrated by the
overall yields of 75% (5) and 48% (7) and the fact that
both macromonomers are obtainable on a 20 30 g scale per
run as analytically pure material. The corresponding G3 and
G4 monomers 10 and 12 were respectively obtained by stan-
dard procedures, as shown in Schemes 2and 3. Purification
was achieved by column chromatography and was associated
with some losses of material. Thus, monomer 10 was ob-
tained in a yield of 53% (from 8a) and monomer 12 in 30%
(from 6b). Finally, the ATRP initiator 13 was prepared ac-
cording to Scheme 4. All new compounds were fully charac-
Scheme 2. Reagents and conditions: a) 8a, HOSu, DCC, DCM, ꢀ208C,
12h (98%); b) 4b, 8b, TEA, MeOH, DCM, 12h (91%); c) 9, MAC,
TEA, DMAP, THF, 08C, 12h (84%).
1
terized by H and 13C NMR spectroscopy, mass spectrome-
try, and correct or almost correct data from combustion
analysis.
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Chem. Eur. J. 2003, 9, 6083 6092

Dendronized Polymethacrylates
6083 6092
merization experiments per-
formed for monomers 5 and 7
to furnish polymers PG1 and
PG2, respectively, are listed in
Tables 1 and 2. Table 1 also lists
a few representative results for
the higher generation mono-
mers 10 and 12. All these ex-
periments were typically per-
formed on a 0.5 g scale for
TRP, and on a 2g scale for
ATRP. Tables 1 and 2list the
results for TRP and ATRP, re-
spectively. Figure 1a and
b
depict GPC elution curves for
some entries in Tables 1 and 2,
respectively. So far we have no
explanation for the multimodal
GPC traces (curves 4 in Fig-
ure 1a and b). Curve 4 in Fig-
ure 1a originates from thermal
polymerization of 12 in DMF
and shows only oligomeric spe-
Scheme 3. Reagents and conditions: a) 6b, 8b, TEA, DCM, MeOH, ꢀ308C, 12h (82%); b) 11, MAC, DMAP,
TEA, THF, 08C, 12h (82%).
cies. In contrast, the ATRP product of 7 (curve 4, Figure 1b)
exhibits a complex GPC trace which covers the whole sepa-
ration range from the upper exclusion limit down to oligo-
meric species. To exclude overloading effects, measurements
were repeated for concentrations which differ by a factor of
10 (i.e., 1 gLꢀ1 and 10 gLꢀ1 injection concentration). How-
ever, the GPC traces did not change at all. Alternatively,
there is the possibility of anomalous elution, as discussed in
more detail below, which is known to occur in very large
polymers or aggregating systems. For the present samples
we have no evidence that the GPC results are significantly
affected by such an anomaly, which, however, can only be
detected by GPC-MALLS (MALLS=multi angle laser light
scattering) coupling. GPC-MALLS in DMF was not yet suc-
cessful in our lab, because particles of 50 nm to 100 nm in
Scheme 4. Reagents and conditions: 4a, TEA, DMAP, 2-bromoisobutyryl
bromide, THF, RT, 12h (90%).
Polymerization: Two polymerization methods were applied:
1) an inadvertent ™spontaneous∫ polymerization, referred to
as thermally induced radical polymerization (TRP), and
2) atom-transfer radical polymerization (ATRP) according
to Matyjaszewski×s procedure.[5,6] A few experiments were
also performed with the con-
ventional
radical
initiator
Table 1. Conditions and results for radical polymerization (TRP and FRP) of monomers 5, 7, 10, and 12.
BCPC. TRP was applied to
monomers 5, 7, 10, and 12, and
ATRP to monomers 5 and 7.
TRP was observed repeatedly
during large-scale purification
procedures, specifically when
the solvent was removed in
vacuo while heating the flask
externally to 558C. For ATRP,
pentamethyldiethylenetriamine
(PMDETA) proved to be the
best ligand for copper(i) bro-
mide, after the alternative li-
Entry Monomer
Conditions[a]
[M]
]
GPC (PG1)[b]
GPC (PMMA)[c]
[I]
Time Yield 10ꢀ4 Mn PDI
DPn
10ꢀ4 Mn
PDI
[mmolLꢀ1
[mmolLꢀ1
]
[h]
[%]
1
2
5
5
0
0
0
0
0
0
0
bulk
bulk
bulk
0.82
1.02
1.36
1.36
0.30
0.30
0.30
0.30
0.60
0.60
0.30
0.14
1.5
3
8
28
18
5.5
18
72
72
75
78
86
75
80
78
89
83
86
56.8
69.5
2.02
3.41
3.13
3.69
4.04
4.26
4.16
2.20
1158 24.2
1417 30.0
3881 83.5
2637 57.9
2529 52.4
3074 65.1
2996 62.0
214 10.4
213 10.3
7.7
9.2
597 28.8
647 31.1
341 34.5
1.97
3.19
2.78
3.26
3.76
3.80
3.83
2.16
1.97
5.37[e]
2.24
3.14
3.20
3.72
1.62
3
5
190.4
129.4
124.1
150.8
147.0
24.1
4
5
5
5
6
5
7
5
8
7
0.89[d]
9
7
1.48[d]
24.0
5.94
1.99
[e]
10
11
12[f]
13[f]
14[f]
15[f]
7
7
7
7
10
12
2.96[d]
7285
72
26
48
30
16.7
148
190
0
0
0
0
0
79
75
86
50
88
21.4
67.3
73.0
81.9
15.0
2.28
3.33
3.39
3.97
1.61
gands
2,2’-bipyridyl
and
1,1,4,7,10,10-hexamethyltriethy-
lenetetramine had been briefly
screened. Some representative
48
30
6.1
[a] In benzene at 558C. [b] Calibrated with light-scattering data. [c] Calibrated with PMMA standard.
results of the numerous poly- [d] BCPC as initiator. [e] Multimodal. [f] In DMF at 558C.
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M. Schmidt, A. D. Schl¸ter et al.
FULL PAPER
Table 2. Conditions and results for ATRP of monomers 5 and 7 at 558C in toluene.
size were permanently eluted,
which most probably originate
from the packing material.
Entry Monomer
Conditions[a]
GPC (PG1)[c]
GPC
(PMMA)[d]
[b]
[M]/molLꢀ1 [M]:[13] Time Yield 10ꢀ4 Mn,calcd
10ꢀ4 Mn PDI DPn 10ꢀ4 Mn PDI
[mmolLꢀ1
]
[h]
[%]
Absolute calibration of GPC
for the G1 polymers in DMF:
The absolute molar masses of
some selected samples from
Tables 1 and 2were determined
by light scattering (LS; for de-
tails, see below), and the values
obtained used for GPC calibra-
tion (Table 3). An absolute cali-
bration curve was established
by an iteration procedure utiliz-
ing the experimental peak re-
tention times and identifying
the initial peak molar masses
with Mw. With this calibration
1
2
3
4
5
6
7
8
5
5
5
5
5
5
5
5
5
5
7
7
7
1.02
1.02
50:1
100:1
0.5
1.0
852
20
0.16
92
55
3.4
4.0
2.3
2.7
4.6
5.7
1.56
94 2.5
1.34
1.08
1.12 116 2.7
1.02100:1
1.02100:1
1.02100.0:1
1.02100:1
1.02
1.02
1.02
1.02
0.45
69
6.5
6.9
1.153.1132 1.11
1.14 141 31.211
81
4.2 7.0
86
1.15 143 31.211
4.2 7.5
93
92
86
87
86
85
84
4.5
1.13 153 3.5
1.10
100:1
300:1
100:1
300:1
100:1
200:1
300:1
15
16
24
24
48
48
48
4.6
13.5
4.2
12.8
9.7
9.2
20.9
8.9
1.28 188 4.2
1.21 426 9.0
1.34 181 4.1
1.23 143 3.3
1.28 106 5.3
8.74[f] 96 5.1
2.69[f] 118 6.0
1.24
1.20
1.25
1.17
9[e]
10[e]
11
12
13
7.0
12.0
10.8
13.3
1.25
0.45
0.45
18.0
28.4
7.51[f]
2.54[f]
[a] [PMDETA]:[CuBr]:[13]=3:1:1. [b] Mn,calcd =yieldîmolar mass of monomerî[M]:[13]. [c] Calibrated with
light-scattering data. [d] Calibrated with PMMA standard. [e] 908C. [f] Multimodal.
Table 3. Light-scattering and GPC data in DMF utilizing the absolute
calibration curve as described in the text for some selected PG1 samples.
Table
Entry
0.118
10ꢀ6 Mw (GPC)
10ꢀ6 Mw (LS)
Rg,z
[nm]
[gmolꢀ1
]
[gmolꢀ1
]
27
2
0.116
0.10[a]
0.287
8
0.253
13.3
0.250[a]
1.14
(12.0[a]
26.7
)
1
1
1
1
1.147
2.37
(4.77)
2
2.3
44.6
7[b]
(22.5)
(217)
(21.4[a]
)
(165[a]
)
[a] Measured in MeOH. [b] For table/entry 1/7 no reliable results could
be obtained, as described in the text.
curve Mw (GPC) was calculated from the experimental elu-
tion curves and compared to Mw (LS). Whereas at inter-
mediate retention times good agreement was observed, sig-
nificant deviations were found at both very small and very
large retention volumes. Such deviations are typical when
calibration data are missing at the low or high molar mass
end of the elution curves, because extrapolated calibration
curves, in contrast to interpolated curves, are not reliable,
particularly when close to the exclusion limits. ™Artificial∫
data points -one at high and one at low retention time–
were therefore added until the resulting calibration curve
yielded good agreement for all values of Mw (GPC) and Mw
(LS), except for the highest molar mass, as shown in
Table 3. For comparison, the PG1 and the classical, standard
PMMA calibration curves are shown in Figure 2.
The retention time of the samples of highest molar mass
is so close to the upper size-exclusion limit that the GPC
columns utilized are not suitable for reliably providing the
molar masses and molar mass distributions. For instance,
Zimm plot analysis of sample 7, Table 1 yields a radius of
gyration on the order of 200 nm (see below and Figure 5).
For such large particles anomalous elution might yield irreg-
ular elution curves, as was demonstrated for similar samples
Figure 1. GPC elution curves (1 4) of a) PG1 PG4 samples of Table 1
(1: entry 6; 2: entry 14; 3: entry 11; 4: entry 15) obtained by thermally in-
duced and free-radical polymerization and b) PG1 and PG2 samples of
Table 2(1: entry 8; :2 entry 11; 3: entry 6; 4: entry 1)2 prepared by
ATRP.
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Chem. Eur. J. 2003, 9, 6083 6092

Dendronized Polymethacrylates
6083 6092
larger Kuhn statistical segment length of the dendron-
ized polymers as compared to linear PMMA leads to a
larger hydrodynamic volume. This increase, however,
cannot compensate the opposite effect of the drastically
increased mass per r.u. which, under the present experi-
mental conditions, leads to the observed discrepancies in
the GPC results.
3) It seems that TRP of monomer 5 in bulk produces in-
creasing molar masses with increasing reaction time,
which is unexpected for a radical polymerization. It is
also noteworthy that truly high molar masses (entry 3)
can be achieved under these conditions. Similarly to
linear (unbranched) macromonomers,[11] the polymeriza-
tion of dendronized macromonomers in benzene tends
to give higher molar masses for higher concentrations
(compare, e.g., entries 4 and 5 with 6 and 7 and entry 11
with entries 12and 13). Finally, it is noteworthy that the
third-generation macromonomer 10, despite its consider-
able steric crowding near the polymerizable unit, fur-
nishes polymer PG3 with respectable apparent molar
masses of Mn =820000 and Mw =3400000.
4) The apparent molar masses of PG2 are lower than those
of PG1 (cf. entries 11 13 and 4 7). This effect is larger
than the uncertainty in molar mass determination caused
by the improper PG1 calibration curve used for PG2
(see above). For polymerizations with added initiator
(entries 8 10) the PDI values become extremely broad
once a certain initiator concentration is exceeded (com-
pare entries 8 and 9 with entry 10). Polymerizations of 7
were carried out in saturated benzene solution ([M]=
0.30 molLꢀ1). Experiments in bulk could not be per-
formed because the melting point of this monomer is too
high. The same holds for the higher generation mono-
mers 10 and 12. Because of the decreasing solubility of
the monomers in benzene with increasing generation,
polymerizations were performed in DMF (entries 12
15). Comparison of entry 11 (benzene) with entries 12
and 13 (DMF) shows that in the latter cases much
higher apparent molar masses were achieved. It seems
that the solubility aspect overcompensates the higher
chain-transfer rate of DMF as compared to benzene. The
maximum concentration for polymerization of G3 mono-
mer 10 in DMF was 0.30 molLꢀ1 (entry 14). Monomer
12 furnishes more or less oligomeric material in respect-
able yields. The GPC elution curves of representative
samples of each generation (Figure 1a) show that the de-
viations from monomodality are largest for PG4 and
smallest for PG1.
*
Figure 2. Calibration curves for PG1 based on light scattering ( ) and a
&
PMMA standard ( ). The open circles at low and high elution volumes
represent artifical points for stabilizing the fit for the calibration curve.
by means of a light-scattering detector.[10] Very large mole-
cules which should elute at the upper exclusion limit are re-
tarded to larger elution volumes by an as-yet unknown elu-
tion mechanism. This would explain why the largest molar
masses determined by light scattering are always much
larger than those obtained by GPC. Another explanation
could be that the highest molar masses form a significant
fraction of aggregates which either fall apart during the
GPC experiment or remain on the columns. However, this
possibility is less likely, because the LS results for such sam-
ples were quite reproducible and did not show the typical
signature of aggregates, that is, large fluctuations in count
rate and loss of concentration by filtration.
Note that the LS calibration curve yields correct molar
masses and molar mass distributions only for the PG1 sam-
ples. When applied to higher generation polymers the molar
masses are most probably smaller than the true ones. Since
the effect of the mass of the larger repeat unit (r.u.) will be
counterbalanced somewhat by an increase in chain stiffness
(see below), the true molar masses are difficult to estimate.
Unfortunately, all light-scattering investigations on PG2,
PG3, and PG4 in solvents such as MeOH, DMF, and THF
failed so far, because of irreproducible results caused by the
tendency of such polymers to form aggregates. To solve this
problem a better solvent is needed.
The following conclusions can be drawn for the data of
Table 1:
1) All yields of polymers are high (>75%), except for
monomer 10 (entry 14).
2) For PG1 (entries 1 7) the DMF data referenced to
PMMA were compared with those calibrated by LS. The
latter are consistently higher by a factor 2.4 than those
obtained by PMMA calibration. Normalizing to the
same degree of polymerization, that is, taking into ac-
count the significantly higher r.u. mass of PG1
(490 gmolꢀ1) compared to PMMA (100 gmolꢀ1), the
factor should be even larger. This, of course, requires the
flexibility of the main chain and the solvent quality for
PMMA and the dendronized polymer to be similar. The
Two main conclusions can be drawn from Table 2:
1) Considering the other monomers used so far for ATRP,
those employed here are among those with the highest
molar masses. Nevertheless, the molar masses of PG1
and PG2, as well as the PDIs, are well within the range
of those reported for ATRP, and the yields are high
throughout.
2) As expected for a controlled radical polymerization, the
dependency of molar mass on conversion (yield) is prac-
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M. Schmidt, A. D. Schl¸ter et al.
FULL PAPER
tically linear (entries 2 7 and Figure 3). The dependency
of ln([M]0/[M]t) on polymerization time is also reasona-
bly linear for conversions up to almost 80%, which are
reached after 1 h (Figure 3). In contrast to many other
ATRPs, monomer 5 polymerizes at a very high rate. Al-
ready after 10 min a conversion of at least 55% is
reached.
Figure 5. Zimm plot of PG1 (Table 1, entry 7) in DMF.
segment length lk can be estimated by Equation (1)[12,13]
,
ðm þ 2Þlk l2k
lk3
R2g;z
¼
ꢀ
þ
6y
4
4 mðm þ 1Þ
ð1Þ
ꢀ
ꢁ
lk4
8 mðm þ 1Þ
ymþ2
þ
y2ꢀ
m
ðy þ 2=lkÞ
Figure 3. Kinetics (filled squares) and PDI dependence (filled circles) of
ATRP of 5 on polymerization time. For polymerization conditions, see
Table 2(entries 2and 7).
where y=(m+1)/Lw and Lw is the weight-average contour
length given by Lw =Pwl (Pw is the weight-average degree of
polymerization), l the contour length of a monomer unit,
and m the Schulz Zimm convolution parameter, which is re-
lated to the polydispersity by Mw/Mn =1+mꢀ1 The best fit
of the Rg,z data to Equation (1) is obtained with a Kuhn stat-
istical segment length of lk =6 nm (Table 4), which indicates
a significant stiffening of the methacrylate main chain, most
probably caused by the steric repulsion of the bulky side
chains.
Static and dynamic light scattering: Static and dynamic light
scattering was performed on five selected G1 samples; the
results are summarized in Table 3. Figures 4 and 5 show the
Zimm plots of PG1 samples 1/1 and 1/7, respectively.
Sample 1/1 shows a linear q2 dependence of the reduced
scattering intensity, that is, molar mass and radius of gyra-
tion could be reliably determined. Figure 4 is representative
for all samples measured. Only for the highest molar mass
sample could Mw and the square root of the mean square
radius of gyration Rg,z not be reliably determined, because
the scattering envelopes were slightly curved and Rg,z was
too large to meet the condition qRg,z <1. Utilizing the
Kratky Porod wormlike-chain model the Kuhn statistical
Table 4. Comparison of the experimental and calculated radii of gyration
for some selected samples.[a]
Table
Entry
10ꢀ6 Mw (LS)
Rg,z
[nm]
Lw [nm]
[nm]
m
Rg,z (calcd)
[gmolꢀ1
]
27
2
1
0.116
<10
13.3
26.7
1
59
146
580
4
5
1
7.9
12.2
29.4
8
1
22
0.287
1.14
44.6
1.3
1170
41.8
[a] For the calculated values according to Equation (1) the Kuhn statisti-
cal segment length of lk =6 nm and the Zimm convolution parameter m
as shown in the table were utilized.
Note that the above analysis is based on the assumption
that excluded-volume effects are negligible. This is most
probably justified because lk does not increase with molar
mass, which would artificially result for excluded-volume
chains, and because of the poor solubility of the polymers. It
is also assumed that the contour length of the chains is
given by the fully stretched conformation, that is, 0.25 nm
per monomer unit. As known for polymacromonomers with
linear side chains[10,11b] this assumption may not be realistic
Figure 4. Zimm plot of PG1 (Table 1, entry 1) in DMF.
6088
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2003, 9, 6083 6092

Dendronized Polymethacrylates
6083 6092
TOF experiments THA was used as matrix. Elemental analysis was per-
formed on a Perkin-Elmer EA 240. The samples were dried rigorously
under vacuum prior to analysis to remove strongly adhering solvent mol-
ecules. Gel permeation chromatography (GPC) measurements were car-
ried out using Waters ultra styragel columns (104 +103 +102 nm) with RI
(refractive index) and UV (268 nm) detectors (poly(methyl methacrylate)
standards, DMF+1 gLꢀ1 LiBr as eluent, room temperature). To exclude
that the high molar masses observed are influenced by concentration ef-
fects it was verified for some selected samples (curves 1 and 4 in Figure-
s 1a and b, respectively) that the elution curves do not change when the
injection concentration is changed from 10 gLꢀ1 to 1 gLꢀ1. Measurements
were typically performed in a concentration range of 2 3 gLꢀ1. Static
light-scattering measurements were performed with an ALV-SP86 goni-
ometer, an Uniphase HeNe laser (25 mW output power at 632.8 nm
wavelength) and an ALV/High QE APD avalanche diode fiberoptic de-
tection system. The dilute polymer solutions in DMF or MeOH (typically
4 5 concentrations in the range 0.1ꢁcꢁ2gLꢀ1) were measured from 30
to 1508 in steps of 58. Prior to measurement the solutions were filtered
through 0.2 mm pore Dimex filters (Millipore LG). The refractive index
increment was measured by a home-built Michelson interferometer, as
described elsewhere,[17] and determined to dn/dc=0.0802cm 3 gꢀ1 in DMF
and dn/dc=0.176 cm3 gꢀ1 in MeOH. PG1 samples showed a slight tenden-
cy to aggregate, which could be minimized by selection of proper solvents
(DMF and MeOH) and by careful filtration. Control measurements in
MeOH gave identical results within experimental error of ꢂ10% for Mw
and Rg,z. LS investigations on PG2 samples were not successful, that is,
not reproducible in DMF, MeOH, CHCl3, and THF, because of a signifi-
cant tendency to aggregate. All measurements resulted in curved scatter-
ing envelopes and in an unacceptably large variance between different
concentrations.
if the polymers adopt the shape of cylinders. In this case the
length of the cylinder could be significantly smaller than the
fully stretched main chain, that is, the main chain might
adopt a locally coiled conformation. According to Equa-
tion (1) a smaller contour length Lw results in a larger Kuhn
statistical segment length. Thus, the value of lk =6 nm given
above represents the lower limit of chain stiffness, provided
the excluded-volume effects do not have a significant influ-
ence.
Conclusion
Thermally induced radical polymerization can be successful-
ly applied to the first- to fourth-generation macromonomers
5, 7, 10, and 12. It is superior to ATRP as far as high molar
mass materials are concerned. Experimentally, TRP is
simple since no addition of any reagent is required. The
mere fact that these enormously sterically crowded mono-
mers can polymerize without intentional addition of initiator
mirrors a considerable and somewhat unexpected reactivity.
ATRP can be performed with dendronized macromonomers
up to G2, but reaction conditions could not be found which
allowed these monomers to be used at initiator ratios great-
er than 300:1 (for 5) and 100:1 (for 7) and yet still furnish
monomodal material. This limited the achievable molar
masses in both cases to approximately 100000 gmolꢀ1.
Furthermore, the data in Table 1 show that it is essential
for all monomers to use the most concentrated polymeriza-
tion media possible to achieve high molar masses. Insuffi-
cient concentration makes polymerization to very high
molar masses impossible and may give the false impression
that it is infeasible.
The true molar masses determined by light scattering
were significantly higher than those obtained by GPC with a
linear PMMA calibration curve. For the presently investigat-
ed polymers the polydispersity determined by calibration
curves utilizing absolute light-scattering molar masses and
linear PMMA standards were comparable. The Kuhn statis-
tical segment length of the PG1 generation was estimated to
a minimum value of lk =6 nm by wormlike-chain analysis of
the radius of gyration.
3,5-Bis-[3-(tert-butyloxycarbonylamino)propyl]benzyl alcohol (4a):
A
solution of 3a (30 g, 64.6 mmol) in THF (200 mL) was added dropwise to
a slurry of LiAlH4 (3.68 g, 97.0 mmol) in THF (600 mL) over 1 h at 08C.
The reaction mixture was warmed to room temperature, stirred for 16 h,
then quenched by dropwise addition of water (30 mL), 15% NaOH
(40 mL), and water (30 mL). The resulting precipitate was filtered, and
THF evaporated off. Chromatographic separation (hexane/ethyl acetate
3/1) gave 4a as a colorless oil (25.4 g, 93%). 1H NMR (CDCl3): d=1.39
(s, 18H; CH3), 1.73 (m, 4H; CH2), 2.54 (m, 4H; CH2Ph), 2.72 (br, 1H;
OH), 3.05 (m, 4H; CH2NH), 4.56 (s, 2H; OCH2Ph), 4.73 (br, 2H; NH),
6.85 (s, 1H; Ph), 6.94 ppm (s, 2H; Ph); 13C NMR (CDCl3): d=28.33,
31.51, 32.80, 39.96, 64.96, 79.04, 124.60, 127.57, 141.34, 141.77,
156.00 ppm; FABMS (3 kV): m/z (%): 423 (4.30) [M+H]+. elemental
analysis (%) calcd for C23H38N2O5 (422.56): C 65.37, H 9.06, N 6.63;
found: C 65.19, H 9.02, N 6.41.
3,5-Bis-(3-aminopropyl)benzyl alcohol¥2HCl (4b): 25% HCl (18.14 g,
124.2 mmol) was added to a solution of 4a (10.5 g, 24.85 mmol) in THF
(300 mL) at 08C, and the mixture stirred for 4 h. Evaporation of the sol-
vent at room temperature yielded 4b as a colorless semisolid product
(7.04 g, 96%). 1H NMR (D2O): d=1.98 (m, 4H; CH2), 2.71 (m, 4H;
CH2Ph), 3.00 (m, 4H; CH2NH), 4.59 (s, 2H; OCH2Ph), 7.13 ppm (s, 3H;
Ph); 13C NMR (D2O): d=30.85, 34.12, 41.51, 66.12, 127.71, 130.27,
143.40, 144.08 ppm; FABMS (3 kV): m/z (%): 223 (5.51) [Mꢀ2HCl+H]+
; elemental analysis (%) calcd for C13H24Cl2N2O (295.25): C 52.88, H
8.19, N 9.49; found: C 52.68, H 8.15, N 9.27.
Experimental Section
General procedures: Compounds 1,[14] 3a,[8] 3b,[15] and 8a[8] were synthe-
sized according to literature methods. Other reagents were purchased
from Aldrich or Fluka. Methacryloyl chloride (MAC) was freshly distil-
led before use. CuBr (95%) was purified according to a literature proce-
dure.[16] THF was refluxed over LAH, and dichloromethane (DCM) was
dried by distilling over CaH2. All other reagents and solvents were used
as received. All reactions were performed under nitrogen atmosphere.
For determination of the macromonomer concentration the volume
change associated with a large mass dissolved in a small volume of solute
was taken into account. Silica gel 60M (Macherey-Nagel, 0.04 0.063 mm/
230 400 mesh) was used as the stationary phase for column chromatogra-
3,5-Bis-(3-tert-butoxycarbonylaminopropyl)benzyl methacrylate (5):
A
solution of MAC (7.42g, 71.0 mmol) in THF (100 mL) was added drop-
wise to a mixture of 4a (20 g, 47.3 mmol), triethylamine (TEA; 14.4 g,
142.3 mmol), and dimethylaminopyridine (DMAP; 0.2 g) in dry THF
(200 mL) at 08C over 30 min. The mixture was stirred for 12h at room
temperature, then washed with aqueous NaHCO3 and brine. The organic
phase was dried with magnesium sulfate, and the solvents were evaporat-
ed under vacuum at RT. Chromatographic separation (silica gel, ethyl
acetate/hexane 1/3), performed twice, yielded
5 as a colorless solid
1
(21.9 g, 94%). M.p. 858C. H NMR (CDCl3): d=1.41 (s, 18H; CH3), 1.77
(m, 4H; CH2), 1.94 (t, 3H; CH3), 2.59 (m, 4H; CH2Ph), 3.12(m, 4H;
CH2NH), 4.60 (br, 2H; NH), 5.10 (s, 2H; OCH 2Ph), 5.56 (m, 1H; C=
CH2), 6.12(m, 1H; C =CH2), 6.93 (s, 1H; Ph), 6.97 ppm (s, 2H; Ph); 13C
NMR (CDCl3): d=18.32, 28.39, 31.62, 32.86, 40.09, 66.36, 78.67, 125.72,
128.33, 136.30, 142.02, 155.96, 165.00 ppm; FABMS (3 kV): m/z (%): 491
1
phy. H and 13C NMR spectra were recorded on Bruker AM 270 and AC
500 spectrometers at room temperature. Mass spectrometry was carried
out on a Varian MAT 711 spectrometer. The FAB experiments were car-
ried out with 3-nitrobenzyl alcohol (MNBA)/CH2Cl2, for the MALDI-
6089
Chem. Eur. J. 2003, 9, 6083 6092
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. Schmidt, A. D. Schl¸ter et al.
FULL PAPER
(1.58) [M+H]+ ; elemental analysis (%) calcd for C27H42N2O6 (490.63): C
66.10, H 8.63, N 5.71; found: C 65.83, H 8.49, N 5.47.
161.91, 167.89, 169.28 ppm; FABMS (7 kV): m/z (%): 1171 (16.69)
[M+H]+ ; elemental analysis (%) calcd for C63H91N7O14 (1170.44): C
64.65, H 7.84, N 8.38; found: C 64.32, H 8.08, N 8.41.
3,5-[Bis(3-{3,5-bis[3-(tert-butyloxycarbonylamino)propyl]benzoyl}amino)-
propyl]benzyl alcohol (6a): N-Hydroxybenzotriazole (9.16 g, 67.80 mmol)
was added to a solution of acid 3b (28.20 g, 64.60 mmol) in dry DCM
(200 mL) at room temperature. After 10 min N-(3-dimethylaminoprop-
yl)-N’-ethylcarbodiimide hydrochloride (13.62g, 71.04 mmol) was added
at ꢀ308C, and the reaction mixture was stirred until the hydrochloride
was dissolved completely (ca. 3 h). Then a solution of TEA (16.32g,
161.2mmol) and 4b (9.04 g, 30.62mmol) in methanol/DCM (100 mL, 1/
1) was added dropwise at ꢀ208C. The resulting mixture was warmed to
room temperature, stirred for 14 h, and then washed with aqueous
NaHCO3 and brine. The organic layer was dried with magnesium sulfate,
and the solvent removed in vacuo. Chromatographic separation (silica
gel, ethyl acetate/hexane 2/1, 5/1) yielded 6a as a colorless foam (21.0 g,
65%). 1H NMR (CDCl3): d=1.39 (s, 36H; CH3), 1.71 (m, 8H; CH2),
1.89 (m, 4H; CH2), 2.58 (m, 12H; CH2Ph), 3.03 (m, 8H; CH2NH), 3.36
(m, 4H; CH2NH), 4.55 (s, 2H; OCH2Ph), 4.81 (br, 4H; NH), 6.90 (s, 1H;
Ph), 6.97 (s, 2H; Ph), 7.03 (s, 2H; Ph), 7.09 (br, 2H; NH), 7.35 ppm (s,
4H; Ph); 13C NMR (CDCl3): d=28.42, 30.79, 31.37, 32.51, 33.29, 39.64,
64.96, 79.19, 124.80, 127.63, 131.51, 134.83, 141.55, 141.81, 141.93, 156.13,
167.78 ppm; FABMS (3 kV): m/z (%): 1060 (0.12) [M+H]+, 1082(0.06)
[M+Na]+ ; elemental analysis (%) calcd for C59H90N6O11 (1059.38): C
66.89, H 8.56, N 7.93; found: C 66.53, H 8.41, N 7.79.
3,5-Bis-{3-[3,5-bis(3-{3,5-bis-(3-tert-butoxycarbonylaminopropyl)benzoyl-
amino}propyl)benzoylamino]propyl}benzyl alcohol (9): Compound 4b
(0.50 g, 1.69 mmol) and TEA (0.68 g, 6.77 mmol) in methanol (20 mL)
were added dropwise to a solution of 8b (4.17 g, 3.56 mmol) in CH2Cl2
(100 mL) over 15 min at ꢀ308C. The resulting mixture was warmed to
room temperature and stirred overnight. After washing with NaHCO3
and brine, the organic layer was dried with magnesium sulfate, and the
solvent removed in vacuo. Chromatographic separation (silica gel, DCM/
methanol 25/1) gave 9 as a colorless foam (3.60 g, 91%). 1H NMR
(CDCl3): d=1.38 (s, 72H; CH3), 1.70 (m, 16H; CH2), 1.85 (m, 12H;
CH2), 2.53 (m, 24H; CH2Ph), 3.00 (m, 16H; CH2NH), 3.31 (m, 12H;
CH2NH), 4.53 (s, 2H; CH2O), 4.88 (br, 8H; NH), 6.98 (s, 3H; Ph), 7.03
(s, 6H; Ph), 7.32(s, 4H; Ph), 7.41 (s, 8H; Ph), 7.48 ppm (br, 6H; NH);
13C NMR (CDCl3): d=28.57, 30.47, 31.23, 32.73, 32.84, 39.75, 39.79,
73.77, 79.06, 124.85, 130.42, 131.60, 134.42, 141.77, 145.81, 156.12, 161.70,
168.03 ppm; FABMS (3 kV): m/z (%): 2332 (4.71) [M+H]+ ; elemental
analysis (%) calcd for C131H194N14O23 (2331.44): C 67.44, H 8.38, N 8.41;
found: C 67.19, H 8.29, N 8.35.
3,5-Bis-{3-[3,5-bis-(3-{3,5-bis-(3-tert-butoxycarbonylaminopropyl)benzoyl-
amino}propyl)benzoylamino]propyl}benzyl methacrylate (10): MAC
(0.18 g, 1.72mmol) in THF (50 mL) was added dropwise to a solution of
9 (2.60 g, 1.11 mmol), DMAP (0.1 g), and TEA (0.45 g, 4.44 mmol) in
THF (150 mL) over 15 min at 08C. The resulting mixture was stirred
overnight. After washing with NaHCO3 and brine, the organic layer was
dried with magnesium sulfate, and the solvent removed in vacuo at room
temperature. Chromatographic separation (silica gel, hexane/ethyl ace-
tate 1/5) gave 10 as a colorless foam (2.25 g, 84%). 1H NMR (CDCl3):
d=1.34 (s, 72H; CH3), 1.70 (m, 16H; CH2), 1.81 (m, 12H; CH2), 1.88 (s,
3H; CH3), 2.52 (m, 24H; CH2Ph), 2.62 (m, 4H; CH2Ph), 3.01 (m, 16H;
CH2NH), 3.30 (m, 8H; CH2NH), 3.39 (m, 4H; CH2NH), 4.90 (br, 8H;
3,5-[Bis(3-{3,5-bis[3-amino propyl]benzoyl}amino)propyl]benzyl alco-
hol¥4HCl (6b): 25% HCl (1.42 g, 9.72 mmol) was added to a solution of
6a (2.06 g, 1.94 mmol) in THF (150 mL) at 08C, and the mixture stirred
for 4 h. Evaporation of the solvent at room temperature yielded 6b as a
1
colorless foam (1.51 g, 97%). H NMR (CD3OD): d=1.94 2.05 (m, 12H;
CH2), 2.64 (m, 4H; CH2Ph), 2.75 (m, 8H; CH2Ph), 2.96 (m, 8H;
CH2NH), 3.40 (m, 4H; CH2NH), 4.55 (s, 2H; CH2O), 6.99 (s, 1H; Ph),
7.04(s, 2H; Ph), 7.36 (s, 2H; Ph), 7.56(s, 4H; Ph), 8.04 ppm (br, 2H;
NH); 13C NMR (CD3OD): d=29.79, 31.81, 33.14, 34.19, 40.32, 41.04,
65.12, 125.78, 126.37, 128.53, 133.10, 135.38, 142.61, 143.09, 170.36 ppm;
FABMS (3 KV), m/z (%): 659 (100) [Mꢀ4HCl+H]+ ; elemental analysis
(%) calcd for C39H62Cl4N6O3 (802.36): C 58.21, H 7.77, N 10.44; found: C
58.01, H 7.68, N 10.31.
NH), 5.02(s, 2H; CH 2O), 5.52(m, 1H; CH =), 6.07 (s, 1H; CH2=), 6.97
2
(s, 2H; Ph), 7.02 (s, 5H; Ph), 7.32 (s, 6H; Ph), 7.40 ppm (s, 8H; Ph); 13C
NMR (CDCl3): d=18.24, 28.37, 30.80, 31.27, 32.44, 32.81, 39.30, 39.60,
77.47, 124.86, 131.50, 134.45, 141.70, 156.15, 167.95 ppm; FABMS (7 kV):
m/z (%): 2300 (56.66) [MꢀBoc]+, 2401 (20.10) [M+H]+ ; elemental anal-
ysis (%) calcd for C135H198N14O24 (2399.47): C 67.53, H 8.31, N 8.17;
found: C 67.41, H 8.19, N 8.06.
3,5-[Bis-(3-{3,5-bis[3-(tert-butyloxycarbonylamino)propyl]benzoyl}ami-
no)propyl]benzyl methacrylate (7):
A solution of MAC (2.82 g,
26.98 mmol) in THF (100 mL) was added dropwise to a mixture of 6a
(19 g, 17.94 mmol), TEA (5.45 g, 53.8 mmol), and DMAP (0.2g) in dry
THF (200 mL) at 08C over 30 min. The mixture was stirred for 12h at
room temperature, then washed with aqueous NaHCO3 and brine, and
dried with magnesium sulfate. After evaporation of the solvent under
vacuum at room temperature, chromatographic separation (silica gel,
ethyl acetate/hexane 2/1), performed twice, yielded 7 as a colorless foam
(19.4 g, 96%). M.p. 1088C. 1H NMR (CDCl3): d=1.40 (s, 36H; CH3),
1.73 (m, 8H; CH2), 1.91 (m, 7H; CH2 +CH3), 2.56 (m, 8H; CH2Ph), 2.66
3,5-Bis-{3-[3,5-bis(3-{3,5-bis-(3-[3,5-bis-(3-tert-butoxycarbonylamino pro-
pyl)benzoylamino]propyl)benzoylamino}propyl)benzoylamino]propyl}-
benzyl alcohol (11): A mixture of 6b (0.32g, 0.40 mmol) and TEA
(0.81 g, 8.00 mmol) in methanol (10 mL) was added dropwise to 8b
(2.34 g, 2.00 mmol) in CH2Cl2 (150 mL) at ꢀ308C over 10 min. The re-
sulting mixture was warmed to RT and stirred overnight. After washing
with NaHCO3 and brine, the organic phase was dried over magnesium
sulfate, and the solvent removed in vacuo. Chromatographic separation
(silica gel, DCM/methanol 20/1) yielded 11 as a colorless foam (1.6 g,
82%). 1H NMR (CDCl3): d=1.37 (s, 144H; CH3), 1.69 (m, 32H; CH2),
1.80 (br, 28H; CH2), 2.51 (m, 56H; CH2Ph), 2.63 (br, 4H; CH2Ph), 3.00
(br, 32H; CH2NH), 3.28 (br, 24H; CH2NH), 4.50 (s, 2H; CH2O), 4.98
(br, 16H; NH), 7.00 (s, 7H; Ph), 7.03 (s, 14H; Ph), 7.36 (s, 8H; Ph), 7.43
(s, 16H; Ph), 7.50 (br, 8H; NH), 7.68 ppm (br, 6H; NH); 13C NMR
(CDCl3): d=28.38, 30.55, 31.27, 32.50, 32.75, 39.28, 39.67, 79.00, 124.90,
131.54, 131.62, 134.51, 141.74, 141.83, 156.19, 168.07, 168.27 ppm. MS
(MALDI-TOF): m/z (%): 4903.9 (100%) ca. [M+Na]+ ; elemental analy-
sis (%) calcd for C275H402N30O47 (4877.00): C 67.68, H 8.30, N 8.61; found:
C 67.59, H 8.17, N 8.52.
(m, 4H; CH2Ph), 3.04 (m, 8H; CH2NH), 3.42(m, 4H; CH NH), 4.74 (br,
2
4H; NH), 5.07 (s, 2H; OCH2Ph), 5.54 (m, 1H; C=CH2), 6.10 (s, 1H; C=
CH2), 6.97 (br, 2H; NH), 7.00 (br, 3H; Ph), 7.04 (s, 2H; Ph), 7.38 ppm (s,
4H; Ph); 13C NMR (CDCl3): d=18.33, 28.40, 30.95, 31.32, 33.11, 39.55,
66.39, 79.15, 124.81, 125.88, 128.45, 131.53, 134.87, 141.75, 142.06, 156.08,
162.62, 167.80 ppm; FABMS (3 kV): m/z (%): 1128 (0.66) [M+H]+, 1150
(0.25) [M+Na]+ ; elemental analysis (%) calcd for C63H94N6O12 (1127.45):
C 67.11, H 8.40, N 7.45; found: C 66.89, H 8.29, N 7.31.
3,5-Bis-{3-[3,5-bis(3-tert-butoxycarbonylamino-propyl)benzoylamino]pro-
pyl}benzoic acid 2,5-dioxopyrrolidin-1-yl ester (8b): N-hydroxysuccini-
mide (HOSu; 0.67 g, 5.82mmol) was added at room temperature to a sol-
ution of 8a (5.20 g, 4.85 mmol) in dry CH2Cl2 (300 mL). The mixture was
stirred for 15 min, then dicyclohexylcarbodiimide (DCC; 1.25 g,
6.06 mmol) was added at ꢀ208C. The resulting mixture was warmed to
room temperature and stirred overnight. After the precipitate was fil-
tered off, chromatographic separation (silica gel, hexane/ethyl acetate 1/
2) gave 8b as a colorless foam (5.59 g, 98%). 1H NMR (CDCl3): d=1.38
(s, 36H; CH3), 1.70 (m, 8H; CH2), 1.91 (m, 4H; CH2), 2.53 (m, 8H;
CH2Ph), 2.66 (m, 4H; CH2Ph), 2.86 (s, 4H; CH2), 3.01 (m, 8H; CH2NH),
3.38 (m, 4H; CH2NH), 4.79 (br, 4H; NH), 7.02 (s, 2H; Ph), 7.23 (br, 2H;
NH), 7.34 (s, 1H; Ph), 7.40 (s, 4H; Ph), 7.72ppm (s, 2H; Ph); 13C NMR
(CDCl3): d=25.47, 28.34, 30.75, 31.21, 32.33, 32.76, 39.30, 39.49, 79.03,
124.82, 125.13, 127.96, 131.52, 134.66, 135.46, 141.70, 142.70, 156.07,
3,5-Bis-{3-[3,5-bis-(3-{3,5-bis(3-[3,5-bis(3-tert-butoxycarbonylaminopro-
pyl)benzoylamino]propyl)benzoylamino}propyl)benzoylamino]propyl}-
benzyl methacrylate (12): MAC (33 mg, 0.31 mmol) in THF (20 mL) was
added dropwise to a mixture of 11 (1.02g, 0.21 mmol), DMAP (0.15 g),
and TEA (84 mg, 0.84 mmol) in THF (150 mL) at 08C over 10 min, and
the resulting mixture was stirred overnight. After washing with NaHCO3
and brine, the organic phase was dried over magnesium sulfate. Chroma-
tographic separation (silica gel, DCM/methanol 20/1) yielded 12 as a col-
orless foam (0.85 g, 82%). 1H NMR (CDCl3): d=1.34 (s, 144H; CH3),
1.65 (br, 32H; CH2), 1.75 1.82(br, 31H; CH 3 +CH2), 2.45 (br, 60H;
CH2Ph), 2.92 (br, 32H; CH2NH), 3.23 (br, 28H; CH2NH), 4.95 (s, 2H;
CH2O), 5.04 (br, 16H; NH), 5.54 (s, 1H; CH2=), 6.02(s, 1H; CH =), 6.88
2
6090
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 6083 6092

Dendronized Polymethacrylates
6083 6092
(s, 7H; Ph), 6.98 (s, 14H; Ph), 7.32(s, 8H; Ph), 7.39 (s, 16H; Ph), 7.54
(br, 8H; NH), 7.70 ppm (br, 6H; NH); 13C NMR (CDCl3): d=18.14,
28.26, 30.48, 31.14, 32.38, 32.64, 39.14, 39.53, 67.72, 78.79, 124.78, 125.57,
125.76, 131.45, 134.47, 134.61, 135.92, 141.61, 141.68, 141.91, 156.07,
167.11, 167.90, 168.08 ppm; MS (MALDI-TOF): m/z (%): 4972.9 (100%)
ca. [M+Na]+. Elemental analysis (%) calcd for C279H406N30O48 (4945.03):
C, 67.72; H, 8.27; N, 8.49. Found: C, 67.59; H, 8.09; N, 8.35.
ing to procedure C, CuBr (0.97 mg), PMDETA (3.54 mg), 13 (5.07 mg), 7
(2.0 g), and DMF (1.0 mL) were used. After chromatographic separation,
the polymer was lyophilized from dioxane to give PG2 (1.7 g, 85%) as a
colorless foam. 1H NMR (CDCl3): d=0.65 (br, 2H; CH2), 0.78 (br, 3H;
CH3), 1.30 (br, 36H; CH3), 1.59 (br, 8H; CH2), 1.70 (br, 4H; CH2), 2.37
(br, 12H; CH2Ph), 2.88 (br, 8H; CH2NH), 3.20 (br, 4H; CH2NH), 4.65
(br, 2H; CH2O), 5.30 (br, 4H; NH), 6.82(br, 3H; Ph), 6.94 (br, 2H; Ph),
7.43 ppm (br, 4H; Ph); 13C NMR (CDCl3): d=18.98, 28.38, 31.18, 32.49,
39.68, 41.17, 44.99, 78.66, 124.97, 128.11, 131.48, 134.56, 141.74, 156.18,
167.99, 176.98 ppm; elemental analysis (%) calcd for (C63H94N6O12)n
(1127.45)n: C 67.11, H 8.40. N 7.45; found: C 66.86, H 8.23, N 7.39.
3,5-Bis-(3-tert-butoxycarbonylaminopropyl)benzyl
(13): A solution of 2-bromoisobutyryl bromide (0.74 g, 3.22 mmol) in
THF (40 mL) was added dropwise to solution of 4a (0.91 g,
2-bromoisobutyrate
a
2.15 mmol), TEA (0.65 g, 6.42 mmol), and 0.2 g of DMAP in THF
(50 mL) over 15 min at 08C. The mixture was warmed to room tempera-
ture and stirred for 12h, washed with saturated aqueous NaHCO 3 and
brine, and dried with magnesium sulfate. After evaporation of the sol-
vent, chromatographic separation (silica gel, ethyl acetate/hexane 1/3)
Poly(3,5-bis-{3-[3,5-bis-(3-{3,5-bis(3-tert-butoxycarbonylamino-propyl)-
benzoylamino}propyl)benzoylamino]propyl}benzyl methacrylate) (PG3,
entry 14 in Table 1): According to procedure B, monomer 10 (0.60 g), and
DMF (0.30 mL) were used. After chromatographic separation the poly-
mer was lyophilized from dioxane to yield PG3 (0.30 g, 50%) as a color-
gave 8 as a colorless viscous oil (1.10 g, 90%), which solidified after
1
1
less foam. H NMR (CDCl3): d=0.66 (br, 3H; CH3), 0.80 (br, 2H; CH2),
some time. H NMR (CDCl3): d=1.42(s, 18H; CH ), 1.77 (m, 4H; CH2),
3
1.27 (br, 72H; CH3), 1.58 (br, 28H; CH2), 2.39 (br, 28H; CH2Ph), 2.90
3.18 (br, 28H; CH2NH), 5.17 (br, 10H; CH2O+NH), 6.92(br, 10H; Ph),
7.38 (br, 11H; Ph), 7.76 ppm (br, 6H; NH); 13C NMR (CDCl3): d=28.50,
31.31, 32.68, 39.97, 78.79, 125.04, 131.44, 134.82, 141.92, 156.30,
168.08 ppm; elemental analysis (%) calcd for (C135H198N14O24)n
(2401.10)n: C 67.53, H 8.31, N 8.17; found: C 67.41, H 8.32, N 8.34.
1.93 (s, 6H; CH3), 2.59 (m, 4H; CH2Ph), 3.10 (m, 4H; CH2NH), 4.59 (br,
2H; NH), 5.12 (s, 2H; OCH 2Ph), 6.94 (s, 1H; Ph), 6.98 ppm (s, 2H; Ph);
13C NMR (CDCl3): d=28.40, 30.76, 31.59, 32.84, 40.08, 67.49, 79.25,
125.49, 128.54, 135.62, 142.04, 155.95, 174.4 ppm; FABMS (3 kV): m/z
(%): 571 (0.69) [M+H]+ ; elemental analysis (%) calcd for C27H43BrN2O6
(571.54): C 56.74, H 7.58, N 4.90; found: C 56.45, H 7.44, N 4.76.
Poly(3,5-bis{3-[3,5-bis(3-{3,5-bis(3-[3,5-bis(3-tert-butoxycarbonylamino-
propyl)benzoylamino]propyl)benzoylamino}propyl)benzoylamino]pro-
pyl}benzyl methacrylate) (PG4; entry 15 in Table 1): According to proce-
dure B, monomer 12 (0.50 g) and DMF (0.25 mL) were used. After chro-
matographic separation the polymer was lyophilized from dioxane to
yield PG4 (0.44 g, 88%) as a colorless foam. 1H NMR (CDCl3): d=0.72
(br, 3H; CH3), 0.85 (br, 2H; CH2), 1.30 (br, 144H; CH3), 1.66 (br, 60H;
CH2), 2.42 (br, 60H; CH2Ph), 2.94 (br, 32H; CH2NH), 3.21 (br, 28H;
CH2NH), 4.96 (br, 2H; CH2O), 5.28 (br, 16H; NH), 6.93 (br, 16H; Ph),
7.45 (br, 29H; Ph), 7.84 8.20 ppm (br, 14H; NH); 13C NMR (CDCl3):
d=28.37, 30.58, 31.23, 32.52, 39.70, 78.77, 124.94, 131.52, 134.52, 141.79,
156.23, 168.04 ppm; elemental analysis (%) for (C279H406N30O48)n
(4945.03)n: C 67.72, H 8.27, N 8.49; found: C 67.80, H 8.13, N 8.41.
General procedure of TRP in bulk (A): The monomer and DCM were
placed in a 100 mL flask. The flask was connected to a rotary evaporator
and immersed in a water bath at 558C. After complete removal of the
solvent with stirring, the flask was kept rotating in the bath for a further
8 h. The polymer formed during that period was dissolved in DCM and
purified by column chromatography (silica gel, DCM eluent).
General procedure of TRP in solvent (B): The monomer and the solvent
were placed in a Schlenk tube, and the mixture stirred until it became ho-
mogeneous. The concentration of the monomer was kept around
75 wt%. The mixture was immediately degassed by several freeze
pump thaw cycles, and then kept at 558C for a predetermined time.
After polymerization, the polymer was dissolved in DCM and purified by
column chromatography (silica gel, DCM eluent).
General procedure of ATRP (C): The monomer, toluene, CuBr, and
PMDETA were placed a Schlenk tube, and the resulting mixture stirred
until it turned homogeneously green (for detailed conditions, see
Table 2). The mixture was immediately degassed several times by freeze
pump thaw cycles, then initiator 13 was added. As soon as the initiator
was added, the system turned homogeneously blue-green, indicating the
start of polymerization. The mixture was kept at 558C for a predeter-
mined time. After polymerization, the catalyst was removed by adsorp-
tion filtration through a short silica column, and the resulting polymer
was purified on a silica column with DCM as eluent.
Acknowledgement
This work was financially supported by the Deutsche Forschungsgemein-
schaft (Sfb 448, TP A1) and the Fonds der Chemischen Industrie. We are
thankful to Drs. Peter Franke and Andreas Sch‰fer for performing
MALDI-TOF MS and some of the NMR measurements.
Poly{3,5-bis(3-tert-butoxycarbonylaminopropyl)benzyl
methacrylate}
(PG1; entry 3 in Table 1): According to procedure A, monomer 5 (4.0 g)
and DCM (50 mL) were used. After chromatographic separation the pol-
ymer was lyophilized from dioxane to give PG1 (3.4 g, 86%) as a color-
[1] A. D. Schl¸ter, Top. Curr. Chem. 1998, 197, 165 191.
[2] A. D. Schl¸ter, J. P. Rabe, Angew. Chem. 2000, 112, 860 880;
Angew. Chem. Int. Ed. 2000, 39, 864 883; A. Zhang, L. Shu, Z. Bo,
A. D. Schl¸ter, Macromol. Chem. Phys. 2003, 204, 328 339.
[3] L. Shu, A. D. Schl¸ter, C. Ecker, N. Severin, J. P. Rabe, Angew.
Chem. 2001, 113, 4802 4805; Angew. Chem. Int. Ed. 2001, 40,
4666 4669; J. Barner, F. Mallwitz, L. Shu, A. D. Schl¸ter, J. P. Rabe,
Angew. Chem. 2003, 115, 1976 1979; Angew. Chem. Int. Ed. 2003,
42, 1932 1935.
1
less foam. H NMR (CDCl3): d=0.72(br, 2H; CH 2), 0.93 (br, 3H; CH3),
1.38 (br, 18H; CH3), 1.70 (br, 2H; CH2), 2.49 (br, 2H; CH2Ph), 3.02(br,
2H; CH2NH), 4.79 (br, 2H; NH), 5.27 (br, 2H; CH 2O), 6.87 ppm (br,
3H; Ph); 13C NMR (CDCl3): d=28.54, 31.56, 32.87, 40.20, 78.78, 125.86,
128.34, 135.30, 142.15, 156.17 ppm; elemental analysis (%) calcd for
(C27H42N2O6)n (490.63)n: C 66.10, H 8.63, N 5.71; found: C 65.90, H 8.44,
N 5.62.
[4] L. Shu, I. Goessl, J. P. Rabe, A. D. Schl¸ter, Macromol. Chem. Phys.
2002, 203, 2540 2550.
Poly{3,5-bis-(3-tert-butoxycarbonylaminopropyl)benzyl
methacrylate}
(PG1; entry 6 in Table 2): According to procedure C, CuBr (1.94 mg),
PMDETA (7.07 mg), 13 (7.77 mg), 5 (2.0 g), and toluene (1.2 mL) were
used. After chromatographic separation the polymer was lyophilized
from dioxane to yield PG1 (1.72g, 86%) as a colorless foam. 1H NMR
(CDCl3): d=0.72(br, 2H; CH 2), 0.93 (br, 3H; CH3), 1.38 (br, 18H;
CH3), 1.70 (br, 2H; CH2), 2.49 (br, 2H; CH2Ph), 3.02(br, 2H; CH 2NH),
4.79 (br, 2H; NH), 5.27 (br, 2H; CH 2O), 6.87 ppm (br, 3H; Ph); 13C
NMR (CDCl3): d=28.54, 31.56, 32.87, 40.20, 78.78, 125.86, 128.34, 135.30,
142.15, 156.17 ppm; elemental analysis (%) calcd for (C27H42N2O6)n
(490.63)n: C 66.10, H 8.63, N 5.71; found: C 66.40, H 8.41, N 5.67.
[5] For example, see M. F. Cunningham, Prog. Polym. Sci. 2002, 27,
1039 1067; M. Sawamoto, M. Kamigaito, Macromol. Symp. 2002,
177, 17 24; J. Qiu, B. Charleux, K. Matyjaszewski, Prog. Polym. Sci.
2001, 26, 2083 2134; M. Sawamoto, M. Kamigaito in Mater. Sci.
Techn. Series, Vol. 18 ™Synthesis of Polymers∫ (Ed.: A. D. Schl¸ter),
Wiley-VCH, Weinheim, 1999.
[6] K. Matyjaszewski, Macromol. Symp. 2002, 183, 71 81; K. Matyjas-
zewski, Chem. Rev. 2001, 101, 2921 2990.
[7] A series of dendronized polymers with short spacers is in prepara-
tion.
Poly{3,5-[bis(3-{3,5-bis[3-(tert-butyloxycarbonylamino)propyl]benzoyl}-
amino)propyl]benzyl methacrylate} (PG2; entry 12 in Table 2): Accord-
[8] A. Zhang, S. Vetter, A. D. Schl¸ter, Macromol. Chem. Phys. 2001,
202, 3301 3315.
6091
Chem. Eur. J. 2003, 9, 6083 6092
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. Schmidt, A. D. Schl¸ter et al.
FULL PAPER
[9] The same reduction applied to higher generation dendrons with car-
boxylic acids at their focal points did not work in our hands.
[10] M. Gerle, K. Fischer, A. H. E. M¸ller, M. Schmidt, S. S. Sheiko, S.
Prokhorova, M. Mˆller, Macromolecules 1999, 32, 2629 2637.
[11] Y. Tsukahara, S.-I. Namba, J. Iwasa, Y. Nakano, K. Kaeriyama, M.
Takahashi, Macromolecules 2001, 34, 2624 2629.
[14] D. W. Lamson, J. Org. Chem. 1973, 38, 2928 2931.
[15] R. Klopsch, S. Koch, A. D. Schlueter, Eur. J. Org. Chem. 1998,
1275 1283.
[16] K. Matyjaszewski, B. Goebelt, H. Paik, C. P. Horwitz, Macromole-
cules 2001, 34, 430 440.
[17] A. Becker, W. Kˆhler, B. M¸ller, Ber. Bunsen-Ges. 1995, 99, 600
[12] R. C. Oberth¸r, Makromol. Chem. 1978, 179, 2693 2701.
[13] M. Schmidt, Macromolecules 1984, 17, 553 560.
605.
Received: May 15, 2003 [F5142]
6092
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 6083 6092