Reactive dendronized copolymer of styryl dendron and maleic anhydride: A single molecular scaffold

Article abstract of DOI:10.1021/ma047449n

Novel dendronized copolymers bearing reactive anhydride groups along the backbones are reported in this paper. They were synthesized through copolymerizations of styryl macromonomers bearing Frechet-type dendrons of the first to the fourth generation and

Full text of DOI:10.1021/ma047449n

Macromolecules 2005, 38, 5069-5077
5069
Reactive Dendronized Copolymer of Styryl Dendron and Maleic
Anhydride: A Single Molecular Scaffold
Yanhong Zhang, Jin Huang, and Yongming Chen*
State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Sciences and
Materials, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, P. R. China
Received December 11, 2004; Revised Manuscript Received April 14, 2005
ABSTRACT: Novel dendronized copolymers bearing reactive anhydride groups along the backbones are
reported in this paper. They were synthesized through copolymerizations of styryl macromonomers bearing
Fre´chet-type dendrons of the first to the fourth generation and maleic anhydride (MAn) through
conventional radical polymerization. The dendritic macromonomers were prepared by an accelerated
convergent approach, i.e., a reaction of the dendritic bromide of lower generation with a styrene derivative
bearing a 3,5-dihydroxybenzyl group. The dendronized copolymers with rather high molar masses were
obtained under mild conditions, even for the fourth-generation dendritic monomer as determined by static
light scattering (SLS). For example, the degree of copolymerization for the third-generation monomer
reached 487. Owing to the reactivity of the anhydride, functional groups, which were buried by the grafted
dendrons along the backbone, could be easily introduced as follows: (1) by the hydrolysis under acid
conditions, the amphiphilic copolymers with a structure of dendron-alt-2COOH were prepared; (2) by
reacting with alkyl primary amine, the copolymers with dendron-alt-linear alkyl chain were obtained in
a quantitatively yields; (3) when reacted with a primary amino dendron of its generation different from
the pendent dendron, a series of new dendronized copolymers with their side dendrons grafted in an
alternative generation structure were produced. Therefore, the novel reactive dendronized copolymer
presented herein can be a single molecular scaffold to be applied in nanomaterials and nanotechnologies
of one dimension.
Introduction
DP. The second one is the “coupling to” approach, of
which to attach dendrons directly to a backbone-to-be
polymer containing anchor groups.19-21 However, its
disadvantage is obvious; i.e., it is difficult to ensure
completely coverage. Therefore, the coupling chemistry
selection and the characterization method on the cou-
pling efficiency are rather important. An extended study
has been made by Hawker et al. on the degree of the
coverage considering the factors of dendron size and the
spacer between two anchor groups along the polymer
backbone.22 The third one is the “grafting from” or
divergent approach. Dendrons grow up step by step from
the backbone of the polymer, through which extremely
long dendronized polymer of high generation can be
achieved.23 Similarly, it has the same problem with the
second approach. Some recent review articles have
summarized the synthetic strategies in detail.24,25 Fur-
thermore, dendronized polymers have also been pro-
duced through noncovalent interactions.26
Dendronized polymers are linear polymers of their
repeating units pendent with dendritic wedges as the
bulky side groups along the main chains.1-3 The most
important feature concerning these novel grafted poly-
mers is the conformation of the whole polymers. With
increase of the steric repulsion between the bulky side
groups along the backbone, the polymer main chains
prone to extend and transfer from random coils to
rodlike cylinders. When the main chains are longer
enough and dendritic wedges are large enough, huge
single molecular nanorods have been obtained.4-8 Since
the size and branch number of the side dendron are
tailored precisely during the synthesis of dendron by
changing generation number, diameter and flexibility
of the dendronized polymers can be controlled precisely.
These rodlike polymers, together with the cylindrical
polymer brushes, have attracted much attention in
recent years.9,10
The interior and the periphery of the dendrimers
having different chemistry can supply a single molecular
microenvironment, which is used as catalyst support,
encapsulation, release, etc.27-29 This is one of the most
interesting features that have attracted researcher’s
attention since the dendrimers emerged one and half
decades ago. Therefore, incorporation of functional
groups along the main chains of dendronized polymers
can be very important to extend their applications for
nanoreactors and one-dimensional nanoparticle arrays
being wrapped by dendron wedges. There are two ways
to introduce the functional groups on the dendronized
polymers. One is introduction of functional groups on
the periphery of the polymers.23 Scrivante et al. have
tried to prepare dendronized polymers which carry
dendritic polypyridine as side groups by the mac-
romonomer approach for complexation studies.12 But
The syntheses of dendronized polymers have been
achieved through three approaches. The first one is the
so-called macromonomer approach, which refers to
homopolymerization of the dendritic macromonomer
through selected polymerization techniques, such as
radical polymerization,11-13 polycondensation,14-17 living
polymerization,18 and so on. The advantage of this
approach is the uniform structures of the resulting
polymers can be guaranteed since every repeat unit
bears one dendron. However, it becomes difficult to get
the polymers with higher degrees of polymerization (DP)
for the dendritic monomers of higher generation due to
the steric hindrance. High monomer concentration
during the polymerizations was crucial to increase the
* Corresponding author: phone +0086-10-62659906; Fax +0086-
10-62559373; e-mail ymchen@iccas.ac.cn.
10.1021/ma047449n CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/20/2005

5070 Zhang et al.
Macromolecules, Vol. 38, No. 12, 2005
Scheme 1. Cartoon Presentation of Dendronized
Copolymer with Reactive Anhydride Groups along
the Backbone
HT-2, HT-3, and HT-4; the effective molar mass ranges were
100-10000, 500-30000, and 5000-600000, respectively. Lin-
ear polystyrene standards were applied as the calibration. The
eluent was THF at a flow rate of 1.0 mL/min at 35 °C. A
commercial laser light scattering (LLS) spectrometer (ALV/
DLS/SLS-5022F) equipped with a multi-τ digital time corr-
elator (ALV5000) and a cylindrical 22 mW UNIPHASE He-
Ne laser (λ0 ) 632 nm) was used. The dn/dc value was
measured by a refractometer (Dawn DSP, Wyatt Technology
Corp.). All samples were dissolved in THF solvent, and the
solutions were filtered through a 0.45 µm PTFE membrane
prior to use. The solutions were put in 10 mm diameter glass
cells. Static light scattering (SLS) measurements were made
from 30° up to 150° at 25.0 °C. The data acquisition was done
with the ALV Correlator Control software. MALDI-TOF
(matrix-assisted laser desorption and ionization time-of-flight)
mass spectrometry was performed on a Bruker Biflex III
spectrometer equipped with a 337 nm nitrogen laser. Both
matrix 4-hydroxy-R-cyanocinnamic acid (CCA) and sample
were dissolved in 1:1 (v/v) acetonitrile:water with 1% trifluo-
roacetic acid. 0.5 µL of this mixture solution was placed on a
metal sample plate and air-dried at ambient temperature.
Mass spectra were acquired in positive reflector mode using
an acceleration voltage of 19 kV. External mass calibration
was performed using a standard peptide mixture. Spectra were
obtained by setting the laser power close to the threshold of
ionization, and generally 100 pulses were acquired and aver-
aged. FT-IR spectra were recorded by a deuterate triglycine
sulfate (DTGS) detector on a Bruker EQUINOX 55 spectrom-
eter and processed by the Bruker OPUS program. THF
solution (20 mg/mL) was dropped on KBr flake and dried
polymerization of the third-generation monomer only
gave the oligomer. The other one is modifying the
backbone of the dendronized polymer, and this may
open the possibility to engineer the interior of the
polymer. However, to the best of our knowledge, only
one example of the dendronized cyclocopolymer bearing
pyrrolidinopyridine functional groups was reported
recently, and the polymer was used as a catalyst of
esterification.27 The functionalities of the polymer were
dispersed randomly along the backbone.
In this paper, we present a family of the dendronized
copolymers bearing anhydride groups uniformly dis-
tributed along the main chains, as depicted in Scheme
1. It is well-known that copolymerization of maleic
anhydride (MAn) and styrene or its derivatives gives
alternative copolymers in radical copolymerization. It
is likely to incorporate anhydride groups, which are
highly reactive, into the backbones of the dendronized
polymers through the copolymerization of MAn and the
styrene derivatives bearing dendron wedges. Herein, we
synthesized the novel dendronized copolymers through
the radical copolymerization of maleic anhydride (MAn)
and styryl-type macromonomers carrying Fre´chet-type
polyether dendrons of the first to the fourth generation,
respectively. By this way, reactive anhydride groups
were easily incorporated alternatively into the backbone
with the dendrons pendent. The copolymers with rather
high molar masses were obtained even for the third-
generation monomer under mild conditions. The func-
tionalization was easily manipulated through chemical
reactions of anhydride groups, leading to a series of
novel dendronized copolymers with functionalities being
buried in the bulky dendrons along the main chain.
1
before tested. H NMR and 13C NMR spectra were recorded
on a Bruker DMX300 spectrometer.
Preparation of Molecules 2, 3, 4, 5, and [G-1]-NH2. See
Supporting Information for details.
Synthesis of Monomer 6 [G-1]. [G-1]-OH (10.0 g, 31.2
mmol) was added to THF (100 mL) solution of sodium hydride
(1.62 g, 40.6 mmol). The solution was stirred under nitrogen
for 30 min. A solution of 4-vinylbenzyl chloride (5.87 mL, 37.5
mmol) in THF (40 mL) was added, and the reaction mixture
was refluxed for 48 h. After the flask was cooled to room
temperature, water was added carefully until no bubble
escaped. Dilute hydrogen chloride aqueous solution (1 equiv)
was added until the pH value reached 5-6. After THF removed
by rotary evaporator, the reaction mixture was extracted with
dichloromethane, and the combined organic layers were dried
over anhydrous sodium sulfate. A kind of viscous oil was
obtained after filtration and removal of the solvent. The crude
product was purified by column chromatography using petro-
leum ether/ethyl acetate (16:1 v/v) as eluent. A white powder
1
was obtained; 6.01 g (yield: 44%). H NMR (CDCl3) δ: 4.49
Experimental Section
(s, 2H, ArCH2O), 4.52 (s, 2H, CH2dCHArCH2O), 5.04 (s, 4H,
PhCH2O), 5.25 (d, 1H, J ) 12, CH2dCH), 5.76 (d, 1H, J ) 18,
CH2dCH), 6.56 (s, 1H, ArH), 6.62 (s, 2H, ArH), 6.72 (q, 1H, J1
) 12, J2 ) 18, CH2dCH), 7.26-7.44 (m, 14H, PhH and CH2d
CHArH). 13C NMR (CDCl3) δ: 70.1 (PhCH2O), 71.8, 71.9
(CH2OCH2), 101.4, 106.6 (ArC), 113.8 (CH2dCH), 126.3, 127.6,
128.0, 128.6 (CH2dCHArC and PhC), 136.6, 136.9, 137.9, 140.8
(CHdCH2, PhC and ArC), 160.1 (ArC). Elemental analysis:
Calcd for C30H28O3: C, 82.54; H, 6.46. Found: C, 82.64; H,
7.11. MALDI-TOF Mass spectrum: Calcd: [M+] m/z ) 436.2.
Found: [M + Na+]+ ) 459.2.
General Procedure for the Synthesis of Monomer 6
[G-2, -3, -4]. A mixture of [G-1]-Br, [G-2]-Br, or [G-3]-Br (2.1
equiv), 5 (1.0 equiv), potassium iodide (2.1 equiv), potassium
carbonate (3 equiv), and 18-crown-6 (0.1 equiv) in dry acetone
was refluxed under nitrogen for 48 h. The mixture was allowed
to cool and evaporated to dryness on rotary evaporator, and
the residues were partitioned with dichloromethane and water.
The combined organic layers were dried over sodium sulfate
and filtered. After removing the solvent, the crude product was
purified by column chromatography.
Materials. 3,5-Dihydroxybenzoic acid (97%, Acros), 4-
vinylbenzyl chloride (tech 90%, Acros), 18-crown-6 (18-C-6;
99%, Acros), lithium tetrahydroaluminate (LiAlH4; typically
97%, Alfa), sodium hydride (NaH; 60% dispersed in mineral
oil, Aldrich), carbon tetrabromide (CBr4; 99%, Aldrich), 3,4-
dihydro-2H-pyran (DHP; 99%, Acros), potassium iodide (KI;
Beijing Chemicals Co.), anhydrous potassium carbonate (K2-
CO3; AR, Beijing Chemicals Co.), triphenyl phosphine (PPh3;
CP, Shanghai Chemicals Co.), 1-butylamine (CP, Beijing
Chemicals Co.), and laurylamine (CP, Beijing Chemicals Co.)
were used as received. 2,2′-Azobisisobutyronitrile (AIBN) was
recrystallized from ethanol. Maleic anhydride (MAn) was
recrystallized from benzene. Tetrahydrofuran (THF) was
distilled from sodium/benzophenone before use. Chloroform
was dried over CaH2 and distilled before use. Other reagents
were used without further purification.
Fre´chet-type dendrons, [G-n]-Br and [G-n]-OH, were pre-
pared according to the literature procedure ([G-n] is the
generation number of dendron, and X (X ) Br, OH) is the
functionality of the focal point according to the literature).30
Measurement. Polydispersities of polymers, Mw/Mns, were
obtained by SEC equipped with a Waters 515 pump, a Waters
2414 refractive index detector, and a combination of Styragel
Synthesis of Monomer 6 [G-2]. This was prepared from
[G-1]-Br and purified by column chromatography, eluting with
8:1 petroleum ether/ethyl acetate followed by 4:1 petroleum

Macromolecules, Vol. 38, No. 12, 2005
Reactive Dendronized Copolymers 5071
ether/ethyl acetate to give 6 [G-2] as a white powder. Yield:
and butylamine (or laurylamine, or [G-1]-NH2) were added in
an ampule with mole ratio of 1:1, and THF was added to make
the concentration of 7 to 0.05 mol/L. After sealed under
vacuum, the ampule was kept in an oil bath at 70 °C for 48 h.
After removal of the most solvent, the reaction mixture was
precipitated in ether for two times and hexane for one time.
After drying in a vacuum desiccator overnight, white powder
was obtained. Yield: >90%. Elemental analysis: (1) Calcd for
(C38H41NO6)n (9 [G-1]): N, 2.30; C, 75.10; H, 6.80. Found: N,
2.30; C, 72.68; H, 6.98. (2) Calcd for (C66H65NO10)n (9 [G-2]):
N, 1.36; C, 76.80; H, 6.35. Found: N, 1.35; C, 74.69; H, 6.35.
(3) Calcd for (C46H57NO6)n (10 [G-1]): N, 1.95; C, 76.74; H, 7.98.
Found: N, 2.03; C, 74.57; H, 7.95. (4) Calcd for (C74H81NO10)n
(10 [G-2]): N, 1.22; C, 77.66; H, 7.13. Found: N, 1.25; C, 76.18;
H, 7.04. (5) Calcd for (C130H129NO18)n (10 [G-3]): N, 0.70; C,
78.33; H, 6.52. Found: N, 0.88; C, 77.43; H, 6.51. (6) Calcd for
(C242H225NO34)n (10 [G-4]): N, 0.38; C, 78.74; H, 6.14. Found:
N, 0.56; C, 77.03; H, 6.23.
1
69%. H NMR (CDCl3) δ: 4.48 (s, 2H, ArCH2O), 4.51 (s, 2H,
CH2dCHArCH2O), 4.97 (s, 4H, ArCH2O), 5.01 (s, 8H, PhCH2O),
5.22 (d, 1H, J ) 12, CH2dCH), 5.73 (d, 1H, J ) 18, CH2dCH),
6.53 (s, 1H, ArH), 6.56 (s, 2H, ArH), 6.59 (s, 2H, ArH), 6.65 (s,
4H, ArH), 6.64 (q, 1H, J1 ) 18, J2 ) 12, CH2dCH), 7.28-7.42
(m, 24H, PhH and CH2dCHArH). 13C NMR (CDCl3) δ: 69.8
(ArCH2O), 70.0 (PhCH2O), 71.7 (CH2dCHArCH2O), 71.8
(ArCH2O), 101.3, 101.4, 106.2, 106.5 (ArC), 113.8 (CHdCH2),
126.2, 127.5, 128.0, 128.5 (CH2dCHArC and PhC), 136.4,
136.7, 136.9, 137.7, 139.2, 140.7 (CHdCH2, PhC and ArC),
159.9, 160.1 (ArC). Elemental analysis: Calcd for C58H52O7:
C, 80.91; H, 6.09. Found: C, 81.99; H, 6.36. MALDI-TOF mass
spectrum: Calcd: [M+] m/z ) 860.4. Found: [M + Na+]+
883.2.
)
Synthesis of Monomer 6 [G-3]. It was prepared from
[G-2]-Br and purified by column chromatography, eluting with
4:1 dichloromethane/petroleum ether to give 6 [G-3] as a white
powder. Yield: 81%. 1H NMR (CDCl3) δ: 4.46 (s, 2H, ArCH2O),
4.50 (s, 2H, CH2dCHArCH2O), 4.95 (s, 12H, ArCH2O), 5.00
(s, 16H, PhCH2O), 5.20 (d, 1H, J ) 12, CH2dCH), 5.71 (d, 1H,
J ) 18, CH2dCH), 6.54-6.66 (m, 22H, ArH and CHdCH2),
7.25-7.40 (m, 44H, PhH and CH2dCHArH). 13C NMR (CDCl3)
δ: 69.8 (ArCH2O), 69.9 (PhCH2O), 71.7 (CH2dCHArCH2O),
71.8 (ArCH2O), 101.2, 101.4, 106.2, 106.5 (ArC), 113.7 (CHd
CH2), 126.2, 127.5, 127.7, 127.9, 128.5 (CH2dCHArC and Ph
C), 136.4, 136.6, 136.8, 137.6, 139.1, 139.2, 140.7 (CHdCH2,
PhC and ArC), 159.9, 160.0 (ArC). Elemental analysis: Calcd
for C114H100O15: C, 80.07; H, 5.89. Found: C, 80.64; H, 6.27.
MALDI-TOF mass spectrum: Calcd: [M+] m/z ) 1709.7.
Found: [M + Na+]+ ) 1732.0.
Synthesis of Monomer 6 [G-4]. This was prepared from
[G-3]-Br and purified by column chromatography, eluting with
4:1 dichloromethane/petroleum ether and gradually increasing
to dichloromethane to give 6 [G-4] as a white solid. Yield: 83%.
1H NMR (CDCl3) δ: 4.43 (s, 2H, ArCH2O), 4.47 (s, 2H, CH2d
CHArCH2O), 4.91 (s, 28H, ArCH2O), 4.97 (s, 32H, PhCH2O),
5.17 (d, 1H, J ) 12, CH2dCH), 5.68 (d, 1H, J ) 18, CH2dCH),
6.47-6.65 (m, 45H, ArH and CHdCH2), 7.26-7.42 (m, 94H,
PhH and CH2dCHArH). 13C NMR (CDCl3) δ: 69.9 (ArCH2O),
70.0 (PhCH2O), 71.7 (CH2dCHArCH2O), 71.8 (ArCH2O), 101.4,
101.5, 106.3, 106.6 (ArC), 113.8 (CHCH2), 126.2, 127.5, 127.7,
127.9, 128.5 (CH2dCHArC and PhC), 136.4, 136.7, 137.7,
139.2, 139.3, 140.6 (CHdCH2, PhC and ArC), 160.0 (ArC).
Elemental analysis: Calcd for C226H196O31: C, 79.65; H, 5.80.
Found: C, 78.98; H, 5.91. MALDI-TOF mass spectrum:
Calcd: [M+] m/z ) 3407.4. Found: [M + Na+]+ ) 3430.2.
General Procedure for the Copolymerization of 6 [G-1,
-2, -3, -4] and MAn: Synthesis of Polymer 7 [G-1, -2, -3,
-4]. MAn, 6 [G-1, -2, -3, -4], AIBN, and dry chloroform were
placed in a Schlenk flask with a magnetic stir bar and a rubber
septum. After degassing by bubbling with nitrogen for 30 min,
the reaction was carried on at the appropriate temperature
in an oil bath, until the magnetic stir bar could not move,
usually in 2-8 h. The polymer was dissolved in chloroform
and precipitated in diethyl ether until no monomer remained
as analyzed by SEC and 1H NMR. See Supporting Information
for details.
Results and Discussion
Synthesis of Styryl Dendrons. To prepare the
styryl dendron, one method is by Williamson reaction
of [G-n]-OH of Fre´chet-type dendron with 4-vinylbenzyl
chloride, leading to styryl [G-n]-monomer, 6 [G-n].
However, it is tedious and time-consuming for the high-
generation dendrons. Another choice is to synthesize a
styrene derivative 5 that serves as a branching molecule
since it bears two hydroxyl groups. By the reaction of 5
and the [G-n]-Br dendron, the expected monomer of
higher generation, 6 [G-(n+1)], can be obtained. This
is the so-called accelerated convergent strategy being
applied in the literature.31-33 The advantages of the
latter approach are obvious. Increasing generation
number and introducing styryl group can be achieved
in one step. Therefore, the synthesis is more efficient.
Comparison of two methods is exhibited in Scheme 2.
The former one was applied to synthesize the first
generation monomer, 6 [G-1], whereas the accelerated
approach was used to prepare the higher generation
monomers, i.e., 6 [G-2], 6 [G-3], and 6 [G-4].
The protection and deprotection technique were ap-
plied for preparation of 5 as shown in Scheme 3. Methyl
3,5-dihydroxybenzoate (1) reacted with 3,4-dihydro-2H-
pyran (DHP) catalyzed by concentrated hydrogen chlo-
ride. The crude product 2 was used for the next step of
reduction with lithium tetrahydroaluminate (LiAlH4)
without further purification. The resulted alcohol 3 was
used in the following step of etherification directly.
Molecule 4 was produced through Williamson reaction
of 3 and 4-vinylbenzyl chloride, and the overall yield
was as high as 78%. Removal of the protection groups
of tetrahydropyran was made by reacting with dilute
aqueous HCl, and the product 5 was given. This
molecule was unstable in dryness since it became an
insoluble material. Therefore, functional monomer 5
was kept in solution of acetone. This phenomenon was
reported previously with a similar molecule, 4-hy-
droxymethylene styrene.34
General Procedure for the Hydrolysis of the Copoly-
mer 7 [G-1, -2, -3, -4]: Synthesis of 8 [G-1, -2, -3, -4]. The
copolymers 7 [G-1, -2, -3, -4] were dissolved in THF at room
temperature to give the solutions of concentration of 10 mg/
mL in ampules. Concentrated hydrochloric acid aqueous
solution (36-38%) was added slowly until the solution became
cloudy, and then water of ca. 1/3 weight of the polymer solution
was added. After frozen with liquid nitrogen, the ampule was
sealed under vacuum. The reaction proceeded at 70 °C in oil
bath for 48 h before opening the ampule. After removal of the
most solvent, the reaction mixture was precipitated in diethyl
ether for two times and hexane for one time. The products were
dried in a vacuum overnight. Yield: 71.6% (8 [G-1]); 45.5% (8
[G-2]); 51.8% (8 [G-3]); 94.5% (8 [G-4]).
The structures of 6 [G-1, -2, -3, -4] were confirmed by
1H NMR and 13C NMR spectroscopy, element analysis,
and MALDI-TOF mass spectrometry, respectively. The
1H NMR spectra of 6 [G-2] are shown in Figure 1 (see
Figure S1 in Supporting Information for the spectra of
four monomers). The quadruple peaks between 6.68 and
6.61 ppm were assigned to the proton of -CHdCH2. The
double peaks over 5.76-5.70 and 5.24-5.20 ppm having
coupling constant 18 and 12 Hz, respectively, were
assigned to the trans and cis protons of -CHdCH2, and
with the increase of generation the position of the two
General Procedure for the Amidolysis of the Copoly-
mer 7 [G-1, -2, -3, -4]: Synthesis of 9 [G-1, -2], 10 [G-1, -2,
-3, -4], and 11 [G-2, -3, -4]. The copolymers 7 [G-1, -2, -3, -4]

5072 Zhang et al.
Macromolecules, Vol. 38, No. 12, 2005
Scheme 2. Comparison of Two Approaches for the
Synthesis of the Monomer 6 Taking [G-3]-Monomer as
an Example
Figure 1. 1H NMR spectrum of 6 [G-2] monomer with
assignment.
Figure 2. 13C NMR spectrum of 6 [G-2] monomer with
assignment.
Scheme 3. Synthesis of Branched Molecule 5
Containing Styrene
CdC group of styrene were recognized in 13C NMR
spectrum of 6 [G-2] at about 113.8 and 136.4 ppm; the
other carbon signals could be assigned to the corre-
sponding carbons of the dendron as shown in Figure 2
(see Figure S2 in Supporting Information for the spectra
of four monomers).
Size exclusion chromatography (SEC) was applied to
characterize the purities of the monomer 6 series from
the first to the fourth generation. As demonstrated in
Figure 3, very narrow peaks were obtained, indicating
the coupling reaction and separation were efficient. The
actual molar masses were determined by MALDI-TOF
mass spectrometry, and the results corresponded to the
theoretical values. As listed in Table 1, the molar
masses given by SEC were underestimated comparing
to the actual values due to the calibration was made by
linear standard polystyrenes.
Copolymerization of 6 [G-1, -2, -3, -4] and MAn
Initiated by AIBN. It is known that the copolymeri-
zation of styrene and maleic anhydride (MAn) can
produce alternating copolymers through a charge-
transfer complex (CTC). Styrene derivatives with para-
substituent electron-donor groups may increase the
protons shifted slightly to high field because of the
increase of shielding effect due to the electron-donor
para-substituent group of styrene. The multipeaks at
7.42-7.28 ppm were attributed to the protons of mono-
and 1,4-disubstituent phenyl groups of Fre´chet-type
dendron, and the proton signals of trisubstituent phenol
groups lay in 6.65-6.53 ppm. The carbon signals of the

Macromolecules, Vol. 38, No. 12, 2005
Reactive Dendronized Copolymers 5073
Figure 4. 1H NMR spectrum of 7 [G-2] copolymer with
assignment.
Figure 3. SEC traces for 6 [G-1, -2, -3, -4] monomer.
As shown in Table 2, the copolymerizations proceeded
easily under mild conditions, and the yields were high
for a radical polymerization. Since the data were
underestimated by SEC analysis with polystyrene as
the calibration, absolute molar masses were determined
by static light scattering (SLS). The degrees of copoly-
merizations (DPws), defined as one pair of the comono-
mers, of the 6 for the first and the second generation
were over 500, which were rather high. Each copolym-
erization reaction has been repeated at least for one
time and good repeatability was given. The copolymer-
ization of the third-generation monomer with MAn was
carried out at different temperature; high DPw was
given at relatively low temperature as shown in Table
2. It should be mentioned that actual polymer length
should double the DPws since the DPw used here
represented one styrene unit and one MAn unit. There-
fore, the dendronized polymers in this system were
rather long. However, the DPw of the copolymers of the
fourth-generation monomer and MAn decreased greatly,
and average DPw was ca. 90. The low DPw for 6 [G-4]
was reasonable since the huge size of the monomer
would bury its double bond. Moreover, the monomer
molar concentrations during the copolymerization were
lowered due to the molar mass of 6 [G-4] being very
large. These two factors were not helpful to increase the
DPw of 6 [G-4].
Table 1. Molar Masses and Polydispersities from SEC
and Mass Spectra of 6 [G-1, -2, -3, -4] Monomers
SEC data
monomer
molar massa
[M + Na+]+
Mn
Mw/Mn
6 [G-1]
6 [G-2]
6 [G-3]
6 [G-4]
436.53
861.04
1710.04
3407.96
459.2b
215
504
1162
3371
1.01
1.02
1.02
1.04
883.2b
1732.0b
3430.2b
a Calculated according to the atom weight. b Determined by
MALDI-TOF mass spectrometry.
Scheme 4. Radical Copolymerization of 6 [G-1, -2, -3,
-4] and Maleic Anhydride (the Sector Represent
Fre´chet-Type Dendron of [G-1, -2, -3, -4])
The homopolymerizations of the similar monomers
with 6 [G-1, -2, -3, -4] were reported by Neubert et al.,37
which proceeded at higher temperature and at lower
initiator concentration. However, the products of the
fourth-generation copolymer were oligomers. Comparing
with that, the copolymerizations of 6 [G-1, -2, -3, -4] and
MAn easily gave the dendronized copolymers with high
molar masses in 2-8 h reaction period. The reason for
the present results may be attributed to the steric
hindrance of the dendrons being reduced by its comono-
mer (MAn) relative to the homopolymerization of similar
styryl dendrons.37 However, alternative copolymeriza-
tion was more likely to produce the copolymers of high
molar masses since the polymerization of CTC was
normally much faster than homopolymerization of
styrene.
Table 2. Copolymerization Conditions and Results of the
Four-Generation Copolymersa
concc
(mol/L)
temp yield
d
sample
feedb
(°C)
(%)
Mw SLS
DPw
7 [G-1]-1 50:50:2
7 [G-1]-2 50:50:2
7 [G-2]-1 50:50:2
7 [G-2]-2 50:50:2
7 [G-3]-1 50:50:4
7 [G-3]-2 50:50:4
7 [G-4]-1 50:50:4
7 [G-4]-2 50:50:5
1.0
1.0
1.0
1.0
0.3
0.3
0.3
0.5
50
50
50
50
60
50
60
60
64
83
43
85
74
52
66
69
338 100
424 000
668 100
558 900
349 900
880 500
244 900
309 000
535
793
697
583
194
487
70
88
a Solvent was chloroform. b Molar ratio of [G-n]:MAn:AIBN.
c Concentration of two monomers in solvent. d Taking one pair of
dendritic monomer 6 [G-1, -2, -3, -4] and one MAn as one repeating
unit and calculated from the Mw determined by SLS.
The 1H NMR spectra of different generation of 7 [G-n]
copolymers showed not too much difference, but the
integral areas were in accordance with the correspond-
ing copolymers. Figure 4 shows the spectrum of 7 [G-2]
copolymers with the assignment (see Figure S3 in
Supporting Information for the spectra of four copoly-
mers). The broaden peaks were given, and this was
typical for dendronized polymers due to the high molar
mass and chain stiffness. No vinyl protons could be
found, indicating the unreacted monomers were re-
moved completely after the copolymerization. However,
electron density of monomer, favoring to form alterna-
tive structure.35,36 Therefore, the styryl dendrons we
designed were likely to have a strong alternating
tendency of copolymerization with MAn (Scheme 4). The
copolymerizations of the monomer 6 of four generations
and MAn were made in chloroform initiated by AIBN
at 50 or 60 °C; the results are summarized in Table 2.

5074 Zhang et al.
Macromolecules, Vol. 38, No. 12, 2005
Scheme 5. Hydrolysis and Amidolysis of Succinic
Anhydride Units of 7 [G-1, -2, -3, -4]
lie in 138.9-134.9 ppm. After analyzing the proton
broad band decoupling and the gated decoupling 13C
NMR spectrum of 6 [G-1] and the DEPT 13C NMR
spectra of 7 [G-1], we achieved the assignment as shown
in Figure 5. The position of C3 was 138.5 ppm among
the alternating period aforementioned. Thus, the con-
clusion can be made that the copolymer of 7 [G-1] has
a strict alternating sequence in microstructure. But for
the higher-generation dendronized copolymers of 7 [G-2,
-3, -4], the precise assignment of 13C NMR spectra was
difficult because the similar carbon in para-substituent
polyether-type dendrons of styrene interfered the weak
peak of C3.
Figure 5. 13C NMR spectrum of homopolymer of 6 [G-1] (a)
and copolymer 7 [G-1] (b) with assignment.
While we tried to calculate the molar ratio of 6 [G-1,
-2, -3, -4] and MAn units in the copolymers 7 [G-1, -2,
-3, -4] according to the integral areas of 1H and 13C NMR
spectra, we encountered the same problem, i.e., the
weak and overlapped signals. As increasing generation
the mass proportions of MAn in the copolymers 7 [G-1,
-2, -3, -4] decreased dramatically, and the signals
became too weak to detect.
Though there was no direct evidence of alternative
structure for the copolymers with pendent dendrons in
higher generations, the copolymers were likely to be the
expected structure on the basis of the following analysis.
First, Fre´chet-type vinyl monomers at higher generation
was difficult to give the homopolymers with high DP in
short reaction time due to the bulky dendron shielding
the vinyl group.37 Introduction of a spacer has been tried
to increase the DP of the dendronized polymers of
Fre´chet-type dendron wedges.40 Second, it is known that
MAn cannot radically homopolymerize. Therefore, the
dendronized copolymers with high DP readily produced
under the molar feed ratio of 1:1 (7 [G-1, -2, -3, -4]: MAn)
could attribute to preferential alternative copolymeriza-
tions of the two monomers. The composition of the
modified copolymers in followed sections further con-
firmed the expected structure indirectly.
Hydrolysis of Succinic Anhydrides in Copoly-
mers 7 [G-1, -2, -3, -4]. The functionalization of the
succinic anhydride units located along the backbones
of the copolymers has been studied extensively. The
hydrolysis of the succinic anhydride along the den-
dronized copolymers is the simplest one, and each unit
may produce two COOH groups, as shown in Scheme
5. The reactions were completely as confirmed by FT-
IR spectroscopy (Figure 6). The absorption peaks at
1861 and 1779 cm-1 of 7 were characteristic bands of
anhydride, assigned to asymmetrical and symmetrical
νCdO of succinic anhydride moieties, respectively. Peaks
at 1595, 1498, and 1454 cm-1 were the νCdC of the
the alternating sequence structure of the copolymers
could not be confirmed from the 1H NMR spectrum since
the MAn unit only had two protons, which were too
weak and also overlapped with other protons in the
spectra. Two methods may be used to prove the alterna-
tive sequence according to the literature. One was
through determining the chemical shift of the carbon
of the methylene along the backbones of the St-MAn
copolymers according to distortionless enhancement by
polarization transfer (DEPT) spectroscopy,38 but the
signal of the carbon of the methylene was too weak to
detect for the copolymer of 7 [G-1] due to the high molar
mass. The other was through determining the chemical
shift of the quaternary aromatic “next to polymer chain”
carbon of styrene in the copolymer in 13C NMR spec-
troscopy.39 Herein, we applied the latter method to
characterize the alternative structure of the copolymer
7 [G-1] because the signals of the copolymers of 7 [G-2,
-3, -4] were weak and complicated due to the similar
carbon in para-substituent polyether-type dendron of
styrene.
For the 13C NMR spectrum of the copolymer of styrene
and MAn, the chemical shifts of sequence distribution,
nonalternating (111), semialternating (011 + 110), and
alternating (010) triad subpeaks of the aromatic “next
to polymer chain” carbon of styrene (1 represents the
donor monomer styrene; 0 represents the acceptor
monomer MAn), lay in 147.5-145, 146-141.5, and
140.5-136.5 ppm, respectively.39 But for the copolymer
7 [G-1] we should consider the effect of para-substituent
dendron of styrene. So we synthesized the homopolymer
of 6 [G-1] and tested its 13C NMR spectra. It was found
that the position of the aromatic “next to polymer chain”
carbon (C3 in Figure 5) lay in 145.6-143.8 ppm; that is
to say, the para-substituent induced the position of C3
shifting 1.6 ppm toward high field, so the chemical shift
of the alternating triad subpeaks of C3 of 7 [G-1] should

Macromolecules, Vol. 38, No. 12, 2005
Reactive Dendronized Copolymers 5075
Figure 7. FT-IR spectra of before and after amidolysis of 7
[G-2].
Figure 6. FT-IR spectroscopy of the four-generation copoly-
mers before (7 [G-1, -2, -3, -4]) and after (8 [G-1, -2, -3, -4])
hydrolysis.
phenyl groups of the dendrons. The peak at 1159 cm-1
was assigned to the νC-O of anhydride or carboxylic acid.
The position of corresponding peaks of the copolymer
of different generation has no much difference. But with
increase of the dendron generation, the characteristic
peaks of anhydride at 1861 and 1779 cm-1 became
smaller relative to those of phenyl moieties. After
hydrolysis of anhydride, the characteristic peaks of
anhydride at 1861 and 1779 cm-1 disappeared and the
peaks at 1779 and 1713 cm-1 belonging to dicarboxylic
acid appeared, indicating that the anhydride moieties
have been switched to dicarboxylic acid successfully.
And the broad absorbance around 3000 cm-1 of car-
boxylic acid also supported this conclusion. SEC traces
of the hydrolyzed samples showed no distinct differences
with those of the unhydrolyzed samples.
Figure 8. 1H NMR spectrum of 7 [G-1] and 10 [G-1].
Scheme 6. Amidolysis of Succinic Anhydride Units of
7 [G-2, -3, -4] with [G-1]-NH2 and Formation of
Different Dendron Hybrid Structure
Amidolysis of Succinic Anhydrides in the Co-
polymer 7 [G-1, -2, -3, -4]. Primary amine may react
with anhydride in a quantitative conversion. The den-
dronized copolymers were reacted with two kinds of
aliphatic amine, 1-butylamine and 1-laurylamine,
(Scheme 5). The reactions proceeded completely as
demonstrated by FT-IR spectra (Figure 7). After the
reaction, the characteristic absorbances of anhydride at
1861 and 1779 cm-1 disappeared completely, and the
absorbance of amide at 1718 cm-1 was observed. Simi-
larly, with the increasing of generation of polyether
dendron, the absorbances at 1861, 1779, 1718, and
around 3000 cm-1 relating to anhydride or aliphatic
amide moieties became weaker compared to those of
phenyl moieties at 1595, 1498, and 1454 cm-1. In
another aspect the protons of aliphatic chains on the
polymer 10 [G-1, -2, -3, -4] could be found clearly in 1H
NMR spectra (as shown in Figure 8 for 10 [G-1], see
Figure S4 in Supporting Information for others). The
proton peak of aliphatic alkyl methylenes was at 1.22
ppm while the protons of the methyl at one end was
located at 0.86 ppm. This result further demonstrated
the introduction of alkyl groups. Above the amidolysis
of the anhydride moieties of dendronized copolymer 7
[G-1, -2, -3, -4] with linear aliphatic amine produced the
copolymers with a structure of dendron-alt-linear alkyl
chain.
When the reactive copolymer 7 [G-2, -3, -4] reacted
with an amino dendron of the generation different from
itself, a new kind of dendronized copolymers with their
side dendrons grafted in an alternative generation was
produced (Scheme 6). The amidolysis of the anhydride
moiety was confirmed from the FT-IR spectrum, in
which the absorbances of anhydrides disappeared (Fig-
ure 9). However, SEC analysis showed slightly differ-
ence before and after the reaction. Introduction of
dendritic wedges in these dendronized polymers would
increase the stiffness of the copolymer chain.
The composition of the copolymers of MAn and St may
be determined by elemental analysis. However, the
mass fractions of MAn units in the dendronized copoly-
mers and element content difference were too small to
give reliable composition results by elemental analysis,

5076 Zhang et al.
Macromolecules, Vol. 38, No. 12, 2005
Table 3. Molar Content of Maleic Anhydride in the Copolymer 9 [G-1, -2] and 10 [G-1, -2, -3, -4] Deduced from the
Nitrogen Content
9[G-1]
9[G-2]
10[G-1]
10[G-2]
10[G-3]
10[G-4]
N %a (calcd/found)
xb (calcd/found)
ratioc
2.30/2.30
0.28/0.28
0.99
1.36/1.35
0.17/0.17
1.03
1.95/2.03
0.39/0.42
1.12
1.22/1.25
0.24/0.25
1.01
0.70/0.88
0.14/0.18
1.33
0.38/0.56
0.08/0.11
1.49
a Nitrogen content of calculated and found values. b Weight content of succinic unit in copolymer: x(calcd) ) Msuccinic unit/(Msuccinic unit
+
M7[Gn]); x(found) ) N% (found in copolymer)/N% (succinic unit). c Ratio of succinic unit: 7 unit ) x × M7[Gn]/(1 - x) × Msuccinic unit
.
prepared as well; linear polymer chains will be grafted
from the macroinitiators by controlled radical polym-
erization to give polymers with interesting structure.
These works are ongoing, and the results will be
published elsewhere.
Acknowledgment. Financial support by the
BAIREN Project and the Directional Innovation Project
(KJCX2-SW-H07) of the CAS is greatly acknowledged.
Supporting Information Available: Synthesis of 5,
1
[G-1]-NH2, and copolymer 7; Figures S1-S4 of the H NMR
and 13C NMR spectra of monomer 6 of four generations and
1H NMR spectra of copolymers 7 and 10 of four generations.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Figure 9. FT-IR spectroscopy of amidolysis products of 7 [G-2,
-3, -4] with [G-1]-NH2.
especially for those copolymers from high-generation
monomers. After coupling with the alkylamine, estima-
tion of the composition of two components through
elemental analysis became possible since the mass
fraction of succinic monoamide increased and elemental
content difference of two components became larger.
Therefore, elemental analyses were made for the ami-
dolysis products 9 [G-1, -2] and 10 [G-1, -2, -3, -4]. Table
3 lists calculated and found data of nitrogen content,
weight content of succinic unit, and ratio of two units
in the copolymer 9 [G-1, -2] and 10 [G-1, -2, -3, -4] based
on the nitrogen content. We may notice that the found
values agreed with the expected ones, and the molar
ratios of succinic unit to dendron unit were around 1:1.
The ratio for the higher-generation dendron showed a
higher difference, owing to the nitrogen contents were
too small and analysis error became large.
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MA047449N