Amphiphilic dendronized homopolymers

Article abstract of DOI:10.1007/s11426-010-4136-3

A series of second generation of amphiphilic dendronized homopolymers are efficiently synthesized, and their thermoresponsiveness in aqueous solutions and secondary structures in methanol solutions are described. These polymers are constructed in each rep

Full text of DOI:10.1007/s11426-010-4136-3

SCIENCE CHINA
Chemistry
December 2010 Vol.53 No.12: 2509–2519
doi: 10.1007/s11426-010-4136-3
• ARTICLES •
· SPECIAL TOPIC · Highly Branched Polymers – Promising Architectural Macromolecules
Amphiphilic dendronized homopolymers
LI Wen1 & ZHANG AFang1,2*
1Institute of Polymers, Department of Materials, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland
2Department of Polymer Materials, College of Materials Science and Engineering, Shanghai University, Shanghai 201800, China
Received August 11, 2010; accepted September 2, 2010
A series of second generation of amphiphilic dendronized homopolymers are efficiently synthesized, and their thermorespon-
siveness in aqueous solutions and secondary structures in methanol solutions are described. These polymers are constructed in
each repeat unit with various generations of hydrophobic 4-aminoproline and hydrophilic oligoethylene glycol (OEG)-based
dendrons, and their over-all hydrophilicity is tuned by varying these dendron generations. Polymers with or without the first
generation of proline dendron show good water solubility at room temperature, but exhibit typical thermoresponsive behaviors
at elevated temperatures as characterized by turbidity measurements using UV-vis spectroscopy, while the polymer with the
secondary generation of proline dendron is not soluble in water. All polymers show ordered secondary structures as evidenced
by the optical rotation and circular dichroism experiments. Finally, assembly of these amphiphilic homopolymers into porous
films via breath figure (BF) technique is described, and polymer structures are found to show significant influence on the
morphology of porous film.
amphiphilic polymer, dendronized polymer, dendritic macromolecule, supramolecular structure
zation, reversible addition-fragmentation chain transfer
1 Introduction
(RAFT) polymerization or atom transfer radical polymeri-
zation (ATRP), and therefore, strict experimental conditions
are required. Differently, syntheses of homopolymers are
much robust and conventional free radical polymerization
could be applied, but little attention has been drawn for the
synthesis of homopolymers with amphiphilic characteristics.
Different from the conventional amphiphilic copolymers
consisting of covalently linked blocks or segments (large
scale) with either hydrophilic or hydrophobic philicity [10],
amphiphilic homopolymers are a novel class of homopoly-
mers constituted in each repeat unit (on monomer level)
with both hydrophilic and hydrophobic moieties. These
moieties are located oppositely along the polymer main
chain at small scale, possibly rendering novel assembles.
Up to now only a few amphiphilic linear homopolymers
constructed by small molecular repeat units were reported.
Tang and coworkers [11] reported a series of homopolymers
constructed by hydrophilic amino acid pendants and the
hydrophobic conjugated polyacetylene main chain. These
Many natural biological molecules such as phospholipids,
cholesterol and bile salt possess amphiphilic properties,
which direct their specific functions in living systems. To
imitate them, various kinds of amphiphilic polymers com-
posed of both hydrophilic and hydrophobic units, with ar-
chitectures from random-, block- to alternating copolymers,
were designed and synthesized. They have been explored
for many applications in material science and biomedicine
areas [1–4]. Among them, amphiphilic block copolymers
with either linear [5–7] or nonlinear (comb or star-shaped
and dendritic) [8, 9] architectures have been intensively
studied due to their abilities to self-assemble into versatile
superstructures in solution, in bulk or on interface. These
polymers were conventionally synthesized via living (con-
trolled) polymerization techniques, such as ionic polymeri-
*Corresponding author (email: azhang@shu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2010
chem.scichina.com
www.springerlink.com

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LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
polymers could self-assemble to form well-defined mor-
phologies under different conditions, including rings, glob-
ules, cages as well as nanofibers. Homopolymers based on a
polystyrene backbone and hydrophilic carboxylic acid and
hydrophobic alkyl chain or benzyl as pendent groups were
reported by Thayumanavan’s group [12]. These polymers
were demonstrated to be able to form both micelle and in-
verse micelle-like assemblies in different solvents.
and hydrophobic 4-aminoproline-based dendrons [34]
into one macromonomer cored by a lysinol unit (Figure 1).
The structure design is based on the following considera-
tions: (1) The hydrophilicity of the polymers could be eas-
ily tuned via changing the dendron generation; (2) the in-
troduction of the lysinol unit not only connects these two
different dendrons together, but also provides a space for
their segregation; (3) the existing of the chiral centers
close to the main chain may induce helical conformation
of the polymer; (4) OEG dendron may afford the polymer
thermoresponsiveness and also bio-compatibility. The
synthesis of these polymers, their secondary structures and
thermoresponsive behaviors will be described, furthermore,
their self-assembly into porous films via BF technique will
be illustrated in some detail.
Dendronization of a linear polymer reduces the attainable
backbone conformations and renders a random coil polymer
into a cylindrically shaped molecular object, and thus, leads
to the formation of a novel class of nano-sized polymer,
named dendronized polymer [13, 14]. This kind of polymer
can be prepared via either macromonomer [15] or attach-to
route [16]. Up to now, various structures of dendronized
polymers have been reported, including homo- [17], block
[18–20] or alternating (co-)polymers [21], some even
showing ordered morphology in bulk [22], unique ther-
moresponsiveness [23, 24] or highly stable helical confor-
mation [25] in solutions. Regarding amphiphilic ho-
mopolymers with large dendron repeat units, Bo et al. [26,
27] first reported the synthesis of several representatives
with conjugated backbone via Suzuki polycondensation of
dendritic macromonomers. These polymers contain both
hydrophobic and hydrophilic dendrons around the backbone
which provides the chance to form lengthwise segregation.
This property is quite different from that of amphiphilic
block copolymers whose self-assembly normally follows
perpendicular segregation along their molecular chain. It
was found these conjugated polymers could either form
monolayer LB films at air-water interface or form nanosized
wires or nanorices via self-assembly in solution. But the
main drawback of these polymers is their low molar masses
due to the difficulty in Suzuki polycondensation. Besides,
there are no functional groups available for further modifi-
cation.
Porous polymer films are interesting due to their poten-
tial applications in various areas [28], and formation of
these porous polymer films via “breath figure” (BF) has
attracted much attention in recent decades due to its ease,
high efficiency and low cost [29, 30], and the regularity and
size of the pores can be easily tuned by several parameters,
including air flow rate and humidity, the concentration and
molar mass of the polymer [31–33]. It was found polymers
with different architectures could form ordered honey-comb
porous films by this method, including star-shaped, hyper-
branched and comb-like polymers as well as linear and
dendritic-linear amphiphilic block copolymers. But to use
amphiphilic homopolymers for this process has not yet been
addressed.
Figure 1 Chemical structures of the amphiphilic dendronized polyme-
thacrylates PG2(0), PG2(1) and PG2(2) designed in this work. The
chemical structures of dendronized homopolymers PG1(MT), ProG1 and
ProG2 reported in previous work [23, 25] are included for comparison.
Nomenclature: G1 or G2 presents the first or secondary generation of
branching units, and the number within the brackets represents the hydro-
phobic proline dendron generation.
Based on the successful synthesis of water-soluble and
insoluble dendrons in our group, here we present the struc-
ture design and synthesis methods for a series of novel am-
phiphilic homopolymers based on the dendronized polymer
concept by introduction of hydrophilic OEG-based [23]

LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
2511
2.2 Synthesis
2 Experimental
General procedure for saponification of methyl ester by
LiOH·H2O (A)
2.1 General experimental
LiOH·H2O was added into a solution of methyl ester in
methanol and water at −5 °C with stirring, and then the re-
action temperature was allowed to rise to room temperature.
After stirred for 6 h, the solvents were evaporated in vacuo
at room temperature, and the residue was dissolved with
DCM. The pH value of the solution was adjusted carefully
to around 5–6 with 10% KHSO4 aqueous solution. The or-
ganic phase was washed with brine. All aqueous phase was
extracted with DCM three times. The combined organic
phase was dried over MgSO4. After filtration, the solvent
was evaporated in vacuo. Purification by column chroma-
Materials
Compounds 1a, 4 and 6a were synthesized according to the
previous reports [23, 34]. Tetrahydrofuran (THF) was re-
fluxed over lithium aluminum hydride (LAH) and dichloro-
methane (DCM) was distilled from CaH2 for drying. Azo-
bis(isobutyronitrile) (AIBN) was recrystallized twice from
methanol. Other reagents and solvents were purchased at
reagent grade and used without further purification. All reac-
tions were run under a nitrogen atmosphere. Macherey-Nagel
pre-coated TLC plates (silica gel 60 G/UV254, 0.25 mm)
were used for thin-layer chromatography (TLC) analysis.
Silica gel 60 M (Macherey-Nagel, 0.04–0.063 mm, 230–400
mesh) was used as the stationary phase for column chroma-
tography.
:
:
tography with DCM/MeOH (15 1 then 10 1, v/v) afforded
the corresponding acid.
General procedure for Pfp active ester (B)
DCC was added into a solution of acid and pentafluorophe-
nol (Pfp-OH) in DCM at −15 °C, and the mixture was
stirred at room temperature over night. After the solid was
filtered off, purification by column chromatography with
Instrumentation and measurements
1H and 13C NMR spectra were recorded on Bruker AV
500, and chemical shifts are reported as δ values (ppm)
relative to internal Me4Si. High resolution MALDI-TOF-
MS and ESI-MS analyses were performed by the MS ser-
vice of the Laboratorium für Organische Chemie, ETH
Zürich, on IonSpec Ultra instruments. Gel Permeation
Chromatography (GPC) measurements were carried out
by using a PL-GPC 220 instrument with a 2 × PL-Gel
Mix-B LS column set (2 × 30 cm) equipped with refrac-
:
DCM/MeOH (30 1, v/v) afforded the corresponding active
ester.
General procedure for amide coupling (C)
The amine and DiPEA in dry DCM was added into a solu-
tion of active ester in dry DCM at −15 °C. After stirring
over night, the mixture was washed successively with
NaHCO3 and brine, and all aqueous phases were extracted
with DCM three times. The combined organic phases were
dried over MgSO4. After filtration, the solvent was evapo-
rated in vacuo. Purification with column chromatography
afforded the product.
o
tive index (RI), viscosity, and light scattering (LS; 15
o
and 90 ) detectors, and LiBr (1 g/L) in DMF as eluent at
45 oC. Universal calibration was performed with
poly(methyl methacrylate) standards in the range of mp
2680~3900000 (Polymer Laboratories Ltd., UK). UV-vis
turbidity measurements were carried out for the LCST
determination on a Varian Cary 100 Bio UV-vis spectro-
photometer equipped with a thermostatically regulated
bath. Solutions of the polymers in de-ionized water were
filtered with a 0.45 μm filter before adding into a cuvette
(path length 1 cm), which was placed in the spectropho-
tometer and heated or cooled at a rate of 0.2 °C/min. The
absorptions of the solution at λ 500 nm were recorded
every minute. Optical rotation measurements were carried
out on a Perkin-Elmer 241 polarimeter with a 1 dm cu-
vette. Circular dichroism (CD) measurements were per-
formed on a JASCO J-715 spectropolarimeter with a
thermo-controlled 1 mm quartz cell (5 accumulation, con-
tinues scanning mode, scanning speed 20 nm/min, data
pitch: 1 nm, response: 1 s, band width: 5.0 nm). Scanning
electron microscopy (SEM) images were obtained on a
Zeiss Leo 1530 field-emission SEM operated at 3 kV with
secondary electron detection.
General procedure for the synthesis of macromonomer (D)
MAC was dropped into a solution of the dendron alcohol,
triethyl amine (TEA), and 4-dimethylaminopyridine (DMAP)
in dry DCM at −5 °C. The mixture was stirred for another 4 h
at room temperature. MeOH was added to quench the reac-
tion. It was then washed successively with saturated
NaHCO3 and brine. All aqueous phases were extracted with
DCM three times, and the combined organic phase was
dried over MgSO4. After filtration, the solvent was evapo-
rated in vacuo at room temperature. Purification with col-
umn chromatography afforded the colorless oil, which was
kept at −4 °C before use.
General procedure for polymerization in DMF solution (E)
The required amounts of monomer and AIBN (0.5 wt % to
the monomer) were dissolved in DMF in a Schlenk tube.
The solution was thoroughly deoxygenated by several
freeze-pump-thaw cycles and then stirred at certain tem-

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LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
perature for the designed time. After cooling to room tem-
perature, the polymer was dissolved in DCM and purified
by silica gel column chromatography with DCM as eluent.
H-Lysinol(Boc) (2c)
Pd/C (1.30 g, 10% by weight) was added to a solution of 2b
(12.58 g, 34.30 mmol) in ethanol/ethyl acetate (200 mL,
1/1) in a hydrogenation flask. The mixture was hydrogen-
ated under 3 bar of H2 at rt over night. After filtration, the
solvent was evaporated. Further purification of the residue
3,4,5-tris(2-(2-(2-Methoxyethoxy)ethoxy)ethoxy)benzoic acid
(1b)
:
by column chromatography with DCM/MeOH (10 1, v/v)
According to general procedure A from LiOH·H2O (6.06 g,
144.53 mmol) and compound 1a (9.00 g, 14.45 mmol) in
MeOH (60 mL) and H2O (12 mL). 1b was yielded as color-
then MeOH afforded 2b as a white solid (13.00 g, 93 %). 1H
NMR (CDCl3): δ 1.30−1.46 (m, 15H, CH3+CH2), 2.47 (s,
3H, NH2+NH), 2.82 (s, 1H, CH), 3.10 (s, 2H, CH2), 3.29 (t,
1
less oil (8.00 g, 91%). H NMR (CD2Cl2): δ 3.34 (s, 9H,
1H, CH2 ), 3.56 (d, 1H, CH2 ), 4.65 (br, 1H, OH). 13C NMR
(CDCl3): δ 23.26, 28.57, 30.27, 33.76, 40.36, 52.9, 66.42,
79.29, 156.27. HR-MS (ESI): m/z calcd for C11H24N2O3
[M+H]+ 233.18; found 233.1857.
a
b
CH3), 3.50–3.71 (m, 24H, CH2), 3.78 (t, 2H, CH2), 3.86 (t,
4H, CH2), 4.19–4.24 (m, 6H, CH2), 7.35 (s, 2H, CH). 13C
NMR (CD2Cl2): δ 58.74, 68.90, 69.72, 70.49, 70.52, 70.58,
70.65, 70.71, 70.85, 72.02, 72.55, 109.18, 124.93, 142.78,
152.40, 169.88. HR-MS (MALDI): m/z calcd for
C28H48O14Na [M+Na]+ 631.30; found 631.2940.
6-(tert-Butoxycarbonylamino)-2-(3,4,5-tris(2-(2-(2-metho-
xyethoxy)ethoxy)ethoxy)benzamido)hexyl alcohol (3a)
According to general procedure C from 1c (4.20 g, 5.42
mmol) in DCM (10 mL), 2c (1.51 g, 6.50 mmol) and
DiPEA (3.50 g, 27.10 mmol) in DCM (40 mL). Purification
3,4,5-tris(2-(2-(2-Methoxyethoxy)ethoxy)ethoxy)benzoic pen-
tafluoro-phenol ester (1c)
According to general procedure B from DCC (3.86 g, 18.73
mmol), 1b (7.60 g, 12.49 mmol) and pentafluorophenol
(2.76 g, 14.98 mmol) in DCM (40 mL), purification by
column chromatography with DCM/MeOH (30:1, v/v)
afforded 1c as colorless oil (8.70 g, 90 %). 1H NMR (CD2Cl2):
δ 3.32, 3.34 (2s, 9H, CH3), 3.48–3.71 (m, 24H, CH2), 3.80 (t,
2H, CH2), 3.88 (t, 4H, CH2), 4.24 (t, 4H, CH2), 4.29 (t, 2H,
CH2), 7.47 (s, 2H, CH). 13C NMR (CD2Cl2): δ 58.70, 69.18,
69.67, 70.53, 70.55, 70.60, 70.67, 70.78, 70.92, 71.98,
72.03, 72.08, 72.09, 72.75, 110.01, 121.35, 137.12, 139.11,
140.61, 142.59, 144.35, 152.80, 162.30. HR-MS (MALDI):
m/z calcd for C34H47F5O14Na [M+Na]+ 797.29; found
797.2792.
:
with column chromatography using DCM/MeOH (15 1, v/v)
1
afforded 3a as a colorless oil (3.70 g, 83%). H NMR
(CD2Cl2): δ 1.39 (br, 11H, CH3+CH2), 1.49–1.67 (m, 4H,
a
CH2), 3.05–3.13 (m, 2H, CH2), 3.20 (br, 1H, CH2 ),
b
3.31–3.34 (m, 9H, CH3), 3.48–3.68 (m, 25H, CH2+CH2 ),
3.75–3.84 (m, 6H, CH2), 4.05 (br, 1H, CH), 4.16–4.21 (m,
6H, CH2), 4.78 (br, 1H, NH), 6.72 (d, 1H, NH), 7.12 (s, 2H,
CH). 13C NMR (CD2Cl2): δ 23.23, 28.25, 30.14, 30.67,
40.05, 52.33, 58.72, 58.74, 64.90, 69.21, 69.87, 70.42,
70.52, 70.60, 70.69, 70.74, 72.01, 72.05, 72.52, 78.83,
107.17, 130.03, 141.39, 152.60, 156.25, 167.35. HR-MS
(MALDI): m/z calcd for C39H70N2O16Na [M+Na]+ 845.47;
found 845.4603.
6-(tert-Butoxycarbonylamino)-2-(3,4,5-tris(2-(2-(2-metho-
xyethoxy)ethoxy)ethoxy)benzamido)hexyl methacrylate (3b)
Z-Lysinol(Boc) (2b)
LiBH4 (1.66 g, 76.00 mmol) was added to a solution of
commercially available 2a (15.00 g, 38.00 mmol) in dry
THF (150 mL) at −10 °C. The mixture was stirred for 2 h
followed by over night at room temperature. The reaction
was quenched by successive dropwise addition of ethyl
acetate and water. After evaporation of the solvents in
vacuo at room temperature, the residue was dissolved in
DCM and washed with brine. The organic phase was col-
lected and dried over MgSO4. Purification by column
According to general procedure D from 3a (0.72 g, 0.88
mmol), TEA (0.44 g, 4.37 mmol), DMAP (0.1 g), MAC
(0.27 g, 2.62 mmol) and DCM (30 mL). Purification with
:
column chromatography using DCM/MeOH (20 1, v/v) af-
forded 3b as colorless oil (0.65 g, 83%). 1H NMR (CD2Cl2):
δ 1.39–1.66 (m, 15H, CH3 + CH2), 1.93 (s, 3H, CH3), 3.08
(s, 2H, CH2), 3.32–3.34 (m, 9H, CH3), 3.49–3.69 (m, 24H,
CH2), 3.75–3.85 (m, 6H, CH2), 4.17–4.26 (m, 8H, CH2 +
a
b
CH + CH2 ), 4.36 (br, 1H, CH2 ), 4.69 (br, 1H, NH), 5.58 (s,
a
b
:
chromatography with DCM/MeOH (20 1, v/v) afforded 2b
1H, CH2 ), 6.10 (s, 1H, CH2 ), 6.34 (d, 1H, NH), 7.03 (s, 2H,
CH). 13C NMR (CD2Cl2): δ 18.22, 23.24, 28.24, 30.02,
31.40, 40.34, 49.24, 58.72, 66.28, 69.13, 69.79, 70.50,
70.61, 70.65, 70.69, 70.83, 72.03, 72.05, 72.53, 78.71,
106.74, 125.83, 130.06, 136.35, 141.31, 152.65, 155.97,
166.67, 167.56. HR-MS (MALDI): m/z calcd for
C43H74N2O17Na [M+Na]+ 913.5; found 913.4896. Elemental
analysis (%) calcd for C43H74N2O17 (891.05): C, 57.96; H,
8.37; N, 3.14. Found: C, 57.79; H, 8.17; N, 3.00.
1
as white powder (13.00 g, 93 %). H NMR (CD2Cl2): δ
1.34–1.57 (m, 15H, CH3 + CH2), 3.08–3.09 (m, 2H, CH2),
3.56–3.62 (m, 2H, CH2), 4.75 (br, 1H, CH), 5.08 (s, 2H,
CH2), 5.24 (br, 1H, NH), 7.32–7.36 (m, 5H, CH). 13C NMR
(CDCl3): δ 22.79, 28.27, 29.93, 30.05, 30.70, 39.89, 52.50,
64.96, 66.64, 78.98, 128.04, 128.11, 128.57, 137.04, 156.37.
HR-MS (ESI): m/z calcd for C19H30N2O5Na [M+Na]+
389.22; found 389.2048.

LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
2513
a
6-Amino-2-(3,4,5-tris(2-(2-(2-methoxyethoxy)ethoxy)etho-
xy)benzamido)hexyl alcohol hydrochloride (3c)
CH), 4.36 (br, 1H, CH), 5.58 (s, 1H, CH2 ), 6.10 (s, 1H,
b
CH2 ), 6.48 (br, 1H, NH), 6.55 (br, 1H, NH), 7.05 (s, 2H,
CH), 7.23 (br, 1H, NH). 13C NMR (CD2Cl2): δ 18.22, 23.09,
28.20, 28.30, 29.03, 31.11, 32.79, 39.20, 49.22, 50.25,
53.16, 55.39, 58.72, 59.66, 66.24, 69.08, 69.78, 70.49,
70.51, 70.60, 70.64, 70.68, 70.83, 72.02, 72.04, 72.53,
78.91, 80.63, 106.76, 125.84, 130.03, 136.34, 141.25,
152.61, 155.34, 155.91, 166.68, 167.55, 172.52. HR-MS
(MALDI): m/z calcd for C53H90N4O20Na [M + Na]+ 1125.61;
found 1125.609. Elemental analysis (%) calcd for
C53H90N4O20 (1103.31): C, 57.70; H, 8.22; N, 5.08. Found:
C, 56.79; H, 8.04; N, 4.99.
25% HCl (5.39 g, 36.94 mmol) was added to a solution of
3a (1.52 g, 1.85 mmol) in THF (15 mL) at 0 °C. The mix-
ture was stirred for another 10 h. After evaporation of the
solvent and HCl, the residue was dissolved in water and
washed with DCM. The aqueous phase was collected and 3c
was obtained as a high viscous colorless oil (1.28 g, 91%)
after evaporation of water. 1H NMR (D2O): δ 1.31–1.34 (m,
2H, CH2), 1.44–1.60 (m, 4H, CH2), 2.86 (t, 2H, CH2),
3.21–3.23 (m, 9H, CH3), 3.44–3.64 (m, 26H, CH2), 3.72 (br,
2H, CH2), 3.81 (br, 4H, CH2), 3.98–3.99 (m, 1H, CH), 4.15
(br, 6H, CH2), 7.03 (s, 2H, CH). 13C NMR (D2O): δ 22.44,
26.59, 29.77, 39.42, 51.89, 58.13, 58.15, 63.65, 68.56,
69.33, 69.56, 69.59, 69.66, 69.75, 69.79, 69.96, 70.33,
71.11, 72.21, 106.81, 129.95, 139.92, 151.99, 169.98.
HR-MS (ESI): m/z calcd for C34H62N2O14Na [M+Na]+
745.42; found 745.4054.
(2S,4S)-1-[(2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-butoxyca-
rbonylamino)pyrrolidine-2-carbonyl]-4-[(2S,4S)-1-(tert-bu-
toxycarbonyl)-4-(tert-butoxy-carbonyl-amino)pyrrolidine-
2-carbonylamino]-proline (6b)
According to general procedure A from LiOH⋅H2O (1.44 g,
34.32 mmol) and compound 6a (3.30 g, 4.29 mmol) in MeOH
(80 mL) and H2O (8 mL). 6b was yielded as a white foam
6-((2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-butoxycarbonyla-
mino)pyrrolidine-2-carbonylamino)-2-(3,4,5-tris(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy)benzamido)hexyl alcohol (5a)
1
(2.75 g, 85%). H NMR (CD2Cl2): δ 1.24–1.43 (m, 36H,
CH3), 1.85–2.43 (m, 6H, CH2), 3.40–3.73 (m, 5H, CH2 +
b
CH2a), 3.98–4.68 (m, 7H, CH + CH2 ). Only the signal from
According to general procedure C from 3c (0.68 g, 0.90
mmol) and DiPEA (1.16 g, 9.00 mmol) in DCM (3 mL),
and compound 4 (0.67 g, 1.34 mmol) in DCM (25 mL),
purification with column chromatography using DCM/
Boc can be detected in 13C NMR spectrum. HR-MS (ESI): m/z
calcd for C35H58N6O12Na [M+Na]+ 777.41; found 777.4004.
(2S,4S)-1-[(2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-butoxyca-
rbonylamino)pyrrolidine-2-carbonyl]-4-[(2S,4S)-1-(tert-bu-
toxycarbonyl)-4-(tert-butoxy-carbonyl-amino)pyrrolidine-
2-carbonylamino]-proline pentafluorophenol ester (6c)
:
MeOH (15 1, v/v) afforded 5a as a white solid (0.79 g,
1
85%). H NMR (CD2Cl2): δ 1.39 (br, 20H, CH3+CH2),
1.57–1.65 (m, 4H, CH2), 2.14 (br, 2H, CH2), 3.12 (br, 1H,
CH2 ), 3.25 (br, 2H, CH2 +CH2 ), 3.32 and 3.34 (2s, 9H,
CH3), 3.48–3.69 (m, 27H, CH2+CH2 ), 3.75–3.84 (m, 6H,
CH2), 4.06 (br, 1H, CH), 4.16–4.22 (m, 7H, CH2 + CH),
4.29 (br, 1H, CH), 6.52 (br, 1H, NH), 6.75 (br, 1H, NH),
7.13 (s, 2H, CH), 7.25 (br, 1H, NH). 13C NMR (D2O): δ
23.23, 28.20, 28.29, 29.11, 30.55, 39.12, 50.25, 55.38,
58.72, 59.68, 65.17, 69.21, 69.86, 70.40, 70.51, 70.59,
70.67, 70.73, 72.01, 72.03, 72.51, 78.97, 80.27, 80.71,
107.27, 141.38, 152.57, 155.35, 167.42, 170.46, 172.68.
HR-MS (MALDI): m/z calcd for C49H86N4O19Na [M+Na]+
1057.59; found 1057.576.
a
b
m
n
According to general procedure B from DCC (1.17 g, 5.68
mmol), 6b (1.95 g, 2.58 mmol) and pentafluorophenol (0.95
g, 5.17 mmol) in DCM (40 mL), purification by column
:
chromatography with DCM/MeOH (30 1, v/v) afforded 6c
1
as white foam (1.90 g, 80 %). H NMR (CD2Cl2): δ 1.08–
1.44 (m, 36H, CH3), 1.67–2.20 (m, 5H, CH2+CH2 ), 2.39–
2.47 (m, 1H, CH2 ), 3.29–3.61 (m, 5H, CH2+CH2 ), 4.18–
4.37 (m, 4H, CH+CH2 ), 4.44–4.84 (m, 3H, CH), 6.14–6.33
a
b
m
n
(m, 2H, NH), 7.82 (2br, 1H, NH). 13C NMR (CD2Cl2): δ
25.13, 25.77, 28.07, 28.22, 31.20, 32.44, 33.99, 34.14,
34.27, 35.10, 35.96, 36.37, 49.14, 49.33, 49.40, 50.32,
52.19, 52.34, 54.38, 54.94, 55.17, 56.61, 56.69, 57.57,
57.66, 59.53, 78.82, 79.12, 80.23, 81.01, 137.01, 139.01,
140.24, 142.27, 153.18, 154.41, 155.35, 156.24, 168.35,
172.69, 172.91, 173.03. HR-MS (ESI): m/z calcd for
C41H57F5N6O12Na [M+Na]+ 943.40; found 943.3859.
6-((2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-butoxycarbonyla-
mino)pyrrolidine-2-carbonylamino)-2-(3,4,5-tris(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy)benzamido)hexyl methacry-
late (5b)
According to general procedure D from 5a (0.88 g, 0.85
mmol), TEA (0.43 g, 4.25 mmol), DMAP (0.10 g), MAC
(0.36 g, 3.40 mmol) and DCM (30 mL), purification with
6-((2S,4S)-1-[(2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-buto-
:
xycarbonylamino) pyrrolidine-2-carbonyl]-4-[(2S,4S)-1-
(tert-butoxycarbonyl)-4-(tert-butoxy-carbonylamino)pyrro-
lidine-2-carbonylamino]-pyrolidine-2-carbonylamino)-2-
(3,4,5-tris(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzami-
do)hexyl alcohol (7a)
column chromatography using DCM/MeOH (20 1, v/v)
1
afforded 5b as a white solid (0.80 g, 85%). H NMR
(CD2Cl2): δ 1.42 (br, 20H, CH3+CH2), 1.57–1.65 (m, 4H,
CH2), 1.92 (s, 3H, CH3), 2.14 (br, 2H, CH2), 3.25 (br, 2H,
CH2), 3.32 and 3.34 (2s, 9H, CH3), 3.49–3.69 (m, 27H, CH2
n
+ CH2 ), 3.75–3.85 (m, 6H, CH2), 4.16–4.27 (m, 10H, CH2+
According to general procedure C, from 3c (0.73 g, 0.96

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LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
mmol) and DiPEA (1.12 g, 8.69 mmol) in DCM (3 mL),
compound 6c (0.80 g, 0.87 mmol) in DCM (25 mL). Purifi-
cation with column chromatography using DCM/MeOH
column chromatography with DCM as eluent. PG2(0) was
yielded (0.26 g, 65%) as a colorless solid. 1H NMR
(CD2Cl2): δ 0.92–1.88 (m, 20H, CH3+CH2), 2.92–3.67 (m,
41H, CH3+CH2), 4.03–4.15 (m, 9H, CH2+CH), 5.98 (br, 1H,
NH), 7.08 (br, 2H, CH), 7.84 (br, 1H, NH). Elemental
analysis (%) calcd for (C43H74N2O17)n (891.05)n: C, 57.96;
H, 8.37; N, 3.14. Found: C, 57.15; H, 8.44; N, 3.10.
:
:
(20 1 then 15 1, v/v) afforded 7a as a colorless foam (1.10
1
g, 87%). H NMR (CD2Cl2): δ 1.27–1.49 (m, 38H, CH3+
CH2), 1.59 and 1.73 (2br, 4H, CH2), 2.11–2.38 (m, 7H,
a
CH2+ OH), 3.03–3.07 (m, 1H, CH2 ), 3.32–3.34 (m, 10H,
b
m
CH3 + CH2 ), 3.44–3.84 (m, 37H, CH2 + CH2 ), 3.94–4.39
n
PG2(1)
(m, 12H, CH+CH2 ), 4.63 and 4.72 (2br, 2H, CH), 6.23–
According to general procedure E from 5b (0.50 g, 0.45
mmol), AIBN (2.50 mg), DMF (0.2 mL), polymerization for
16 h at 80 °C yielded PG2(1) as a colorless solid (0.30 g,
60%). 1H NMR (CD2Cl2): δ 0.81–2.25 (m, 31H, CH3+CH2),
3.02–4.03 (m, 54H, CH3+CH2+CH), 6.56 (br, 1H, NH),
7.08 (br, 2H, CH), 7.52 (br, 1H, NH). 7.85 (br, 1H, NH).
Elemental analysis (%) calcd for (C53H90N4O20)n (1103.31)n:
C, 57.70; H, 8.22; N, 5.08. Found: C, 56.66; H, 8.26; N,
5.00.
6.31 (m, 2H, NH), 7.01–7.47 (m, 4H, CH+NH), 8.51–8.60
(2br, 1H, NH). 13C NMR (CD2Cl2): δ 17.14, 18.38, 23.23,
28.21, 28.30, 28.92, 35.28, 35.53, 37.41, 42.06, 49.07,
49.19, 50.07, 50.29, 52.17, 53.16, 56.69, 58.72, 58.74,
59.99, 60.29, 69.13, 69.83, 70.42, 70.49, 70.59, 70.64,
70.73, 72.00, 72.49, 79.00, 80.12, 107.15, 129.96, 141.15,
152.50, 153.11, 154.28, 155.19, 155.38, 166.99, 172.14.
HR-MS (MALDI): m/z calcd for C69H118N8O25Na [M+Na]+
1481.82; found 1481.8070.
6-((2S,4S)-1-[(2S,4S)-1-(tert-Butoxycarbonyl)-4-(tert-buto-
PG2(2)
xycarbonylamino) pyrrolidine-2-carbonyl]-4-[(2S,4S)-1-
(tert-butoxycarbonyl)-4-(tert-butoxy-carbonylamino)pyrro-
lidine-2-carbonylamino]-pyrolidine-2-carbonylamino)-2-
(3,4,5-tris(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzami-
do)hexyl methacrylate (7b)
According to general procedure E from 7b (0.50 g, 0.33
mmol), AIBN (2.50 mg), DMF (0.2 mL), polymerization
for 18 h at 60 °C yielded PG2(2) as a white solid (0.20 g,
40%). 1H NMR (CD2Cl2): δ 0.85–2.34 (m, 53H, CH3+CH2),
3.03–4.31 (m, 62H, CH3+CH2+CH), 6.51 (br, 2H, NH),
7.09 (br, 2H, CH), 8.06 (br, 3H, NH). Elemental analysis (%)
calcd for (C73H122N8O26)n (1527.80)n: C, 57.39; H, 8.05; N,
7.33. Found: C, 56.48; H, 8.19; N, 7.14.
According to general procedure D from 7a (1.00 g, 0.68
mmol), TEA (0.35 g, 3.42 mmol), DMAP (0.10 g), MAC
(0.29 g, 2.74 mmol) and DCM (30 mL), purification with
:
column chromatography using DCM/MeOH (15 1, v/v)
1
afforded 7b as a colorless foam (0.94 g, 90%). H NMR
2.3 Preparation of polymer films
(CD2Cl2): δ 1.36–1.40 (m, 38H, CH3 + CH2), 1.58 and 1.73
a
b
The films were prepared in a chamber by casting 20 μL of a
chloroform solution of the polymer (10 mg/mL) onto
freshly cleaved mica via a microsyringe under a flow of
moist nitrogen (70% RH at room temperature). The moist
nitrogen was generated by flowing nitrogen through a
two-necked flask filled with water. The films were obtained
after evaporation of all the solvents and water (within a few
minutes).
(2br, 5H, CH2 + CH2 ), 2.02 (d, 1H, CH2 ), 2.14 (s, 3H,
CH3), 2.30 and 2.40 (2br, 4H, CH2), 3.32–3.33 (m, 11H,
m
CH3 + CH2), 3.42–3.85 (m, 35H, CH2 + CH2 ), 4.15–4.38
n
p
(m, 14H, CH + CH2 ), 4.70 (br, 2H, CH), 5.58 (s, 1H, CH2 ),
q
6.10 (s, 1H, CH2 ), 6.24–6.38 (m, 2H, NH), 6.52–6.71 (m,
1H, NH), 7.05 and 7.06 (2s, 2H, CH), 7.14–7.36 (m, 1H,
NH), 8.41–8.68 (m, 1H, NH). 13C NMR (CD2Cl2): δ 18.22,
23.00, 23.35, 28.30, 28.84, 31.09, 35.54, 37.30, 39.36,
39.64, 49.07, 49.23, 49.39, 50.03, 50.28, 53.16, 56.63,
58.72, 60.28, 66.30, 69.09, 69.80, 70.47, 70.51, 70.59,
70.62, 70.66, 70.82, 72.02, 72.03, 72.53, 79.01, 80.07,
86.94, 106.83, 125.97, 129.83, 136.31, 141.31, 152.60,
153.13, 154.27, 154.81, 155.19, 166.68, 167.62, 172.06.
HR-MS (MALDI): m/z calcd for C73H122N8O26Na [M+Na]+
1549.85; found 1549.837. Elemental analysis (%) calcd for
C73H122 N8O26 (1527.80): C, 57.39; H, 8.05; N, 7.33. Found:
C, 56.55; H, 8.12; N, 7.23.
3 Results and discussion
3.1 Synthesis and characterization
Macromonomer route was selected to synthesize the den-
dronized polymers in order to ensure well-defined structures
and high molar mass, and the detail synthetic sequences to
the macromonomers are delineated in Scheme 1. First, the
methoxy terminated OEG dendron ester 1a was converted
to the acid 1b via hydrolysis with LiOH∙H2O. After reaction
with pentafluorophenol in the presence of DCC, 1b was
converted to the active ester 1c. The commercially available
benzyloxycarbonyl (Cbz) and tert-butyloxycarbonyl (Boc)
doubly-protected lysine ester 2a was selected as the connec-
PG2(0)
Monomer 3b (0.40 g, 0.45 mmol) and AIBN (2.00 mg)
were added into a Schlenk tube. The mixture was thor-
oughly deoxygenated by several freeze-pump-thaw cycles
o
and then stirred at 60 C for 17 h. After cooling to rt, the
polymer was dissolved in DCM and purified by silica gel

LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
2515
Scheme 1 Synthesis procedures. Reagents and conditions: (a) LiOH∙H2O, MeOH, H2O, −5–25 °C, 6 h (85%–91%); (b) DCC, pentafluorophenol, DCM, 12
h, −15–25 °C (80%–90%); (c) LiBH4, THF, −5–25 °C, over night (93%); (d) Pd/C, ethanol, ethyl acetate, 3 bar of H2, 25 °C, over night, (93%); (e) DiPEA,
DCM, over night, −15–25 °C (85%–87%); (f) MAC, DMAP, TEA, −5–25 °C, 4 h (83%–90%). DCC = N,N′-Dicyclohexylcarbodiimide, LiBH4 = lithium
boron hydride, DiPEA = diisopropylethylamine, MAC = methacryloyl chloride; DMAP = 4-dimethylaminopyridine; TEA = triethylamine.
tion unit. After reduction with LiBH4 and dehydrogenation,
the aminoalcohol lysinol 2c was obtained. The dendron ac-
tive ester 1c was then successfully attached to the aminoal-
cohol via amide coupling to afford compound 3a. It was
then either reacted with methacryloyl chloride (MAC) to get
the macromonomer 3b or deprotected with concentrated
HCl to achieve the ammonium 3c. Amide coupling of 3c
with G1 proline active ester 4 [34] afforded the amphiphilic
dendron alcohol 5a, which was then reacted with MAC to
furnish the macromonomer 5b. Similar with previous pro-
cedures, from G2 proline ester 6a [34], followed by hy-
drolysis and condensation reaction, G2 proline active ester
6c was synthesized. It was then attached to ammonium 3c
via amide coupling to afford the amphiphilic dendron alco-
hol 7a. After reaction with MAC, amphiphilic macro-
monomer 7b was successfully prepared. All the steps were
performed with high yield (≥ 80%) and easy purification. All
PG2(2) with slightly reduced molar masses. Detailed po-
lymerization conditions are summarized in Table 1 and
1
typical H NMR spectra of the polymers are shown in Fig-
ure 2. These polymers exhibit different solubility in water.
With the Boc-protected lysinol unit or the hydrophobic
proline G1 dendron incorporated into the OEG dendron,
PG2(0) and PG2(1) are still quite hydrophilic, and highly
water-soluble, but when more hydrophobic G2 proline den-
dron was incorporated, the corresponding polymer PG2(2)
is not soluble anymore in water.
3.2 Thermoresponsive behavior
PG2(0) and PG2(1) are soluble well in water at room tem-
Table 1 Conditions for the results from the polymerization of macro-
monomers
1
new compounds were characterized by H and 13C NMR
spectroscopy as well as high resolution mass spectrometry.
All of the macromonomers and polymers were also charac-
terized by elemental analysis to ensure their high purities.
Free radical polymerization of the liquid macromonomer
3b was carried out in bulk to afford PG2(0) with high molar
mass. For the solid macromonomers 5b and 7b, the polym-
erization were carried out in highly concentrated DMF solu-
tions, and furnished the respective polymers PG2(1) and
Polymerization conditions a)
monomer solvent time (h)
GPC results b)
Mn (×10−5) DPn PDI
Yield
(%)
Entries
1
2
3
3b
5b
7b
Bulk
DMF
DMF
18
17
14
65
60
40
4.6
2.6
1.4
516
236
92
2.3
2.9
2.5
a) Polymerizations were carried out at 60 °C (entries 1 and 3) and at
80 °C (entry 2) with AIBN as the initiator (0.5 wt% based on monomer).
b) All GPC measurements were done in DMF (1% LiBr) as eluent at 45 °C.

2516
LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
Figure 2 1H NMR spectroscopy of PG1(0), PG1(1) and PG1(2) in
DMSO at 80 °C. The signals from DMSO are marked as (*).
perature, but show thermoresponsiveness at elevated tem-
peratures. Their turbidity curves are shown in Figure 3. The
apparent lower critical solution temperatures (LCSTs) of
PG2(0) and PG2(1) were determined to be 46.7 and 37.7 °C,
respectively. Obviously, the LCSTs of the resulted polymers
are smaller when compare to the parent polymer, OEG-based
homopolymer PG1(MT) as shown in Figure 1 [23]. The dif-
ference here indicates that arrangement of the hydrophobic
G1 proline dendron side-by-side of the hydrophilic OEG
dendron in each repeat unit contribute significantly to the
over-all hydrophilicity. This is quite different from previous
result that the interior part of the dendronized polymers
shows negligible contribution to the LCST: by changing the
interior hydrophilic OEG units into hydrophobic alkyl units,
only minor change of the LCSTs from the polymers was ob-
served [23, 35]. Besides, the sharpness of the phase transition
of PG2(0) remains the same as PG1(MT) (Figure 3(a)),
while introduction of G1 proline dendron in the case of
PG2(1) leads to much broader phase transitions and obvi-
ously hysteresis between heating and cooling processes (Fig-
ure 3(b)). This should be due to the presence of strong hy-
drogen bonding from the proline unit, which is absence in the
OEG-based polymer system [36].
Figure 3 Plots of transmittance vs. temperature for 0.25 wt% aqueous
solutions of PG2(0) (a) and PG2(1) (b). Heating and cooling rate = 0.2
°C/min.
Table 2 Specific rotations of all monomers and polymers a)
[α]2D5 (°)
Sample
monomer
−14.4
−40.1
polymer
−3.2
−10.8
−19.3
G2(0)
G2(1)
G2(2)
−42.7
a) All measurements were done at 25 °C with a 1 dm cuvette in MeOH.
solutions at room temperature are shown in Figure 4. All
polymers show different CD spectra than their correspond-
ing macromonomers, which demonstrates that the polymers
adopt ordered secondary structures. Comparing the CD
spectra of different polymers, one can conclude that intro-
duction of the chiral proline dendron doesn’t enhance the
chirality of the corresponding polymers, which may be due
to the lose linkage between the proline dendrons and main
chain. Therefore, the ordered structure resulted from the
chiral center in the lysinol unit.
3.3 Secondary structure analysis
The secondary structures of these polymers were investigated
with optical rotation (OR) and circular dichroism (CD) spec-
troscopy, and the results are summarized in Table 2 and
Figure 4. The OR values of all polymers are smaller than
that of their corresponding monomers. Though the differ-
ences are not so pronounced due to the relatively high rigid-
ity of the dendronized polymers [25, 37], these results nev-
ertheless suggest polymers adopt different conformations
than monomers and possibly possess ordered secondary
structures. To further characterize their conformation, CD
spectroscopy was applied, and the spectra of methanolic
3.4 Fabrication of porous films with the “breath fig-
ure” technique
The basic principle of the BF method is based on condensa-
tion of water from the flowing moist air into droplets onto
the cold polymer organic solution (on a substrate), which
form a closely packed droplet array on the liquid surface.

LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
2517
After the evaporation of both organic solvent and water from
the droplets, an imprint of the water droplets with an ordered
3-D array in the dried polymer film is thus formed. The
self-assembly of these polymers into porous films with the
BF method on a mica surface was investigated. The typical
procedures and conditions for the preparation of the films in
the present work are as follows: in a small chamber with
70% humidity, about 20 µL of the polymer solution (10
mg/mL) in chloroform was dropped onto the mica surface
(1 × 1 cm). After evaporation of all the solvent and water
within a few minutes, the films with cavities were formed
and the morphologies were investigated by SEM (Figure 5).
The films formed from PG2(0) and PG2(1) are all transpar-
ent. No porous film formed from PG2(0) and only a flat film
was observed (Figure 5(a)). Some holes appeared from
PG2(1), but they are either irregular or with quite small size
(Figure 5(b)). This result may be due to the strong hydro-
philicity of these two polymers, which destabilize the water
droplets on the polymer surface and most of the water drop-
lets were dissolved into the polymers. For comparison, the
hydrophobic polymers ProG1 and ProG2 (Figure 1) were
also tested and turbid films were obtained. As shown in Fig-
ure 5(c) and (d), both polymers formed porous film, but the
pore sizes are widely distributed. Differently, films prepared
from PG2(2) under the same condition show regularly po-
rous morphologies with round shaped pores with size around
1 µm in diameter (Figure 5(e)), though some holes with
smaller size and in irregular shape also exist. Additional ex-
perimental conditions were applied to examine when small
amount of the hydrophobic ProG1 (10 wt%) was mixed
with PG2(2), a flat film with much more regularly arranged
holes with size about 1 µm was obtained (Figure 5(f)).
Figure 4 CD spectra of all monomers (a) and polymers (b) in MeOH at
25 °C.
Figure 5 SEM images of porous films on mica surface cast from different dendronized polymer solutions: (a) PG2(0); (b) PG2(1); (c) ProG1; (d) ProG2;
(e) PG2(2); (f) PG2(2)+10% ProG1.

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LI Wen, et al. Sci China Chem December (2010) Vol.53 No.12
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4 Conclusions
A series of amphiphilic homopolymers with high molar
masses based on the structure concept of dendronized
polymer were efficiently synthesized by free radical polym-
erization of their corresponding macromonomers carrying
both hydrophilic OEG and hydrophobic proline dendrons. By
changing the generation of hydrophobic proline dendron, the
over-all hydrophilicity of the polymers could be easily
tuned. The polymers with or without G1 proline dendron are
water-soluble and thermoresponsive, but the polymer car-
rying the G2 proline dendron is water insoluble. The ar-
rangement style of the hydrophobic and hydrophilic units
within these polymers shows significant influences on their
thermoresponsiveness: with hydrophobic units constructed
side-by-side to the hydrophilic units, the LCST decreases
greatly and the phase transitions become very broad, which
proves the hydrophobic dendron show contribution to the
chain collapse in this case. The secondary structures of
these polymers were characterized with OR and CD spec-
troscopy, and found that the ordered structures aroused from
the densely packing and chirality of the lysinol core unit.
These polymers were employed to fabricate porous films
with the BF technique, and only the most hydrophobic
PG2(2) could self-assemble into an ordered pattern under
proper conditions, especially when addition of external hy-
drophobic polymers. With less robust conditions needed,
the present results provide the first successful example to
form ordered porous films by using amphiphilic den-
dronized homopolymers. All these results proved the possi-
bility to fabricate micro-sized materials with this kind of
thick polymers. There are also other interesting properties
including their possible helical confirmation, thermorespon-
siveness, which would open new gate to their potential ap-
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We thank Prof. GAUCKLER L (ETH Zurich) for kindly providing access to
SEM measurements. COLUSSI M is thanked for his assists with GPC
measurements. LI W thanks Prof. SCHLÜT AD (ETH Zurich) for the as-
sists in her PhD thesis. This work was financially supported by ETH Re-
search Grant ETH-1608-1, the Swiss National Science Foundation
(200021- 113690) and the National Natural Science Foundation of China
(20374047 & 20574062).
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