Synthesis of starlike PtBA-g-PEO amphiphilic graft copolymer via highly efficient Cu-catalyzed SET-NRC reaction at ambient temperature

Article abstract of DOI:10.1002/pola.24392

Two new amphiphilic star graft copolymers bearing hydrophobic poly(tert-butyl acrylate) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains with different molecular weights were synthesized by sequential reversible addition fragmentation chain

Full text of DOI:10.1002/pola.24392

Synthesis of Starlike PtBA-g-PEO Amphiphilic Graft Copolymer via Highly
Efficient Cu-Catalyzed SET-NRC Reaction at Ambient Temperature
1
,2
1
1
1
2
1
1
YAOGONG LI, YAQIN ZHANG, SUJUAN ZHAI, YAN DENG, HUIMING XIONG, GUOLIN LU, XIAOYU HUANG
1
Key Laboratory of Organofluorine Chemistry and Laboratory of Polymer Materials, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, People’s Republic of China
2
Department of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Shanghai Jiao Tong
University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China
Received 6 September 2010; accepted 15 September 2010
DOI: 10.1002/pola.24392
Published online 3 November 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Two new amphiphilic star graft copolymers bearing
hydrophobic poly(tert-butyl acrylate) backbone and hydrophilic
poly(ethylene oxide) (PEO) side chains with different molecular
weights were synthesized by sequential reversible addition
fragmentation chain transfer (RAFT) polymerization and single
electron transfer-nitroxide radical coupling (SET-NRC) reaction
under mild conditions. RAFT homopolymerization of tert-butyl
temperature via grafting-onto strategy. The critical micelle con-
centration values of the obtained amphiphilic star graft copoly-
mers in aqueous media and brine were determined by
fluorescence probe technique using pyrene as probe. Diverse
micellar morphologies were formed by varying the content of
hydrophilic PEO segment as well as the initial concentration of
stock solution. In addition, poly(acrylic acid)-g-PEO double
2
-((2-bromopropanoyloxy)methyl)acrylate was mediated by a
hydrophilic star graft copolymers were obtained by selective
acidic hydrolysis of hydrophobic PtBA starlike backbone
without affecting PEO side chains. VC 2010 Wiley Periodicals,
four-armed chain transfer agent in a controlled way to afford a
well-defined starlike backbone with a narrow molecular weight
distribution (M
w
/M
n
¼ 1.26). The target poly(tert-butyl acrylate)-
Inc. J Polym Sci Part A: Polym Chem 49: 23–34, 2011
g-PEO (PtBA-g-PEO) star graft copolymers were synthesized by
SET-NRC reaction between Br-containing PtBA-based starlike
backbone and PEO end functionalized with 2,2,6,6-tetramethyl-
KEYWORDS: amphiphilic; graft copolymers; reversible addition
fragmentation chain transfer (RAFT); single electron transfer
(SET); synthesis
0
0
00
piperidine-1-oxyl (TEMPO) group using copper/N,N,N ,N ,N -
pentamethyldiethylenetriamine as catalytic system at ambient
INTRODUCTION Generally, highly complex biological systems
are constructed via a few, but very efficient, organic reac-
tions among the countable building units showing the high
of their photosensitivity, thermal instability, and shock sensi-
1
3
tivity. Thus, establishing a new and highly efficient cou-
pling reaction for the macromolecular design is a challenging
task for the researchers majoring in polymer synthetic
chemistry.
1
simplicity and efficiency of chemistry that exists in nature.
Enlightened by this fact, Sharpless and coworkers proposed
2
‘
‘click’’ chemistry in 2001, among which Cu-catalyzed azide/
As early as 1998, on the basis of atom transfer radical addi-
alkyne cycloaddition (CuAAC) reaction has been regarded as
the most excellent one because of its quick speed, high regio-
selectivity, quantitative yield (often above 95%), high toler-
1
4
tion reaction, Matyjaszewski et al. had realized the simple
and efficient synthesis of various alkoxyamines for stable
free radical polymerization and they used excess copper
1
,3,4
ance of functional groups, and insensitivity to solvents.
0
II
(
Cu ) and catalytic amounts of copper salts (Cu ) to yield
CuAAC reaction was first used only in traditional organic
synthesis, and then polymer chemists began to apply CuAAC
reaction in the synthesis of polymeric materials from
I
the reactive species (Cu complexes) in situ for reacting with
organic halides. This reaction is very selective and easy to
workup with a relatively high yield (up to 95%). In 2008,
5
,6
2
004, which served as the prelude of the application of
1
3,15–20
Huang and coworkers
successfully introduced this
click chemistry in polymer and materials chemistry. Recently,
click chemistry, especially CuAAC reaction, has been widely
applied in the preparation of complex polymer architectures
and the construction of biological and functional nanomateri-
reaction into polymer synthesis and developed a new cou-
pling reaction called atom transfer nitroxide radical coupling
(ATNRC) chemistry based on nitroxide stable free radical
1
,4,7–12
21
als.
However, azide compounds used in CuAAC reac-
chemistry
and atom transfer radical polymerization
2
2
tion are inconvenient to be operated and reserved because
(ATRP), which implemented the highly efficient conjunction
Correspondence to: H. Xiong (E-mail: hmxiong@sjtu.edu.cn) or X. Huang (E-mail: xyhuang@mail.sioc.ac.cn)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 23–34 (2011) V
2010 Wiley Periodicals, Inc.
C
SYNTHESIS OF STARLIKE PtBA-g-PEO COPOLYMER, LI ET AL.
23

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of PtBA-g-PEO and PAA-g-PEO star graft copolymers.
of a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing
polymer with another Br-end-functionalized polymer in the
poly(ethylene oxide) (PEO) side chains, that is, star poly
(tert-butyl acrylate)-g-PEO (s-PtBA-g-PEO). A well-defined
starlike PtBA-based backbone was first prepared via reversi-
ble addition fragmentation chain transfer (RAFT) homopoly-
merization of tert-butyl 2-((2-bromopropanoyloxy)methyl)a-
crylate (tBBPMA) mediated by a tetrafunctional star chain
transfer agent (s-CTA). TEMPO-end-functionalized PEO (PEO-
TEMPO) was then grafted onto the starlike backbone by
SET-NRC technique at ambient temperature to provide the
desired amphiphilic star graft copolymers. Furthermore,
hydrophobic PtBA backbone was selectively hydrolyzed to
hydrophilic PAA backbone in acidic environment to form
starlike poly(acrylic acid)-g-PEO (s-PAA-g-PEO) double
hydrophilic graft copolymers (Scheme 1).
0
0
00
presence of CuBr/N,N,N ,N ,N -pentamethyldiethylenetri-
amine (PMDETA). The terminal Br of the polymer, serving as
the oxidant, reacts with CuBr, serving as the reductant, to
afford macromolecular carbon radicals, which are immedi-
ately captured by TEMPO radical of another polymer to form
a stable ACAOA linkage between these two polymers.
ꢀ
ATNRC process is irreversible below 110 C, and its coupling
1
5,16
efficiency is reported to be as high as 90%,
which is
similar to that of CuAAC reaction. As a relatively convenient
and safe way with a ‘‘click-like’’ efficiency, ATNRC has already
been successfully used in the syntheses of well-defined
1
3,15–20,23
block, graft, and star copolymers.
However, ATNRC reaction needs to be performed under a
relatively high temperature (ꢁ90 ꢀC), which could cause
side reactions such as crosslinking and chain transfer.
Inspired by the mechanism of single-electron-transfer (SET)
EXPERIMENTAL
Materials
tert-Butyl acrylate (tBA, 98%; Aldrich) was washed with 5%
aqueous NaOH solution to remove the inhibitor, and then
washed with water, dried over CaCl and distilled twice from
2
4–36
process in which Percec et al.
postulated that copper
0
2
(
Cu ) was the activating species, ATNRC approach was opti-
CaH2 under reduced pressure before use. Tetrahydrofuran
0
mized by using copper (Cu ) instead of CuBr at ambient
(
THF, 99%; Aldrich) and toluene (99.8%; Aldrich) were dried
temperature (ꢁ25 ꢀC) in 2009,
23,37
which was named as
over CaH2 and distilled from sodium and benzophenone
SET-nitroxide radical coupling (SET-NRC). Moreover, Mon-
under N before use. Dichloromethane (99.5%; Aldrich) and
3
8
2
teiro and coworkers also modified ATNRC process using
chloroform (99%; Aldrich) were distilled from CaH2 under
N2 before use. Triethylamine (TEA, 99.5%; Aldrich) was
dried over KOH and distilled from CaH under N before use.
CuBr/Me TREN (tris(2-aminoethyl)amine) as catalytic system
6
and toluene/dimethylsulphoxide (DMSO) as solvent, and
three-armed polystyrene stars were successfully synthesized
at room temperature with an extremely high speed.
2
2
0
2
,2 -Azobis(isobutyronitrile) (AIBN, 98%; Aldrich) was
recrystallized from anhydrous ethanol. Pyrene (98%;
Aldrich) was purified by recrystallization in ethanol for three
times. Pentaerythritol tetrakis(2-bromopropionate) (4BrPr)
In this work, SET-NRC reaction was run at room temperature
to yield the first amphiphilic star graft copolymer containing
24
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
SCHEME 2 Preparation of tetrafunctional star chain transfer agent 2.
3
9
was prepared according to previous literature. 2-Bromo-
propionic acid (99%; Aldrich), copper powder (99%;
Aldrich), magnesium (98%; Aldrich), bromobenzene (99%;
Aldrich), iodine (99.8%; Aldrich), formalin (38 wt %;
Aldrich), 4-(dimethylamino)pyridine (DMAP, 99%; Aldrich),
thionyl chloride (99%; Aldrich), succinic anhydride (99%;
Aldrich), PEO monomethyl ether (PEO-OH, Mn ¼ 750;
was used as solvent with a flow rate of 1.0 mL/min; detectors:
Wyatt Optilab rEX refractive index detector and Wyatt DAWN
HELEOS 18-angle light scattering detector with a 50-mW
solid-state laser operating at 658 nm. Steady-state fluorescent
spectra of pyrene were recorded on a HITACHI F-4500 spec-
trofluorometer with the band widths of 10 nm for excitation
and 2.5 nm for emission, and the excitation wavelength (kex)
was 339 nm.
Aldrich),
(
4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl
HTEMPO, 97%; Aldrich), PMDETA (99%; Aldrich), N,N -dicy-
0
clohexylcarbodiimide (99%; Aldrich), trifluoroacetic acid
TFA, 99%; Aldrich), 1,4-diazabicyclo[2.2.2]octane (98%;
Preparation of tBBPMA
Br-containing acrylate monomer 1 was prepared using com-
mercial tBA, formalin, and 2-bromopropionic acid as starting
(
Aldrich), and carbon disulfide (CS , 99.9%; Aldrich) were
2
4
0,41
used as received.
materials according to our previous work.
tBA was first
treated with formalin to give the key intermediate of tert-
butyl(2-hydroxymethyl)acrylate (77.0% yield) via base-cata-
lyzed Baylis-Hillman reaction followed by the esterification
reaction with 2-bromopropionic acid to afford tBBPMA 1 ac-
rylate monomer (94.4% yield).
Measurements
Fourier transform infrared (FTIR) spectra were recorded on a
Nicolet AVATAR-360 FTIR spectrophotometer with a resolution
ꢂ1
1
13
of 4 cm . All H NMR (500 MHz) and C NMR (125 MHz)
þ
analyses were performed on a Bruker Avance 500 spectrome-
ESI-MS (m/z): found (M-56) : 237. HRMS (m/z): 236.9765
1
þ
ter in CDCl , except that H NMR spectrum of PEO-TEMPO
(M -C H , C H O Br requires m/z 236.9762). ELEM. ANAL.:
3
4
9
7 10 4
was measured in CD OD in the presence of stoichiometric
Anal. Calcd. for C H O Br: C, 45.07%; H, 5.85%. Found: C,
11 17 4
3
5
1
1
ꢂ1
HCOONH and Pd/C. Tetramethylsilane (TMS) ( H NMR) and
45.37%; H, 5.58%. FTIR: t (cm ): 2979, 2934, 1748, 1720,
4
3
1
1
CDCl ( C NMR) were used as internal standards. Elemental
1643, 1448, 1394, 1369, 1146, 1063, 848, 816, 761, 515. H
3
analysis was carried out on an Elementar Vario EL III system.
Electrospray ionization mass spectrometry (ESI-MS) and high
resolution mass spectrometer (HRMS) were measured by an
Agilent LC/MSD SL system and a Waters Micromass GCT,
respectively. MALDI-TOF-MS was measured by an Applied Bio-
systems Voyager DE-STR spectrometer using a-cyano-4-hydrox-
ylcinnamic acid as matrix. Relative molecular weights and mo-
lecular weight distributions were measured by conventional
gel permeation chromatography (GPC) system equipped with a
Waters 1515 Isocratic HPLC pump, a Waters 2414 refractive
index detector, and a set of Waters Styragel columns [HR3
NMR: d (ppm): 1.38 (9H, C(CH ) ), 1.71 (3H, CH CH), 4.31
3
3
3
(1H, CH CH), 4.72 (2H, CO CH ), 5.71 and 6.17 (1H, CH ¼¼ C).
3
2
2
2
1
3
C NMR: d (ppm): 21.5 (CH CH), 27.9 (C(CH ) ), 39.6
3
3 3
(CH CH), 63.6 (CO CH ), 81.3 (C(CH ) ), 126.5 (CH ¼¼ C),
3
2
2
3 3
2
136.1 (CH ¼¼ C), 163.9 (CO C(CH ) ), 169.4 (CO CH ).
2
2
3 3
2
2
Preparation of Tetrafunctional s-CTA
Tetrafunctional s-CTA 2 was prepared in three steps via bro-
mobenzene and CS as shown in Scheme 2. Magnesium
2
(0.3260 g, 13.42 mmol), a grain of iodine, and dry THF (10
mL) were added to a 100-mL three-necked flask (flame dried
under vacuum before use) sealed with a rubber septum
(500–30,000), HR4 (5000–600,000), and HR5 (50,000–
4
,000,000), 7.8 ꢃ 300 mm, particle size: 5 lm]. GPC measure-
under N followed by adding bromobenzene (1.4 mL, 13.37
2
ꢀ
ments were carried out at 35 C using THF or N,N-dimethyl-
formamide (DMF) as eluent with a flow rate of 1.0 mL/min.
The system was calibrated with linear polystyrene standards.
Absolute molecular weights were determined by GPC equipped
with a multiangle light scattering detector (GPC/MALS). THF
mmol) in dry THF (15 mL) dropwise in 1 h. The mixture
ꢀ
was stirred at 40 C for another 30 min and then CS
2
(0.8
mL, 13.37 mmol) in dry THF (15 mL) was added dropwise.
Finally, 4BrPr (2.0280 g, 3.000 mmol) in dry THF (15 mL)
was added dropwise followed by immersing the flask into an
SYNTHESIS OF STARLIKE PtBA-g-PEO COPOLYMER, LI ET AL.
25

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢀ
oil bath preset at 80 C. The reaction was terminated by
ing over MgSO overnight. The filtrate was concentrated and
4
adding deionized water (40 mL) after 24 h. THF was
removed by rotary evaporation, and the remainder was
extracted by diethyl ether for three times. All organic layers
were collected and dried over MgSO4 overnight. About
dried in vacuo overnight to give 16.2522 g of white solid,
carboxyl-functionalized PEO (PEO-COOH, 95.6% yield).
ꢂ1
FTIR: m (cm ): 3508, 2871, 1961, 1737, 1643, 1455, 1350,
1
1
298, 1251, 1109, 949, 852. H NMR: d (ppm): 2.64 (4H,
2.2090 g (76.0%) of s-CTA 2 (red viscous liquid) was
CH CH CO H), 3.38 (3H, OCH ), 3.58 (2H, CO CH CH ), 3.65
2
2
2
3
2
2
2
obtained by silica column chromatography [eluent: diethyl
13
(
4H, OCH CH ), 4.25 (2H, CO CH CH ). C NMR: d (ppm):
2 2 2 2 2
ether:hexane (v:v) ¼ 2:5].
2
8.9 (CH CH CO H), 58.8 (OCH ), 63.6 (CO CH CH ), 70.4
2 2 2 3 2 2 2
ꢂ1
FTIR: t (cm ): 3056, 2978, 2932, 1741, 1590, 1445, 1377,
(OCH CH2 and CO CH CH ), 172.1 (CO CH CH ), 173.7
2
2
2
2
2
2
2
1
1
1
312, 1237, 1154, 1044, 877, 762, 686. H NMR: d (ppm):
.64 (12H, CS CHCH ), 4.12 (8H, CO CH ), 4.73 (4H,
(CH
2 2 2
CH CO H).
2
3
2
2
PEO-COOH (10.00 g, 11.76 mmol) and thionyl chloride (68.3
mL, 940.8 mmol) were added to a 100-mL flask, and then
the mixture was stirred at room temperature for 3 h.
CS CHCH ), 7.37 (8H, o-H of phenyl), 7.53 (4H, p-H of phe-
2
3
1
3
nyl), 7.97 (8H, m-H of phenyl). C NMR: d (ppm): 16.2
(
CS CHCH ), 42.4 (CO CH C), 48.1 (CS CHCH ), 62.7
2 3 2 2 2 3
Unreacted thionyl chloride was removed under vacuum at
(
CO CH ), 127.0 (m-C of phenyl), 128.4 (o-C of phenyl),
2 2
ꢀ
50
C to give acyl chloride-functionalized PEO (PEO-COCl).
1
32.8 (p-C of phenyl), 144.1 (S ¼¼ CC), 170.4 (CO
2 2
CH ), 225.6
Next, HTEMPO (7.350 g, 42.67 mmol), DMAP (0.1724 g,
.4112 mmol), TEA (1.7 mL, 11.76 mmol), and dry THF (200
(CS CHCH ).
2 3
1
RAFT Homopolymerization of tBBPMA
Mediated by s-CTA
mL) were added to a 500-mL three-necked flask, and then
ꢀ
the solution was cooled to 0 C for adding PEO-COCl in 150
ꢀ
mL of dry THF. The system was stirred at 0 C for 1 h and
AIBN (0.0105 g, 0.0637 mmol) was first added to a 25-mL
Schlenk flask (flame dried under vacuum before use) sealed
with a rubber septum for degassing and kept under N2.
Next, s-CTA 2 (0.1851 g, 0.1910 mmol) in dry toluene (1.0
mL) and tBBPMA 1 (2.4429 g, 8.3319 mmol) were charged
via a gas-tight syringe. The flask was degassed by three
cycles of freezing-pumping-thawing followed by stirring at
room temperature for 10 min. The flask was then immersed
was increased to room temperature with further stirring for
1 day. Water was added to terminate the reaction. The sol-
vent was removed by rotary evaporation, and the crude
product was dissolved in water. The aqueous system was
washed with a mixture of ethyl acetate and hexane (v:v ¼
1
:1) for several times and then extracted by CH Cl . All or-
2 2
ganic layers were merged followed by drying over MgSO4
ꢀ
overnight. The filtrate was concentrated and dried in vacuo
into an oil bath preset at 70 C. The polymerization was ter-
minated by immersing the flask into liquid N after 15 h. Ac-
overnight to give a red solid of TEMPO-functionalized PEO
2
etone was added to dilute the solution, and the solution was
precipitated into n-hexane. After repeated purification by dis-
solving in acetone and precipitating in n-hexane, 1.3460 g of
pink powder was obtained after drying in vacuo. AIBN was
used to remove the dithiobenzoate moiety according to pre-
(PEO-TEMPO) 4 (10.2247 g, 86.6%).
þ
ꢂ1
MALDI-TOF-MS (m/z): found M : 916. FTIR: t (cm ): 2870,
1
958, 1736, 1642, 1462, 1349, 1297, 1248, 1113, 1039, 949,
1
854.
H NMR (CD OD in the presence of Pd/C and
3
HCOONH ): d (ppm): 1.16 (12H, CH of TEMPO), 1.52, 1.85
4
3
4
2
vious report.
Finally, 1.1014 g of white powder, star-
(
4H, CH2 of TEMPO), 2.60 (4H, CH CH CO ), 3.36 (3H,
2 2 2
PtBBPMA (s-PtBBPMA) 3, was obtained after drying in
vacuo. GPC: Mn,GPC ¼ 14,600, M /M ¼ 1.39. GPC/MALS: M
OCH ), 3.56 (2H, CO CH CH ), 3.65 (4H, OCH CH ), 4.23 (2H,
3
2
2
2
2
2
13
w
n
w
CO CH CH ), 5.00 (CH of TEMPO). C NMR (CD OD in the
2
2
2
3
¼
36,700, M /M ¼ 1.26, M
¼ 29,000.
w
n
n,GPC/MALS
presence of Pd/C and HCOONH
4
3
): d (ppm): 19.9 (CH of
ꢂ1
TEMPO), 31.3 (CH of TEMPO and CH CH CO ), 58.7 (OCH ),
FTIR: t (cm ): 2980, 2934, 1731, 1448, 1369, 1338, 1253,
2
2
2
2
3
1
6
0.8 [C(CH ) of TEMPO], 63.6 (CO CH CH ), 69.8 (OCH CH ,
1155, 1073, 998, 970, 840, 740. H NMR: d (ppm): 1.48 (9H,
3 2 2 2 2 2 2
CO CH CH and CH of TEMPO), 168.8 (CH CH CO ).
C(CH ) ), 1.87 (2H, CH CCO and 3H, CH CHBr), 4.52 (1H,
2
2
2
2
2
2
3
3
2
2
3
3
1
CH
3
CHBr and 2H, CO
2
2 3
CH ). C NMR: d (ppm): 21.7 (CH CH),
SET-NRC between Starlike PtBBPMA and PEO-TEMPO
Cu powder (0.0211 g, 0.3325 mmol) and s-PtBBPMA 3
0.1100 g, Mn,GPC/MALS ¼ 29,000, M /M ¼ 1.26) were added
27.8 (C(CH ) ), 40.7 (CH CCO and CH CH), 49.8 (CH CCO ),
3 3 2 2 3 2 2
6
4.9 (CO CH ), 83.4 (C(CH ) ), 169.2 (CO CH ), 171.8
2
2
3 3
2
2
(
w
n
(
CO C(CH ) ).
2 3 3
to a 50-mL Schlenk flask (flame dried under vacuum before
use) sealed with a rubber septum under N . After three
cycles of evacuating and purging with N , PEO-TEMPO 4
Preparation of PEO-TEMPO
In a typical procedure, PEO-OH (15.00 g, M
mmol), succinic anhydride (5.0035 g, 50.00 mmol), DMAP
0.2443 g, 2.000 mmol), and dry chloroform (250 mL) were
2
n
¼ 750, 20.00
2
(0.3005 g, 0.2993 mmol) in 10 mL of dry toluene and
PMDETA (0.070 mL, 0.3325 mmol) were charged via a gas-
tight syringe. The flask was degassed by three cycles of
(
added to a 500-mL three-necked flask, and then the mixture
ꢀ
ꢀ
was stirred at 80 C for 20 h. Chloroform was removed by
freezing-pumping-thawing followed by stirring at 25 C for 2
rotary evaporation, and the crude product was dissolved in
water. Unreacted succinic anhydride was eliminated by
washing with a mixture of ethyl acetate and hexane (v:v ¼
days and it was terminated by putting the flask into liquid
N . The reaction mixture was diluted with THF and passed
2
through a neutral alumina column to remove the residual
copper complex. The purification of crude product was per-
1
:1) for several times. The aqueous phase was extracted by
CH Cl , and all organic layers were merged followed by dry-
formed by dissolving in CH OH and filtering through an
2
2
3
26
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
ultrafiltration membrane separator. The remaining CH OH
3
solution in the separator was concentrated and dried in
vacuo overnight to provide 0.2242 g of s-PtBA-g-PEO 5a.
GPC: M ¼ 70,900, M /M ¼ 1.42.
n
w
n
ꢂ1
FTIR (film): t (cm ): 2977, 2872, 1736, 1451, 1370, 1252,
1
1
150, 998, 841, 748. H NMR: d (ppm): 1.21 (3H, CH3 of
TEMPO), 1.48 [9H, C(CH ) , 4H, CH of TEMPO, and 3H,
3
3
2
CH CHON], 1.86 (3H, CH CHBr, 2H, CH CCO , and 4H, CH of
3
3
2
2
2
TEMPO), 2.62 (4H, CH CH CO ), 3.38 (3H, OCH ), 3.57 (2H,
2
2
2
3
CO
2
CH
CH
2 2
), 3.65 (4H, OCH
CH
2 2
2 2 2
), 4.25 (2H, CO CH CH ),
4
.50 (1H, CH CHON, 1H, CH CHBr, and 2H, CHCO CH ), 5.01
3 3 2 2
1
3
(1H, CH of TEMPO).
C NMR: d (ppm): 21.0, 21.9
(
CH CHON, CH CHBr, and CH of TEMPO), 28.1 (C(CH3)3),
3
3
3
2
9.6 (CH CH CO ), 33.6 (CH of TEMPO), 40.4 (CH CCO and
2 2 2 2 2 2
CH CHBr), 44.3 [C(CH ) of TEMPO], 49.4 (CH CCO ), 59.0
3
3 2
2
2
(
(
(
3 2 2
OCH ), 60.2 (CHCO CH ), 66.9 (CH of TEMPO), 69.0
CH CHON), 70.5 (OCH CH ), 83.1 (C(CH ) ), 169.5
3
2
2
3 3
CHCO CH ), 171.8, 172.3 (CO C(CH ) and O CCH CH CO ).
2
2
2
3 3
2
2
2
2
Determination of Critical Micelle Concentration
Acetone solution of pyrene (0.3 mM) was added to a large
amount of water until the concentration of pyrene reached
0.0006 mM. Different amounts of THF solutions of s-PtBA-g-
PEO 5 (20, 10, 1, 0.1, 0.01, 0.001, or 0.0001 mg/mL) were
added to pyrene-containing water ([pyrene] ¼ 0.0006 mM).
Micelle Morphology
THF solution of s-PtBA-g-PEO 5 (1 or 10 mg/mL) was slowly
added to water under vigorous stirring until the concentra-
tion of graft copolymer was 0.06 mg/mL. THF was evapo-
rated by moderately stirring at room temperature for 15 h.
For transmission electron microscopic (TEM) studies, 10 lL
of micellar solution was deposited on an electron microscopy
copper grid coated with carbon film, and water was evapo-
rated at room temperature.
1
13
FIGURE 1 FTIR (A), H NMR (B), and C NMR (C) spectra of s-
CTA 2.
RESULTS AND DISCUSSION
Preparation of Four-Armed s-CTA 2
It is clear that Br-containing tBBPMA 1 monomer cannot be
homopolymerized via ATRP mechanism because of the cross-
linking, whereas it can be homopolymerized only via RAFT
Selective Acidic Hydrolysis of s-PtBA-g-PEO
In a typical procedure, s-PtBA-g-PEO 5a (0.0980 g, Mn,GPC
40,41
mechanism.
We have previously reported that RAFT
¼
homopolymerization of tBBPMA 1 could be efficiently medi-
7
CH
0,900, Mn,NMR ¼ 75,200, M /M ¼ 1.42) was dissolved in
23,40,41
w
n
ated by cumyl dithiobenzoate (CDB).
In the current
2
Cl
2
(10 mL) and treated with excess TFA (0.6 mL, 8.10
work, a well-defined four-armed starlike PtBBPMA backbone
needs to be constructed first via RAFT mechanism, implying
a demand of a suitable four-armed starlike RAFT agent.
Therefore, we designed and prepared a new tetrafunctional
s-CTA 2 possessing the same dithioester group of CDB with
a relatively high yield of 76.0%, although another four-
armed RAFT agent bearing trithiocarbonate groups has been
ꢀ
mmol) at 40 C for 24 h. The solution was concentrated and
precipitated into cold n-hexane. After filtration, 0.0785 g of
s-PAA-g-PEO 6a double hydrophilic graft copolymer was
obtained after drying in vacuo overnight.
ꢂ1
FTIR (film): t (cm ): 3467, 2926, 1740, 1450, 1350, 1246,
1
1
161, 956, 839. H NMR (acetone-d ): d (ppm): 1.29 (3H,
6
4
3
CH
1
2
3
of TEMPO), 1.36 (2H, CH
.85 (3H, CH CHBr, 2H, CH CCO
.61 (4H, CH CH CO ), 3.30 (3H, OCH3), 3.61 (2H,
2
of TEMPO and 3H, CH
3
CHON),
reported before. 4BrPr was treated with excess benzyl
dithiocarbonate prepared in situ via Grignard reaction to
guarantee the complete functionalization of all four arms,
and the mechanism of this reaction is similar to that of thio-
bromo ‘‘click’’ chemistry newly developed by Percec and
3
2
2
and 2H, CH of TEMPO),
2
2
2
2
CO CH CH and 4H, OCH CH ), 4.21 (2H, CO CH CH ), 4.45
2
2
2
2
2
2
2
2
(
1H, CH CHON, 1H, CH CHBr, and 2H, CHCO CH ), 5.00 (1H,
3 3 2 2
1
3
44,45
1
13
CH of TEMPO). C NMR (acetone-d ): d (ppm): 20.7, 21.6
cowrokers.
FTIR, H NMR, and C NMR were used to
6
(
CH CHON, CH CHBr, and CH of TEMPO), 29.0 (CH CH CO ),
examine the chemical structure of s-CTA 2. The typical sig-
3
3
3
2
2
2
3
2.9 (CH
2
of TEMPO), 41.1 (CH
2
CCO
2
and CH
3
CHBr), 44.2
nals of the carbonyl and C ¼¼ S double bond appeared at 1741
ꢂ1
[C(CH3)2 of TEMPO], 58.0 (OCH ), 60.2 (CHCO CH ), 66.2
and 1044 cm
in FTIR spectrum [Fig. 1(A)], respectively.
3
2
2
ꢂ1
(
CH of TEMPO), 68.7 (CH CHON), 70.3 (OCH CH ), 169.0,
The peaks at 3056, 1590, 1445, 762, and 686 cm corre-
sponded to the phenyls. In particular, the sharp bands at
3
2
2
172.0 (CHCO CH and CH CH CO ), 173.9 (CO H).
2 2 2 2 2 2
SYNTHESIS OF STARLIKE PtBA-g-PEO COPOLYMER, LI ET AL.
27

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢂ1
7
62 and 686 cm demonstrated the existence of monosub-
stituted benzene ring in s-CTA 2. The signals of 20 protons
of the phenyls were located at 7.37, 7.53, and 7.97 ppm in
1
H NMR spectrum as shown in Figure 1(B). The peaks at
1.64, 4.12, and 4.73 ppm were attributed to 12 protons of
CS CHCH , eight protons of CO CH , and four protons of
2
3
2
2
CS CHCH , respectively. The characteristic peaks at 127.0,
2
3
1
3
1
28.4, 132.8, 144.1, and 225.6 ppm in C NMR spectrum
[
Fig. 1(C)] also illustrated the presence of dithiobenzoate
group. All these aforementioned evidences confirmed the
successful synthesis of tetrafunctional dithiobenzoate-based
RAFT chain transfer agent 2.
Construction of Well-Defined Four-Armed PtBA-Based
Backbone
Generally, two different strategies of ‘‘arm-first’’ and ‘‘core-
first’’ were used to prepare the star polymers according to
4
6,47
the features of synthetic approaches.
tion
A coupling reac-
4
8,49
50,51
or a multivinyl crosslinking agent
is needed for
the ‘‘arm-first’’ strategy to form starlike polymer after the
preparation of linear arms. However, slow diffusion of poly-
mer chains and ‘‘dead’’ polymer chains could make some
cores incompletely coupled with the arms, resulting in star
polymers with different numbers of arms. While the ‘‘core-
first’’ strategy was applied, the arms were obtained via living
polymerization of certain monomer initiated by the multi-
functional initiation groups of the core molecule, and the
arm number depended on the number of functional groups
1
FIGURE 2 H NMR spectra of s-PtBBPMA 3 before (A) and after
1
3
(
B) the removal of dithiobenzoate moiety and C NMR spec-
trum of s-PtBBPMA 3 (C).
be shifted from 163.9 to 171.4 ppm [Fig. 2(C)] after the
polymerization because of the disappearance of the double
bond. Moreover, only a unimodal and symmetrical peak
5
2–55
with a relatively low polydispersity (M /Mn ¼ 1.39) as
w
of the core molecule.
This method has been extensively
listed in Table 1 appeared in GPC curve after RAFT
homopolymerization.
used for synthesizing well-defined star polymers with pre-
cise arm number although the molecular weight of the arms
cannot be measured directly.
The molecular weight of branched polymer measured by
conventional GPC was much lower than the ‘‘real’’ value;
5
6
In the current work, RAFT homopolymerization of tBBPMA 1
thus, in the current example, GPC/MALS was used to deter-
mine the absolute molecular weight of s-PtBBPMA 3. GPC/
MALS curve showed a unimodal and symmetrical elution
peak with a narrow molecular weight distribution (M /M ¼
was performed in toluene using AIBN as initiator and s-CTA
2
as chain transfer agent to provide a four-armed starlike
PtBBPMA backbone. Because the moiety of dithiobenzoate
end group may influence the next Cu-catalyzed SET-NRC cou-
pling reaction and its pink color [inset in Fig. 2(A)] may
interfere in observing the reaction phenomenon, the dithio-
w
n
1
.26), indicating the efficient mediation of s-CTA 2 for RAFT
homopolymerization of tBBPMA 1. The number of tBBPMA
repeating unit of every arm of s-PtBBPMA 3 (ntBBPMA) can
be evaluated according to eq 1 (356 and 293 are the molec-
ular weights of the core and tBBPMA, respectively) from the
absolute molecular weight (Mn ¼ 29,000) obtained from
GPC/MALS, and the value is calculated to be 24.4. Thus, we
can conclude that s-PtBBPMA 3 four-armed starlike back-
bone has a well-defined structure and every arm possesses
4
2
benzoate end group was removed by AIBN without affect-
ing the polymeric architecture, and then a white powder
[
inset in Fig. 2(B)] was obtained after the reaction, indicating
the absence of dithiobenzoate residue. The signals of 20 pro-
1
tons of the phenyls (peaks d–f) in H NMR spectrum before
reacting with AIBN [Fig. 2(A)] were found to disappear after
reacting with AIBN [Fig. 2(B)], which witnessed the perfect
removal of dithiobenzoate moiety.
24.4 repeating units.
After RAFT homopolymerization, the characteristic peak of
the double bond (1643 cm ) of tBBPMA 1 in FTIR spec-
ntBBPMA ¼ ð29;000 ꢂ 356Þ=ð293 ꢃ 4Þ:
(1)
ꢂ1
trum disappeared, so did the resonance signals of the double
1
13
bond in H NMR [Fig. 2(B)] and C NMR [Fig. 2(C)] spectra.
The peaks at 1.48 and 1.87 ppm belonged to the protons of
polyacrylate backbone as shown in Figure 2(B). The peak at
Functionalization of PEO with TEMPO
PEO-OH was first esterified by succinic anhydride so that it
was transformed into PEO-COOH. A new peak appeared at
ꢂ1
4
.53 ppm was attributed to one proton of CHBr group, which
illustrated that this pivotal group for next coupling reaction
remained intact during the polymerization. The signal of the
1737 cm in FTIR spectrum after the reaction, indicating
1
the existence of carbonyl. Figure 3(A) shows H NMR spec-
trum after the esterification, and the peaks c–e also demon-
strated the successful incorporation of carbonyl. The signal
1
3
carbonyl of CO C(CH ) in C NMR spectrum was found to
2
3 3
28
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
TABLE 1 Synthesis of Well-Defined Four-Armed PtBA-Based Backbone
a
a
b
b
c
Sample
M
n
(g/mol)
M
w
/M
n
M
n,MALS (g/mol)
M /M
w n
(MALS)
n
tBBPMA
3
14,600
1.39
29,000
1.26
24.4
a
ꢀ
Measured by GPC in THF at 35 C.
b
c
ꢀ
Measured by GPC/MALS in THF at 35 C.
The number of tBBPMA repeating unit per arm.
1
3
at 173.7 ppm in C NMR spectrum after the esterification
[
weight of PEO-OH (M ¼ 750 g/mol), and the value is 16.3
n
Fig. 4(A)] clearly evidenced the introduction of carboxyl.
(Table 2) for PEO-TEMPO 4.
Next, PEO-COOH was almost quantitatively converted to
Synthesis of s-PtBA-g-PEO Graft Copolymer via SET-NRC
The desired four-armed star graft polymers were established
via the grafting-onto strategy by Cu-catalyzed SET-NRC reac-
tion between the Br-containing four-armed s-PtBBPMA 3
PEO-COCl by reacting with SOCl , and HTEMPO was added
2
in situ to be connected with PEO chain. The obtained sample
is orange, which is entirely different from the colorless PEO-
OH starting material; this fact pointed out the existence of
TEMPO radical in PEO chain. The incorporation of TEMPO
ꢀ
2
9,37
0
backbone and PEO-TEMPO 4 in toluene at 25 C.
Cu
powder (99%; Aldrich 207780, US $41.60/500 g) was used
as an economical catalyst at room temperature in compari-
son with CuBr (98%; Aldrich 212865, US $70.90/250 g) cat-
1
radical was verified by the appearance of typical H NMR
1
3
and C NMR resonance signals at 1.16 (CH ), 1.52, 1.85
3
(
CH ) ppm [Fig. 3(B)] and 19.9 (CH ), 60.8 (CH) ppm [Fig.
ꢀ
2
3
alyst and the high reaction temperature (90 C) of ATNRC.
0
4(B)], respectively. The peak at 2.60 ppm attributed to four
Macroradicals were generated by Cu powder instead of
protons of CO
2
CH CH CO confirmed the covalent connection
2
2
2
CuBr according to the mechanism of SET living radical poly-
merization (SET-LRP).
5
7–65
between TEMPO end group and PEO segment. The molecular
weight of TEMPO-functionalized PEO derived from PEO-OH
After the coupling reaction, GPC curve showed that the crude
product was a mixture of starlike PtBA-g-PEO graft copoly-
mer 5 with a high molecular weight and unreacted PEO-
TEMPO 4 with a low molecular weight. Therefore, the mix-
ture was separated by an ultrafiltration membrane separator
to provide pure s-PtBA-g-PEO 5 graft copolymer. The molec-
ular weights of both purified starlike graft copolymers meas-
ured by GPC are much higher than that of s-PtBBPMA 3 as
listed in Table 3, which witnessed that SET-NRC coupling
reaction was performed. GPC curves of both the copolymers
after the ultrafiltration showed a unimodal and symmetrical
elution peak without tailing or shoulder, indicating the
(
Mn ¼ 750 g/mol) was 916 g/mol determined by MALDI-
TOF-MS as shown in Figure 5, which well accorded with the
theoretical value (1004 g/mol). Thus, all aforementioned evi-
dences confirmed the successful functionalization of PEO
with TEMPO end group. The approximate number of EO
repeating unit per chain was evaluated from the molecular
1
13
FIGURE 4 C NMR spectra of PEO-COOH (A) and PEO-TEMPO
FIGURE 3 H NMR spectra of PEO-COOH (A) and PEO-TEMPO
4
(B).
4 (B).
SYNTHESIS OF STARLIKE PtBA-g-PEO COPOLYMER, LI ET AL.
29

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
a
TABLE 2 Preparation of TEMPO-Functionalized PEO
b
c
d
e
Sample
M
n
(g/mol)
M
n
(g/mol)
M /M
w n
N
EO
4
1,004
916
1.03
16.3
a
Synthesized from PEO-OH, M
Theoretical molecular weight.
Measured by MALDI-TOF-MS.
n
¼ 750.
b
c
d
e
ꢀ
Measured by GPC in DMF at 35 C.
The number of EO repeating unit per chain.
age between the backbone and PEO side chains was also evi-
denced by the peaks at 21.0, 21.9 (CH3 of TEMPO), 33.6
(CH
2 3 2
of TEMPO), 44.3 [C(CH ) of TEMPO], and 66.9 (CH of
TEMPO) ppm.
The number of grafted PEO side chains (nPEO) and the ‘‘abso-
lute’’ molecular weights (Mn,NMR) of s-PtBA-g-PEO 5 graft
1
copolymers were determined by H NMR according to eq 2
[S is the peak area; NEO (16.3) is the number of EO repeating
unit per side chain; and 24.4 is the number of tBA repeating
unit in each arm] and eq 3 (29,000 is the molecular weight
of the backbone, 1004 is the theoretical molecular weight of
PEO-TEMPO 4; and 79.9 is the atomic weight of Br). Further-
more, the grafting densities of PEO side chain (Dgraft) esti-
mated via eq 4 are summarized in Table 3, and the percent-
age of Br group left after the coupling reaction can be
calculated as (1 ꢂ Dgraft). The grafting efficiencies were simi-
lar to the recent reports of synthesizing the graft copolymers
FIGURE 5 MALDI-TOF mass spectrum (linear mode) of PEO-
TEMPO 4.
absence of intra- or inter-termination between the stars dur-
3
7
ing the coupling process.
The molecular weights also
increased with the increase of the composition of PEO-
TEMPO 4 in the feed ratios (Table 3).
15
via ATNRC and the CuAAC ‘‘grafting-onto’’ reaction with the
6
6
Proton resonance signals of both starlike PtBA-based back-
moderate coupling efficiencies (36–75%). Actually, it is not
easy to achieve the high coupling efficiency in synthesizing
the graft copolymer via the grafting-onto strategy in compar-
ison with that of the block copolymer because of the steric
1
bone and PEO side chains were found in H NMR spectrum
as shown in Figure 6(A). The peaks at 2.62 (4H,
CH CH CO ), 3.38 (3H, OCH ), 3.57 (2H, CO CH CH ), 3.65
2
2
2
3
2
2
2
1
5,66
(
4H, OCH CH ), and 4.25 (2H, CO CH CH ) ppm were attrib-
hindrance of the dense structure of the graft copolymer.
2
2
2
2
2
uted to PEO side chains. The strong peak at 1.48 ppm com-
prised the signals of nine protons of tert-butyl of PtBA-based
Sa;b;c=ðSg;m;o þ Sh;k;p þ SiÞ ¼ ððNEO ꢂ 1Þ ꢃ 4 þ 5ÞnPEO=
backbone, four protons of CH of TEMPO, and three protons
ð16 ꢃ n
PEO
þ 14 ꢃ 4 ꢃ 24:4Þ; (2)
2
of CH CHON of the backbone. The minor peak at 5.01 ppm
3
Mn;NMR ¼ 29; 000 þ nPEO ꢃ ð1004 ꢂ 79:9Þ;
Dgraft ¼ nPEO=ð24:4 ꢃ 4Þ:
(3)
(
peak f) belonged to one proton of CH of piperdine, which
illustrated the existence of TEMPO connection between the
starlike backbone and PEO side chains. Figure 7(A) shows
(4)
1
3
C NMR spectrum of s-PtBA-g-PEO 5, and the resonance sig-
nals of PEO side chains appeared at 29.6 (CH CH CO ), 59.0
OCH ), and 70.5 (OCH CH ) ppm when compared with
Apparently, it can be concluded that both s-PtBA-g-PEO 5
star graft copolymers possess well-defined structure: a four-
armed starlike poly(tert-butyl acrylate)-based backbone
(24.4 repeating units per arm) and 50.0 or 86.4 grafted PEO
side chains with a certain length (16.3 EO repeating units
per side chain).
2
2
2
1
3
(
C
3
2
2
NMR spectrum of PEO-OH [Fig. 7(C)]. The peaks at 28.1
C(CH ) ) and 83.1 (C(CH ) ) ppm corresponded to tert-
(
3
3
3 3
butyl of PtBA-based backbone. The presence of TEMPO link-
a
TABLE 3 Synthesis of s-PtBA-g-PEO Star Graft Copolymer
b
b
c
d
e
Sample
[4]/[Br group]
M
n
(g/mol)
M
w
/M
n
M
n,NMR (g/mol)
n
PEO
D
graft (%)
CMC (g/mL)
ꢂ6
5
5
a
0.9/1
1.2/1
70,900
91,100
1.42
1.54
75,200
50.0
86.4
51.2
88.5
2.07 ꢃ 10
ꢂ6
b
108,800
1.89 ꢃ 10
a
b
c
ꢀ
ꢀ
d
e
1
Catalyzed by Cu/PMDETA at 25 C for 2 days.
Measured by GPC in DMF at 35 C.
The number of grafted PEO side chain obtained by H NMR.
Grafting density of PEO side chain.
1
Obtained by H NMR.
30
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
1
3
FIGURE 7 C NMR spectra of s-PtBA-g-PEO 5 (A) and PEO-OH
C) in CDCl and s-PAA-g-PEO 6 (B) in acetone-d
(
3
6
.
mers in aqueous media were measured by the fluorescence
technique using pyrene as probe. The intensity ratios (I1/
1
FIGURE 6 H NMR spectra of s-PtBA-g-PEO 5 (A) in CDCl
s-PAA-g-PEO 6 (B) in acetone-d
3
and
67
6
.
I3) were plotted against the concentration of s-PtBA-g-PEO 5
to determine CMC as the onset of micellization [Fig. 8(A)].
The CMC values of s-PtBA-g-PEO 5 as summarized in Table 3
Self-Assembly of s-PtBA-g-PEO Star Graft Copolymer in
Aqueous Media
6
8–70
are comparable with those of polymeric amphiphiles.
As is well known, fluorescence spectrum of pyrene is sensi-
tive to the surrounding and the polarity of its environment.
Pyrene can be solubilized within the interior of the hydro-
phobic part in the presence of micelles so that the values of
The CMC value of amphiphilic copolymer can be severely
influenced by adding inorganic salt to increase the ionic
strength of solution, which would affect the hydrophobic seg-
ment to make the CMC value descend or ascend. Here, the
CMC values of s-PtBA-g-PEO 5b in NaCl solutions with two
different concentrations were measured as listed in Table 4.
The CMC values of s-PtBA-g-PEO 5b decreased
7
1
I /I of the emission spectrum of pyrene can decrease
1
3
remarkably. In the current case, the critical micelle concen-
tration (CMC) values of s-PtBA-g-PEO 5 star graft copoly-
FIGURE 8 Dependence of (A) flu-
orescence intensity ratios of py-
rene emission bands on the
concentrations of s-PtBA-g-PEO
5
a and 5b in pure water and (B)
the CMC value of s-PtBA-g-PEO
b on the ionic strength.
5
SYNTHESIS OF STARLIKE PtBA-g-PEO COPOLYMER, LI ET AL.
31

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
a
TABLE 4 Effect of Ionic Strength on CMC
(diameter: ca. 400 nm and length: 1.5–3.5 lm) as shown in
Figure 9(B). Next, another two solutions with a high initial
copolymer concentration of 10 g/L were prepared to study
the effect of initial concentration of graft copolymer on mi-
cellar structures. Micellar morphologies formed by s-PtBA-g-
PEO 5 with a high initial concentration are obviously differ-
ent from those with a low initial concentration. The spherical
morphology of s-PtBA-g-PEO 5a changed to branched short
rods [Fig. 9(C)] and s-PtBA-g-PEO 5b formed vesicles (ca.
100 nm) as shown in Figure 9(D). It is clear that the diverse
micellar morphologies can be obtained by varying the con-
tent of hydrophilic PEO segment as well as the initial con-
centration of graft copolymer.
CMC (g/mL)
Sample [NaCl] ¼ 0 mM [NaCl] ¼ 10 mM [NaCl] ¼ 20 mM
5b
1.89 ꢃ 10ꢂ6
1.14 ꢃ 10ꢂ6
9.65 ꢃ 10ꢂ7
a
Determined by fluorescence spectroscopy using pyrene as probe.
monotonically while the concentration of NaCl increased
from 0 to 20 mM [Fig. 8(B)], which can be explained by the
fact that the addition of NaCl led to the salting out effect on
the hydrophobic PtBA-based backbone to increase its hydro-
phobicity so that the hydrophobic backbone was easier to
aggregate to form the micelles and the value of CMC
lowered.
Selective Hydrolysis of Starlike PtBA-Based Backbone
CF COOH was used for the acidic selective hydrolysis of
3
In the current work, micellar morphologies were visualized
under TEM and we first investigated the effect of the content
of hydrophilic PEO segment on micellar structures. Figure
hydrophobic PtBA-based backbone to hydrophilic PAA-based
7
2,73
backbone in CH Cl according to previous examples.
The
2
2
1
13
hydrolyzed product was characterized by H NMR, C NMR,
and FTIR. The integration area of the peak at 1.36 ppm in
9(A,B) shows different micellar morphologies formed by s-
1
PtBA-g-PEO 5a and 5b when the initial concentration of co-
polymer was 1 g/L. s-PtBA-g-PEO 5a graft copolymer aggre-
gated into spherical micelles (ca. 400 nm) as shown in Fig-
ure 9(A), whereas s-PtBA-g-PEO 5b with a high PEO content
formed coexisted spheres (ca. 100 nm) and long spindles
H NMR spectrum after the hydrolysis [Fig. 6(B)] was much
smaller than that before the hydrolysis [Fig. 6(A)] because of
the disappearance of the signal of nine protons of tert-butyl
of the backbone. The typical signals of C(CH ) group at 28.1
3
3
[Peak p in Fig. 7(A)] and 83.1 [Peak o in Fig. 7(A)] ppm in
FIGURE
micelles formed by s-PtBA-g-PEO
a (A and C) and 5b (B and D)
9 TEM
images
of
5
with different initial concentra-
tions: for A and B, [polymer] ¼ 1
g/L; for C and D, [polymer] ¼ 10
g/L.
32
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
The authors thank the financial support from the National Nat-
ural Science Foundation of China (20904065), the Shanghai Sci-
entific and Technological Innovation Project (10431903000),
the Shanghai Nano-Technology Program (0952nm05800), and
the Shanghai Pujiang Program (10PJ1405400).
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FIGURE 10 FTIR spectra of s-PtBA-g-PEO 5 (curve a) and s-
PAA-g-PEO 6 (curve b).
6
Helms, B.; Mynar, J. L.; Hawker, C. J.; Fr e´ chet, J. M. J. J Am
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3
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2
197–2208.
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a new broad peak at 3467 cm in FTIR spectrum after the
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Binder, W. H.; Sachsenhofer, R. Macromol Rapid Commun
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hydrolysis (Fig. 10, curve b) in comparison with that before
the hydrolysis (Fig. 10, curve a), witnessing the presence of
ACOOH. The minor peak at 5.00 ppm (peak f) still appeared
in Figure 6(B), which demonstrated the remaining of TEMPO
linkage after the hydrolysis. Furthermore, representative sig-
nals of PEO side chains were kept intact in Figures 6(B) and
2
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210, 987–992.
during the hydrolysis. Thus, we can make sure that s-PtBA-
g-PEO 5 amphiphilic star graft copolymer was selectively
hydrolyzed to s-PAA-g-PEO 6 double hydrophilic star graft
copolymer without affecting PEO side chains. The studies on
s-PAA-g-PEO double hydrophilic star graft copolymer are
being carried out by our group.
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In summary, we present the first example of amphiphilic star
graft copolymer containing PEO side chains via the combina-
tion of RAFT polymerization and highly efficient SET-NRC
reaction. SET-NRC reaction was carried out at ambient tem-
perature using Cu/PMDETA as catalytic system, and the reac-
tion efficiency was as high as ꢁ90%. The architecture of the
backbone and the side chains are both clear. The CMC value
of starlike PtBA-g-PEO amphiphilic graft copolymer was
apparently affected by the ionic strength, and its value
decreased with the increase of the concentration of NaCl.
These amphiphilic star graft copolymers aggregated in aque-
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initial concentration of graft copolymer. Moreover, starlike
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obtained by the selective acidic hydrolysis of hydrophobic
PtBA backbone.
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