A novel well-defined amphiphilic diblock copolymer containing perfluorocyclobutyl aryl ether-based hydrophobic segment

Article abstract of DOI:10.1016/j.polymer.2010.02.036

A series of well-defined binary hydrophilic-fluorophilic diblock copolymers were synthesized by successive atom transfer radical polymerization (ATRP) of methoxylmethyl acrylate (MOMA) and 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate (TPFCBBMA

Full text of DOI:10.1016/j.polymer.2010.02.036

Polymer 51 (2010) 1752e1760
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
A novel well-defined amphiphilic diblock copolymer containing
perfluorocyclobutyl aryl ether-based hydrophobic segment
,
b
b,
*
Dong Yang a, Liang Tong b, Yongjun Li b, Jianhua Hu a , Sen Zhang , Xiaoyu Huang
**
a Key Laboratory of Molecular Engineering of Polymers (Ministry of Education), Laboratory of Advanced Materials and Department of Macromolecular Science,
Fudan University, 220 Handan Road, Shanghai 200433, PR China
b Key Laboratory of Organofluorine Chemistry and Laboratory of Polymer Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of well-defined binary hydrophilic-fluorophilic diblock copolymers were synthesized by
successive atom transfer radical polymerization (ATRP) of methoxylmethyl acrylate (MOMA) and 4-(40-p-
tolyloxyperfluorocyclobutoxy)benzyl methacrylate (TPFCBBMA) followed by the acidic selective hydro-
lysis of the hydrophobic poly(methoxymethyl acrylate) (PMOMA) segment into the hydrophilic poly
(acrylic acid) (PAA) segment. ATRP of MOMA was initiated by 2-MBP at 50 ꢀC in bulk to give two different
PMOMA homopolymers with narrow molecular weight distributions (Mw/Mn ꢁ 1.15). PMOMA-b-
PTPFCBBMA well-defined diblock copolymers were synthesized by ATRP of TPFCBBMA at 90 ꢀC in anisole
using Br-end-functionalized PMOMA homopolymer as macroinitiator and CuBr/PMDETA as catalytic
system. The final PAA-b-PTPFCBBMA amphiphilic diblock copolymers were obtained via the selective
hydrolysis of PMOMA block in dilute HCl without affecting PTPFCBBMA block. The critical micelle
concentrations (cmc) of PAA-b-PTPFCBBMA amphiphilic copolymers in aqueous media were determined
by fluorescence spectroscopy using pyrene as probe and these diblock copolymers showed different
micellar morphologies with the changing of the composition.
Received 3 December 2009
Received in revised form
14 February 2010
Accepted 21 February 2010
Available online 1 March 2010
Keywords:
ATRP
Block copolymers
Perfluorocyclobutyl aryl ether
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
perfluorocyclobutanes [3e7]. The stereo-random PFCB rings
provided amorphous polymers with excellent solubility and
Fluoropolymers have been found to possess many advantages
though their solubility and processability are generally low, such as
the increased thermal and oxidative stability, optical transparency,
solvent compatibility and environmental stability etc., compared to
the conventional carbon-hydrogen-containing polymers because
of the incorporation of fluorocarbon functionality [1]. Therefore,
fluoropolymers including polychlorotrifluoroethylene, Teflon-AF,
Cytop and various copolymers of polytetrafluoroethylene with low
crystallinity have been modified to improve the processability [1].
Recently, perfluorocyclobutyl (PFCB) aryl ether polymer has
received considerable attention since its discovery by Dow Chemical
Co. in early 1990s [1,2]. The predominant head-to-head thermal
processability compared with the ordinary fluoropolymers. PFCB
aryl ether polymers have the common properties of fluoropolymer
and they also possess many other advantages including optical
transparency and improved processability [8,9]. Thus, PFCB
polymers are attractive for a multitude of new applications often
inaccessible using commercial fluoropolymer preparative routes
due to the combination of solution processability and thermal
stability as reviewed by Smith et al [9].
Most recent studies of PFCB-based polymers focused on the
synthesis of homopolymers and random copolymers via the
thermal polymerization of different TFVE monomers in which PFCB
connection was employed as a way to link different functionalities
[10e14]. However, the unusual polymerization mechanism
[2
p
þ 2
p] cyclopolymerization of aryl trifluorovinyl ethers (TFVE)
proceed to form a stable diradical intermediate followed by rapid
([2
p
þ 2
p] cycloaddition) and relatively high polymerization
ring closure to afford a mixture of cis- and trans-1,2-disubstituted
temperature (at least >150 ꢀC) made the studies on the synthesis of
the copolymers via TFVE and commonly used vinyl monomers very
limited and it was found to be difficult to regulate the number of
PFCB unit in copolymers in those cases [15e18]. Thus, it is necessary
to combine the high performance of PFCB-based fluoropolymer
with other commercial polymer to enlarge the application range of
PFCB-based fluoropolymer.
* Corresponding author. Tel.: þ86 21 54925310; fax: þ86 21 64166128.
** Corresponding author. Tel.: þ86 21 55665280; fax: þ86 21 65640293.
E-mail addresses: hujh@fudan.edu.cn (J. Hu), xyhuang@mail.sioc.ac.cn
(X. Huang).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.02.036

D. Yang et al. / Polymer 51 (2010) 1752e1760
1753
O
O
O
F
F
F
F
1. AIBN, NBS,CCl4, 70oC
1. KOH, BrCF2CF2Br
2. Zn,CH3CN 3. 200oC
O
O
F
OH
F
F
F
2. CH2C(CH3)COONa , 30oC
F
F
F
F
O
1
O
O
2-MBP, 50 o
CuBr, PMDETA
C
CuBr,PMDETA,
Br
O
O
n
O
m
TPFCBBMA 1 , 90oC
n
O
O
O
O
O
O
O
O
O
O
F
2
F
F
F
O
F
F
O
O
3
O
m
n
O
O
O
HCl, H2O, rt
HO
F
F
F
F
O
F
F
O
4
Scheme 1. Synthesis of PAA-b-PTPFCBBMA amphiphilic diblock copolymer.
Fig. 1. 1H NMR spectra of TPFCBBMA 1 (A) and PTPFCBBMA (B) in CDCl3.

1754
D. Yang et al. / Polymer 51 (2010) 1752e1760
washing in 0.1 N HCl followed by drying at 140 ꢀC in vacuo overnight.
Table 1
Synthesis of PMOMA 2 macroinitiator.a
CuBr (Aldrich, 98%) was purified by stirring overnight over CH3CO2H
at room temperature, followed by washing the solid with ethanol,
diethyl ether and acetone prior to drying at 40 ꢀC in vacuo for 1 day.
Pyrene (Aldrich, 98%) was purified by recrystallization in ethanol for
three times. Anisole (Aldrich, 99%) was dried over CaH2 and distilled
in vacuo prior to use. BrCF2CF2Br was prepared by condensing
equimolar amounts of Br2 and CF2CH2 at ꢂ195 ꢀC followed by
warming up to 22 ꢀC [38]. 4-Methylphenol (Aldrich, 99%), methyl 2-
bromopropionate (2-MBP, Aldrich, 99%), methacrylic acid (Aldrich,
99%), acrylic acid (Aldrich, 99%), chloromethyl methylether (Aldrich,
b
Sample
[MOMA]:[2-MBP]
Time (h)
Mnb (g/mol)
Mw/Mn
2a
2b
50:1
50:1
3
9
2800
4300
1.13
1.15
a
Polymerization temperature: 50 ꢀC, [2-MBP]:[PMDETA]:[CuBr] ¼ 1:1:1.
b
Measured by GPC in THF at 35 ꢀC.
Block copolymer with
a stable connection between two
different segments may be a suitable choice to realize the above
consideration. Generally, block copolymer is synthesized by the
sequential feeding of different monomers via living polymerization
[19] including anionic polymerization [20,21], cationic polymeri-
zation [22,23], group transfer polymerization [24] and living radical
polymerization [25e28] or the strategy of mechanism trans-
formation via different polymerization approaches [29e31]. In
particular, atom transfer radical polymerization (ATRP) has been
easily employed to synthesize amphiphilic block copolymers
[32,33]. However, the synthesis of well-defined semi-fluorinated
amphiphilic block copolymers as well as their self-assembly
behaviors in aqueous media were rarely reported [34e37].
In this work, we report the synthesis of a new well-defined PFCB-
based amphiphilic diblock copolymer consisting of hydrophilic
PAA segment and hydrophobic PTPFCBBMA segment synthesized
by sequential ATRP of methoxy- methyl acrylate (MOMA) and 4-(40-
p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate (TPFCBBMA)
followed by the selective hydrolysis of PMOMA block as shown
in Scheme 1. Moreover, the self-assembly behavior of PAA-b-
PTPFCBBMA amphiphilic diblock copolymer in pure water was
preliminarily explored by measuring the critical micelle concen-
tration and visualizing the diverse micellar morphologies Scheme 1.
99%), a-bromoisobutyryl bromide (Aldrich, 98%), N-bromosuccini-
mide (NBS, Aldrich, 99%), N,N,N’,N’,N’’- pentamethyldiethylenetri-
amine (PMDETA, Aldrich, 99%), CCl4 (Aldrich, 99.5%) and dimethyl
sulfoxide (DMSO, Aldrich, 99.9%) were used as received.
2.2. Measurements
FT-IR spectra were recorded on a Nicolet AVATAR-360 FT-IR
spectrophotometer with a resolution of 4 cmꢂ1. All 1H NMR
(500 MHz), 13C NMR (125 MHz) and 19F NMR (470 MHz) analyses
were performed on a Bruker Avance 500 spectrometer. TMS
(1H NMR) and CDCl3 and acetone-d6 (13C NMR) were used as internal
standards, respectively; CF3CO2H was used as external standard for
19F NMR. ESI-MS was measured by an Agilent LC/MSD SL system.
Relative molecular weights and molecular weight distributions
(Mw/Mn) were measured by a Waters gel permeation chromatog-
raphy (GPC) system equipped with a Waters 1515 Isocratic HPLC
pump, a Waters 2414 refractive index detector (RI) and a set of
Waters Styragel columns (HR3 (500e30,000), HR4 (5000e600,000)
and HR5 (50,000e4,000,000), 7.8 ꢃ 300 mm, particle size: 5
mm).
2. Experimental section
GPC measurements were carried out at 35 ꢀC using tetrahydrofuran
(THF) as eluent with a flow rate of 1.0 mL/min. The system was
calibrated with linear polystyrene standards. Steady-state fluores-
cent 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, where the excitation wavelength (lex) was
2.1. Materials
2,20-Azobis(isobutyronitrile) (AIBN, Aldrich, 98%) was recrystal-
lized from anhydrous ethanol. Granular zinc was activated by
Fig. 2. 1H NMR spectrum of PMOMA 2 macroinitiator in CDCl3.

D. Yang et al. / Polymer 51 (2010) 1752e1760
1755
to our previous reports [39e41]. 1H NMR:
5.34 (2H, COOCH2O), 5.91, 6.50 (2H, CH2]CH), 6.17 (1H, CH2]CH).
d
(ppm): 3.50 (3H, CH3O),
Table 2
Synthesis of PMOMA-b-PTPFCBBMA 3 using PMOMA 2 macroinitiator.a
b
Sample
Macroinitiator
[1] : [2]
Time (h)
Mnb (g/mol)
Mw/Mn
3a
3b
3c
3d
3e
2a
2a
2a
2a
2b
40:1
40:1
40:1
40:1
100:1
12
18
24
48
9
12,700
14,200
16,900
18,600
18,200
1.33
1.36
1.30
1.28
1.32
2.5. ATRP homopolymerization of MOMA
In a typical procedure, CuBr (0.0507 g, 0.353 mmol) was first
added to a 10 mL Schlenk flask (flame-dried under vacuum prior to
use) sealed with a rubber septum under N2. After three cycles of
evacuating and purging with N2, MOMA (2 mL, 17.6 mmol),
PMDETA (0.0737 mL, 0.353 mmol) and 2-MBP (0.0393 mL,
0.353 mmol) were charged via a gastight syringe. The flask was
degassed by three cycles of freezing-pumping-thawing followed by
immersing the flask into an oil bath thermostated at 50 ꢀC. The
polymerization lasted 3 h and was terminated by putting the flask
into liquid N2. THF was added to dissolve the viscous crude product
and the solution was passed through a short Al2O3 column to
remove the residual copper catalyst. The solution was concentrated
and precipitated into cold n-hexane. The precipitation was dried in
vacuo overnight to afford 1.435 g of glassy solid, poly(methox-
ymethyl acrylate) (PMOMA) 2a. GPC: Mn ¼ 2800, Mw/Mn ¼ 1.13. 1H
a
Polymerization temperature: 90 ꢀC, [2]:[PMDETA]:[CuBr] ¼ 1:4:4.
b
Measured by GPC in THF at 35 ꢀC.
339 nm. Transmission electron microscope (TEM) images were
obtained by a JEOL JEM-1230 instrument operated at 80 kV.
2.3. Preparation of TPFCBBMA 1
The
intermediate,
4-(40-p-tolyloxyperfluorocyclobutoxy)
] cyclo-
toluene, was first prepared via the bulk thermal [2
p
þ 2
p
addition (200 ꢀC) of p-trifluorovinyloxytoluene obtained by the
fluoroalkylation of 4-methylphenol with BrCF2CF2Br followed by
Zn-mediated elimination [2]. The dimer was obtained by silica
column chromatography with a yield of 92.0%. 1H NMR:
d
(ppm):
2.33 (3H, CH3), 7.01 (4H, C6H4CH3), 7.12 (4H, C6H4eOC4F6OeC6H4).
13C NMR: (ppm): 20.6 (CH3), 105.0e115.2 (4C, PFCB). 19F NMR:
(ppm): ꢂ127.3 to ꢂ132.6 (6F, PFCB).
NMR:
(1H, CH2CH), 3.44 (3H, OCH3), 3.63 (3H, COOCH3), 4.28 (1H, CHBr),
5.20 (2H, COOCH2O). 13C NMR:
(ppm): 31.7 (CH2CH), 41.4 (CH2CH),
d (ppm): 1.13 (3H, CH3CH), 1.57, 1.74, 2.01 (2H, CH2CH), 2.39
d
d
57.9 (OCH3), 92.0 (COOCH2O), 174.1 (COOCH2).
d
TPFCBBMA 1 monomer was obtained through the bromination
of 4-(40-p-tolyloxyperfluorocyclobutoxy)toluene with NBS and
AIBN in CCl4 (yield: 42.0%) followed by reacting with sodium
methacrylate in DMSO (yield: 57.6%). ESI-MS (m/z): calcd (M þ Na)þ
2.6. ATRP block copolymerization of TPFCBBMA 1
ATRP block copolymerization of TPFCBBMA 1 was initiated by
PMOMA 2 macroinitiator to provide a series of well-defined
PMOMA-b-PTPFCBBMA 3 diblock copolymers. In a typical proce-
dure, CuBr (0.0258 g, 0.18 mmol) and PMOMA 2a (0.126 g,
0.045 mmol of ATRP initiation group, Mn ¼ 2800, Mw/Mn ¼ 1.13) in
1.8 mL of anisole were first added to a 10 mL Schlenk flask (flame-
dried under vacuum prior to use) sealed with a rubber septum
under N2. After three cycles of evacuating and purging with N2,
TPFCBBMA 1 (0.828 g, 1.8 mmol) and PMDETA (0.0376 mL,
0.18 mmol) were introduced via a gastight syringe. The flask was
degassed by three cycles of freezing-pumping-thawing followed by
immersing the flask into an oil bath preset at 90 ꢀC. The
polymerization was terminated by putting the flask into liquid N2
after 48 h. THF was added to the flask for dilution and the solution
483.1, found 483.1. FT-IR:
n
(cmꢂ1): 3060, 2950, 1722, 1639, 1600,
1509, 1456, 1201, 1157, 963, 817. 1H NMR:
d (ppm): 1.97 (3H, CH2]
CeCH3), 2.33 (3H, C6H4CH3), 5.17 (2H, C6H4CH2O), 5.60, 6.16 (1H,
CH2]CeCH3), 7.02 (2H, C6H4CH3), 7.11 (4H, C6H4eOC4F6OeC6H4),
7.35 (2H, C6H4CH2O). 13C NMR:
d (ppm): 18.3 (CH2]CeCH3), 20.6
(C6H4CH3), 65.6 (C6H4CH2O), 105.0e115.2 (4C, PFCB), 118.3, 126.0
(CH2]CeCH3), 130.3 (phenyl), 134.9, 136.2 (CH2]CeCH3), 150.5,
167.2 (C]O). 19F NMR:
d
(ppm): ꢂ127.3 to ꢂ132.6 (6F, PFCB).
2.4. Preparation of MOMA
MOMA monomer was prepared by reacting acrylic acid with
chloromethyl methyl ether in CH2Cl2 at room temperature according
Fig. 3. GPC traces of PMOMA 2a, PMOMA-g-PTPFCBBMA 3a, 3b, 3c and 3d.

1756
D. Yang et al. / Polymer 51 (2010) 1752e1760
Fig. 4. 1H NMR spectra of PMOMA-b-PTPFCBBMA 3 in CDCl3 (A) and PAA-b-PTPFCBBMA 4 in acetone-d6 (B).
was filtered through a short Al2O3 column to remove the residual
copper catalyst. The resulting solution was concentrated and
precipitated into cold n-hexane. After repeated purification by
dissolving in THF and precipitating in cold n-hexane for three times,
the final product, PMOMA-b-PTPFCBBMA 3d, was obtained after
C6H4eOC4F6OeC6H4), 7.22 (2H, C6H4CH2O). 13C NMR:
d (ppm): 21.4
(CH3), 30.5 (CH2C), 41.7 (CH2C), 44.6 (CH2C), 58.0 (OCH3), 68.2
(C6H4CH2O), 91.1 (OCH2O), 105.0e115.0 (4C, PFCB), 118.1, 130.4,
135.0, 150.5, 174.1, 176.4, 177.1. 19F NMR:
(6F, PFCB).
d
(ppm): ꢂ127.3 to ꢂ132.6
drying in vacuo overnight. GPC: Mn ¼ 18,600, Mw/Mn ¼ 1.28. FI-IR:
(cmꢂ1): 2948, 2926, 2837, 1735, 1612, 1509, 1452, 1407, 1324, 1198,
1142, 963. 1H NMR:
(ppm): 0.67, 0.88 (3H, CCH3), 1.78 (2H, CH2C),
n
2.7. Acidic selective hydrolysis of PMOMA-b-PTPFCBBMA 3
d
2.26 (3H, C6H4CH3), 2.44 (1H, CH2CH), 3.47 (3H, OCH3), 4.84 (2H,
C6H4CH2O), 5.23 (2H, COOCH2O), 6.97 (2H, C6H4CH3), 7.06 (4H,
PMOMA-b-PTPFCBBMA 3 was dissolved in THF and treated with
excess 1 M HCl for 2 h at room temperature. The reaction mixture
Fig. 5. 13C NMR spectra of PMOMA-b-PTPFCBBMA 3 in CDCl3 (A) and PAA-b-PTPFCBBMA 4 in acetone-d6 (B).

D. Yang et al. / Polymer 51 (2010) 1752e1760
1757
Table 3
was washed with water until the aqueous phase became neutral
cmc of PAA-b-PTPFCBBMA 4 diblock copolymers.a
and then with brine followed by drying over anhydrous MgSO4.
Next, the solution was concentrated and precipitated into cold
n-hexane. After filtration PAA-b-PTPFCBBMA 4 amphiphilic diblock
Sample
Nhydrophilic/Nfluorophilic
cmc (g/mL)
4a
4b
4c
4d
4e
22.7/21.5
22.7/24.8
22.7/30.7
22.7/34.3
35.6/30.2
3.78 ꢃ 10ꢂ6
1.76 ꢃ 10ꢂ6
6.31 ꢃ 10ꢂ7
5.67 ꢃ 10ꢂ7
5.61 ꢃ 10ꢂ6
copolymer was obtained after drying in vacuo overnight. FT-IR:
(cmꢂ1): 3422 (COOH), 2961, 1734, 1612, 1510, 1451, 1320, 1198, 1119,
962. 1H NMR (acetone-d6):
(ppm): 0.73, 0.92 (3H, CCH3), 1.77 (2H,
n
d
CH2C), 2.24 (3H, C6H4CH3), 2.51 (1H, CH2CH), 4.92 (2H, C6H4CH2O),
a
Critical micelle concentration determined by fluorescence spectroscopy.
7.06 (2H, C6H4CH3), 7.17 (4H, C6H4eOC4F6OeC6H4), 7.39 (2H,
C6H4CH2O). 13C NMR:
d (ppm): 20.0 (CH3), 25.5 (CH3), 29.5 (CH2C),
elimination according to the standard procedure [2]. The dimer, 4-
39.9 (CH2C), 44.8 (CH2C), 66.0 (C6H4CH2O), 105.0e116.3 (4C, PFCB),
(40-p-tolyloxyperfluorocyclobutoxy)toluene, was obtained by the
118.0, 130.3, 135.9, 150.6, 176.5, 177.1. 19F NMR:
d
(ppm): ꢂ127.3 to
thermal [2
p
þ 2p] cycloaddition of p-trifluorovinyloxytoluene.
ꢂ132.6 (6F, PFCB).
Finally, the mono-brominated product of the dimer reacted with
sodium methacrylate to provide the desired PFCB-linkage-con-
taining methacrylate monomer, TPFCBBMA 1.
2.8. Determination of critical micelle concentration
The chemical structure of TPFCBBMA 1 was characterized by FT-
IR, 1H NMR, 19F NMR and 13C NMR in detail. The typical signals of
the double bond and the carbonyl appeared at 1639 and 1722 cmꢂ1
in FT-IR spectrum, respectively. The peaks at 963, 1456, 1509 and
1600 cmꢂ1 demonstrated the successful incorporation of PFCB
linkage. Moreover, the para-disubstituted benzene ring structure of
PFCB aryl ether unit was confirmed by the sharp band centered at
817 cmꢂ1 1H NMR spectrum of TPFCBBMA 1 is shown in Fig. 1A and
the typical resonance signals of the double bond were found to
locate at 5.60 and 6.16 ppm. The peaks at 7.02, 7.11 and 7.25 ppm
were attributed to 8 protons of benzene ring in PFCB aryl ether unit.
The resonance signals of 2 carbons of the double bond also
appeared at 126.0 and 136.2 ppm in 13C NMR spectrum of 1. The
peak at 167.2 ppm corresponded to the carbon of the carbonyl and
a series of peaks between 105.0 and 115.2 ppm belonged to 4
carbons of PFCB linkage. Furthermore, the presence of PFCB linkage
was illustrated by the peaks between ꢂ127.3 and ꢂ132.6 ppm in 19F
NMR spectrum of 1. All the above results showed the successful
synthesis of PFCB-linkage-containing monomer 1.
Pyrene was used as fluorescence probe to measure the critical
micelle concentration (cmc) of PAA-b-PTPFCBBMA 4 amphiphilic
block copolymer. 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 PAA-b-
PTPFCBBMA 4 (20 mg/mL) were added to pyrene-containing water
([pyrene] ¼ 0.0006 mM). All fluorescence spectra were recorded at
25 ꢀC.
2.9. TEM images
THF solution of PAA-b-PTPFCBBMA 4 (20 mg/mL) was added
dropwise to water with vigorous stirring until the concentration of
the copolymer was 0.1 mg/mL. THF was evaporated by stirring for
another several hours. For TEM studies, a drop of micellar solution
was deposited on an electron microscopy copper grid coated with
carbon film and the water was evaporated at room temperature.
3. Results and discussion
This semi-fluorinated methacrylate monomer is suitable for ATRP.
Its ATRP homopolymerization can be initiated by 2-MBP at 90 ꢀC in
anisole using PMDETA/CuBr as catalytic system. When the feed ratio
of [TPFCBBMA]:[2-MBP]:[PMDETA]:[CuBr] was 50:1:4:2, a well-
defined PTPFCBBMA homopolymer (Mn ¼ 31,400, Mw/Mn ¼ 1.05)
was obtained after 6 h with a high conversion of 93.8% determined by
GC. ATRP mechanism was confirmed by the minor peak at 3.55 ppm
attributed to 3 protons of COOCH3 in ATRP initiation group as
shown in Fig. 1B.
3.1. TPFCBBMA 1 semi-fluorinated methacrylate monomer
Commercially available 4-methylphenol was used as starting
material to prepare p-trifluorovinyloxytoluene in two steps via the
fluoroalkylation with BrCF2CF2Br followed by Zn-mediated
Fig. 7. Dependence of fluorescence intensity ratios of pyrene emission bands on the
concentration of PAA-b-PTPFCBBMA 4a.
Fig. 6. FT-IR spectra of PAA-b-PTPFCBBMA 4 (A) and PMOMA-b-PTPFCBBMA 3 (B).

1758
D. Yang et al. / Polymer 51 (2010) 1752e1760
3.2. Br-end-functionalized PMOMA 2 macroinitiator
selected due to its mild acidic hydrolysis conditions without steric
effect [39e41].
PMOMA
It was found that the ester group of PTPFCBBMA homopolymer
could be hydrolyzed into the carboxyl in basic surrounding;
however, it was stable in acidic environment. Moreover, acrylic acid
can not be polymerized by ATRP. For the targeted PAA-b-
PTPFCBBMA diblock copolymer, a suitable polyacrylate segment
which can be easily hydrolyzed into poly(acrylic acid) segment
under mild acidic conditions should be chosen. Thus, MOMA was
2 homopolymers with narrow molecular weight
distributions (Mw/Mn ꢁ 1.15) were obtained via bulk ATRP at 50 ꢀC
using 2-MBP as initiator and CuBr/PMDETA as catalytic system
(Table 1). From the data of molecular weight, it was estimated that
every PMOMA 2a and 2b chain possess 22.7 and 35.6 MOMA
repeating units, respectively. Fig. 2 shows 1H NMR spectrum of
PMOMA 2. The peaks of 3 protons of the double bond at 5.90, 6.17
Fig. 8. TEM images of PAA-b-PTPFCBBMA 4a (A), 4b (B), 4c (C), 4d (D) and 4e (E) in aqueous media, [copolymer] ¼ 0.1 mg/mL.

D. Yang et al. / Polymer 51 (2010) 1752e1760
1759
and 6.50 ppm disappeared after ATRP homopolymerization and the
resonance signals of polyacrylate backbone appeared at 1.57, 1.74,
2.01 and 2.39 ppm. The peaks “b” (4.29 ppm), “c” (3.63 ppm) and
“g” (1.13 ppm) were attributed to the protons of ATRP initiation
group, this verifying ATRP mechanism of the homopolymerization.
In particular, the peak at 4.29 ppm indicated the existence of active
ATRP initiation group as end group of PMOMA 2, which meant
PMOMA 2 can initiate ATRP of another monomer to obtain
PMOMA-containing block copolymer.
would change sharply as a result, which showed pyrene probes
transferred to a more hydrophobic micro-environment. The ratios
of the intensity (I1/I3) against the logarithm of the concentration of
the copolymer are plotted in Fig. 7. The I1/I3 ratios almost kept
constant ranging from 1.7 to 1.8 when the concentration of PAA-b-
PTPFCBBMA 4a was low, which meant that pyrene probes located in
a hydrophilic environment. With the increasing of the concentra-
tion of 4a, I1/I3 ratios dropped quickly and an inflection point
([4a] ¼ 3.78 ꢃ 10ꢂ6 g/mL) appeared in the curve, which was
determined to be the cmc of PAA-b-PTPFCBBMA 4a. The cmc values
of PAA-b-PTPFCBBMA 4 are all around 10ꢂ7 g/mL as listed in Table 3
which is very low compared to the common surfactants or
polymeric amphiphiles [47e50]. These low cmc values are related
with the semi-fluorinated PTPFCBBMA segment. Moreover, the
values of cmc decreased with the raising of the length of fluo-
rophilic PTPFCBBMA segment (4d < 4c < 4b < 4a) while keeping
the length of hydrophilic PAA block constant; when the lengths of
PTPFCBBMA segment were similar (NTPFCBBMA ¼ 30.7 and 30.2 for
4c and 4e, respectively), cmc values increased with the rising of the
length of PAA block (4c < 4e).
3.3. Synthesis of PMOMA-b-PTPFCBBMA 3 diblock copolymer
PMOMA-b-PTPFCBBMA 3 diblock copolymers were synthesized
via ATRP of TPFCBBMA
1 initiated by Br-end-functionalized
PMOMA 2 at 90 ꢀC in anisole using CuBr/PMDETA as catalytic
system and the results are listed in Table 2. All obtained diblock
copolymers' molecular weights were much higher than those of
PMOMA 2, this indicating the occurring of ATRP of TPFCBBMA 1.
The molecular weights of the copolymers increased with the
extending of polymerization time and all copolymers showed
unimodal and symmetrical GPC curves (Fig. 3) with narrow
molecular weight distributions (Mw/Mn ꢁ 1.36), which were the
characteristics of ATRP [42,43].
Micellar morphologies were visualized under TEM. Fig. 8 show
micellar morphologies formed by PAA-b-PTPFCBBMA
4 with
different compositions in aqueous media. When the content of
fluorophilic TPFCBBMA unit was low (4a, 4b and 4e), the copoly-
mers aggregated to form spherical micelles as shown in Fig. 8A, B
and E. With the increasing of the content of TPFCBBMA unit (4c
and 4d), spherical micelles turned to pearl-necklace-like micelles
(Fig. 8C and D).
FT-IR, 1H NMR and 13C NMR were employed to characterize
PMOMA-b-PTPFCBBMA 3 diblock copolymer. The signal of the
double bond at 1639 cmꢂ1 in FT-IR spectrum disappeared after the
copolymerization and the bands at 963, 1452, 1509 and 1612 cmꢂ1
demonstrated the existence of PFCB aryl ether unit. The peaks at
3.47 and 5.23 ppm in 1H NMR spectrum (Fig. 4A), and the peaks at
58.0 and 91.1 ppm in 13C NMR spectrum (Fig. 5A) corresponded to
the methoxymethyls of PMOMA block. The presence of PFCB aryl
ether unit was also verified by the resonance signals at 6.97, 7.06
and 7.22 ppm in 1H NMR spectrum and a series of peaks between
105.0 and 115.0 ppm in 13C NMR spectrum. Specially, the peak of 2
protons of C6H4CH2O in PTPFCBBMA segment shifted to 4.84 ppm
compared to that of TPFCBBMA 1 at 5.17 ppm because the double
bonds disappeared after ATRP of 1. All these results confirmed the
chemical structure of PMOMA-b-PTPFCBBMA 3.
4. Conclusion
In summary, we present the synthesis and self-assembly of
a well-defined semi-fluorinated amphiphilic diblock copolymer
with hydrophilic PAA and fluorophilic PTPFCBBMA segments.
A new PFCB-based methacrylate monomer was first prepared in 5
steps using 4-methylphenol as starting material and this monomer
is suitable for ATRP. Well-defined PMOMA-b-PTPFCBBMA diblock
copolymers with narrow molecular weight distributions were
obtained by sequential ATRP of MOMA and TPFCBBMA and they
were selectively hydrolyzed into PAA-b-PTPFCBBMA diblock
copolymers in acidic environment. Pyrene was used as fluorescence
probe to determine the cmcs of these amphiphilic copolymers and
they aggregated to form micelles with different morphologies
while changing the compositions.
3.4. Selective hydrolysis of PMOMA-b-PTPFCBBMA 3
Dilute HCl was employed to hydrolyze PMOMA-b-PTPFCBBMA 3
diblock copolymers into PAA-b-PTPFCBBMA 4 diblock copolymers
at room temperature in THF according to previous literatures
[39e41]. 1H NMR (3.47 and 5.23 ppm) and 13C NMR (58.0 and
91.1 ppm) signals of the methoxymethyls disappeared after the
hydrolysis as shown in Figs. 4B and 5B, this confirming the
complete hydrolysis of PMOMA block. The resonance signals of
PFCB aryl ether units remained in Figs. 4B and 5B, which meant that
PTPFCBBMA segment was not affected during the hydrolysis. In
addition, it was found that a new broad peak appeared at
3407 cmꢂ1 in FT-IR spectrum after the hydrolysis (Fig. 6A)
compared to that before the hydrolysis as shown in Fig. 6B, this
indicating the formation of PAA block.
Acknowledgement
The authors thank the financial support from National Natural
Science Foundation of China (20674094 and 50873029), Ministry of
Science and Technology of “National High Technology Research and
Development Program” (2006AA03Z541), Shanghai Scientific and
Technological Innovation Project (08431902300) and Shanghai
Nano- Technology Program (0952nm05800).
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