Novel perfluorocyclobutyl aryl ether-based well-defined amphiphilic block copolymer

Article abstract of DOI:10.1002/pola.24884

A series of fluorine-containing amphiphilic diblock copolymers comprising hydrophobic poly(p-(2-(p-tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) (PTPFCBPMA) and hydrophilic poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) segments were synthesized via successive reversible addition fragmentation chain transfer (RAFT) polymerizations. RAFT homopolymerization of p-(2-(p-tolyloxy)perfluorocyclobutoxy)phenyl methacrylate was first initiated by 2,2′-azobisisobutyronitrile using cumyl dithiobenzoate as chain transfer agent, and the results show that the procedure was conducted in a controlled way as confirmed by the fact that the number-average molecular weights increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.30. Dithiobenzoate-capped PTPFCHPMA homopolymer was then used as macro-RAFT agent to mediate RAFT polymerization of 2-(diethylamino)ethyl methacrylate, which afforded PTPFCBPMA-b-PDEAEMA amphiphilic diblock copolymers with different block lengths and narrow molecular weight distributions (M _w/M_n ≤ 1.28). The critical micelle concentrations of the obtained amphiphilic diblock copolymers were determined by fluorescence spectroscopy technique using N-phenyl-1-naphthylamine as probe. The morphology and size of the formed micelles were investigated by transmission electron microscopy and dynamic light scattering, respectively.

Full text of DOI:10.1002/pola.24884

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ARTICLE
Novel Perfluorocyclobutyl Aryl Ether-Based Well-Defined
Amphiphilic Block Copolymer
Wenqiang Yao, Yongjun Li, Sen Zhang, Hao Liu, Xiaoyu Huang
Key Laboratory of Organofluorine Chemistry and Laboratory of Polymer Materials, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China
Correspondence to: Y. Li (E-mail: liyongjun78@mail.sioc.ac.cn) or X. Huang (E-mail: xyhuang@mail.sioc.ac.cn)
Received 24 May 2011; accepted 8 July 2011; published online 28 July 2011
DOI: 10.1002/pola.24884
ABSTRACT: A series of fluorine-containing amphiphilic diblock
copolymers comprising hydrophobic poly(p-(2-(p-tolyloxy)per-
fluorocyclobutoxy)phenyl methacrylate) (PTPFCBPMA) and
hydrophilic poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA)
segments were synthesized via successive reversible addition
fragmentation chain transfer (RAFT) polymerizations. RAFT
homopolymerization of p-(2-(p-tolyloxy)perfluorocyclobutoxy)-
phenyl methacrylate was first initiated by 2,20-azobisisobutyroni-
trile using cumyl dithiobenzoate as chain transfer agent, and the
results show that the procedure was conducted in a controlled
way as confirmed by the fact that the number-average molecular
weights increased linearly with the conversions of the monomer
while the polydispersity indices kept below 1.30. Dithiobenzoate-
capped PTPFCHPMA homopolymer was then used as macro-
RAFT agent to mediate RAFT polymerization of 2-(diethylami-
no)ethyl methacrylate, which afforded PTPFCBPMA-b-PDEAEMA
amphiphilic diblock copolymers with different block lengths and
narrow molecular weight distributions (Mw/Mn ꢀ 1.28). The criti-
cal micelle concentrations of the obtained amphiphilic diblock
copolymers were determined by fluorescence spectroscopy tech-
nique using N-phenyl-1-naphthylamine as probe. The morphol-
ogy and size of the formed micelles were investigated by
transmission electron microscopy and dynamic light scattering,
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2011 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 49: 4433–4440, 2011
KEYWORDS: block copolymers; perfluorocyclobutyl; RAFT; self-
assembly; synthesis
INTRODUCTION Most block copolymers containing a fluori-
nated segment have unconventional phase behaviors.1,2 In
comparison with the usual hydrocarbon-based polymers, the
fluorinated relevant polymers are more rigid and less misci-
ble for their fluorophobic effect. Therefore, the replacement
of hydrocarbon block with fluorinated block in amphiphilic
copolymers can imbue favorable properties to nanomaterials
such as thermal stability, chemical resistance, low surface
energy, low refractive index, and high insulating ability.3–5 In
particular, the incorporation of fluorinated segments into
amphiphilic block copolymers can result in interesting self-
assembly characteristics due to the combination of hydro-
phobicity and lipophobicity in fluorinated polymers.6,7 Percec
et al. reported fluorinated liquid crystal molecules with per-
fluorinated alkane chains, which can produce a microsegre-
gation at the molecular level, and this process can be alone
responsible for the formation of lamellar thermotropic and
lyotropic mesophases.8–21 Ni and coworkers22 prepared
amphiphilic hyperbranched star-block copolymers containing
polycations and fluoropolymer segment, which can directly
self-organize into supramolecular multicompartment micelles
with different diameters. Although these interesting results
were concerned with the polymers with flexible fluorinated
alkane side chains, seldom have been reported on the self-
assembly behaviors of amphiphilic copolymers bearing rigid
fluorine-containing side groups, which may self-assemble
into more different nanostructures.
A new kind of partially fluorinated polymer, perfluorocyclo-
butyl (PFCB) aryl ether polymers, which was discovered by
Babb et al. of Dow Chemical in early 1990s,23–26 has
attracted much interests in many fields such as photonics,27
polymer light-emitting diodes,28,29 and proton exchange
membranes for fuel cells.30 Because of their low crystallinity,
PFCB aryl ether-based polymers have improved processabil-
ity, which have solved to some extent the manufacturing
problems of fluoropolymers compared with traditional fluo-
ropolymers.31 PFCB aryl ether-based homopolymers or
copolymers are commonly synthesized by free radical-medi-
ated [2p þ 2p] step-growth thermal cyclopolymerization of
monomers bearing two or three trifluorovinyl ether function-
32–35
ꢁ
alities at a temperature region of 150–200 C.
However,
because of the unusual polymerization mechanism and rela-
tive higher polymerization temperature, seldom has reported
the incorporation of PFCB groups into commonly used
monomers, which can be polymerized by conventional chain
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growth polymerization approaches. Therefore, it obviously
poses a limitation in the variety and application of PFCB aryl
ether-based polymers. Recently, our group has developed a
novel type of (meth)acrylate monomers with PFCB-contain-
ing ester group,36–39 which can be polymerized via tradi-
tional or living/controlled radical polymerization, it enabled
us to obtain tailor-made PFCB aryl ether-based homopoly-
mers or copolymers with well-defined architecture and func-
tion, which has certainly widen the application of PFCB aryl
ether-based fluoropolymers.
Amphiphilic block copolymers are macromolecules composed
of hydrophilic and hydrophobic chains connected at their ter-
minal. The covalently connected thermodynamically incompat-
ible segments give rise to self-assembly of the components
into ordered structures with periodicity or compositional
heterogeneityon.40,41 Synthesis of amphiphilic block copoly-
mers can be conducted by anionic,42,43 cationic,44,45 and
living/controlled radical polymerization.46,47 The living/con-
trolled radical polymerization, including stable free radical
polymerization,48 atom transfer radical polymerization,49–51
reversible addition fragmentation chain transfer (RAFT)52,53
polymerization, and single electron transfer-living radical po-
lymerization,54–58 has become a powerful tool in the prepara-
tion of well-defined polymers. Specially, RAFT polymerization
has many advantages such as more tolerant to a wide range
of monomers and milder polymerization condition over other
methods.59
SCHEME 1 Synthesis of PTPFCBPMA-b-PDEAEMA amphiphilic
diblock copolymer.
reported procedures.61 4-Methoxyphenol (99%; Aldrich), p-
cresol (99%; Aldrich), BBr3 (1.0 M in CH2Cl2; Aldrich), and
methacryloyl chloride (97%; Alfa Aesar) were used as
received.
The objectives of this article concern the synthesis and solu-
tion behavior of a new well-defined PFCB aryl ether-based
amphiphilic block copolymer, poly(p-(2-(p-tolyloxy)perfluoro-
Measurements
Fourier transform infrared (FTIR) spectra were recorded on
a Nicolet AVATAR-360 FTIR spectrophotometer with a reso-
lution of 4 cmꢂ1. All NMR analyses were performed on a
Bruker Avance 500 spectrometer (500 MHz). Tetramethyl-
silane (1H NMR) and CDCl3 (13C NMR) were used as internal
standards, and CF3CO2H was used as an external standard
for 19F NMR. EI-MS was measured by an Agilent 5937N sys-
tem. Conversions of TPFCBPMA were determined by 1H
NMR. Relative molecular weights and molecular weight dis-
tributions were measured by conventional gel permeation
chromatography (GPC) system equipped with a Waters 1515
Isocratic HPLC pump, a Waters 2414 refractive index detec-
tor, and a set of Waters Styragel columns [HR3 (500–
30,000), HR4 (5,000–600,000), and HR5 (50,000–4,000,000),
7.8 ꢃ 300 mm2, particle size: 5 lm]. GPC measurements
were carried out at 35 ꢁC using tetrahydrofuran (THF) as
eluent with a flow rate of 1.0 mL/min, and the system was
calibrated with linear polystyrene standards. Steady-state flu-
orescence spectra of PNA were measured on a Hitachi F-
4500 spectrofluorometer with the bandwidth of 5 nm for ex-
citation and emission; the emission intensity at 418 nm was
recorded to determine the CMC with an excitation wave-
length (kex) of 340 nm. Transmission electron microscope
(TEM) images were obtained by a JEOL JEM-1230 instru-
ment operated at 80 kV. Hydrodynamic diameter (Dh) was
measured by dynamic light scattering (DLS) with a Malvern
Nano-ZS90 Zetasizer.
cyclobutoxy)phenyl
methacrylate)-b-poly(2-(diethylami-
no)ethyl methacrylate) (PTPFCBPMA-b-PDEAEMA), which
were synthesized via successive RAFT of p-(2-(p-tolyloxy)-
perfluorocyclobutoxy)phenyl methacrylate (TPFCBPMA) and
2-(diethylamino)ethyl methacrylate (DEAEMA) as shown in
Scheme 1. The aqueous self-assembly behavior of the amphi-
philic diblock copolymers have been investigated by meas-
uring the critical micelle concentrations (CMCs) and the size
of the micelles and visualizing the micellar morphologies.
EXPERIMENTAL
Materials
2,20-Azobisisobutyronitrile (AIBN, 99%; Aldrich) was recrys-
tallized twice from ethanol. l,2-(Diethylamino)ethyl methac-
rylate (DEAEMA, 97%; Alfa Aesar) was purified by distilling
under vacuum. Granular zinc was activated by washing in
ꢁ
0.1 M HCl followed by drying at 140 C in vacuo for 10 h. N-
Phenyl-1-naphthylamine (PNA, 97%; Alfa Aesar) was purified
by recrystallization in ethanol for three times. 2-Butanone
(99%; Aldrich) was dried with CaCl2 and then distilled under
vacuum. 1,4-Dioxane (99%; Aldrich) was dried with CaH2
and then distilled under vacuum. 1,2-Dibromotetrafluoro-
ethane was prepared by condensing equimolar amounts of
ꢁ
Br2 and tetrafluoroethylene at ꢂ195 C followed by warming
up to 22 ꢁC according to previous literature.60 RAFT agent,
cumyl dithiobenzoate (CDB), was prepared according to the
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TABLE 1 RAFT Homopolymerization of TPFCBPMA 1a
Synthesis of TPFCBPMA
p-(Trifluorovinyloxy)toluene and p-(trifluorovinyloxy)anisole
were first prepared from 4-methoxyphenol and p-cresol,
respectively, via standard fluoroalkylation followed by Zn-
mediated dehalogenation.32 p-(Trifluorovinyloxy)toluene
(41.2 mL, 0.22 mol) and p-(trifluorovinyloxy)anisole (50.1 g,
0.25 mol) were added to a predried flask, and the mixture
b
b
c
Sample [1]:[CDB]:[AIBN] Mn (KDa) Mw/Mn
NTPFCBMA
2a
2b
a
30:2:1
80:2:1
8.2
1.14
1.16
18
31
13.9
Polymerization temperature: 70 ꢁC, polymerization time: 24 hours,
solvent: 2-butanone.
ꢁ
was heated at 150 C for 1 day under N2. The cross-dimer, a
b
Measured by GPC in THF at 35 ꢁC.
c
colorless oil of 4-(2-(p-tolyloxy)perfluorocyclobutoxy)anisole
(38.9 g, yield: 45.3%), was obtained by column chromatogra-
phy (eluent: hexane: ethyl acetate ¼ 100:1).
The number of TPFCBPMA repeating unit obtained from GPC.
1.75 (2H, CH2), 2.25 (3H, ArCH3), 6.98, 7.06 (4H, phenyl).
19F NMR: d (ppm): ꢂ127.6 to ꢂ133.3 (m, cyclobutyl-F6).
1H NMR: d (ppm): 2.31 (s, 3H), 3.78 (d, 3H), 6.89 (dd, 2H),
7.10 (m, 6H). 19F NMR: d (ppm): ꢂ127.5 to ꢂ133.2 (m,
cyclobutyl-F6). 13C NMR: d (ppm): 20.8, 20.9, 55.4, 55.5,
114.5, 114.6, 118.2, 118.6, 119.8, 120.1, 122.9, 130.0, 135.4,
135.9, 145.9, 146.2, 150.3, 150.5, 156.9, 157.1, 157.9. FTIR
(KBr): m (cmꢂ1): 2956, 2860, 1507, 1193, 962 (PFCB). EI-
MS: m/z 392.
RAFT Block Copolymerization of DEAEMA
The procedures used for block copolymerization of DEAEMA
were similar to the RAFT homopolymerization of TPFCBPMA.
A 10-mL Schlenk flask (flame-dried under vacuum prior to
use) was first filled with AIBN (1.1 mg, 0.0067 mmol) and
PTPFCBPMA 2a (Mn ¼ 8,200 g/mol, Mw/Mn ¼ 1.14, 0.164 g,
0.020 mmol). The contents were purged with N2 for 10 min
to eliminate the dissolved oxygen for three times, and
DEAEMA (0.40 mL, 2.0 mmol) and 1,4-dioxane (4.0 mL)
were charged via a gastight syringe. The flask was degassed
by three cycles of freezing–pumping–thawing, and it was
Demethylation of 4-(2-(p-tolyloxy)perfluorocyclobutoxy)ani-
sole was carried out by treating with BBr3 to provide 4-(2-
(p-tolyloxy)perfluorocyclobutoxy)phenol. The above-prepared
phenol (3.16 g, 0.0084 mol) and triethylamine (1.35 mL,
0.0096 mol) were dissolved in 25 mL of 2-butanone, and the
mixture was stirred at 0–5 ꢁC. Methacryloyl chloride
(0.95 mL, 0.0096 mol) in 2-butanone (10 mL) was added
dropwise within 30 min, and the mixture was stirred for
another 1 h. The organic phase was washed twice with water
after filtration. The solution was dried over MgSO4 and puri-
fied by column chromatography (eluent: hexane: ethyl acetate
¼ 50:1) after concentration. The monomer, TPFCBPMA 1 (col-
orless oil), was obtained with a yield of 81.2%.
ꢁ
placed in an oil bath preset at 70 C for 1 day. The polymer-
ization was quenched by putting the flask into liquid N2. The
mixture was dissolved in THF and precipitated into 100 mL
of cold n-hexane for three times. The obtained white solid,
PTPFCBPMA-b-PDEAEMA, 3c, was again washed with a small
amount of n-hexane and then dried in vacuo overnight.
GPC: Mn ¼ 12,200, Mw/Mn ¼ 1.28. FTIR (KBr): m (cmꢂ1):
2972, 2875, 1766, 1606, 1507, 1320, 1204, 1140, 962. 1H
NMR: d (ppm): 0.89, 1.36 (3H, CCH3), 1.06 (6H, NCH2CH3)
1.48, 1.81, 1.90 (2H, CH2), 2.26 (3H, ArCH3), 2.61 (4H,
NCH2CH3), 2.73 (2H, COOCH2CH2), 4.02 (2H, COOCH2CH2),
6.99, 7.05 (4H, phenyl). 19F NMR: d (ppm): ꢂ127.8 to
ꢂ133.8 (m, cyclobutyl-F6)
FTIR (KBr): m (cmꢂ1): 2930, 1740, 1638, 1503, 1319, 1187,
1
1123, 962 (PFCB), 817. H NMR: d (ppm): 2.04 (s, 3H), 2.31
(s, 3H), 5.75 (s, 1H), 6.33 (s, 1H), 7.10 (m, 8H). 19F NMR: d
(ppm): ꢂ127.7 to ꢂ133.2 (m, cyclobutyl-F6). 13C NMR: d
(ppm): 18.6, 20.9, 118.2, 118.6, 119.4, 119.8, 123.0, 127.7,
130.4, 130.5, 135.4, 135.9, 148.3, 149.9, 150.2, 165.9. EI-MS:
m/z 446.
Determination of CMC
RAFT Homopolymerization of TPFCBPMA
PNA was used as fluorescence probe to measure the CMC of
PTPFCBPMA-b-PDEAEMA 3. Acetone solution of PNA (1 mg/
mL) was added to a large amount of water until the concen-
tration of PNA reached 0.001 mg/mL. Then, different
amounts of THF solutions of PTPFCBPMA-b-PDEAEMA 3 (1,
0.1, or 0.01 mg/mL) were added to water containing PNA
([PNA] ¼ 0.001 mg/mL). All fluorescence spectra were
In a typical procedure of RAFT homopolymerization of
TPFCBPMA, CDB (109.0 mg, 0.40 mmol) and AIBN (32.8 mg,
0.20 mmol) were first added to a 10-mL Schlenk flask
(flame-dried under vacuum prior to use) with a magnetic
stir bar. The contents were purged with N2 for 10 min to
eliminate the dissolved oxygen for three times, and
TPFCBPMA (2.67 g, 6.0 mmol) and 2-butanone (5.0 mL)
were then charged via a gastight syringe. After three freez-
ing-pumping-thawing cycles, the Schlenk flask was placed in
ꢁ
recorded at 20 C.
ꢁ
an oil bath thermostated at 70 C for 1 day. The polymeriza-
TEM Images
tion was terminated by placing the flask into liquid N2. The
contents were dissolved in THF and precipitated in 200 mL
of methanol twice. The obtained polymer, PTPFCBPMA 2a,
was dried at room temperature in vacuo overnight.
A total of 0.5 mL of water was added slowly (0.36 mL/h) to
0.5 mL of THF solution of PTPFCBPMA-b-PDEAEMA 3
(1 mg/mL), and THF was removed by dialysis. The copper
grid (400 meshes) was immersed in a drop of the aqueous
polymer solution and then dried at room temperature for 1
day prior to measurement.
GPC: Mn ¼ 8,200, Mw/Mn ¼ 1.14. 1H NMR: d (ppm): 0.87,
1.36 (3H, CCH3), 1.27 (6H, C(CH3)2 of CDB moiety), 1.46,
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belonged to the protons of polymethacrylate backbone.
Moreover, the sharp peak at 2.28 ppm corresponded to three
protons of tolyl.
To confirm the controlled nature of AIBN-initiated and CDB-
mediated RAFT homopolymerization of TPFCBPMA, we stud-
1
ied the polymerization kinetics by H NMR to draw the semi-
logarithmic plot of ln([M]0/[M])([M]0 is the initial monomer
concentration and [M] is the monomer concentration) versus
time in Figure 2(A). The linearity between ln([M]0/[M]) and
the polymerization time indicated a constant number of prop-
agating species throughout the polymerization and the appa-
rent first-order polymerization rate with respect to the concen-
tration of the monomer. Furthermore, the molecular weights
increased linearly with the conversions of monomer, whereas
the molecular weight distributions kept narrow throughout
the polymerization (Mw/Mn ꢀ 1.30) as shown in Figure 2(B).
All these observations suggested that the RAFT homopolymeri-
zation of TPFCBPMA is seen to be well controlled.62
Synthesis of PTPFCBPMA-b-PDEAEMA
FIGURE
1
1H NMR spectra of PTPFCBPMA
2
(A) and
After the discovery of living radical polymerizations, sequen-
tial addition of the monomers is more widely used than cou-
pling of two appropriately end-functionalized chains63,64 and
mechanism transformation strategy65–67 to synthesize the
block copolymers. We adopted RAFT, which is one method of
living radical polymerizations discovered recently, to synthe-
size PTPFCBPMA-b-PDEAEMA diblock copolymers for its
more tolerance to a wide range of monomers and solvents,
conservation of end groups, and well control over molecular
weights.
PTPFCBPMA-b-PDEAEMA 3 (B).
RESULTS AND DISCUSSION
Synthesis of PTPFCBPMA
TPFCBPMA 1 monomer was prepared from 4-methoxyphenol
and p-cresol following the previously reported procedure.36–39
RAFT homopolymerization of TPFCBPMA was carried out in
2-butanone at 70 ꢁC using AIBN as initiator and CDB as
chain transfer agent (CTA). The molecular weights of the
resulting PTPFCBPMA 2 homopolymers with narrow molecu-
lar weight distributions (Mw/Mn ꢀ 1.16) were tuned by the
feeding ratios of TPFCBPMA to CDB as listed in Table 1. The
homopolymers were characterized by 1H NMR as shown in
Figure 1(A). The signals of the vinylidene of TPFCBPMA
monomer at 5.75 and 6.33 ppm disappeared after polymer-
ization, this indicating the occurrence of RAFT homopolyme-
rization. The peaks at 0.87, 1.36, 1.46, and 1.75 ppm
PDEAEMA is a member of amino-containing polymethacry-
lates family and a biocompatible weak polyelectrolyte, and it
is soluble in acidic solution as a weak cationic polyelectro-
lyte due to the protonation of tertiary amine group. Its block
copolymers often exhibit interesting associative behaviors.68–70
In this work, we chose DEAEMA as the hydrophilic monomer
to prepare the amphiphilic diblock copolymers using the
hydrophobic PTPFCBPMA with two different molecular
weights as macro-CTA agent. The block length of PDEAEMA
FIGURE 2 Kinetic plot (A) and dependence of molecular weight (Mn) and molecular weight distribution (Mw/Mn) on the conversion
of monomer (B) for RAFT polymerization of TPFCBPMA 2 mediated by CDB.
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TABLE 2 Synthesis of PTFCBPMA-b-PDEAEMA 3 Diblock
mediate RAFT polymerization of DEAEMA. In addition, all
GPC curves of macro-CTAs and diblock copolymers exhibited
unimodal and symmetrical peaks with narrow molecular
weight distributions (Mw/Mn ꢀ 1.28), which meant an
almost 100% efficiency of PTPFCBPMA macro-CTA. From the
above-mentioned results, it can be concluded that
PDEAEMA-b-PTPFCBPMA well-defined diblock copolymers
have been successfully synthesized.
Copolymera
d
d
e
Sample [DEAEMA]:[2]:[AIBN] Mn (KDa) Mw/Mn NDEAEMA
3ab
3bb
3cb
3dc
3ec
3fc
a
90: 3:1
9.3
10.6
12.2
15.1
16.0
18.2
1.13
1.18
1.28
1.20
1.17
1.27
6
13
22
6
150: 3:1
300: 3:1
90: 3:1
Self-assembly of PTPFCBPMA-b-PDEAEMA
in Aqueous Media
150: 3:1
300: 3:1
11
23
CMCs of PTPFCBPMA-b-PDEAEMA 3 diblock copolymers in
aqueous solution were determined by fluorescence technique
using PNA as probe. PNA can display higher fluorescence ac-
tivity in nonpolar surroundings, and its fluorescence can be
very easily quenched by polar solvents, such as water.71–74
Figure 4 shows the relationship of the fluorescence intensity
ratio (I/I0) and the concentration of PTPFCBPMA-b-
PDEAEMA 3c at 20 ꢁC. We can clearly see from the figure
that I/I0 increased sharply when the concentration of
PTPFCBPMA-b-PDEAEMA 3c exceeded a certain value, which
meant PNA probe was incorporated into the hydrophobic
region of micelles. Thus, the intersection of two straight lines
with a value of 3.98 ꢃ 10ꢂ6 g/mL was determined to be the
CMC of PTPFCBPMA-b-PDEAEMA 3c. Diblock copolymers
form micelles above the critical concentration and below this
concentration, micelles disaggregate into unimers. The CMC
values of PTPFCBPMA-b-PDEAEMA 3 are listed in Table 3,
which are slightly lower than those of the common surfac-
tants or polymeric amphiphiles.75–78 It was found that the
CMC values of PTPFCBPMA-b-PDEAEMA 3 rose with the
increasing of the block length of hydrophilic PDEAEMA
segment.
Polymerization temperature: 70 ꢁC, polymerization time: 24 hours,
solvent: dioxane.
b
Initiated by PTPFCBPMA 2a macroinitiator (Mn ¼ 8,200, Mw/Mn¼ 1.14).
c
Initiated by PTPFCBPMA 2b macroinitiator (Mn
¼
13,900,
M
w/Mn¼
1.16).
d
Measured by GPC in THF at 35 ꢁC.
e
The number of DEAEMA repeating unit obtained from GPC.
segment was tuned by varying the feeding ratio of DEAEMA
to PTPFCBPMA macro-CTA as summarized in Table 2. Two se-
ries of PDEAEMA-b-PTPFCBPMA 3 diblock copolymers with
the same hydrophobic segment length and the different
hydrophilic block length were obtained and well characterized
1
by H NMR, FTIR, and GPC.
Figure 1(B) shows 1H NMR spectrum of PDEAEMA-b-
PTPFCBPMA diblock copolymer. The peaks at 0.89 and 1.36
ppm were attributed to the respective methyl protons
(C(CH3)) of the polymethacrylate backbone. The signals at
1.48, 1.81, and 1.90 ppm originated from the methylene pro-
tons of the main chain. The signals of the ester group of
PDEAEMA segment were located at 1.06, 2.61, 2.73, and 4.02
ppm, respectively. GPC traces of PTPFCBPMA macro-CTAs
and PTPFCBPMA-b-PDEAEMA block copolymers are shown
in Figure 3. The molecular weights of all copolymers are
much higher than those of macro-CTAs, which demonstrated
that RAFT-polymerized PTPFCBPMA can act as macro-CTA to
DLS was used to analyze the size of the micelles prepared
via direct dissolution method. As shown in Figure 5(A),
when the number of DEAEMA repeating unit increased from
6 of 3a to 22 of 3c, the diameter of the micelles enlarged
FIGURE 4 Dependence of fluorescence intensity ratio of PNA
emission band at 418 nm on the concentration of PTPFCBPMA-
b-PDEAEMA 3c.
FIGURE 3 GPC curves of PTPFCBPMA 2 and PTPFCBPMA-b-
PDEAEMA 3 in THF.
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TABLE 3 Self-assembly of PTFCBPMA-b-PDEAEMA 3 in
observed. Eisenberg et al. have shown that LCMs are reverse
micelles in an almost continuous insoluble blocks in the bulk
and surrounded by a hydrophilic surface, which provide col-
loidal stabilization.82,83 Although LCMs have been considered
no longer in their thermodynamic equilibrium, the formation
of LCMs is favored because of the higher glass transition
Aqueous Solution
CMCb (g/mL)
Dh (nm)
a
c
Sample
NTFCBPMA-b-NDEAEMA
3a
3b
3c
3d
3e
3f
18-b-6
3.56 ꢃ 10ꢂ6
3.80 ꢃ 10ꢂ6
3.98 ꢃ 10ꢂ6
3.31 ꢃ 10ꢂ6
3.61 ꢃ 10ꢂ6
4.07 ꢃ 10ꢂ6
246.9
303.1
332.8
182.1
326.7
372.2
18-b-13
18-b-22
31-b-6
temperature,
Tg,36
of
the
core-forming
segment
PTPFCBPMA.83 When adding water into the copolymer solu-
tion, the solvent becomes progressively worse for
PTPFCBPMA block, which resulted in the microphase separa-
tion of the copolymer solution; and after the formation of
the polymer aggregates and subsequent isolation into water,
the structures of the aggregates become locked because
PTPFCBPMA chains are below their Tg.83 With the continu-
ous adding of water, the interactions between the corona
chains and the solvent can no longer stabilize the aggregates,
therefore the aggregates undergo a secondary aggregation to
form large compound micelles to minimize free energy.
31-b-11
31-b-23
a
The composition of the block copolymer obtained from GPC.
b
Critical micelle concentration determined by fluorescence spectro-
scopy using PNA as probe.
c
Hydrodynamic diameter determined by DLS.
from 246.9 to 332.8 nm; when the number of DEAEMA
repeating unit increased from 6 of 3d to 23 of 3f, the dia-
meter of the micelles also shifted from 182.1 nm to
372.2 nm [Fig. 5(B)]. It was found that the size of the
micelles was raised as the length of PDEAEMA segment
ascended. As the length of PDEAEMA segment lifts, the
hydrophilic segment coronas become thicker. As a result, the
size of micelles was heightened.
CONCLUSIONS
Amphiphilic diblock copolymers based on fluorine-containing
monomer TPFCBPMA and hydrophilic monomer DEAEMA
have been successfully synthesized via two steps of succes-
sive RAFT polymerizations. PTPFCBPMA was first synthe-
sized via CDB-mediated and AIBN-initiated RAFT polymeriza-
tions. Then, well-defined PTPFCBPMA-b-PDEAEMA diblock
copolymers with narrow molecular weight distribution (Mw/
Mn ꢀ 1.28) was synthesized via RAFT polymerization of
DEAEMA mediated by PTPFCBPMA capped with dithioben-
zoate. Self-assembly of PTPFCBPMA-b-PDEAEMA in aqueous
solution was studied by fluorescence spectroscopy, dynamic
laser light scattering, and TEM. The CMC values of
PTPFCBPMA-b-PDEAEMA increased with the rising of the
content of hydrophilic segment. The diameter of the micelles
raised as the length of PDEAEMA segment lifted. All copoly-
mers we obtained could self-assemble into spherical large
compound micelles in deionized water. This type of micelles
would throw light on the potential application of PFCB-con-
taining polymers.
Amphiphilic block copolymers can self-assemble into
micelles, vesicles, and other morphologies in selective solu-
tion according to their different chemical compositions and
molecular architectures.79–81 In particular, amphiphilic
diblock copolymers can spontaneously form micelles with
hydrophobic segment as core and hydrophilic segment as co-
rona in aqueous solution. The micellar solution of
PTPFCBPMA-b-PDEAEMA 3 amphiphilic diblock copolymers
with different block lengths were prepared by adding deion-
ized water into the THF solution of the copolymers with vig-
orous stirring. After removal of THF via dialysis, the micellar
morphologies were visualized by TEM (Fig. 6). Under the
same condition, all copolymers mainly aggregated into well-
ordered spherical large compound micelles (LCMs) with
diameters of 400–600 nm and no other morphology was
FIGURE 5 Hydrodynamic diameter distributions of micelles formed by PTPFCBPMA-b-PDEAEMA 3, (A) 3a, 3b, and 3c and (B) 3d
and 3f.
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