NMR and fluorescence studies of the self-association behavior of an amphiphilic polyanion bearing hydrocarbon and fluorocarbon hydrophobes

Article abstract of DOI:10.1016/j.polymer.2011.02.015

The association behavior of the terpolymers of sodium 2-acrylamido-2- methylpropanesulfonate (NaAMPS), N-dodecylmethacrylamide (DodMAm), and N-(2-(perfluorooctyl)ethyl)methacrylamide (PFOEMAm) (A/H(x)/F(y)) and their reference copolymers of NaAMPS and PFOEMAm (A/F(y)) was characterized using ¹⁹F and ¹H NMR, steady state fluorescence, and dynamic light scattering techniques in water (or D₂O) containing 0.1 M NaCl. The terpolymers formed micelle-like aggregates where hydrophobic microdomains are formed by hydrophobic associations among the perfluorooctylethyl (PFOE) and dodecyl (Dod) groups, the PFOE group exhibiting a stronger tendency for interpolymer association than the Dod groups. A careful analysis of the characterization data led to a conclusion that the hydrophobic microdomain formed from the terpolymer is microscopically phase separated into the fluorocarbon phase and hydrocarbon phase.

Full text of DOI:10.1016/j.polymer.2011.02.015

Polymer 52 (2011) 1546e1553
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
NMR and fluorescence studies of the self-association behavior of an amphiphilic
polyanion bearing hydrocarbon and fluorocarbon hydrophobes
a
,
a
a
b
*
Akihito Hashidzume , Kentaro Matsuda , Takahiro Sato , Yotaro Morishima
a
Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
Faculty of Engineering, Fukui University of Technology, 6-3-1 Gakuen, Fukui, Fukui 910-8505, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 October 2010
Received in revised form
The association behavior of the terpolymers of sodium 2-acrylamido-2-methylpropanesulfonate
(
NaAMPS), N-dodecylmethacrylamide (DodMAm), and N-(2-(perfluorooctyl)ethyl)methacrylamide
(
PFOEMAm) (A/H(x)/F(y)) and their reference copolymers of NaAMPS and PFOEMAm (A/F(y)) was
28 January 2011
characterized using F and 1H NMR, steady state fluorescence, and dynamic light scattering techniques
19
Accepted 8 February 2011
Available online 13 February 2011
in water (or D
hydrophobic microdomains are formed by hydrophobic associations among the perfluorooctylethyl
PFOE) and dodecyl (Dod) groups, the PFOE group exhibiting a stronger tendency for interpolymer
2
O) containing 0.1 M NaCl. The terpolymers formed micelle-like aggregates where
(
Keywords:
Amphiphilic polyanion
Hydrocarbon
association than the Dod groups. A careful analysis of the characterization data led to a conclusion that
the hydrophobic microdomain formed from the terpolymer is microscopically phase separated into the
fluorocarbon phase and hydrocarbon phase.
Fluorocarbon
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
polymers bearing both fluorocarbon and hydrocarbon hydrophobes
show unique association behavior because of their incompatibility.
Amphiphilic polyelectrolytes (APEs), which possess hydro-
phobic and electrolyte units on the same polymer chain, form
various types of aggregates in aqueous media depending on the
balance between hydrophobic attraction among hydrophobes and
electrostatic repulsion among charges [1e3]. Their association
behavior is an important subject of investigation not only because
they are useful as simple models for the formation of higher order
structures of biological macromolecules but also because they are
used in various fields of applications including cosmetics, drug
delivery systems, paints, coatings, and personal care goods [4e6].
Therefore, a number of research groups have focused on the asso-
ciation behavior of APEs in the last two or more decades. Some
results of these studies allow one to control, to some extent, the
association behavior of APEs by changing the chemical structure of
the polymer.
To the best of our knowledge, however, there are only a few
examples of water soluble polymers of statistical sequences bearing
both fluorocarbon and hydrocarbon hydrophobes [23e25]
although there are larger numbers of reports on the association
behavior of linear and star polymers of fluoro- and hydrocarbon
hydrophobic block sequences [26e34].
The association behavior of random copolymers of sodium
2-acrylamido-2-methylpropanesulfonate (NaAMPS) and N-dode-
cylmethacrylamide (DodMAm) (A/H(x), where x denotes mol %
content of DodMAm, Scheme 1) have been extensively investigated
with use of various characterization techniques, and it is known
that A/H(x) copolymers show a stronger tendency for intrapolymer
association [35e40]. We were thus motivated to study how the
association behavior alters when fluorocarbon groups are bound to
A/H(x) copolymers. In the present study, perfluorooctylethyl (PFOE)
group was chosen as a fluorocarbon hydrophobe because it has
been reported that viscosities of aqueous solutions of poly(sodium
acrylate) (NaPAA) modified with PFOE groups (7 mol %) are
comparable to or only slightly higher than those of NaPAA modified
with dodecyl (Dod) groups of the same content [14]. In this study,
the association behavior of terpolymers of NaAMPS, DodMAm, and
N-(2-(perfluorooctyl)ethyl)methacrylamide (PFOEMAm) (A/H(x)/F
Since fluorocarbon groups have such distinct features as water
and oil repellency [7], chemical and heat resistance [8,9], and
solubility in supercritical carbon dioxide [10,11], fluorocarbon-
modified water soluble polymers have attracted considerable
interest from researchers [12e22]. It is expected that water soluble
(
y)) and reference copolymers of NaAMPS and PFOEMAm (A/F(y))
*
Corresponding author. Tel.: þ81 6850 5462; fax: þ81 6 6850 5461.
E-mail address: akihito@chem.sci.osaka-u.ac.jp (A. Hashidzume).
19
1
(Scheme 1) was characterized by F and H NMR, steady state
0
032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.02.015

A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
1547
the organic layer was washed with water (20 mL), with dimethyl
sulfoxide (20 mL), and then with water (10 mL). The organic layer
was concentrated under reduced pressure to obtain a dark organic
liquid. To the liquid, hydrazine monohydrate (10 mL, 200 mmol)
and Raney nickel (0.3 g, 5 mmol) were added and the mixture was
ꢀ
heated using an oil bath thermostated at 60 C with stirring for
4
(
0 h. After cooling down to room temperature, diethyl ether
200 mL) was added to the reaction mixture. The insoluble fraction
was removed by filtration. After washing with water (50 mL), the
organic layer was dried with Na SO overnight. After evaporation of
the solvent, crude 2-(perfluorooctyl)ethylamine was obtained.
-(Perfluorooctyl)ethylamine was purified by distillation under
reduced pressure: yield 19.7 g, 43% based on PFOE-I; bp
2
4
2
ꢀ
1
ꢀ
3
3.5e34.5 C at 0.17 mmHg; H NMR (400 MHz, CD OD, 30 C):
3
d
2.34 (m, 2H, methylene), 2.95 (m, 2H, methylene).
Triethylamine (10.5 mL, 75 mmol) was added to a solution of
2-(perfluorooctyl)ethylamine (19.7 g, 42 mmol) in diethyl ether
(
8
400 mL) with vigorous stirring. Methacryloyl chloride (8.2 mL,
4 mmol) was added dropwise to the mixture with stirring at 0 C
ꢀ
using an ice bath. After completion of the addition, stirring was
ꢀ
continued for 22 h at 30 C. The triethylamine hydrochloride
formed was removed by filtration. The diethyl ether solution was
washed with 0.5 M HCl (40 mL), with water (50 mL), with 0.5 M
NaHCO
3
(100 mL), and then with saturated NaCl (40 mL). The
SO overnight. After evapo-
organic layer was then dried with Na
2
4
ration of the solvent, crude PFOEMAm was obtained. PFOEMAm
was recrystallized from tetrahydrofuran: yield 17.3 g, 33% based on
ꢀ
1
ꢀ
3
, 30 C): d 1.97
PFOE-I; mp 79.6e80.9 C; H NMR (270 MHz, CDCl
s, 3H, -methyl), 2.41 (m, 2H, methylene), 3.67 (m, 2H, methylene),
.37 (s, 1H, vinyl), 5.69 (s, 1H, vinyl), 6.03 (broad, 1H, amide).Anal.
Calcd. for (C14 10NOF17): C, 31.65; H, 1.90; N, 2.64. Found: C, 31.71;
H, 1.81; N, 2.84.
(
5
a
H
Scheme 1. Chemical structures of the A/H(x)/F(y) terpolymers and A/H(x) and A/F(y)
copolymers used in this study.
2.3. Polymers
Polymers were prepared by homogeneous free radical poly-
fluorescence, and dynamic light scattering in aqueous solutions. On
the basis of characterization data, we will discuss association
characteristics of the PFOE and Dod groups covalently linked
together to a polyanion.
merization of AMPS, DodMAm, and PFOEMAm in the presence of
AIBN in DMF. A typical procedure is described below: Using a flask
equipped with a three-way stopcock, monomers were dissolved in
DMF under an argon atmosphere. To the monomer solution was
added a DMF solution of AIBN (0.5 mol% on the basis of the total
monomer concentration). The reaction mixture was warmed using
2
. Experimental
ꢀ
an oil bath thermostated at 65 C with stirring. After 17 h, the
2.1. Materials
reaction mixture was poured into a large excess of diethyl ether to
precipitate a polymer. The polymer obtained was further purified
by reprecipitation from methanol into a large excess of diethyl
ether three times, and then dissolved in water. The polymer solu-
tion was adjusted at pH 11 by adding a few drops of 1 M NaOH. The
polymer aqueous solution was dialyzed against water for several
days and finally recovered by lyophilization.
2
-Acrylamido-2-methylpropanesulfonic acid (AMPS) was pur-
chased from Wako Pure Chemicals and used without further purifi-
cation. 2,2’-Azobis(isobutyronitrile) (AIBN) was recrystallized from
methanol. N,N-Dimethylformamide (DMF) was distilled under an
argon atmosphere. N-Dodecylmethacrylamide (DodMAm) was
prepared as reported previously [41]. Pyrenewas recrystallized twice
from ethanol. N-(1-Pyrenylmethyl)heptadecafluorononanoylamide
2
2
.4. Measurements
(
PFO-Py) was prepared as reported previously [42]. Water was
purified by a Millipore Milli-Q system. Other reagents were used as
received.
.4.1. Gel permeation chromatography
Gel permeation chromatography (GPC) measurements were
ꢀ
performed at 40 C with a JASCO GPC-900 equipped with a Shodex
Asahipak GF-7M HQ column in combination with a JASCO UV-975
2.2. Preparation of N-(2-(Perfluorooctyl)ethyl)methacrylamide
(
PFOEMAm)
and RI-930 detectors. A methanol solution containing 0.2 M LiClO
4
ꢁ
1
was used as eluent at a flow rate of 0.6 mL min . Molecular weights
were calibrated with poly(ethylene glycol) and poly(ethylene oxide)
standard samples purchased from Scientific Polymer Products.
2
-(Perfluorooctyl)ethylamine was prepared from 2-(per-
fluorooctyl)ethyl iodide (PFOE-I) according to the procedure of
Trabelsi et al. [43]. A mixture of PFOE-I (57.9 g, 100 mmol), a 30%
aqueous solution of sodium azide (15.8 g, 240 mmol), and Capriquat
(
9
2.4.2. NMR
1
9
23.0 g, 57 mmol) was heated using an oil bath thermostated at
F NMR spectra were recorded on a JEOL JNM LA500 spec-
ꢀ
ꢀ
1
0 C with stirring for 10 h. After the aqueous layer was removed,
trometer using D O as a solvent at 30 C. H NMR spectra were
2

1548
A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
Table 1
Basic characteristics of the polymers used in this study.
Polymer code Content of DodMAma Content of PFOEMAma
M
/
M
M
w
w
/
4
c
c
10
n
In feed In polymer (x)b In feed In polymer (y)b
A
0
20
30
40
50
0
0
0
0
0
0
17
25
32
39
0
0
0
0
0
0
0
14
26
36
47
0
0
0
0
0
0.5
1
5
10
15
20
30
10
10
10
10
0
0
0
0
1.4
2.3
2.2
2.1
2.3
2.0
1.5
2.4
2.4
3.4
2.8
2.2
2.6
2.5
2.9
2.7
3.7
3.4
2.9
2.4
2.2
4.1
3.7
4.3
4.4
4.5
3.8
2.1
3.1
2.7
2.3
2.3
A/H(17)
A/H(25)
A/H(32)
A/H(39)
A/F(0.4)
A/F(0.8)
A/F(3.7)
A/F(6.5)
A/F(12)
A/F(16)
A/F(26)
0
0.4
0.8
3.7
6.5
12
0
0
16
26
7
7
7
A/H(14)/F(7) 20
A/H(26)/F(7) 30
A/H(36)/F(7) 40
A/H(47)/F
10)
A/H(16)/F
12)
A/H(25)/F
15)
A/H(43)/F
20)
50
20
30
40
10
(
16
25
43
20
20
20
12
15
20
2.5
1.6
2.1
2.4
2.2
1.7
(
(
(
a
b
c
In mol %.
Determined by NMR in D
Determined by GPC using methanol containing 0.2 M LiClO
2
O.
4
as eluent. Molecular
weight was calibrated with poly(ethylene glycol) and poly(ethylene oxide)
standards.
2
recorded with a JEOL JNM EX270 spectrometer using D O as
ꢀ
19
1
a solvent at 30 C. Chemical shifts in F and H NMR were refer-
enced to 2,2,2-trifluoroethanol (ꢁ75.76 ppm [44]) used as an
internal reference and to the solvent signal (4.70 ppm), respec-
19
1
tively. F and H spin-lattice relaxation times (T
using a conventional inversion-recovery technique with a 180 -
1
) were determined
ꢀ
s
-
Fig. 1. 19F NMR spectra for A/F(y) copolymers at 10 g Lꢁ1 in D O containing 0.1 M NaCl
ꢀ
9
0 pulse sequence [45e47].
2
ꢀ
1
at 30 C (a) and the fraction of associated PFOE groups as a function of y calculated
using F NMR spectra measured at 10 (circle), 5 (square), and 1 g L (triangle) (b).
D
2
O solutions were prepared as follows [38]: Solid polymer
9
ꢁ1
ꢀ
samples were dissolved in D
2
O above 90 C for 10 min. After cooling
the solutions to room temperature, a predetermined amount of
NaCl was added to the polymer solutions to adjust the ionic
strength and then heated above 90 C for 10 min. The solutions
ꢀ
heated above 90 C for 10 min. After cooling the solutions to room
ꢀ
temperature, a predetermined amount of NaCl was added to the
polymer solutions to adjust the ionic strength and then heated
above 90 C for 10 min. The solutions were stored overnight for
equilibration. Sample solutions of polymers were filtered with a 0.2
or 0.45 mm pore size PTFE membrane filter prior to measurement.
were stored overnight for equilibration before measurements.
ꢀ
2.4.3. Steady state fluorescence
Steady state fluorescence spectra were recorded on a Hitachi F-
500 fluorescence spectrophotometer at room temperature.
4
Emission spectra for pyrene and PFO-Py solubilized in polymer
solutions were measured with excitation at 337 and 341 nm,
respectively. The slit widths for both the excitation and emission
sides were kept at 2.5 nm during measurement.
An aqueous pyrene solution was prepared as follows: A small
amount of pyrene-saturated methanol was added in a large amount
of water. The turbid pyrene solution was sonicated for several hours
and allowed to stand for 1 day, and then the pyrene solution was
2
.4.4. Dynamic light scattering
Dynamic light scattering (DLS) data were obtained at varying
ꢀ
ꢀ
ꢀ
scattering angles (
q
¼ 30 e130 ) at 25 C with an Otsuka Elec-
tronics Photal DLS-7000 light scattering spectrometer equipped
with a multi- digital time correlator (ALV-5000E). An argon ion
laser (40 mW at 488 nm) was used as a light source. To obtain the
relaxation time distribution ( A( )), the inverse Laplace transform
ILT) analysis was performed using the REPES algorithm [48].
s
s
s
(
filtered with a 0.2
mm pore size PTFE membrane filter. An aqueous
solution of PFO-Py was prepared as follows: A small amount of
Z
ꢁ
4
ð1ÞðtÞ ¼
1
ꢂ 10 M PFO-Py methanol solution was added to water giving
g
s
Að
s
Þexpðꢁt=
s
Þdln
s
(1)
ꢁ
6
a final concentration of 1 ꢂ 10 M for PFO-Py. The solution was
Here,
relation function. The relaxation rate (
translational diffusion coefficient (D) was calculated from ILT
s
is the relaxation time and g(1)(t) is the normalized autocor-
sonicated for 2e3 h and allowed to stand for 1 day.
ꢁ1
Sample solutions were prepared as follows: Solid polymer
samples were dissolved in an aqueous solution of pyrene or PFO-Py
G
¼
s
) is a function of q. The
ꢀ
2
above 90 C for 10 min. After cooling the solutions to room
moments as D ¼ (
G
/q )
, where q ¼ (4
pn/l)sin(q/2). The
q
/ 0
temperature, the solutions were diluted by the aqueous solution of
pyrene or PFO-Py to prepare solutions of varying polymer
hydrodynamic radius (R ) was calculated using the StokeseEinstein
H
equation, R ¼ k T/(6phD), where k is Boltzmann’s constant, T is the
H
B
B
ꢁ
5
concentrations (c) ranging from 10 e10 g/L. The solutions were
absolute temperature, and
h
is the solvent viscosity.

A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
1549
Fig. 3. Relaxation time distributions obtained at
q
¼ 90ꢀ by DLS for A/F(0.4) (a), A/F
ꢁ
6
(0.8) (b), A/F(3.7) (c), A/F(6.5) (d), A/F(12) (e), A/F(16) (f), and A/F(26) (g) copolymers in
Fig. 2. Steady state fluorescence spectra for 1 ꢂ 10 M PFO-Py solubilized in A/F(26)
ꢀ
ꢀ
0.1 M NaCl at 25 C.
copolymer in 0.1 M NaCl at 25 C (a) and the fluorescence intensity of PFO-Py solu-
bilized in A/F(y) copolymers as a function of y at varying c (b).
feed was varied in a wide range (i.e., 20 ꢁ 50 mol %) to yield
terpolymers of a wide x range (14 ꢁ 47 mol %). The terpolymers,
A/H(x)/F(y), with x and y values larger than those listed in Table
Aqueous solutions were prepared as follows: Solid polymer
samples were dissolved in water above 90 C for 10 min. After
cooling the solutions to room temperature, a predetermined
amount of NaCl was added to the polymer solutions to adjust ionic
strength to 0.1 and then heated at the same temperature. The
solutions were stored overnight for equilibration. All sample solu-
ꢀ
1
were found to be insoluble in water, and thus they were not
further characterized. As listed in Table 1, weight-average
molecular weights (M ) of the terpolymers and copolymers
were estimated to be (1.4e3.4) ꢂ 10 by GPC using methanol
containing 0.2 M LiClO as eluent, in which the polymers
w
4
4
tions of polymers were filtered with a 0.2 or 0.45
membrane filter prior to measurement.
mm pore size PTFE
dissolve molecularly at lower concentrations.
3
. Results and discussion
3.2. Association behavior of the A/F(y) copolymers
3
.1. Basic characteristics of the ter- and copolymers employed in
First, we characterized the association behavior of the A/F(y)
19
this study
copolymers using an F NMR technique, a useful characterization
tool for the association behavior of fluoroalkyl surfactants and flu-
oroalkyl-modified water soluble polymers [15e18,49e54]. Fig. 1a is
The terpolymers and the two series of reference copolymers
19
prepared in the present study are abbreviated as A/H(x)/F(y),
A/H(x), and A/F(y), respectively, where x and y denote the mol %
a typical example of F NMR spectra for A/F(y) at a polymer
ꢁ1
concentration of 10 g L . The spectra for A/F(y) of y ꢃ 0.8 exhibit
contents of DodMAm (x) and PFOEMAm (y) determined by
signals ascribable to CF
3
in PFOE groups at ca. ꢁ80 ppm. On the other
a combination of 1H and F NMR spectra in D
19
O using 2,2,2-
hand, the spectra for A/F(y) of y ꢄ 3.7 mol % exhibit broad signals
around ꢁ82 ppm along with a sharp signal at ca. ꢁ80 ppm, the
2
trifluoroethanol as an internal standard (Scheme 1 and Table 1).
Values of x and y for A/H(x)/F(y) terpolymers and A/H(x) and A/F
former ascribable to CF
3
in associated PFOE groups [15e18] and the
(
y) copolymers were found to be close to or slightly smaller than
latter to CF in free PFOE. Using the ratio of area intensities of the two
3
the mol % contents of DodMAm and PFOEMAm in the monomer
feed. This finding is indicative of the statistical distribution of
the DodMAm and PFOEMAm units in the terpolymers and
copolymers. In the terpolymers, the contents of PFOEMAm in
the monomer feed were fixed at 10 and 20 mol % to provide
lower (7 ꢁ 10 mol %) and higher y values (12 ꢁ 20 mol %),
respectively, whereas the content of DodMAm in the monomer
signals, the fractions of associated PFOE groups were calculated and
plotted in Fig. 1b against y. The fraction commences to increase
markedly around y ¼ 1 mol % up to ca. 97% at y ¼ 26 mol %. It should
be noted here that the fraction is independent of c in the c region
ꢁ1
examined (1 ꢁ10 g L ).
Values of T
for the signals at ca. ꢁ80 and ꢁ82 ppm were
measured using the inversion-recovery technique to confirm that
1

1550
A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
Fig. 5. 1H NMR spectra for A/H(x)/F(y) terpolymers at 10 g L in D
ꢁ1
O containing 0.1 M
Fig. 4. 19F NMR spectra for A/H(x)/F(y) terpolymers at 10 g L in D
ꢁ1
2
2
O containing 0.1 M
ꢀ
NaCl at 30 C (a) and T
1
of CH
3
as a function of x for A/H(x) copolymers (circle) and A/H
x)/F(y) terpolymers of x ¼ 14e16 (square), 25e26 (triangle), and 36e47 mol % (dia-
ꢀ
NaCl at 30 C (a) and T
1
of CF
3
as a function of y for A/F(y) copolymers (circle) and A/H
(
(
x)/F(y) terpolymers of x ¼ 14e16 (square), 25e26 (triangle), and 36e47 mol % (dia-
mond) (b).
mond) (b).
these signals are ascribable to CF
groups, respectively. As can be seen in Fig. S1 in Supplementary
Content, T values were determined to be 0.97e1.14 and ca. 0.45 s
for the signals at ca. ꢁ80 and ꢁ82 ppm, respectively, independent
of y. Since T is usually shorter for a nucleus of a slower rotational
motion in solution NMR [55], the CF groups for the signals around
82 ppm show slower rotational motions than do those for the
signals at ca. ꢁ80 ppm. These observations indicate that the rates of
association and dissociation are slow compared to the time scale of
NMR (zms) and PFOE groups associated show similar restricted
mobilities independent of y.
Steady state fluorescence has commonly been utilized for
characterization of hydrophobic microdomains of hydrophobically
modified water soluble polymers in aqueous media. But it is known
that pyrene, a most commonly used fluorescence probe, cannot be
solubilized in microdomains formed from fluoroalkyl groups
3
in free and associated PFOE
Furthermore, the ratio of the first and the third vibronic peaks (I
3
/
I
1
) is almost constant (ca. 6.8) independent of both y and c (data not
1
shown), indicating that only the PFO chain is incorporated in
hydrophobic microdomains and the pyrene moiety of PFO-Py is
exposed to or exists close to the bulk water phase.
The size of aggregates formed from A/F(y) copolymers was
investigated by DLS. As can be seen in Fig. 3, A/F(y) copolymers of
1
3
ꢁ
ꢁ
1
y ꢃ 3.7 mol % exhibit almost unimodal distributions at 5 g L
.
Since these copolymers do not form hydrophobic microdomains
(see Fig. 2b), it is likely that these polymers are in the unimer state.
On the other hand, A/F(y) copolymers of y ꢄ 6.5 mol % show
bimodal distributions. These observations indicate that A/F(y)
copolymers show a stronger tendency for interpolymer association
than do A/H(x) copolymers [35e38].
3.3. Association behavior of the A/H(x)/F(y) terpolymers
[
(
56,57]. Thus, a pyrene derivative carrying a perfluorooctyl chain
PFO-Py) was employed in this study. Fig. 2a demonstrates a typical
19F NMR spectra were also measured for A/H(x)/F(y) terpoly-
example of steady state fluorescence of PFO-Py solubilized in
aqueous solutions of A/F(26) at varying c. The spectra indicate that
the fluorescence intensity increases with increasing c, indicative of
the formation of hydrophobic microdomains. In Fig. 2b, the inten-
sities at 375 nm were plotted against y at different polymer
concentrations. These plots indicate that A/F(y) copolymers of
y > ca. 10 mol % form hydrophobic microdomains large enough to
mers to investigate their association behavior. Fig. 4a demon-
19
strates a typical example of F NMR spectra for A/H(x)/F(y)
ꢁ
1
terpolymers measured in D O containing 0.1 M NaCl at 10 g L
2
.
Noteworthy is that these spectra exhibit only a broad signal
ascribable to CF around ꢁ82 ppm, contrast to the spectra for A/F
3
(y) copolymers. These observations suggest that the rates of
association and dissociation are faster than the NMR time scale
ꢁ1
incorporate PFO-Py, at c > 1 g L . It should be noted here that more
than 85% of PFOE chains are associated in this y regime.
(zms) or most of all PFOE chains are associated. Values of T were
1
also measured and plotted in Fig. 4b against y. For comparison, the

A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
1551
ꢁ
1
average T
1
values of CF
3
in free and associated PFOE groups in A/F
values
c > 1 g L (see Fig. S2 in Supplementary Content). In Fig. 6b, I
3 1
/I
values at c ¼ 5 g L are plotted against x. These plots demonstrate
that I /I increases with increasing x but is practically independent
ꢁ1
(
y) copolymers are also plotted in this figure. Since all the T
1
obtained for the terpolymers are shorter than or equal to 0.4 s, it is
3 1
likely that most of all PFOE groups are associated in the x and y
ranges examined. T for CF decreases with increasing both x and
1 3
of y. This observation is suggestive of microscopic phase separation
of hydrocarbon and fluorocarbon hydrophobes. Steady state fluo-
rescence spectra for PFO-Py showed a similar tendency, as can be
seen in Fig. S3 in Supplementary Content.
y. Especially, for A/H(x)/F(y) terpolymers of x ¼ 36 ꢁ 47 mol %, T
1
decreases markedly with increasing y. These observations indicate
that PFOE groups show a more restricted mobility in hydrophobic
microdomains formed from A/H(x)/F(y) terpolymer of larger x
and y.
Fig. 7 shows an example of relaxation time distributions
ꢁ
1
obtained by DLS for A/H(x)/F(y) terpolymers at 5 g L . All the
terpolymers examined show bimodal distributions. Especially, A/H
(16)/F(12) terpolymer, where the mole fraction of PFOE in the total
hydrophobes is the highest of all the terpolymers examined, forms
Fig. 5a demonstrates a typical example of 1H NMR spectra for
A/H(x)/F(y) terpolymers measured in D
1
2
O containing 0.1 M NaCl at
0 g L . These spectra exhibit broad signals ascribable to Dod
chains in the region of 0.6e2.0 ppm. T values were also measured
for the signals due to CH in Dod groups and plotted in Fig. 5b
against x. T for CH also decreases with increasing x and y. At an
almost constant y (y ¼ 7 ꢁ 10 or 12 ꢁ 20 mol %), T decreases with
ꢁ
1
larger aggregates of R
These observations also indicate that PFOE group shows a tendency
for interpolymer association.
H
¼ 61 nm as the major component (Fig. 7e).
1
3
1
3
On the basis of characterization data described above, the
association behavior of A/H(x)/F(y) terpolymers may be discussed
as follows: When the T values for CF in A/F(y) copolymers and A/H
1 3
(x)/F(y) terpolymers in Fig. 4b are replotted against x þ y, data
points are on a smooth curve as can be seen in Fig. 8, indicating that
the mobility of the hydrophobic microdomains are dependent on
both x and y, and Dod and PFOE chains interact with each other. On
1
increasing x and vise versa. These observations indicate that Dod
groups show a more restricted mobility in hydrophobic micro-
domains formed from A/H(x)/F(y) terpolymer of larger x and y.
The formation of hydrophobic microdomains was characterized
by steady state fluorescence for A/H(x)/F(y) terpolymers using
pyrene as a fluorescence probe. Fig. 6a demonstrates a typical
example of steady state fluorescence spectra normalized at the first
vibronic peak for pyrene solubilized in aqueous solutions of A/H
3 1
the other hand, Fig. 6b demonstrates that I /I is dependent only on
x but independent of y, suggesting that Dod and PFOE chains exist
separately from each other. These observations can be explained by
the formation of a micelle-like aggregate in which hydrophobic
microdomains are phase separated into fluorocarbon and hydro-
carbon domains.
As described in the Introduction section, Dod and PFOE chains
may undergo microscopic phase separation within a hydrophobic
microdomain to form hydrocarbon and fluorocarbon phases,
(
47)/F(20) terpolymer at varying c. I
indicative of the formation of hydrophobic microdomains [58]. For
all the terpolymers examined, I /I commenced to increase at
3 1
/I increases with increasing c,
3
1
ꢁ
3
ꢁ1
c z 10 g L and leveled off at ca. 0.9e1.0 in the c regime of
Fig. 6. Normalized steady state fluorescence spectra for pyrene solubilized in A/H(47)/
ꢀ
ꢁ1
¼ 90ꢀ by DLS for A/H(14)/F(7) (a), A/
F(20) terpolymer in 0.1 M NaCl at varying c and 25 C (a) and I
a function of x for A/H(x) copolymers (circle) and A/H(x)/F(y) terpolymers of y ¼ 7e10
3
/I
1
at c ¼ 5 g L as
Fig. 7. Relaxation time distributions obtained at q
H(26)/F(7) (b), A/H(36)/F(7) (c), A/H(47)/F(10) (d), A/H(16)/F(12) (e), A/H(25)/F(15) (f),
and A/H(43)/F(20) (g) terpolymers in 0.1 M NaCl at 25 C.
ꢀ
(
square) and 12e20 mol % (triangle) (b).

1552
A. Hashidzume et al. / Polymer 52 (2011) 1546e1553
terpolymer proposed on the basis of the characterization data
described above.
4. Conclusion
The association behavior of A/H(x)/F(y) terpolymers as well as
19
1
reference A/F(y) copolymers was investigated by F and H NMR,
steady state fluorescence, and DLS in water (or D O) containing
.1 M NaCl.
19F NMR spectra for A/F(y) copolymers at 10 g Lꢁ1
sharp and broad signals at ca. ꢁ80 and ꢁ82 ppm ascribable to CF
free and associated PFOE groups, respectively. Using the ratio of
area intensities of the signals due to CF in free and associated PFOE
2
0
exhibited
in
3
3
groups, the fraction of associated PFOE groups was calculated. The
fraction commences to increase markedly around y ¼ 1 mol % up to
ca. 97% at y ¼ 26 mol %. Steady state fluorescence spectra of PFO-Py
solubilized in aqueous solutions of A/F(y) copolymers exhibited an
increase in the fluorescence intensity with increasing c, indicating
that A/F(y) copolymers of y > ca. 10 mol % form hydrophobic
microdomains at c > 1 g L . DLS data for A/F(y) copolymers of
y ꢄ 6.5 mol % exhibited bimodal distributions, indicating that A/F(y)
copolymers have a stronger tendency for interpolymer association
Fig. 8. T
1
of CF
3
as a function of x þ y for A/F(y) copolymers (circle) and A/H(x)/F(y)
terpolymers of x ¼ 14e16 (square), 25e26 (triangle), and 36e47 mol % (diamond) (b).
ꢁ
1
respectively [23e25]. It is worthy of mentioning the mixing
behavior of PFOE-I and n-dodecane for comparison with the phase
separation behavior of the Dod and PFOE chains. The upper limit
mole fraction of PFOE-I (¼[PFOE-I]/{[PFOE-I] þ [n-dodecane]}) to
than do A/H(x) copolymers.
19F NMR spectra for A/H(x)/F(y) terpolymers at 10 g Lꢁ1
3
exhibited only a broad signal ascribable to CF in associated PFOE
ꢀ
yield homogeneous mixing is 0.04 at 25 C. The small value of the
1
groups around ꢁ82 ppm. H NMR spectra for A/H(x)/F(y) terpoly-
upper limit suggests that the mixing of the two small molecules,
PFOE-I and n-dodecane, is primarily entropy driven and there is
little or no enthalpy gain from the mixing. Considering such
entropy driven mixing is extremely unfavorable for polymer
systems, it seems to be reasonable that all the A/H(x)/F(y)
terpolymers examined in this study form microscopically segre-
gated hydrocarbon and fluorocarbon phases in hydrophobic
microdomains because x and y range 14e47 and 7 ꢁ 20 mol %,
respectively, where y/(x þ y) is much higher than the upper limit of
homogenous mixing for PFOE-I in n-dodecane.
ꢁ1
mers at 10 g L showed broad signals ascribable to Dod chains in
1 3 3
the region of 0.6e2.0 ppm. T values for CF in PFOE groups and CH
in Dod groups decreased with increasing both x and y, indicating
that PFOE and Dod groups show a more restricted mobility in
hydrophobic microdomains formed from A/H(x)/F(y) terpolymer of
1 3
higher x and y. In the plot of T values for CF in A/F(y) copolymers
and A/H(x)/F(y) terpolymers as a function of x þ y, all data points
were found on a smooth curve, indicating that Dod and PFOE chains
interact with each other. Steady state fluorescence spectra for
pyrene solubilized in A/H(x)/F(y) terpolymers showed that I
3
/I
1
at
Fig. 9 illustrates a conceptual model for a microscopically phase
separated hydrophobic microdomain formed by the A/H(x)/F(y)
ꢁ1
5
g L increased with increasing x but was practically independent
of y. This observation is indicative of microscopic phase separation
of hydrocarbon and fluorocarbon hydrophobes. DLS data demon-
strated bimodal distributions for all the A/H(x)/F(y) terpolymers
examined. Especially, A/H(16)/F(12) terpolymer, in which the mole
fraction of PFOE in the total hydrophobes is the highest of all the
terpolymers examined, formed larger aggregates of R
the major component. These observations also indicate that PFOE
group shows a tendency for interpolymer association.
H
¼ 61 nm as
Acknowledgments
The authors are grateful to Mr. Seiji Adachi, Department of
Chemistry, Graduate School of Science, Osaka University, for NMR
measurements.
Appendix. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.polymer.2011.02.015.
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