Synthesis and proton conductivity of partially sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) block copolymers

Article abstract of DOI:10.1021/ma0477549

A series of novel, amphiphilic block copolymers comprising of sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) [P(VDF-co-HFP)-b-SPS] were synthesized. The number-average molecular weights of the fluorous and polystyrene segments were 17 900 and 8100 g/mol, respectively. Sulfonation of the polystyrene segment to different extents provided a series of polymers which were cast into films to yield proton exchange membranes with varying ion exchange capacity (IEC). Proton conductivity of the membranes increased significantly when the IEC was increased from 0.5 to 1.2 mmol/g. For 0.9-1.2 mmol/g IEC membranes, the conductivity was similar to Nafion 117, significantly higher than random copolymers of polystyrene and sulfonated polystyrene, and twice that of nonfluorous block copolymer membranes based on sulfonated poly(styrene-b-[ethylene-co-butylene]-b-styrene) (S-SEBS) and sulfonated hydrogenated poly(butadiene-b-styrene) (S-HPBS) copolymers. TEM revealed a disruption in ordered morphology with increasing degree of sulfonation. Morphological structures of membranes having 0.6-1.2 mmol/g IEC comprised of interconnected networks of ion channels, each of 8-15 nm width.

Full text of DOI:10.1021/ma0477549

Macromolecules 2005, 38, 4193-4201
4193
Synthesis and Proton Conductivity of Partially Sulfonated
Poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) Block
Copolymers
Zhiqing Shi and Steven Holdcroft*
Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada, and
Institute for Fuel Cell Innovation, National Research Council (NRC), 3250 East Mall,
Vancouver, BC V6T 1W5, Canada
Received November 2, 2004; Revised Manuscript Received February 18, 2005
ABSTRACT: A series of novel, amphiphilic block copolymers comprising of sulfonated poly([vinylidene
difluoride-co-hexafluoropropylene]-b-styrene) [P(VDF-co-HFP)-b-SPS] were synthesized. The number-
average molecular weights of the fluorous and polystyrene segments were 17 900 and 8100 g/mol,
respectively. Sulfonation of the polystyrene segment to different extents provided a series of polymers
which were cast into films to yield proton exchange membranes with varying ion exchange capacity (IEC).
Proton conductivity of the membranes increased significantly when the IEC was increased from 0.5 to
1.2 mmol/g. For 0.9-1.2 mmol/g IEC membranes, the conductivity was similar to Nafion 117, significantly
higher than random copolymers of polystyrene and sulfonated polystyrene, and twice that of nonfluorous
block copolymer membranes based on sulfonated poly(styrene-b-[ethylene-co-butylene]-b-styrene) (S-SEBS)
and sulfonated hydrogenated poly(butadiene-b-styrene) (S-HPBS) copolymers. TEM revealed a disruption
in ordered morphology with increasing degree of sulfonation. Morphological structures of membranes
having 0.6-1.2 mmol/g IEC comprised of interconnected networks of ion channels, each of 8-15 nm width.
Introduction
Block copolymer ionomers are a potentially useful
family of materials for studying structure-property
relationships in PEMs since they can be prepared with
well-defined structures that confer uniquely ordered
morphologies in the solid state. Several reports on the
morphology and physical properties of proton conducting
membranes based on the polystyrene-containing block
copolymers have been published. These include partially
sulfonated poly(styrene-b-[ethylene-co-butylene]-b-sty-
rene) (S-SEBS),8-16 sulfonated poly(styrene-b-isobutyl-
ene-b-styrene) (S-SIBS),17-21 sulfonated hydrogenated
poly(butadiene-b-styrene) (S-HPBS),22,23 sulfonated poly-
(styrene-b-ethylene-alt-propylene) (S-SEP),24,25 and poly-
(styrene-b-ethylene/propylene-b-styrene) (S-SEPS) co-
polymer.24 In related block copolymer studies, graft
copolymers of PS-g-macPSSA show enhanced conductiv-
ity compared to that of random copolymers of styrene
and styrenesulfonic acid (PS-r-PSSA).26-29 More re-
cently, block copolymers based on sulfonated bisphenol
A polysulfone and poly(vinylidene difluoride) (PSF-b-
PVDF) were observed to exhibit enhanced proton con-
ductivity compared to that of homopolymers of sulfo-
nated bisphenol A polysulfone.30
In this work, proton-conducting diblock copolymers,
sulfonated poly([vinylidene difluoride-co-hexafluoropro-
pylene]-b-styrene) [P(VDF-co-HFP)-b-SPS], incorporat-
ing a nonionic fluorous block and a sulfonated ionic
block are synthesized according to Scheme 1. There are
several motivations to investigate these particular
fluoropolymers. First, the two segments of block polymer
are incompatible which ensures self-assembly and ionic
aggregation. Second, since controlled radical polymer-
ization is employed to grow the polystyrene segment,
the length and/or ionicity of the hydrophilic block, and
thus IEC, can be controlled by adjusting either the
length of the sulfonated polystyrene chains or the degree
of sulfonation. This paper describes the synthesis of a
series of sulfonated fluorous block copolymer mem-
Proton exchange membranes (PEMs) play a central
role in proton exchange membrane fuel cells (PEMFCs),
serving as both electrolyte and separator. An ideal
membrane should possess chemical and electrochemical
stability, mechanical strength and integrity, and high
proton conductivity.1-3 In the past decade, many poly-
mers have been designed and studied in an effort to
address the poor high-temperature proton conductivity,
high methanol permeability, and high cost of perfluoro-
sulfonic acid (PFSA) membranes.4,5 Despite numerous
efforts, alternate materials still fail to meet the strin-
gent requirements for high volume commercial markets.
It is argued that a greater understanding of fundamen-
tal structure-property relationships of PEMs is re-
quired in order to make significant technological break-
throughs.1,6
A rudimentary requirement for PEMs is adequate
proton conductivity. Conductivity is affected by the
polymer’s chemical structure (i.e., its composition and
nature), ion exchange capacity (IEC), water content, and
morphology. PEMs generally consist of ion-containing
polymers that possess a hydrophobic polymer backbone
and pendent proton exchange sites. In a solid-state
matrix of hydrophobic polymer, ionic groups aggregate.7
However, it is not fully understood how these interac-
tions are influenced by the polymer architecture and
how aggregation affects the membrane’s morphology
and conductivity. The search, design, and synthesis of
model polymers that phase separate into proton con-
ducting and hydrophobic domains is an important area
of research both for obtaining insights into proton
transport and for the design and implementation of next
generation membranes.
* To whom correspondence should be addressed. E-mail:
holdcrof@sfu.ca.
10.1021/ma0477549 CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/15/2005

4194 Shi and Holdcroft
Macromolecules, Vol. 38, No. 10, 2005
Scheme 1. Synthetic Scheme for P(VDF-co-HFP)-b-SPS
Membranes were washed several times with Millipore de-
ionized water for 30 min periods.
branes possessing different degrees of sulfonation. The
correlation between composition, structure, and proton
conductivity is reported.
Membranes were equilibrated in 2 M NaCl solution for at
least 4 h at room temperature prior to titration. The protons
released into solution were titrated with 0.025 M NaOH.
Following titration, membranes were placed in 2 M HCl for a
minimum of 4 h in order to reprotonate the membranes, dried
under vacuum for 2 h at 70 °C, and placed in a desiccator to
cool before determining the membrane’s “dry” weight. The IEC
of the membrane (mmol/g) was calculated according to eq 1
Experimental Section
1. Materials. Sulfuric acid (Anachemia, 95-98%, ACS
reagent), acetic anhydride (Caledon, reagent grade), and
1,2-dichloroethane (Caledon, reagent grade) were used as-
received. Nafion 117 (Aldrich) films were pretreated with
3 vol % H2O2 and 5 wt % HNO3 aqueous solution at 90 °C for
30 min, respectively, rinsed with Millipore water three times,
and stored in water. Poly([vinylidene difluoride-co-hexafluo-
ropropylene]-b-polystyrene was synthesized by atom transfer
radical polymerization (ATRP) of styrene initiated by a trichlo-
romethyl-terminated fluorous macroinitiator. The macroini-
tiator was prepared by emulsion polymerization in the pres-
ence of chloroform, which served as a chain transfer agent. A
detailed procedure of this synthesis is reported elsewhere.31
The following conditions for ATRP were used: (1) the concen-
trations of fluoropolymer macroinitiator [P(VDF-co-HFP),
Mn,GPC ) 17 900 g/mol, Mw/Mn ) 1.48], dipyridyl (bpy), copper-
(I) chloride (CuCl), and styrene were 0.012, 0.34, 0.17, and
2.8 M, respectively; (2) the reaction was run for 24 h at
110 °C; (3) the conversion of styrene was terminated at 36.2%
in order to limit the length of the polystyrene block. Based on
the conversion of styrene, the estimated Mn of the polystyrene
segment was 8700 g/mol, and the estimated Mn of the block
copolymer was 26 600 g/mol.
Acid-bearing polymers were prepared by sulfonation of the
polystyrene segment. Sulfonation was carried out in
1,2-dichloroethane using the procedure described in ref 11,
except a reaction temperature of 40 °C was used. A typical
sulfonation reaction is as follows: to a 50 mL three-neck flask
equipped with a dropping funnel and condenser, 15 mL of
1,2-dichloroethane and 0.6 g of P(VDF-co-HFP)-b-PS were
added, and the mixture was heated to 50 °C under N2 and
stirred until the copolymer completely dissolved. Acetyl sulfate
was prepared by injecting 1 mL of acetic anhydride and 3 mL
of dichloroethane into a nitrogen-purged vial. The solution was
cooled to ∼0 °C in a 10% CaCl2 ice bath, and 0.3 mL of
95-97% sulfuric acid was injected. The resultant acetyl sulfate
was immediately transferred to the polymer solution at 40 °C
using a dropping funnel. Samples with different degrees of
sulfonation were periodically extracted and precipitated in
50/50 ethanol/hexanes. The precipitate was washed with water
until the residual water was pH 7. Sulfonated polymers were
dried under vacuum at 60 °C overnight. Highly sulfonated
polymer was dissolved in water, and the solution was purified
by dialysis using a cellulose dialysis tube (Fisherbrand,
Standard Grade, nominal MWCO 12 000-14 000) for 3 days.
The polymer solution was evaporated, and the polymer was
dried at 60 °C for 2 days under vacuum.
V
NaOHMNaOH
IEC )
(1)
Wdry
where VNaOH and MNaOH are the volume (mL) and molar
concentration of NaOH solution used in titration, respectively.
Wdry is the dry weight of the sample.
The membranes were equilibrated in Millipore water over-
night at room temperature and blotted with a Kimwipe to
remove surface water, and the “wet” weight (Wwet) was
measured. The water uptake of the membranes was calculated
as the percentage increase over the “dry” weight according to
eq 2. In contrast, the water content of the membranes was
calculated as the percentage of water in the “wet” membrane
according to eq 3. IEC, water uptake, and water content values
were taken as the average of three samples.
Wwet - Wdry
water uptake )
water content )
× 100%
(2)
(3)
Wdry
Wwet - Wdry
× 100%
Wwet
[H2O]/[SO3-], the number of water molecules per ion exchange
site, was calculated using eq 4.
water uptake (%) × 10
[H2O]/[SO3-] )
(4)
18 × IEC (mmol/g)
The proton concentration in wet membranes was calculated
using eq 5.
Wdry (g)
volwet (cm3)
[H+] )
× IEC (mmol/g)
(5)
3. Techniques. The molecular weight of the block copoly-
mer was determined by gel permeation chromatography (GPC)
using three µ-Styragel columns, a Waters 510 HPLC, polysty-
rene standards, THF eluant, and a Waters 410 differential
refractometer. The degree of sulfonation of the membranes was
estimated by 1H NMR (in d6-acetone) using a 400 MHz Bruker
AMX400 spectrometer. FTIR spectra were recorded on spin-
cast thin films on a sodium chloride disk using a Bomem 155
FT-IR spectrometer. Differential scanning calorimetry (DSC)
was performed on a TA Instruments Q10 differential scanning
2. Membrane Preparation, IEC, and Water Sorption.
Membranes were prepared by dissolving the sulfonated block
copolymers in THF and casting on a Telfon sheet. Films were
dried at room temperature and 60 °C for 2 h in vacuo. The
sulfonated membranes were treated with 2 M HCl overnight.

Macromolecules, Vol. 38, No. 10, 2005
[P(VDF-co-HFP)-b-SPS] Block Copolymers 4195
calorimeter using a heating rate of 10 °C/min under N2. Data
were collected from -100 to 200 °C. Tg values were determined
from the second thermal cycle. Thermal gravimetric analysis
(TGA) of the membranes prepared with various degrees of
sulfonation was performed using a TA Instruments model 2950
at a heating rate of 20 °C/min under N2. Prior to DSC and
TGA measurements, all samples were dried under vacuum at
80 °C overnight.
In-plane proton conductivity was measured by ac impedance
spectroscopy with a HP 8753 network analyzer using a
frequency range of 300 kHz to 1 GHz. A gold-plated coaxial
probe was used as previously described.27,32 The accuracy of
the measurements was verified by the reported values of
Nafion 117 (0.07-0.08 S/cm). An ESPEC SH-240 temperature/
humidity chamber and a conductivity cell similar to that
described in ref 33 were used for the measurement of mem-
brane conductivity under conditions of variable temperature
and humidity.
Samples for transmission electron microscopy (TEM) were
prepared using the following steps: (1) Membranes (∼0.1 mm
thick) were cast from THF solutions and stained by placing
them overnight in a saturated lead acetate solution. (2) Films
were rinsed with water and dried under vacuum at room
temperature for a minimum of 4 h. (3) Membranes were
embedded in Spurr’s epoxy resin. (4) The blocks were sectioned
to yield slices 60-100 nm thick, using a Reichert OM3
microtome, and picked up on copper grids. Images were taken
on a Zeiss 10C transmission electron microscope using an
accelerating voltage of 80 kV.
Figure 1. FTIR spectra of (a) P(VDF-co-HFP), (b) P(VDF-co-
HFP)-b-PS, and (c) sulfonated block copolymer P(VDF-co-
HFP)-b-SPS.
Results and Discussion
Degree of Sulfonation and IEC. The composition
of the poly(VDF-co-HFP) macroinitiator was determined
by 19F NMR spectroscopy, as previously described,31 and
found to comprise of 16.7 mol % of HFP and 83.3 mol %
of VDF. It possessed a number-average molecular
weight of 17 900 g/mol and polydispersity index of 1.48,
as determined by GPC analysis calibrated with poly-
styrene standards. The number of VDF and HFP
repeating units was calculated to be 191 and 38,
respectively. The number-average molecular weight of
poly(VDF-co-HFP)-b-PS block copolymer was 26 000
g/mol and possessed a polydispersity index of 1.35. The
molecular weight of the polystyrene segments is esti-
mated to be 8100 g/mol, and thus the number of styryl
repeat units is 78. The ratio of fluoropolymer to poly-
styrene segments is 2.2:1 based on the respective
molecular weights and 2.9:1 based on the number of
repeat units. The polystyrene units in the block copoly-
mer represent 31 wt %.
FTIR spectroscopy was used to confirm sulfonation
of the block copolymer and to estimate the ion exchange
capacity.28 FTIR spectra of the block copolymer before
and after sulfonation are shown in Figure 1. The strong
absorbance at 1129 cm-1 is due to C-F stretching. The
two peaks situated at 699 and 757 cm-1 are assigned
to the C-H bond of unsubstituted phenyl rings, while
the two peaks at 1453 and 1493 cm-1 are assigned to
stretching vibrations of unsubstituted phenyl rings.
These four characteristic peaks for unsubstituted phenyl
rings in polystyrene segments disappear following sulfo-
nation. The appearance of characteristic peaks due to
symmetric stretching of SO3- at 1035 cm-1 and in-plane
bending of para-substituted phenyl ring at 1008 cm-1
confirm introduction of sulfonic groups.
NMR spectroscopy was used to quantify sulfonation.
1H NMR spectra of both partially sulfonated and fully
sulfonated block copolymers are shown in Figure 2. The
pristine polymers exhibit peaks at 6.4-6.8 ppm (protons
“a”) and 6.9-7.3 ppm (protons “b”) due to ortho and
meta/para protons on the phenyl ring, respectively.
Figure 2. 1H NMR spectra of [P(VDF-co-HFP)-b-PS], partially
sulfonated (DS ) 32%), and fully sulfonated (DS ) 100%).
Upon full sulfonation, a broad peak is observed at
7.62 ppm due to protons adjacent to the sulfonate group
(protons “c”) and peaks due to protons “b” disappear. A
broad peak is also observed at 6.82 ppm and is assigned
to aromatic protons adjacent to the main chain on
sulfonated phenyls (protons “a′”). The partially sulfo-
nated polymers exhibit all the above peaks and the ratio
of integrals was used to quantify the degree of sulfona-
tion, represented as DS (%), according to eq 6
m
m + l
C/2
DS (% ) )
× 100% )
× 100% (6)
C/2 + B/3
where m and l are the number of repeat units of

4196 Shi and Holdcroft
Macromolecules, Vol. 38, No. 10, 2005
Table 1. Properties of [P(VDF-co-HFP)-b-SPS] Block Copolymer Membranes as a Function of Sulfonation Reaction Time
of the Base Polymer
reaction time (min)
5
10
15
30
45
70
49
1.31
1.31
1200
degree of sulfonation (%)
12
17
22
0.62
0.72
32
0.89
0.89
40
1.08
1.18
∼100
calculated IECa (mmol/g) 0.35
0.49
0.53
(0.02
2.40
measured IECb (mmol/g)
0.26
(0.01
(0.08
(0.03
(0.09
conductivityc (S/cm)
water conentd (wt %)
(1.6 ( 0.9) × 10-4 (2.5 ( 0.2) × 10-3 0.016 ( 0.002 0.055 ( 0.001 0.080 ( 0.002 0.076
<1.5
<1.5
12 ( 2
28 ( 3
47 ( 2
80
water uptaked (wt %)
<1.5
<1.5
14 ( 3
38 ( 3
89 ( 7
388
165
0.32
-
[H2O]/[SO3
]
<3
<2
11 ( 1
24 ( 2
42 ( 6
[H+] (M)
0.33 ( 0.03
0.61 ( 0.02
0.77 ( 0.03
0.86 ( 0.10
0.69 ( 0.04
a From NMR and GPC data. b By titration. c Room temperature and 100% RH. d Room temperature.
Figure 4. TGA curves of P(VDF-co-HFP)-b-SPS block copoly-
mer membranes possessing different degrees of sulfonation.
Figure 3. TGA curves of polystyrene, sulfonated polystyrene
(acid form), and P(VDF-co-HFP) copolymer.
uptake of the more highly sulfonated membranes was
verified by DSC analysis (not shown).
sulfonated styrene and unsulfonated styrene; C and B
represent the integrals of “c” and “b” peaks, respectively.
These data are listed in Table 1. The degree of sulfo-
nation is observed to increase with reaction time, and
the polystyrene segments are fully sulfonated after
20 h.
In addition to water loss, TGA curves of the P(VDF-
co-HFP)-b-SPS block copolymer membranes (Figure 4)
exhibit three other regions of mass loss: elimination of
sulfonic acid groups commencing at ∼300 °C; decompo-
sition of the polystyrene block between 350 and 390 °C,
where the onset temperature increases from 352 to
390 °C as the DS increases from 12% to 49%; and
decomposition of the fluoropolymer segment between
430 and 490 °C, where the onset temperature increases
from 457 to 482 °C with increasing DS of the polymer.
It is noted that degradation of this segment occurs at a
higher temperature than P(VDF-co-HFP) copolymer
(449 °C), which is consistent with a previous report
indicating that the stability of sulfonated SEBS block
copolymers is higher than its base polymer (SEBS) and
that the onset temperature for degradation increases
with degree of sulfonation.11
Differential Scanning Calorimetry (DSC). The
first DSC scan (between -100 and 200 °C) of P(VDF-
co-HFP)-b-SPS membranes gives rise to a broad endo-
thermic peak between 80 and 200 °C due to loss of water
absorbed from the atmosphere. Tg’s were readily deter-
mined from the second thermal cycle except for the
membrane possessing a DS of 49%, which exhibits a
persistent endothermic peak after three scans due
to the presence of residual water. DSC curves of
P(VDF-co-HFP)-b-SPS possessing different degrees of
sulfonation are shown in Figure 5. Two Tg’s are ob-
served: one due to the fluoropolymer segment (Tg1),
which occurrs at ∼ -35 °C, and the other due to
partially sulfonated polystyrene (Tg2), which varies in
temperature between 120 and 166 °C. The unsulfonated
block copolymer (DS ) 0%) exhibits Tg’s of -34 and
86 °C for the fluoropolymer and PS, respectively. It also
exhibits additional thermal transitions between 40 and
80 °C due to the fluoropolymer segment.36 Since partial
sulfonation of the polystyrene segment in the block
copolymer is statistically random, this segment is es-
With knowledge of DS and the number of repeat units
in the polystyrene segment, the IEC of the membranes
was calculated. Table 1 lists these values in addition to
IECs determined by titration. There is agreement
between the theoretical and measured IECs and a few
inconsistencies which are most likely due to the inac-
curacy of the GPC and inaccuracies in integrating NMR
peaks for low degrees of sulfonation. The observation
that experimental and theoretical IECs are similar, even
for membranes with very low IECs, suggests that all
sulfonic acid sites are accessible to aqueous solution and
that the hydrophilic domains are interconnected.
Thermal Gravimetric Analysis (TGA). The ther-
mal stability of the membranes was investigated by
TGA. To aid discussion, TGA of related polymers
P(VDF-co-HFP), PS, and PSSA under nitrogen was
performed, and the data are presented in Figure 3. The
temperature of degradation, expressed as the onset
temperature at which significant mass loss occurs, is
393 and 449 °C for PS and P(VDF-co-HFP), respectively.
For PSSA, loss of residual water occurs between 50 and
200 °C, and sulfonic acid groups are eliminated at
∼300 °C.
TGA curves for the [P(VDF-co-HFP)-b-SPS] block
copolymers prepared in this work are shown in Figure
4 for four different degrees of sulfonation. Loss of
residual water begins at 50 °C and continues up to
∼200 °C because of strong interactions with the sulfonic
acid groups.34,35 The percentage decrease in mass due
to water loss (up to 200 °C) increases with the degree
of sulfonation: the loss of water accounts for 8% of the
membrane having a DS of 49% compared to ∼3% for
the membrane having a DS of 40%. This larger water

Macromolecules, Vol. 38, No. 10, 2005
[P(VDF-co-HFP)-b-SPS] Block Copolymers 4197
Figure 5. DSC curves of P(VDF-co-HFP)-b-SPS block copoly-
mer membranes possessing different degrees of sulfonation.
Figure 6. Proton conductivity vs IEC for P(VDF-co-HFP)-b-
SPS block copolymer membranes.
Table 2. Tg’s of P(VDF-co-HFP)-b-SPS Possessing
Different Degrees of Sulfonation
(IEC ) 0.91 mmol/g) absorbs a slightly higher amount
of water than Nafionsits water content and uptake
being 28% and 38%, respectively.
deg of sulfonation (mol %)
0
12
22
32
40
Tg1 (°C)
Tg2 (°C)
-34
86
-36
120
-39
145
-40
164
-43
166
The water content and water uptake values provide
insight into the continuity of the hydrophobic regions
and the ability of the fluoropolymer matrix to oppose
osmotic pressure forcessthe latter tend to favor high
values of lambda (λ ) [H2O]/[SO3-]). If the osmotic
pressure exceeds the elastic forces of the matrix, dis-
solution will occur. It is useful therefore to compare
water sorption properties of other block copolymers with
those of the present system. Relevant data are reported
in Table 1. Water absorption values of partially sulfo-
nated poly(styrene-b-[ethylene-co-butylene]-b-styrene)
(S-SEBS) block copolymer membranes, for a similar
range of IEC38 and/or degree of sulfonation, have been
reported.13 Values for water uptake of ∼15%, ∼40%, and
∼70% were reported by Kim et al. for S-SEBS block
copolymers (28% polystyrene) having degrees of sulfo-
nation of 22%, 34%, and 42%, respectively.13 They also
report that S-SEBS membranes possessing a high
degree of sulfonation (>47%) absorbed large amounts
of water (>100 wt % uptake), and as a result their
mechanical strength is poor.
It is found that when IEC is <0.5 mmol/g and the
degree of sulfonation is <17%, for P(VDF-co-HFP)-b-
SPS the difference in mass between wet and dry
membrane weights cannot be accurately measured. Very
low values of water uptake were also observed for the
S-SEBS block copolymer membranes with low sulfo-
nation degree. Weiss et al.11 report 0.40% and 2.35%
water uptake at room temperature for SEBS block
copolymers (29.8 wt % polystyrene) sulfonated to 5.2 and
11.9 mol %.
Proton Conductivity. Proton conductivities of co-
polymer membranes possessing different degrees of
sulfonation were measured by ac impedance spectros-
copy. Conductivity data are listed in Table 1 and plotted
in Figure 6 as a function of IEC and in Figure 7 as a
function of λ. The conductivity of Nafion 117 is included
for comparison. Generally, proton conductivity increases
with increasing IEC because conductivity depends on
the ion content of the membrane. As shown in Figure
6, the incremental increase in conductivity with IEC is
initially small but increases significantly between 0.5
and 0.8 mmol/g. Conductivity levels off at 1.2 mmol/g
and decreases slightly with a further increase in IEC.
These observations are correlated to the water content
of the membranes. Membranes with low IEC absorb
sentially a random copolymer of sulfonated polystyrene
and polystyrene, and hence only one Tg is observed.
Sulfonation of this segment causes the Tg to increase
due to the bulkiness of the sulfonate group and due to
the ionomeric effect.23 Tg of H-SPS, for example, is
reported to increase from 107 to 158 °C when the DS of
sulfonated polystyrene (H-SPS) increases from 3.4% to
20.1%,37 and Mauritz et al.16 report that the Tg of
S-SEBS is raised from 114 to 166 °C when DS increases
from 2.8 to 14.3%.
Table 2 lists the Tg of the fluoropolymer and sulfo-
nated polystyrene segments as a function of DS. The
Tg of the unsulfonated polystyrene segment in the block
copolymer is 86 °C, which is lower than polystyrene
homopolymer (Tg ) 100 °C), due to the influence of the
low-Tg P(VDF-co-HFP) copolymer matrix. This is con-
sistent with other reports of styrenic block copolymers:
a lower Tg (82 °C16 and 90 °C23) is reported for
polystyrene when coupled to poly(ethylene-co-butylene)
and polybutadiene, respectively. As the degree of sulfo-
nation increases, the Tg of the sulfonated polystyrene
segment increases from 120 °C (DS ) 12%) to 166 °C
(DS ) 40%). Tg of P(VDF-co-HFP) segments varies little
((9 °C) compared to those changes observed in the
sulfonated polystyrene segments. Again, this is consis-
tent with other block copolymer studies: the Tg of the
EB block varies only (3 °C in the S-SEBS block
copolymer series.16
Water Sorption. Water uptake by the membranes
in their protonic form was measured, and their water
contents were calculated. These are listed in Table 1.
As expected, the amount of water absorbed by the
membrane increases with increasing sulfonation. The
membranes are flexible and pliable and can be easily
handled when hydrated. However, membranes compris-
ing of polymers having a DS of 49%, or greater, take up
a very large amount of water (>388% water uptake),
are fragile, and exhibit poor mechanical properties. The
fully sulfonated polymer completely dissolves in water,
and thus only FTIR and NMR data are available. The
water content and water uptake of Nafion 117 were
measured to be 23% and 29%, respectively. The P(VDF-
co-HFP)-b-SPS block copolymer membrane possessing
a similar IEC (0.89 mmol/g, DS ) 32%) to Nafion 117

4198 Shi and Holdcroft
Macromolecules, Vol. 38, No. 10, 2005
Table 3. Proton Conductivity of Sulfonated Polystyrene
Membranes
DS
IEC
conductivity
(S/cm)
polymers
(%) (mmol/g)
ref
P(VDF-co-HFP)-b-SPSa 32
0.89
1.08
0.055
0.080
0.0015
0.0023
0.03
this work
(31 wt % PS)
40
15
12
this work
SPS (random)b
1.24
39
28
38
0.93
S-SEBS triblockc
0.94
1.12
0.05
S-SEBS triblockc
(28 wt % PS)
34
42
(0.92)g
(1.13)g
0.97
0.032
0.037
0.025
13
17
23
28
S-SIBS triblockd
(31 wt % PS)
S-HPBS diblockc
(30 wt % PS)
40
12
(1.15)g
0.015
0.012
SPS (graft)f
1.02
Figure 7. Plot of conductivity vs λ for P(VDF-co-HFP)-b-SPS
block copolymer membranes.
a Sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-
b-styrene) block copolymers. b Sulfonated polystyrene. c Sulfonated
poly(styrene-b-[ethylene-co-butylene]-b-styrene) copolymers (S-
SEBS). d Sulfonated poly(styrene-b-isobutylene-b-styrene) block
copolymers (S-SIBS). e Sulfonated hydrogenated poly(butadiene-
b-styrene) diblock copolymers (S-HPBS). f PS-g-macPSSA graft
copolymers. g Calculated from weight percentage of polystyrene
and degree of sulfonation.
very little water, and the volume of the hydrophilic
regions is not sufficient to form a percolated network of
ions. Between 0.5 and 0.6 mmol/g (DS 17 and 22%) a
percolation threshold is achieved. Sulfonated poly-
(styrene-b-[ethylene-co-butylene]-b-styrene) (S-SEBS)
block copolymer membranes exhibit a similar percola-
tion threshold in the same region of IECsit was found
by Kim et al.13 that proton conductivity of S-SEBS
increased sharply when DS of the PS blocks exceeds
15 mol % (∼0.4 mmol/g IEC). For graft copolymers of
styrene and sodium styrenesulfonate, Ding et al.28 found
that the conductivity increased significantly when the
ion content (equivalent to degree of sulfonation) is
>13%. A similar percolation threshold is observed by
Carretta et al. for a DS of ∼15 mol % for partially
sulfonated polystyrene membranes.39 However, it should
be noted that for sulfonation of PS homopolymers a DS
of ∼15 mol % gives rise to a much higher IEC
(1.24 mmol/g IEC) than the block copolymers because
of the absence of a nonstyrenic phase, and thus care
should be taken in comparing polymers based solely on
DS.
Because of a significant increase in water uptake and
a resulting drop in proton concentration, the proton
conductivity does not increase upon increasing the IEC
of the membranes from 1.18 (0.08 S/cm) to 1.31 mmol/g
(0.076 S/cm). Proton concentrations of the P(VDF-co-
HFP)-b-SPS membranes were calculated using eq 5 and
are listed in Table 1. [H+] for the 1.31 mmol/g IEC
membrane is 0.32 M, which is half that of the
1.18 mmol/g membrane (0.69 M). Similar effects of
increasing water content and decreasing proton con-
centration on proton conductivity have been observed
in other polymer systems. The conductivity of sulfonated
trifluorostyrene copolymers dropped significantly above
1.96 mmol/g IEC due to a substantial decrease in proton
concentration.38 For block copolymers, conductivity of
S-SIBS membranes leveled off at 0.94 mmol/g IEC,17
and for S-SEBS the conductivity did not increase
between 1.12 and 1.71 mmol/g IEC.38 In contrast, the
conductivity of ETFE-g-PSSA radiation graft mem-
branes is reported to continuously increase with IEC
in the range of 2.45-3.27 mmol/g,38 but this is due to
the rigid nature of the base polymer membrane which
prevents the membrane from swelling excessively.
λ for partially sulfonated P(VDF-co-HFP)-b-SPS mem-
branes. For membranes possessing IEC < 0.5, mmol/g
λ is 2-3, indicating an extremely “water-poor” environ-
ment, in the context of aiding proton conductivity, and
consequently, proton conductivities are low (10-4-10-3
S/cm). When the IEC of the membranes is such that the
λ values increase from 11 to 42, the proton conductivity
sharply increases. Note that proton concentrations for
each membrane are similar, indicating that the increase
in conductivitiy is largely due to increased mobility of
the protons. In a similar range of λ, conductivity
increases for sulfonated trifluorostyrene (λ, 10-33) and
S-SEBS block copolymers (λ, 24-46).38 A similar obser-
vation is observed for P(VDF-co-HFP)-b-SPS mem-
branes: when λ is > ∼40, conductivity no longer in-
creases with λ, and as λ is increased from 42 to 165,
the conductivity decreases from 0.08 to 0.076 S/cm.
Similarly, no increase in conductivity was observed for
S-SEBS block membranes when λ increased from 46 to
147.38 It is concluded that for sulfonated block copolymer
membranes increasing λ values (when λ is <40-50)
increases proton conductivity by enhancing proton
mobility, but above this value, increasing λ simply
serves to dilute the proton concentration and this effect
outweighs any further increase in proton mobility.
When the IEC of the P(VDF-co-HFP)-b-SPS mem-
branes lies between 0.9 and 1.1 mmol/g, the conductivity
is 0.06-0.08 S/cm, which is comparable to that of Nafion
117. Table 3 lists conductivity values of several other
sulfonated block, graft, and randomly sulfonated poly-
styrene membranes possessing degrees of sulfonation
between 32 and 40 mol % or IECs between 0.9 and
1.1 mmol/g. For S-SEBS triblock and S-SPBS diblock
membranes, IEC values are calculated according to the
weight percentage of polystyrene and the degree of
sulfonation reported. Partially sulfonated polystyrenes
can be considered to be random copolymers of polysty-
rene and sulfonated polystyrene. The conductivity of
random copolymer membranes is reported to be in
the range 0.0015-0.0023 S/cm for IECs of 0.93-
1.24 mmol/g. The proton conductivities of all the block
or graft copolymer membranes listed in Table 3 lie
between 0.012 and 0.080 S/cm and possess IECs be-
tween 0.89 and 1.15 mmol/g. It can be concluded from
λ indicates the average number of water molecules
associated with each sulfonic acid site. It is reported that
the proton conductivity of perfluorosulfonic acid mem-
branes increases significantly when λ values are >6.40
Figure 7 plots the relationship between conductivity and

Macromolecules, Vol. 38, No. 10, 2005
[P(VDF-co-HFP)-b-SPS] Block Copolymers 4199
Table 3 that the conductivities of the P(VDF-co-HFP)-
b-SPS block copolymer membranes are at least an order
of magnitude higher than those of the randomly struc-
tured sulfonated polystyrene membranes.28,39 Second,
comparing fluorous block copolymer membranes with
nonfluorous (block and graft), it can be observed that
the conductivity of P(VDF-co-HFP)-b-SPS membranes
is higher. For example, the conductivity of P(VDF-co-
HFP)-b-SPS membranes having 0.89 mmol/g IEC is
0.055 S/cm, while that for S-SEBS block membranes is
reported to be 0.03 S/cm for 0.92-0.94 mmol/g IEC, and
the conductivity of S-SIBS block membranes is
0.025 S/cm at 0.97 mmol/g IEC. The conductivity of
P(VDF-co-HFP)-b-SPS block membrane with 1.08 mmol/g
IEC is 0.080 S/cm, while the conductivity of S-SEBS
block membranes is reported to be 0.037-0.05 S/cm for
1.12-1.13 mmol/g IEC; the conductivity of S-HPBS
block membrane is only 0.015 S/cm at 1.15 mmol/g IEC.
The fluorous-containing block copolymer membranes
exhibit almost twice the proton conductivity of non-
fluorinated block and graft copolymer membranes. It is
known that fluoropolymers possess much lower surface
tension than other polymer structures. It can be con-
cluded that the dissimilarity of the two segments
improves phase separation and enhances the proton
conductivity. Nevertheless, poly(vinylidene difluoride)
is only a partially fluorinated polymer, and its surface
tension (33.2 dyn/cm at 20 °C) is higher than perfluo-
ropolymers such as PTFE (23.9 dyn/cm at 20 °C).41
Accordingly, we predict that the proton conductivity of
similar block copolymer membranes prepared with
perfluoropolymer segments would be even higher.
TEM Morphology. Information on membrane mor-
phology can be acquired from TEM images. To investi-
gate phase separation and ionic aggregation, mem-
branes were stained with lead acetate. In the TEM
images, therefore, the dark areas represent regions of
high ionicity and the brighter areas, hydrophobic re-
gions. Morphologies of dry proton conducting mem-
branes reported in the literature are spherical, lamella,
or wormlike. For example, Nafion membranes exhibit
2-10 nm nearly spherical ion clusters,42-45 where-
as wormlike ionic domains are observed for graft
ionomers.26-29 For S-SEBS block copolymer ionomers a
three-phase microstructure consisting of 3-4 nm ionic
domains in 20-30 nm polystyrene block domains was
suggested on the basis of SAXS and TEM analysis. The
TEM image of 27% sulfonation of S-SEBS block copoly-
mer, cast from the THF solution and stained with RuO4,
exhibited a well-ordered lamellar morphology.14
TEM images for the P(VDF-co-HFP)-b-SPS mem-
branes possessing different degrees of sulfonation are
shown in Figure 8. No distinct ion phase separation
morphology is observed for the membrane possessing
the lowest DS (12 mol %, IEC ) 0.26 mmol/g). No clear
phase separation is observed for the 17% DS membrane
(not shown). Both these membranes exhibit poor proton
conductivity (10-4-10-3 S/cm). With increasing DS
(20-40 mol %), a distinct morphology develops as
observed in Figure 8B-D. Ordered ionic channels are
clearly connected and form an ionic channel network
possessing 20-40 nm interdomain spacings. The width
of the channels is estimated to be in the range 8-15
nm. The TEMs indicate the network is 3-dimensional.
Figure 8. TEM images of P(VDF-co-HFP)-b-SPS block co-
polymer membranes: (A) DS, 12%; IEC, 0.23 mmol/g; σ, 1.6
× 10-4 S/cm; (B) DS, 22%; IEC, 0.62 mmol/g; σ, 1.6 ×
10-2 S/cm; (C) DS, 32%; IEC, 0.89 mmol/g; σ, 5.5 × 10-2 S/cm;
(D) DS, 40%; IEC, 1.08 mmol/g; σ, 8.0 × 10-2 S/cm; (E) DS,
49%; IEC, 1.31 mmol/g; σ, 7.6 × 10-2 S/cm; (F) DS, 100%.
the membrane with 100% degree of sulfonation did not
dissolve in lead acetate solution, and hence a TEM
image could be obtained, which is shown in Figure 8F.
It is observed that at this high ion content the interface
between ion channels and the hydrophobic matrix is less
sharp and the ionic domains aggregate, tending toward
disordered structures.
Conductivity as a Function of Temperature and
Humidity. Proton conductivity of polymer membranes
is known to be a function of both temperature and water
content,2,46 and it is therefore pertinent to determine
the influence of external conditions on conductivity so
that limitations of operation can be identified. Gener-
ally, for a given humidity, conductivity increases with
temperature until dehydration becomes a predominant
factor, whereas at constant temperature conductivity
decreases as humidity decreased. As examples, the
conductivity of Nafion 117 under 100% RH increases
from 0.1 to 0.2 S/cm when the temperature is raised
from 30 to 85 °C,47 and at 30 °C the conductivity of
Nafion 117 decreases from 0.066 to 0.000 14 S/cm as
RH decreases from 100% to 34%.48 At 100% RH, the
proton conductivity of sulfonated poly(styrene-b-iso-
butylene-b-styrene) block copolymer membrane (S-SIBS,
0.96 mmol/g IEC) is 0.025 S/cm at 21/22 °C and
increases to 0.083 S/cm at 80 °C.17
As shown in Figure 9, the conductivity of partially
sulfonated P(VDF-co-HFP)-b-SPS copolymer membranes
increases with increasing RH at 30 °C. Comparing the
0.89 mmol/g IEC membranes with Nafion 117, it is
found that P(VDF-co-HFP)-b-SPS block membrane pos-
sesses a similar trend. Since water absorption is directly
related to the ambient RH, these data reflect the change
in conductivity with water content. Because of dehydra-
tion of the membranes at low RH (<65%), the conduc-
tivity of the membranes is less than 0.01 S/cm. With
increasing RH the conductivity of these membranes
increases exponentially. Similar observations are re-
ported for Nafion 11748,49 and S-PEEK.2
Upon traversing the series of membranes with in-
creasing DS, a disruption in ordered morphology is
observed (see Figure 8E,F). Although soluble in water,

4200 Shi and Holdcroft
Macromolecules, Vol. 38, No. 10, 2005
0.62 mmol/g IEC, and 41.2 kJ/mol for 0.45 mmol/g IEC
membranes.17 The activation energies for conductivity
through P(VDF-co-HFP)-b-SPS membranes show a de-
creasing tendency from 25.7 to 17.1 kJ/mol as the IEC
increase, which agrees with the experimental data for
S-SIBS block copolymer membranes where the activa-
tion energy is reported to fall from 41.2 to 18.1 kJ/mol
when the IEC increases from 0.45 to 0.96 mmol/g.17
A
similar trend was reported for S-PEEK membranes: the
activation energy for a 39% DS membrane (∼1.2 mmol/g
IEC) is 41.0 kJ/mol and for a 47% DS S-PEEK
(∼1.35 mmol/g IEC), 33.5 kJ/mol. The lower IEC mem-
branes possess lower ion content and form smaller, more
isolated, ionic clusters; thus, proton conductivity is more
restricted, and temperature plays a more dominant role.
Figure 9. Proton conductivity vs relative humidity for P(VDF-
co-HFP)-b-SPS membranes possessing different IEC, and
Nafion 117, at 30 °C.
Conclusion
Partially sulfonated poly([vinylidene difluoride-co-
hexafluoropropylene]-b-styrene) copolymers were pre-
pared for the purpose of investigating the role of
chemical structure on PEM membrane properties. The
thermal properties of the membranes, characterized by
DSC, show two glass transitions for the two block
segments; the Tg values of the sulfonated polystyrene
segments increases with degree of sulfonation. Very low
water contents are observed for membranes having a
DS < 17%, whereas high λ values (165) are observed
for the membranes sulfonated to >49 mol %. Proton
conductivity is significantly larger when the IEC of the
membranes is in the range 0.5-1.2 mmol/g; between 0.9
and 1.2 mmol/g, the conductivity is similar to that of
Nafion 117. The conductivity of P(VDF-co-HFP)-b-SPS
block copolymer membranes is shown to be higher than
that of partially sulfonated nonfluorous block copolymer
membranes. The microstructure of P(VDF-co-HFP)-b-
SPS membranes shows a disruption in order with
increasing degree of sulfonation. Connected networks
of ion channels having 8-15 nm width are observed for
dry P(VDF-co-HFP)-b-SPS membranes for polymers
with 22-40 mol % sulfonation (0.6-1.2 mmol/g IEC).
It may be concluded that fluoropolymer segments induce
well connected channel networks which enhance proton
transport. The conductivity of the membrane is strongly
related to both chemical structure and morphology. It
also suggests that block copolymers with perfluoro-
polymer segments would lead to even greater proton
conductivity.
Figure 10. Proton conductivity vs temperature for P(VDF-
co-HFP)-b-SPS membranes possessing different IEC, and
Nafion 117, under constant humidity (95% RH).
The relationship between conductivity and tempera-
ture for membranes with different IEC in a 95% relative
humidity environment is shown in Figure 10. The
conductivity of three different IEC membranes increases
with temperature from 30 to 90 °C. Although further
work is required to determine whether this trend
extends to higher temperatures, this is an interesting
observation since not all PEMs continue to increase in
conductivity up to 90 °C. The conductivity of Nafion
117 under the same conditions increases between 30 and
50 °C but decreases above 50 °C. A similar observation
is reported for Nafion (EW ) 1100 g/mol) at 100% RH,
with the maximum conductivity occurring at 60 °C.50
Proton conductivity of S-PEEK membranes at 100% RH
is also reported to decrease above 70 °C.2
From the slopes of natural logarithmic plots of
conductivity vs 1000/T (not shown), the activation
energy for proton transport was found to be 25.7, 13.9,
and 17.1 kJ/mol for P(VDF-co-HFP)-b-SPS membranes
with IEC of 0.72, 0.89, and 1.18 mmol/g, respectively.
Compared with reported values of Nafion 117 mem-
branes (7.8,51 9.6,47 and 13.552 kJ/mol) and Nafion 112
(18.3 kJ/mol),53 the activation energies of P(VDF-co-
HFP)-b-SPS membranes are on average much higher
than Nafion 117. The activation energies for proton
conduction of S-SIBS block copolymer membranes
are reported to be much higher still: 18.1 kJ/mol
for a 0.96 mmol/g IEC membrane, 25.0 kJ/mol for
Research on the synthesis and characterization of
fully sulfonated fluorous block copolymers with varied
length of sulfonated polystyrene chains, and the rela-
tionship between proton conductivity and morphology,
is underway and will be discussed in another paper.
Although it is recognized that sulfonated polystyrene
may not be sufficiently stable under fuel cell operating
conditions, these results may be useful in the design of
alternative PEM materials.
Acknowledgment. The authors thank the Natural
Sciences and Engineering Research Council of Canada
for financial support and Dr. E. Humphrey and Mr. G.
Martens (UBC EMLab) for assistance in TEM.
References and Notes
(1) Brandon, N. P.; Skinner, S.; Steele, B. C. H. Annu. Rev. Mater.
Res. 2003, 33, 183.
(2) Rikukawa, M.; Sanui, K. Prog. Polym. Sci. 2000, 25, 1463.
(3) Savadogo, O. J. New Mater. Electrochem. Syst. 1998, 1, 47.
(4) Heitner-Wirguin, C. J. Membr. Sci. 1996, 120, 1.

Macromolecules, Vol. 38, No. 10, 2005
[P(VDF-co-HFP)-b-SPS] Block Copolymers 4201
(5) Perfluorinated Ionomer Membrane; Eisenberg, A., Yeager, H.
L., Eds.; American Chemical Society: Washington, DC, 1982.
(6) Li, Q.; He, R.; Jensen, J. O.; Bjerrum, N. J. Chem. Mater.
2003, 15, 4896.
(30) Yang, Y. S.; Shi, Z. Q.; Holdcroft, S. Macromolecules 2004,
37, 1678.
(31) Shi, Z.; Holdcroft, S. Macromolecules 2004, 37, 2084.
(32) Gardner, C. L.; Anantaraman, A. V. J. Electroanal. Chem.
1995, 395, 67.
(33) Wang, F.; Hickner, M.; Kim, Y. S.; Zawodzinski, T. A.;
McGrath, J. E. J. Membr. Sci. 2002, 197, 231.
(34) Nasef, M. M. Polym. Degrad. Stab. 2000, 68, 231.
(35) Nasef, M. M.; Saudu, H. Polym. Degrad. Stab. 2000, 70, 497.
(36) Quartarone, E.; Brusa, M.; Mustarelli, P.; Tomasi, C.; Mag-
istris, A. Electrochim. Acta 1998, 44, 677.
(37) Yang, S.; Sun, K.; Risen, W. M. J. Polym. Sci., Part B: Polym.
Phys. 1990, 28, 1685.
(38) Beattie, P. D.; Orfino, F. P.; Basura, V. I.; Zychowska, K.;
Ding, J. F.; Chuy, C.; Schmeisser, J.; Holdcroft, S. J. Electro-
anal. Chem. 2001, 503, 45.
(39) Carretta, N.; Tricoli, V.; Picchioni, F. J. Membr. Sci. 2000,
166, 189.
(40) Gavach, C.; Pamboutzoglou, G.; Nedyalkov, M.; Pourcelly, G.
J. Membr. Sci. 1989, 45, 37.
(41) Wu, S. In Polymer Handbook, 4th ed.; Brandrup, J., Immer-
gut, E. H., Grulke, E. A., Eds.; John Wiley & Sons: New York,
1999; p VI/521.
(42) Ceynowa, J. Polymer 1978, 19, 73.
(43) Cheng, X.; Yi, B.; Han, M.; Zhang, J.; Qiao, Y.; Yu, J. J. Power
Sources 1999, 79, 75.
(44) Rieberer, S.; Norian, K. H. Ultramicroscopy 1992, 41, 225.
(45) Xue, T.; Trent, J. S.; Osseo-Asare, K. J. Membr. Sci. 1989,
45, 261.
(46) Yeo, R. S. J. Electrochem. Soc. 1983, 130, 533.
(47) Ma, C.; Zhang, L.; Mukerjee, S.; Ofer, D.; Nair, B. J. Membr.
Sci. 2003, 219, 123.
(48) Anantaraman, A. V.; Gardner, C. L. J. Electroanal. Chem.
1996, 414, 115.
(7) Eisenberg, A. Macromolecules 1970, 3, 147.
(8) Ehrenberg, S. G.; Serpico, J. M.; Wnek, G. E.; Rider, J. N.
US Patent 5 468 574, 1995.
(9) Lu, X. Y.; Steckle, W. P.; Weiss, R. A. Macromolecules 1993,
26, 6525.
(10) Lu, X. Y.; Steckle, W. P.; Hsiao, B.; Weiss, R. A. Macromol-
ecules 1995, 28, 2831.
(11) Weiss, R. A.; Sen, A.; Willis, C. L.; Pottick, L. A. Polymer
1991, 32, 1867.
(12) Weiss, R. A.; Sen, A.; Pottick, L. A.; Willis, C. L. Polymer
1991, 32, 2785.
(13) Kim, J.; Kim, B.; Jung, B. J. Membr. Sci. 2002, 207, 129.
(14) Kim, J.; Kim, B.; Jung, B.; Kang, Y. S.; Ha, H. Y.; Oh, I. H.;
Ihn, K. J. Macromol. Rapid Commun. 2002, 23, 753.
(15) Lee, W. J.; Jung, H. R.; Lee, M. S.; Kim, J. H.; Yang, K. S.
Solid State Ionics 2003, 164, 65.
(16) Mauritz, K. A.; Blackwell, R. I.; Beyer, F. L. Polymer 2004,
45, 3001.
(17) Elabd, Y. A.; Napadensky, E.; Sloan, J. M.; Crawford, D. M.;
Walker, C. W. J. Membr. Sci. 2003, 217, 227.
(18) Elabd, Y. A.; Walker, C. W.; Beyer, F. L. J. Membr. Sci. 2004,
231, 181.
(19) Storey, R. F.; Chisholm, B. J.; Masse, M. A. Polymer 1996,
37, 2925.
(20) Mauritz, K. A.; Storey, R. F.; Reuschle, D. A.; Tan, N. B.
Polymer 2002, 43, 5949.
(21) Mauritz, K. A.; Storey, R. F.; Mountz, D. A.; Reuschle, D. A.
Polymer 2002, 43, 4315.
(22) Mokrini, A.; Acosta, J. L. Polymer 2001, 42, 9.
(23) Mokrini, A.; Del Rio, C.; Acosta, J. L. Solid State Ionics 2004,
166, 375.
(49) Zawodzinski, T. A.; Derouin, C.; Radzinski, S.; Sherman, R.
J.; Smith, V. T.; Springer, T. E.; Gottesfeld, S. J. Electrochem.
Soc. 1993, 140, 1041.
(24) Mani, S.; Weiss, R. A.; Williams, C. E.; Hahn, S. F. Macro-
molecules 1999, 32, 3663.
(25) Zhang, G.; Liu, L.; Wang, H.; Jiang, M. Eur. Polym. J. 2000,
36, 61.
(50) Rieke, P. C.; Vanderbrogh, N. E. J. Membr. Sci. 1987, 32,
313.
(26) Ding, J. F.; Tang, Q. Y.; Holdcroft, S. Aust. J. Chem. 2002,
55, 461.
(51) Kopitzke, R. W.; Linkous, C. A.; Anderson, H. R.; Nelson, G.
L. J. Electrochem. Soc. 2000, 147, 1677.
(27) Ding, J. F.; Chuy, C.; Holdcroft, S. Adv. Funct. Mater. 2002,
12, 389.
(52) Halim, J.; Buchi, F. N.; Haas, O.; Stamm, M.; Scherer, G. G.
Electrochim. Acta 1994, 39, 1303.
(28) Ding, J. F.; Chuy, C.; Holdcroft, S. Macromolecules 2002, 35,
1348.
(53) Qiu, X.; Li, W.; Zhang, S.; Liang, H.; Zhu, W. J. Electrochem.
Soc. 2003, 150, A917.
(29) Ding, J. F.; Chuy, C.; Holdcroft, S. Chem. Mater. 2001, 13,
2231.
MA0477549