Synthesis and ionic transport of sulfonated ring-opened polynorbornene based copolymers

Article abstract of DOI:10.1016/j.polymer.2011.07.030

The N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide (1a) and N-phenyl-exo-endo-norbornene- 5,6-dicarboximide (1b)monomers were synthesized and copolymerized via ring opening metathesis polymerization (ROMP) using bis(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride (I) and tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2- ylidene][benzylidene] rutheniumdichloride (II). Experiments, at distinct monomer molar ratios, were carried out using catalyst I in order to determine the copolymerization reactivity constants by applying theMayo-Lewis and Fineman- Ross methods. Moreover, both catalysts were used to produce random and block high molecular weight copolymers of 1a with 1b and 1a with norbornene (NB) which were further hydrogenated using a Wilkinson's catalyst. Then, the saturated copolymers underwent a nucleophilic aromatic substitution by reacting with sodium 4-hydroxybenzenesulfonate dihydrate to generate new polynorbornene ionomers bearing fluorinated pendant benzenesulfonate groups. A thorough study on the electrochemical characteristics involving electromotive forces of concentration cells and proton conductivity of cation-exchange membranes based on a block copolymer of norbornene dicarboximides containing structural units with phenyl and fluorinated pendant benzenesulfonate moieties is reported. The study of electromotive forces (emf) of concentration cells with the sulfonated membrane of copolymer 8 separating electrolyte solutions of different concentration indicate that the membranes exhibit high permselectivity to protons and sodium ions at moderately low concentrations. In principle, these results suggest that the membranes can be considered candidates for ionic separation applications.

Full text of DOI:10.1016/j.polymer.2011.07.030

Polymer 52 (2011) 4208e4220
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and ionic transport of sulfonated ring-opened polynorbornene based
copolymers
Arlette A. Santiago , Joel Vargas , Javier Cruz-Gómez , Mikhail A. Tlenkopatchev *, Rubén Gaviño c,
a
a
a
b,
Mar López-González , Evaristo Riande d
Facultad de Química, Universidad Nacional Autónoma de México, CU, Coyoacán, México DF 04510, México
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, CU, Coyoacán, México DF 04510, México
Instituto de Química, Universidad Nacional Autónoma de México, CU, Coyoacán, México DF 04510, México
d,
*
a
b
c
d
Instituto de Ciencia y Tecnología de Polímeros (CSIC), 28006 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 March 2011
Received in revised form
The N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide (1a) and N-phenyl-exo-endo-norbor-
nene-5,6-dicarboximide (1b) monomers were synthesized and copolymerized via ring opening metathesis
polymerization (ROMP) using bis(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride (I) and
tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene]
ruthenium dichloride (II). Experiments, at distinct monomer molar ratios, were carried out using catalyst I
in order to determine the copolymerization reactivity constants by applying the Mayo-Lewis and Fineman-
Ross methods. Moreover, both catalysts were used to produce random and block high molecular weight
copolymers of 1a with 1b and 1a with norbornene (NB) which were further hydrogenated using a Wil-
kinson’s catalyst. Then, the saturated copolymers underwent a nucleophilic aromatic substitution by
reacting with sodium 4-hydroxybenzenesulfonate dihydrate to generate new polynorbornene ionomers
bearing fluorinated pendant benzenesulfonate groups. A thorough study on the electrochemical charac-
teristics involving electromotive forces of concentration cells and proton conductivity of cation-exchange
membranes based on a block copolymer of norbornene dicarboximides containing structural units with
phenyl and fluorinated pendant benzenesulfonate moieties is reported. The study of electromotive forces
18 July 2011
Accepted 22 July 2011
Available online 27 July 2011
Keywords:
Sulfonated polynorbornene
Ionic transport
Monomer reactivity
(
emf) of concentration cells with the sulfonated membrane of copolymer 8 separating electrolyte solutions
of different concentration indicate that the membranes exhibit high permselectivity to protons and sodium
ions at moderately low concentrations. In principle, these results suggest that the membranes can be
considered candidates for ionic separation applications.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Taking into account that the development of fluorine containing
polymeric materials displaying outstanding properties for specialty
Copolymerization is a valuable tool for the synthesis of novel
materials because it allows tuning of the thermal, mechanical and
ionic, among other polymer properties. Owing to this versatility,
materials suitable for applications ranging from electronics to drug
delivery can be obtained [1,2]. However, in order to determine and
foretell the copolymer composition, mechanistic and kinetic
understanding is of great importance and several studies have been
focused on this issue in the past [3,4].
applications is an evolving area in materials science, norbornenes
bearing fluorinated subtituents and subjected to ROMP using
a wide variety of transition metal compounds have been studied
[7e9]. The presence of fluorine containing moieties in the poly-
norbornene dicarboximide structures has shown to be effective to
improve gas permeability due to an increase of the interactions
between the gases and the polar fluorinated moieties as well as in
the free volume which in turns facilitates the diffusion of the gas
molecules through the polymer [10,11]. In particular, sorption
studies carried out recently on membranes of polynorbornene with
pentafluorophenyl moieties attached to the dicarboximide side
groups showed a significant increase in gas solubility [12]. Penta-
fluorophenyl moieties also provide the possibility of further
modifications. They are highly reactive towards the nucleophilic
aromatic substitutions and multiblock copolymers have been
The ROMP has been used to synthesize well controlled copoly-
mers of norbornene derivatives for gas transport applications [5,6].
*
Corresponding authors. Tel.: þ00 52 5556224586; fax: þ00 52 5556161201.
E-mail addresses: tma@servidor.unam.mx (M.A. Tlenkopatchev), mar@ictp.csic.
es (M. López-González).
0
032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.07.030

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4209
ꢀ
successfully prepared by a polycondensation reaction between
fluorinated oligomers and hydroxyl-terminated telechelics under
basic conditions in polar, aprotic solvents [13].
heating cycle conducted at a rate of 10 C/min under nitrogen
atmosphere with a TA Instruments Thermomechanical Analyzer
d
TMA 2940. Onset of decomposition temperature, T , was deter-
Ionomers with hydrocarbon backbones prepared by the sulfo-
nation of polynorbornene and its derivatives are attractive as proton
exchange membranes since the hydrophilic and hydrophobic
domains of a polynorbornene bearing polar strong acid groups (e.g.
sulfuric acid) promote phase segregation resulting in conductance
from the migration of protons through channels [14,15]. In addition,
ultrathin ionomer films, obtained from the sulfonation of surface-
initiated polynorbornene with acetyl sulfate, have reported to
exhibit low resistances against proton transport [16]. The tailorable
functionality of norbornene-based monomers has encouraged the
quest for polyionic materials suitable notonlyas polymer electrolyte
membrane in fuel cells but also for the construction of light
emitting devices (LED) by sequential adsorption of sulfonated pol-
ynorbornenes [17], among other applications. Based on the high
reactivity of the pentafluorinated rings, a new ionomer bearing
highly fluorinated pendant benzenesulfonate groups has lately been
synthesized by the reaction of the hydrogenated poly(N-penta-
fluorophenyl-norbornene-5,6-dicarboximide) with sodium 4-
hydroxybenzenesulfonate dihydrate [18].
mined using thermogravimetric analysis, TGA, which was per-
formed at a heating rate of 10 C/min under nitrogen atmosphere
ꢀ
with a DuPont 2100 instrument. FT-IR spectra were obtained on
a Thermo Nicolet 6700 spectrometer. Molecular weights and
molecular weight distributions were determined with reference to
ꢀ
polystyrene standards on a Waters 2695 ALLIANCE GPC at 35 C in
tetrahydrofuran using a universal column and a flow rate of
ꢁ1
0.5 mL min . X-ray diffraction measurements of copolymer films
as cast were carried out in a Siemens D-5000 diffractometer
ꢀ
between 4 and 70
a
2q, at 35 KV 25 mA, using CuK radiation
(1.54 Å). Mechanical properties under tension, Young’s modulus (E)
and stress ( ), were measured in a Universal Mechanical Testing
s
Machine Instron 1125-5500R using a 50 Kg cell at a crosshead
speed of 10 mm/min according to the method ASTM D1708 in film
samples of 0.5 mm of thickness at room temperature. Tapping
mode atomic force microscopy (TM-AFM) was performed in air
using a Scanning Probe Microscope Jeol JSPM-4210 with a NSC12
mmasch needle (an ultra-sharp silicon probe cantilever provided by
the company MikroMasch, San Jose, CA, USA). The samples were
imaged at ambient conditions.
In the present study, norbornene copolymers containing fluo-
rinated dicarboxylic imide side moieties were prepared through
ROMP using bis(tricyclohexylphosphine)benzylidene ruth-
enium(IV) dichloride (I) and tricyclohexylphosphine[1,3-bis(2,4,6-
trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene]
ruthenium dichloride (II).
2.2. Reagents
Norbornene-5,6-dicarboxylic anhydride (NDA) was prepared
via DielseAlder condensation of cyclopentadiene and maleic
anhydride according to literature [14]. Exo(75%)-endo(25%)
monomer mixture of N-pentafluorophenyl-norbornene-5,6-
dicarboximide (1a) and exo(75%)-endo(25%) monomer mixture of
N-phenyl-norbornene-5,6-dicarboximide (1b) were prepared as
described previously [14,18]. Norbornene (NB), phenol and sodium
4-hydroxybenzenesulfonate dihydrate were purchased from
Aldrich Chemical Co. and used without further purification. 1,2-
Dichloroethane, dichloromethane, p-dioxane, toluene and N,N-
dimethylacetamide were dried over anhydrous calcium chloride
Low conversion copolymerizations were carried out using
catalyst I. Then, the compositions of copolymers were determined
1
by H NMR and the reactivity ratios were calculated from the initial
monomer feed by applying the Mayo-Lewis [19] and Finemann-
Ross [20] methods, respectively. We have reported the synthesis
and ionic transport performance of a non-fluorinated ionic poly-
norbornene dicarboximide [14,15], therefore we have envisioned
the synthesis of high molecular weight copolymers, their homog-
enous post-hydrogenations and even further sulfonations to obtain
copolymers bearing fluorinated pendant benzenesulfonate groups.
Afterwards, we investigated the ionic permselectivity and proton
conductivity of membranes prepared from a copolymer of 1a and
2
and distilled over CaH . Bis(tricyclohexylphosphine)benzylidener-
uthenium(IV) dichloride (I), tricyclohexylphosphine [1,3-bis(2,4,6-
trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene]
1
b for evaluating its potential application as ionomer. To do so, the
3 3
ruthenium dichloride (II) and ClRh(PPh ) were purchased from
electromotive forces of the concentration potential cells of
sulfonated copolymer 8 membranes were measured keeping the
ratio between the concentrations of the concentrated and dilute
compartments in the vicinity of two. As electrolytes, hydrochloric
acid and sodium chloride solutions were used, respectively. From
the electromotive forces the counterion transport numbers were
obtained and the effect of the concentration of the electrolyte
solutions on the counterion transport number was determined.
Aldrich Chemical Co. and used as received.
2.3. Metathesis copolymerization of monomers
Copolymerizations were carried out in glass vials under dry
nitrogen atmosphere. They were quenched by adding a small
amount of ethyl vinyl ether and the solutions were poured into an
excess of methanol. The copolymers were purified by solubilization
in chloroform and precipitation into methanol containing a few
drops of 1 N HCl. The obtained copolymers were dried in a vacuum
2
. Experimental part
ꢀ
oven at 40 C to constant weight.
2.1. Techniques
2
.3.1. Synthesis of random poly(N-pentafluorophenyl-norbornene-
1H NMR, 13C NMR and 19F NMR spectra were recorded on
5,6-dicarboximide-co-N-phenyl-norbornene-5,6-dicarboximide) (2)
Monomer 1a (0.50 g, 1.51 mmol) and monomer 1b (0.36 g,
1.51 mmol) were initially dissolved in 4.34 mL of 1,2-
a Varian spectrometer at 300, 75 and 282 MHz, respectively, in
deuterated chloroform (CDCl ), N,N-dimethylformamide (DMF-d
and dimethylsulfoxide (DMSO-d ). Tetramethylsilane (TMS) and
trifluoroacetic acid (TFA) were used as internal standards, respec-
3
7
)
ꢁ3
6
dichloroethane. Then catalyst I (2.49 ꢂ 10 g, 0.0030 mmol) was
ꢀ
added and the mixture was stirred at 65 C for 2 h (Scheme 1). The
tively. Glass transition temperatures, T
g
, were determined in a DSC-
obtained copolymer 2 was soluble in chloroform and dichloro-
ꢀ
7
Perkin Elmer Inc., at scanning rate of 10 C/min under nitrogen
ethane: Incorporation of 1a in copolymer
¼
48 mol%;
5
ꢀ
ꢀ
1
atmosphere. The samples were encapsulated in standard
aluminum DSC pans. Each sample was run twice on the tempera-
M
n
¼ 2.85x10 ; M
w
/M
n
¼ 1.22; T
g
¼ 205 C; T
d
¼ 425 C; H NMR
(300 MHz, CDCl
3
):
d
(ppm) ¼ 7.45e7.23 (5H, m), 5.78 (2H, s, trans),
ꢀ
ꢀ
ture range between 30 C and 300 C under nitrogen atmosphere.
The T values obtained were confirmed by TMA from the first
5.56 (2H, s, cis), 3.23e3.15 (4H, s), 2.87 (4H, s), 2.21 (2H, s), 1.73 (2H,
13
g
s); C NMR (75 MHz, CDCl
3
):
d
(ppm) ¼ 177.0 (C]O), 174.8 (C]O),

4210
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
Scheme 1. Synthesis of polynorbornene based copolymers via ROMP.
ꢀ
1
4
d
45.1e139.6 (CeF), 136.2 (cis), 131.7 (trans), 129.0, 126.3, 107.2, 50.9,
at 45 C for 0.16 h (Scheme 1). The obtained copolymer 4 was soluble
19
6.1, 41.6;
F
NMR (282 MHz, CDCl
3
,
ref. TFA [-77ppm]):
in chloroform and dichloroethane: Incorporation of 1a in
5
ꢀ
(ppm) ¼ ꢁ142.1, ꢁ142.5, ꢁ143.1, ꢁ150.0, ꢁ150.4, ꢁ159.7, ꢁ160.0;
copolymer ¼ 49 mol%; M
n
¼ 2.11 ꢂ 10 ; M
w
/M
n
¼ 1.25; Tg1 ¼ 44 C;
ꢁ1
ꢀ
ꢀ
1
FT-IR (thin film, cm ): 3018, 2923 (CeH asym str), 2853 (CeH sym
str), 1777 (C]O), 1706 (C]O), 1598 (C]C str), 1514, 1455 (CeN),
T
g2 ¼ 170 C; T
d
¼ 420 C; H NMR (300 MHz, CDCl
3
):
d
(ppm) ¼ 5.77
(1H, s, trans), 5.55 (1H, s, cis), 5.34 (1H, m, trans), 5.22 (1H, m, cis),
13
1356, 1297 (CeF), 1165, 1139, 1066, 1021, 985, 880, 785, 768,
3.27 (2H, s), 2.88 (2H, s), 2.44e2.22 (2H, m), 1.92e1.02 (8H, m);
NMR (75 MHz, CDCl ):
(ppm) ¼ 174.5 (C]O), 147.1e141.2 (C-F),
35.2, 133.7 (cis), 133.3 (cis), 132.5 (trans); 131.9 (trans), 107.3 (CeN),
C
746, 690.
3
d
1
19
2
5
.3.2. Synthesis of block poly(N-pentafluorophenyl-norbornene-
,6-dicarboximide-co-N-phenyl-norbornene-5,6-dicarboximide) (3)
3
51.2, 46.7, 43.1, 41.8, 40.5, 32.1; F NMR (282 MHz, CDCl , ref. TFA
[ꢁ77ppm]):
d
(ppm) ¼ ꢁ142.2, ꢁ142.6, ꢁ143.1, ꢁ150.1, ꢁ150.3,
ꢁ
3
ꢁ1
Monomer 1b (0.36 g, 1.51 mmol) and catalyst I (2.49 ꢂ 10 g,
ꢁ159.8, ꢁ160.1, ꢁ160.7; FT-IR (thin film, cm ): 3008, 2932 (C-H
asym str), 2859 (CeH sym str),1795 (C]O),1727 (C]O),1650 (C]C
str),1513,1452,1370,1356,1294 (CeF),1165,1138, 984, 785, 767, 624.
ꢀ
0
.0030 mmol) were stirred in 2.17 mL of 1,2-dichloroethane at 65 C
for 0.33 h. Then, 0.50 g (1.51 mmol) of monomer 1a dissolved in
2
.17 mL of 1,2-dichloroethane was added to the polymer solution
ꢀ
and stirred at 65 C for 0.66 h (Scheme 1). The obtained copolymer 3
was soluble in chloroform and dichloroethane: Incorporation of 1a
2
.4. Hydrogenation of 3
5
in copolymer ¼ 32 mol%; M
n
¼ 2.60 ꢂ 10 ; M
w
/M
n
¼ 1.15;
):
(ppm) ¼ 7.44e7.24 (5H, m), 5.77 (2H, s, trans), 5.55 (2H, s, cis),
ꢀ
ꢀ
ꢀ
1
T
g1 ¼ 170 C; Tg2 ¼ 224 C; T
d
¼ 424 C; H NMR (300 MHz, CDCl
3
0.5 g of 3 was added to 60 mL of solvent (dichloromethane-p-
d
dioxane, 1:1) in a Schlenk tube. Wilkinson’s catalyst, ClRh(PPh
3 3
) ,
13
3
.25e3.14 (4H, s), 2.87 (4H, s), 2.20 (2H, s), 1.68 (2H, s); C NMR
):
(ppm) ¼ 177.1 (C]O), 174.7 (C]O), 144.9e139.4
CeF), 132.1 (cis), 131.9 (trans), 129.0, 126.6, 107.5 (CeN), 50.9, 46.1,
(5 wt%) was previously introduced into a Parr shaker reactor. The
(
75 MHz, CDCl
3
d
2
solution was degassed and charged into the reactor under N . Then
hydrogen was added. A 99% of hydrogenation, determined by
NMR, for 5 was achieved using a Wilkinson’s catalyst, ClRh(PPh ) ,
3 3
at room temperature and 115 bar (Scheme 2). The obtained poly-
1
(
H
19
41.7;
F
NMR (282 MHz, CDCl
3
,
ref. TFA [ꢁ77ppm]):
d
(ppm) ¼ ꢁ142.2, ꢁ142.7, ꢁ143.2, ꢁ150.0, ꢁ150.3, ꢁ159.7, ꢁ160.0,-
ꢁ
1
ꢁ
160.7; FT-IR (thin film, cm ): 3022, 2925 (CeH asym str), 2838
mer 5 was soluble in chloroform and dichloromethane. Incorpo-
(
(
CeH sym str), 1774 (C]O), 1707 (C]O), 1588 (C]C str), 1517, 1455
CeN), 1360, 1299 (CeF), 1167, 1022, 988, 746, 690.
ꢀ
ꢀ
ration of 1a in copolymer ¼ 32 mol%; Tg1 ¼ 143 C; Tg2 ¼ 198 C;
ꢀ
1
T
d
¼ 460 C; H NMR (300 MHz, CDCl
3
):
d
(ppm) ¼ 7.48e7.23 (5H,
13
m), 3.03e2.93 (2H, m), 2.17, 1.89, 1.60, 1.23; C NMR (75 MHZ,
CDCl ):
(ppm) ¼ 177.9 (C]O), 175.6 (C]O), 144.7e139.1 (CeF),
31.8, 128.9, 128.3, 126.4, 107.4 (CeN), 51.9, 44.0, 42.1, 33.7; F NMR
282 MHz, CDCl (ppm)
ref. TFA [ꢁ77ppm]):
142.2, ꢁ143.1, ꢁ150.2, ꢁ150.3, ꢁ159.8, ꢁ160.2; FT-IR (thin film,
2
5
.3.3. Synthesis of block poly(N-pentafluorophenyl-norbornene-
,6-dicarboximide-co-Norbornene) (4)
3
d
19
1
(
Monomer 1a (0.50 g, 1.51 mmol) and catalyst I (2.49 ꢂ 10ꢁ3 g,
3
,
d
¼
ꢀ
0
.0030 mmol) were stirred in 2.5 mL of 1,2-dichloroethane at 45 C
ꢁ
ꢁ1
for 0.5 h. Then, 0.14 g (1.51 mmol) of norbornene dissolved in 3.5 mL
of 1,2-dichloroethane was added to the polymer solution and stirred
cm ): 2923 (CeH asym str), 2846 (C-H sym str), 1779 (C]O), 1706
C]O), 1517, 1456 (CeN), 1359, 1299, (CeF), 1168, 1036, 988.
(

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4211
Scheme 2. Hydrogenation and further aromatic substitution of polynorbornene based copolymers bearing pentafluorophenyl moieties.
ꢀ
2
.5. Hydrogenation of 4
(N,N-dimethylacetamide-toluene, 10:1) at 120 C for 3 h (Scheme 2).
Progressive precipitation overtime was observed. The product was
then filtered off, washed several times with distilled water and dried
0
.5 g of 4 was added to 60 mL of solvent (dichloromethane-p-
ꢀ
dioxane, 1:1) in a Schlenk tube. Wilkinson’s catalyst, ClRh(PPh
3 3
) ,
in a vacuum oven at 40 C overnight. The resulting polymer 7, a dark-
(
5 wt%) was previously introduced into a Parr shaker reactor. The
brown powder, was soluble in DMSO. Incorporation of 1a in
ꢀ
ꢀ
solution was degassed and charged into the reactor under N
hydrogen was added. A 98% of hydrogenation, determined by
NMR, for 6 was achieved using a Wilkinson’s catalyst, ClRh(PPh
room temperature and 115 bar (Scheme 2). The obtained polymer 6
was soluble in chloroform and dichloromethane. Incorporation of 1a
2
. Then
copolymer ¼ 32 mol%; Yield: 94%; Tg1 ¼ 180 C; Tg2 ¼ 198 C;
1
ꢀ
1
H
T
d
¼ 456 C; H NMR (300 MHz, DMSO-d
(10H, m), 3.64 (2H, s), 3.10, 2.22, 1.91, 1.63, 1.26; C NMR (75 MHZ,
DMSO-d ):
6
):
d
(ppm) ¼ 7.51e6.92
13
3 3
) , at
6
d
(ppm) ¼ 178.3 (C]O), 177.7 (C]O), 127.6 (CeO), 114.8,
1
ꢁ
107.3 (C-N), 51.4; FT-IR (thin film, cm ): 3423, 2927 (CeH asym str),
2850 (C-H sym str),1707 (C]O),1693 (C]O),1684,1506,1494,1357,
1294 (CeF), 1120, 1010, 981, 743, 689, 607.
ꢀ
ꢀ
ꢀ
1
in copolymer ¼ 49 mol%; Tg1 ¼4 C; Tg2 ¼143 C; T
300 MHz, CDCl ):
(ppm) ¼ 3.06 (2H, s), 2.30e1.25 (20H, m);
NMR (75 MHz, CDCl ):
(ppm) ¼ 174.6 (C]O), 147.0e141.3 (CeF),
35.2,107.4 (C-N), 51.1, 46.6, 43.1, 41.7, 40.6, 32.2; F NMR (282 MHz,
CDCl , ref. TFA [-77ppm]):
(ppm) ¼ ꢁ142.2, ꢁ142.5, ꢁ143.1,
150.1, ꢁ150.5, ꢁ159.8, ꢁ160.1, ꢁ160.4; FT-IR (thin film, cm ): 3012,
937 (C-H asym str), 2862 (CeH sym str), 1796 (C]O), 1723 (C]O),
510, 1456, 1378, 1360, 1293 (CeF), 1169, 1135, 986, 785, 767, 620.
d
¼ 454 C; H NMR
13
(
3
d
C
3
d
19
1
2.7. Synthesis of 8
3
d
ꢁ1
ꢁ
Hydrogenated poly(N-pentafluorophenyl-exo-endo-norbornene-
,6-dicarboximide-co-N-phenyl-exo-endo-norbornene-5,6-dicarboxi-
2
5
1
mide) (5) (1.0 g, 1.74 mmol), sodium 4-hydroxybenzenesulfonate
dihydrate (0.61 g, 2.62 mmol) and potassium carbonate (0.44 g,
3.18 mmol) were mixed in a round flask equipped with a DeaneStark
trap and stirred in 22 mL of solvent (N,N-dimethylacetamide-toluene,
2
.6. Synthesis of 7
ꢀ
Hydrogenated poly(N-pentafluorophenyl-exo-endo-norbornene-
,6-dicarboximide-co-N-phenyl-exo-endo-norbornene-5,6-dicarbo-
10:1) at 120 C for 5 h (Scheme 2). Progressive precipitation overtime
5
was observed. The product was then filtered off, washed several times
ꢀ
ximide) (5) (1.0 g, 1.74 mmol), phenol (0.25 g, 2.62 mmol) and
potassium carbonate (0.44 g, 3.18 mmol) were mixed in a round flask
equipped with a DeaneStark trap and stirred in 18 mL of solvent
with distilled water and dried in avacuum oven at 40 C overnight. The
resulting polymer 8, a pale-brown powder, was soluble in DMF and
DMSO. Incorporation of 1a in copolymer ¼ 32 mol%; Yield: 96%;

4212
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
T
T
d
g1 ¼ 198 C; Tg2 ¼ 227 C; Td1 ¼ 272 C (sulfonic group loss);
copolymer ¼ 49 mol%; Yield: 95%; Tg1 ¼ 4 C; Tg2 ¼ 227 C;
ꢀ
1
ꢀ
ꢀ
d2 ¼ 458 C (main chain decomposition); H NMR (300 MHz, DMF-
):
(ppm) ¼ 7.81 (2H, m), 7.53e7.34 (5H, m), 7.27 (2H, m), 3.65 (2H,
s), 3.09, 2.24, 1.90, 1.65, 1.28; C NMR (75 MHZ, DMSO-d
T
d1 ¼ 268 C (sulfonic group loss); Td2 ¼ 448 C (main chain
1
7
d
decomposition); H NMR (300 MHz, DMSO-d
s), 7.19 (2H, s), 3.26 (2H, s), 2.11e1.22 (20H, m); C NMR (75 MHZ,
DMSO-d ):
(ppm) ¼ 174.7 (C]O), 135.2, 128.1 (CeO), 107.3 (CeN),
51.1, 46.3, 43.2, 41.5, 40.5, 32.3; F NMR (282 MHz, DMSO-d
[-77ppm]):
6
):
d
(ppm) ¼ 7.68 (2H,
13
13
6
):
(ppm) ¼ 178.2 (C]O), 177.9 (C]O), 127.9 (CeO), 114.9, 107.5 (CeN),
d
6
d
19
19
51.6;
d
F
NMR (282 MHz, DMF-d
7
,
ref. TFA [-77ppm]):
6
, ref. TFA
(ppm) ¼ ꢁ141.9, ꢁ142.9, ꢁ150.0, ꢁ153.1, ꢁ160.4; FT-IR (thin film,
d
(ppm) ¼ ꢁ142.3, ꢁ143.3, ꢁ150.2, ꢁ153.2, ꢁ160.3; FT-IR
ꢁ
1
ꢁ1
cm ): 3420, 2923 (CeH asym str), 2854 (CeH sym str), 1703 (C]O),
698 (C]O), 1682, 1505, 1492, 1359, 1291 (CeF), 1165 (eSO H, asym
str), 1124, 1033 (eSO H, sym str), 1008, 987, 742, 689, 608.
(thin film, cm ): 3480, 2932 (CeH asym str), 2870 (CeH sym str),
1798 (C]O), 1725 (C]O), 1680, 1515, 1494, 1357, 1299 (CeF),
1
3
3
3 3
1260, 1168 (eSO H, asym str),1139,1032 (eSO H, sym str), 987, 802,
767, 696.
2.8. Synthesis of 9
2.9. Density, water uptake and ion-exchange capacity
Hydrogenated poly(N-pentafluorophenyl-exo-endo-norbornene-
,6-dicarboximide-co-Norbornene) (6) (1.0 g, 2.34 mmol), sodium 4-
5
The density of the dry membrane of copolymer 8 was measured
hydroxybenzenesulfonate dihydrate (0.81 g, 3.48 mmol) and potas-
sium carbonate (0.59 g, 4.27 mmol) were mixed in a round flask
by the flotation method using isooctane as solvent. The value of this
ꢁ
3
parameter is
r
¼ 1380 kg m
.
equipped with a DeaneStark trap and stirred in 26 mL of solvent
Weighed dry membranes from copolymer 8 were immersed
and kept in deionized distilled water overnight. The membranes
were removed from water, gently blotted with filter paper to
remove surface water and weighed. This operation was repeated
three times. Water uptake was obtained by means of the
expression
ꢀ
(
N,N-dimethylacetamide-toluene, 10:1) at 120 C for 5 h (Scheme 2).
Progressive precipitation overtime was observed. The product was
then filtered off, washed several times with distilled water and dried
ꢀ
in a vacuum oven at 40 C overnight. The resulting polymer 9, a dark-
brown powder, was soluble in DMSO. Incorporation of 1a in
weight wet membrane ꢁ weight dry membrane
Water uptake ¼
ꢂ 100
(1)
weight dry membrane
Fig. 1. 1H NMR spectra of exo(75%)-endo(25%) monomer mixtures of 1a (bottom) and 1b (top).

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4213
Fig. 2. 19F NMR spectrum of exo(75%)-endo(25%) monomer mixture of 1a.
To evaluate the ion-exchange capacity, the membranes in the
2.11. Ohmic resistance measurements
acid form were equilibrated with a NaCl solution1M, after the
hydrochloric acid was liberated in the interchange reaction
The ohmic resistance of the membrane in the acid form was
measured with a Novocontrol BDS system comprising a frequency
response analyzer (Solartron Schlumberger FRA 1260) and
a broadband dielectric converter with an active sample head. Gold
disk electrodes were used in the impedance measurements carried
out at several temperatures in the frequency window
R ꢁ H þ Na /R ꢁ Na þ Hþ
þ
the pH of the acid solution was measured. The values of the ion-
exchange capacity (IEC) and the water uptake (w
.286 eq/kg dry membrane and 0.373 kg H O/kg dry membrane. The
theoretical value of IEC is of 0.204 eq/kg dry membrane.
u
) are, respectively,
0
2
ꢁ2
6
4.9 ꢂ 10 e3 ꢂ 10 Hz. The temperature was controlled by
a nitrogen jet (QUATRO from Novocontrol) with a temperature
error of 0.1 K during every single sweep in frequency.
2.10. Electromotive force of concentration cells
The electromotive force of the concentration cell with configu-
3. Results and discussion
ration AgjAgClj electrolyte concentration (m ) jcation-exchange
1
1
membranej electrolyte concentration (m
2
)j AgCljAg, where m
The H NMR spectra of these norbornene dicarboximides show
represents the molal concentration, was measured with a Hioki
signals with rather similar relative intensities and chemical shifts.
The exo and endo olefinic signals of 1a and 1b were well-resolved in
both H NMR spectra and appeared as singlets in the region of
6.5e6.0 ppm (Fig. 1). From the relative intensities of these signals
the ratio of exo and endo isomers was determined to be 75:25. The
other signals showed overlapping owing to the presence of the
ꢀ
potentiometer, at 25 C, for various concentrations of hydrochloric
1
acid and sodium chloride solutions, respectively. Electromotive
forces were monitored as a function of time via a PC. The ratio of the
molal concentrations m /m was kept in the vicinity of 2 in all the
2 1
cases.
Fig. 3. 1H NMR spectrum of copolymer 2.

4214
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
1
Table 1
reached. H NMR was used to determine the incorporation of 1a in
Copolymerization conditions of monomers 1a and 1b for reactivity constants
determination.
the different copolymers synthesized (Fig. 3) by integrating the
area of the olefinic proton region (
aromatic proton region (
d
¼ 5.5e5.8 ppm) relative to
Entry Mass of 1a in Mol % of
Incorporation
Time Yield
d
¼ 7.1e7.4 ppm). Table 1 summarizes the
a
c
the feed (g)
1a in the feed
of 1a in copolymer
(s)
(%)
results of the copolymerizations of 1a and 1b. Since at
the conversion desired (ꢃ15 wt%) monomer 1a was not detected in
b
(%)
1
2
3
4
5
0.3
0.3
0.5
0.3
0.5
20
40
50
60
80
7.9
25
25
25
30
30
14.1
08.9
15.0
12.2
07.4
ꢀ
the copolymer formed when the reactions were conducted at 45 C,
23.4
29.6
41.9
66.6
the experiments for reactivity constant determination were carried
ꢀ
out at 65 C and incorporation of monomer 1a could be successfully
1
quantified by H NMR. Furthermore, as mol percent of 1a in the
a
feed was increased, more reaction time was needed for copoly-
merization to take place until the conversion desired (Table 1,
entries 4 and 5). It has been previously indicated that the more endo
isomer in the mixture feed the lower level of activity that is dis-
Molar ratio of monomer to catalyst ¼ 1000, 1,2-Dichloroethane as solvent,
ꢀ
temperature ¼ 65 C, Initial monomer concentration [M
o
] ¼ 0.7 mol/L.
b
Determined by 1H NMR.
Methanol insoluble polymer.
c
ꢀ
played by I at 45 C [18]. Up to now, research is being carried out to
minor isomer, mainly in the methylene and aromatic proton
regions, and an accurate integration could not be made.
clarify what causes this very low catalytic activity in the presence of
1a at 45 C, a temperature typically used for the ROMP of norbor-
ꢀ
The 19F NMR spectrum of 1a shown in Fig. 2 displays, on one
hand, three major signals corresponding to the exo isomer, that for ‒
F in ortho position occurs at ꢁ142.2 ppm, that for ‒F in meta position
between ꢁ159.7 and ꢁ160.2 ppm and that for ‒F in para position
appears at ꢁ150.1 ppm. On the other hand, four minor signals cor-
responding to the endo isomer are observed and assigned as follows:
those for ‒F in ortho position occur at ꢁ140.3 ppm and ꢁ142.3 ppm,
that for ‒F in meta position appears at ꢁ160.4 ppm and that for ‒F in
para position occurs at ꢁ150.6 ppm. Based on the exo and endo
signals of the fluorine atom in para position, which appear
at ꢁ150.1 ppm and ꢁ150.6 ppm respectively, the exo:endo ratio of 1a
nene dicarboximides. On the basis of the results obtained from the
copolymerization experiments, the reactivity constants r1a and r1b
were determined by using the general copolymerization equation.
By applying the Mayo-Lewis method [19] the values obtained were
r1a ¼ 0.601 and r ¼ 4.235 whereas by applying the Fineman-Ross
1b
method [20] the values obtained were r ¼ 0.449 and r ¼ 3.728
1
a
1b
for monomer 1a and 1b, respectively. The precision of experi-
mentally determined monomer reactivity ratios depends on the
experimental design and technique used to analyze the data.
Results obtained for acrylamide monomer by applying the Mayo-
Lewis and Fineman-Ross methods, for example, are reported to
vary up to 58% from each other [21]. It is worth noting that these
linear methods are used only to give preliminary estimates of
reactivity ratios which are used in nonlinear methods to generate
more accurate results.
19
was also determined from the F NMR spectrum being consistent
with those ratios obtained from other signal integrations as well as
1
with the previous determinations made by H NMR spectroscopy.
Copolymerizations of 1a and 1b, for reactivity constants deter-
ꢀ
mination, were carried out in 1,2-dichloroethane at 65 C,
Block and random high molecular weight copolymers were also
synthesized via ROMP using bis(tricyclohexylphosphine)benzyli-
deneruthenium(IV) dichloride (I) and tricyclohexylphosphine [1,3-
bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzy-
lidene]ruthenium dichloride (II) (Scheme 1). Table 2 summarizes
via ROMP, using bis(tricyclohexylphosphine)benzylidene ruth-
enium(IV) dichloride (I) (Scheme 1). The reactions were conducted
at 20, 40, 50, 60 and 80 mol percent of monomer 1a in the feed and
quenched before a 15 weight percent of monomer conversion was
Table 2
General conditions for copolymerization of monomer 1a with 1b and norbornene (NB), respectively.
Catalysta
[M
Temperature ( C)
ꢀ
Time (min)
Incorporation of 1a
Yield (%)c
ꢁ5d
n
M x10
MWDd
Entry
Comonomer
Fashion
o
] (mol/L)
in copolymer (%)b
1
2
3
4
5
6
7
8
1b
1b
1b
1b
1b
1b
1b
1b
Random
Random
Random
Random
Random
Random
Random
Block
II
II
I
I
I
I
I
I
1.0
0.5
0.7
0.7
0.7
0.7
0.7
0.7
25
25
45
45
45
45
65
65
5
240
5
15
60
42
44
e
91
97
14
65
81
89
97
84
2.45
2.79
0.35
1.53
2.20
2.22
2.85
2.60
1.26
1.38
1.24
1.17
1.19
1.20
1.22
1.15
30
39
43
48
32
120
120
e
20
f
4
20
0
e
f
9
1b
1b
NB
NB
NB
Block
Block
Block
Block
Block
I
I
I
I
I
0.7
0.7
0.5
0.5
0.5
65
65
25
45
45
41
48
21
38
49
88
96
57
83
98
2.73
2.80
1.12
1.87
2.11
1.16
1.20
1.24
1.23
1.25
60
e
f
1
1
1
1
0
1
2
3
20
80
f
20
g
f
10
20
g
f
10
30
g
10
a
b
c
Molar ratio of monomer to catalyst ¼ 1000, 1,2-Dichloroethane as solvent, Mol % of 1a in the feed ¼ 50.
Determined by 1H NMR.
Methanol insoluble polymer.
GPC analysis in tetrahydrofuran with polystyrene calibration standards.
Reaction time for monomer 1b.
Reaction time for monomer 1a.
d
e
f
g
Reaction time for NB.

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4215
Fig. 4. Thermomechanical analysis of random copolymer 2, block copolymer 3, block copolymer 4, homopolymer of 1a and homopolymer of 1b, respectively.
the results of the high conversion copolymerizations of 1a with 1b
and NB, respectively. It is observed that catalyst II produced
random high molecular weight copolymers in the early minutes of
reaction in high yield at room temperature with almost complete
incorporation of 1a in the copolymer (Entry 1). On the contrary,
catalyst I was not able to incorporate monomer 1a in copolymer in
metallacarbene active center inhibiting the polymerization. A
coordination of the ruthenium atom to the fluorine atom of the
perfluoroaromatic moiety of the endo-monomer of 1a is possible in
a similar way that the ruthenium atom is coordinated to the sulfur
atom of certain olefin metathesis initiators bearing sulfoxide
moieties which have exhibited poor activity at room temperature
but a reasonable and increased level of activity at elevated
temperatures. These complexes seemed to be dormant at low
temperature on the contrary the catalysis proceeded quickly when
the temperature was raised [22]. We consider that the least active
catalyst I (in comparison with catalyst II), the Ru-fluorine intra-
molecular interaction and the steric effect of the pentafluorinated
ring in endo-monomer of 1a are factors which difficult the
complete incorporation of the monomer 1a in the copolymer using
I. Fig. 4 shows the thermomechanical analysis performed on the
random and block copolymers synthesized as well as those of the
corresponding homopolymers of 1a and 1b used as references,
ꢀ
the same time even at 45 C (Entry 3) and more reaction time was
needed for the incorporation of 1a to take place and it could be
1
detected by H NMR (Entries 4 and 5). For the same period of time
(
120 min), quantitative incorporation of monomer 1a in copolymer,
in high yield and using catalyst I, was achieved when the poly-
ꢀ
ꢀ
merization was conducted at 65 C rather than 45 C (Entries 6 and
). Block copolymers of 1a with 1b and NB were synthesized in high
7
yields using catalyst I (Entries 8e13). In the first case, the copoly-
ꢀ
merizations were conducted at 65 C and the monomer 1b was
added initially polymerizing completely within 0.33 h (Entries
8
e10). Immediately, monomer 1a was added to the reaction and
quantitative incorporation of 1a in copolymer was detected after
.33 h of being added to the growing polymer (Entry 10). In the
ꢀ
respectively. As expected, a single transition is observed, at 205 C,
1
and interpreted as the glass transition temperature, T
g
, of the
second case, monomer 1a was added firstly and allowed to poly-
merize during 0.5 h. Then, NB was added to the reaction and after
random copolymer 2 whereas two transitions are observed for the
ꢀ
ꢀ
block copolymer 3, at 170 C and 224 C, and attributed to the
corresponding T of 1a and 1b homopolymer regions, respectively.
Similarly, two transitions are also observed for the block copolymer
0
.16 h the copolymerization was inhibited. Quantitative incorpo-
g
ration of 1a in copolymer was detected when the copolymerization
ꢀ
ꢀ ꢀ
was conducted at 45 C (Entry 13). Compared to exo-monomer
4, at 44 C and 170 C, which were interpreted as the T of NB and 1a
g
where functional groups are far from the metal active center the
homopolymer regions, respectively. Furthermore, the thermo-
polar groups of endo-monomer may coordinate to the
oxidative stabilities of block copolymers 3 and 4 were enhanced
Fig. 5. 3-D AFM micrographs (2 ꢂ 2
mm) of (a) block copolymer 3, (b) hydrogenated copolymer 5 and (c) sulfonated copolymer 8.

4216
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
Fig. 6. X-Ray diffraction patterns of (a) random copolymer 2 and (b) block copolymer 3.
ꢀ
exhibits another peak around 9 2q that can be attributed to
by quantitative hydrogenations according to the methodology
previously reported for these kinds of polymers (Scheme 2) [23]. In
Fig. 5, the surface morphologies of (a) block copolymer 3, (b)
hydrogenated copolymer 5 and (c) dried sulfonated copolymer 8
are observed by tapping mode atomic force microscopy in three
dimensions. The surface morphology in (a) shows an oriented
morphological architecture characterized by broad peaks. This
broadening could be attributed to the low surface energy of the
pentafluorophenyl moieties which provide a thermodynamic
driving force for the self-assembly at the surface air-polymer
interface. In contrast, hydrogenation of the block copolymer
seems to disturb the order generated by the presence of the double
bonds and a much more disrupted surface is observed in (b). Finally,
the surface morphology in (c) suggests that the sulfonic hydrophilic
groups aggregate and, to a certain extent, phase separation begins
to be noticeable. The presence of hydrophobic fluorine moieties
affects the copolymer morphology in such a way that a surface
enrichment of fluorine is generated. The latter assumption is
commonly associated to a low surface energy. In fact, this effect of
fluorine containing moieties in copolymers has also been observed
for other fluorocopolymers of low-surface energy [24].
different arrangements adopted by the fluorinated and non-
fluorinated copolymer chain segments which seem to vanish
after the hydrogenation step. It is worth noting that block copoly-
mers are able to spontaneously assemble into a wide variety of
nanostructures and spherical or cylindrical micelles, among other
combinations [25].
Afterwards, we tested the reactivity of copolymer 5 in reaction
with phenol (Scheme 2). The nucleophilic aromatic substitution
reaction was quantitative demonstrating, in this manner, the tail-
orable functionality of the perfluorinated polynorbornene based
copolymers. Once the phenoxy-derivative 7 was successfully
obtained, we reacted the hydrogenated copolymers 5 and 6 with
sodium 4-hydroxybenzenesulfonate dihydrate, following the
procedure previously used for the sulfonation of hydrogenated
poly(N-pentafluorophenyl-exo-endo-norbornene-5,6-
dicarboximide) [18], and progressive precipitation of the ionomers
overtime was observed (Scheme 2). Ionomer films were cast from
sulfonated copolymer 8 and 9 solutions in DMF and DMSO,
respectively. The films were quite flexible when fully hydrated and
19
became somewhat brittle as they dried out. The F NMR spectra of
Fig. 6 shows the X-ray diffraction patterns of the as cast random
copolymer 2 as well as block copolymer 3 films. Both copolymers
the hydrogenated copolymer 6 and the sulfonated copolymer 9 are
19
very similar to the F NMR spectra of copolymers 5 and 8, shown in
Fig. 7, respectively. According to Fig. 7, it is appreciated that the
substitution reaction has taken place in the para position
show typical amorphous patterns with one broad diffraction peak
ꢀ
with a maximum around 20 2
q. Nevertheless, block copolymer 3
Fig. 7. 19F NMR spectra of a) non-sulfonated copolymer 5 and b) sulfonated copolymer 8.

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4217
Fig. 8. 1H NMR spectra of a) non-sulfonated copolymer 6 and b) sulfonated copolymer 9.
1
(
b, ꢁ150.1 ppm) since this signal has almost disappeared when
to be detected by H NMR. Copolymer 8 membranes in proton form
1
ꢀ
a highly sulfonated copolymer is obtained. The H NMR spectra of
a) the saturated copolymer 6 and b) the sulfonated copolymer 9 are
shown in Fig. 8. Clearly it is observed that the copolymer 6 has
(100e150 mg) aged in 500 mL of water at 90 C up to 72 h exhibited
fairly good toughness level as they only broke when the films were
hardly bent.
undergone
a nucleophilic aromatic substitution due to the
appearance of new signals at 7.68 ppm and 7.19 ppm assigned to the
meta and ortho aromatic protons of the phenyl moiety bearing the
sulfonate groups, respectively. In addition, FT-IR allowed us to
confirm the introduction of sulfonate groups in the copolymers by
ꢁ
1
observing the characteristic bands around 1033 and 1165 cm
assigned to symmetric and asymmetric stretching of sulfonate
groups. The acid form copolymers 8 and 9 showed 5% weight losses
ꢀ
ꢀ
of 268 C and 272 C, respectively, which were assigned to the
losses of the sulfonic groups whereas the second weight losses
ꢀ
ꢀ
occurred at 448 C and 458 C were assigned to the thermal
decompositions of the saturated main polymer chains. The
mechanical properties of the copolymer 8 membrane were evalu-
ated after soaking the film sample for 120 h at room temperature.
The Young’s modulus and the maximum stress were determined to
be E ¼ 1615 MPa and
s
¼ 65 Mpa, respectively. The GPC analysis
performed on the copolymers before and after being subjected to
the sulfonation process do not show low molecular weight
compounds. This indicate that the polymer chain scission,
commonly caused by the hydrolysis of the imide ring in the main
chain of linear polyimides, have not occurred during the sulfona-
tion process of copolymer 8 which bears the imide moiety as a side
chain group. The presence of hydrolysis products was neither able
Fig. 9. Evolution of the emf of the copolymer 8 membrane for different c
,) 0.01/0.005, (C) 0.02/0.01, (:) 0.1/0.05, (;) 0.2/0.1, (9) 0.4/0.2, (<) 0.8/0.4, (>)
1.0/0.5.
2 1
/c ratios:
(

4218
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
Table 3
Values of the hydrochloric acid concentration (molality), activity coefficient and
electromotive force for the sulfonated copolymer 8 membrane.
m
1
m
2
g
1
g
2
emf (mV)
0
0
0
0
0
0
0
.00519
.01027
.05072
.10167
.20218
.40288
.50522
0.01027
0.02052
0.10155
0.20207
0.40288
0.79916
0.99157
0.9263
0.9011
0.8324
0.79287
0.7655
0.7580
0.7579
0.9011
0.8753
0.7929
0.76559
0.7580
0.7873
0.8116
34.50
35.89
28.35
27.38
20.59
18.33
15.86
The replacement of the fluorine atom in para position of
the pentafluorophenyl groups in the block hydrogenated
poly(N-phenyl-exo-endo-norbornene-5,6-dicarboximide-co-N-pen-
tafluorophenyl-exo-endo-norbornene-5,6-dicarboximide) using mild
conditions yields an ionomer (8), thus opening new ways to
the preparation of new polyelectrolytes. The permselectivity of
cation-exchange membranes prepared from sulfonated copolymers
with ion-exchange capacity 0.286 eq/kg was performed using
concentration cells with configuration AgjAgCljelectrolyte (m
jmembranejelectrolyte (m )jAgCljAg. As electrolytes HCl and NaCl
were used and the ratio of the molalities m /m was roughly 2. The
1
)
2
2
1
electromotive force (emf) of the concentration cell was measured
under strong stirring in order to avoid polarization effects on the side
of the membranes in contact with the electrolyte solutions. Prior to
the experiments, the membrane was equilibrated with the less
concentrated electrolyte solution. The membrane thickness was
Fig. 10. AFM tapping phase image for the copolymer 8 membrane.
50 mm. As can be seen in Fig. 9, the emf increases with time, initially
rather fast until a maximum is reached, and then rather slowly, for the
less concentrated solutions, andsomewhat more rapidly, for the more
concentrated solutions. The decrease is presumably caused by
osmotic flow and free electrolyte diffusion that tend to decrease the
1.0 M HCl solution for 48 h to ensure the acid form of the
membrane, and repeatedly washed with deionized water. Then,
the membrane in the acid form was equilibrated with a NaCl
solution1M and after the hydrochloric acid was liberated in the
interchange reaction the pH of the acid solution was measured.
The slightly difference between the experimental and theoretical
IECs could be attributed to residual HCl used to protonate the
membrane which could be increasing the pH of the acid solution
and therefore the experimental IEC. Fig. 10 shows the represen-
tative morphology of the copolymer 8 membrane. The molecular
chains of this membrane contain respectively 68% and 32% molar
fractions of phenyl and fluorinated pendant benzenesulfonate
m
2
/m
vs time was taken as the electromotive force of the concentration cell
for the m /m ratio of interest.
1
ratio of the solutions. The emf at the maximum of the curve emf
2
1
The sign of the emf changes when the concentrations in the
compartments flanking the membrane are reversed. This behavior
indicates that the cation-exchange membrane is symmetric.
2 1
Values of the emf of the concentration cells for different m /m
concentration ratios are shown in Tables 3 and 4 for the HCl and
NaCl electrolytes, respectively. As usual, the values of the emf
decrease as the concentration of the electrolyte increases. It is
worth noting that in spite of its relatively low IEC of 0.286 eq/kg
dry membrane (the theoretical value of IEC is of 0.204 eq/kg dry
membrane), the copolymer 8 membrane exhibits an unusual
water uptake of 0.373 kg H
2
O/kg dry membrane as well as a rather
large number of molecules of water per fixed anionic group
(
l
¼ 72.5). This fact suggests that microphases separation in the
latter membrane serves to compartmentalize an excess of water
into the hydrophilic polar side chain domains, specifically in the
vicinity of the dicarboximide side groups. For determining the
experimental IEC, the sulfonated membrane was firstly soaked in
Table 4
Values of the sodium chloride concentration (molality), activity coefficient and
electromotive force for the sulfonated copolymer 8 membrane.
m
1
m
2
g
1
g
2
emf (mV)
0
0
0
0
0
0
0
.00509
.01004
.05008
.10029
.19996
.39985
.49994
0.01004
0.02019
0.10029
0.19996
0.39985
0.79883
1.00003
0.9318
0.9019
0.8180
0.7795
0.7295
0.6813
0.6704
0.9019
0.8647
0.7795
0.7295
0.6813
0.6576
0.6553
36.15
34.98
23.48
16.45
11.41
7.97
Fig. 11. Variation of the apparent proton (squares) and sodium cation (circles) trans-
port numbers with the geometric average of the molality of the HCl and NaCl solutions
flanking the membrane in copolymer 8.
8.82

A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
4219
ꢀ
Fig. 12. Nyquist plots at 20 (-), 30 (B), 50 (:) y 70 C (7) for the copolymer
membrane in the acid form equilibrated with distilled water. Inset: Zoom of
the Nyquist plots at high frequencies. The curves were only used to connect the points.
8
Fig. 14. Arrhenius plot showing the temperature dependence of the copolymer 8
membrane.
moieties bonded to the dicarboximide side groups. It is expected
that these moieties are mutually incompatible and therefore
segregations occur giving rise to nano-size domains observed in
the AFM of copolymer 8.
The following expression is applied for the electromotive force,
E, measurements of the concentration cell of monovalent (1:1)
electrolyte solutions [14]
For an ideal membrane, t ¼ 1, and tþ is given by
þ
D
E
1
t
¼ E=Emax
(3)
þ
where Emax is the electromotive force for an ideally permselective
1
membrane obtained from Eq. (2) using t ¼ 1.
þ
Values of the apparent proton and sodium ion transport
numbers for different concentrations flanking the membrane are
shown in Fig. 11. It can be seen that for very low concentrations the
membrane is ideally permselective to protons and sodium ions, i.e.
a
2
Z
E ¼ ꢁ2
RT
F
2RT
dlna2 ¼ ꢁ F
m2
m1
g
g
2
1
t
þ
t
þ
ln
(2)
a
1
where F is Faraday’s constant,
activity coefficients of the low and high concentration electrolyte
solutions flanking the membranes in the concentration cell and t
is the apparent counterion transport number in the membrane of
the concentration cell.
g
1
and
g
2
represent, respectively, the
þ
t ¼ 1. This behavior is a consequence of the fact that co-ions are
totally excluded from the membrane so that current is exclusively
transported across the membrane by protons and sodium ions,
respectively. As usual, the transport number decreases with
increasing concentration of the electrolyte. At moderate and high
concentrations, however, an increasing amount of coions intervene
in the current transport across the membrane in such a way that
þ
the value of t
number of Na is slightly lower than that of H .
þ
comes close to that of t
ꢁ
. In this region, the transport
þ
þ
The ohmic resistance of the membrane R
M
in the acid form
equilibrated with distilled water was measured at several
temperatures. Two methods were used to determine the resistance
of the membranes R , the Nyquist [26] and the Bode [27] diagrams.
M
Illustrative Nyquist and Bode plots for the copolymer 8 membrane
are shown in Figs. 12 and 13, respectively. The results obtained for
R
M
by the two methods are in rather good agreement. For example
ꢀ
the value of R
M
for the copolymer 8 membrane at 30 C estimated
from the former and the latter plots are respectively 20.24
0.41
Afterwards, the protonic conductivity was obtained by means of
U and
2
U.
the familiar expression [28]
l
s
¼
(4)
R S
0
Fig. 13. Bode diagram showing the variation of the modulus of the impedance jZ*j
where l and S are respectively thickness and area of the membrane
in contact with the electrodes. The values of the proton conduc-
tivity obtained from the Nyquist and Bode diagrams is of
ꢁ
1
00
0
(
lines) and the out-of-phase angle (
f
¼
tan =Z =Z (symbols) with the frequency at
ꢀ
ꢀ
ꢀ
20
C (solid line and filled circles), 40 C (dash line and filled squares), 60 C (dot line
ꢀ
and open triangles) and 80 C (dash dot line and filled circles) for the copolymer 8
membrane in the acid form equilibrated with distilled water. The curves were only
used to connect the points.
ꢁ
1
ꢁ1
ꢀ
s
¼ 0.0135 S m and
s
¼ 0.0134 S m at 30 C, respectively. The
Arrhenius plot representing the temperature dependence of the

4220
A.A. Santiago et al. / Polymer 52 (2011) 4208e4220
membrane, presented in Fig. 14, shows that the activation energy
associated with proton transport across the copolymer
was also supported by the CICYT through the project MAT2008-
06725-C03-01.
8
membrane is of 7.0 ꢄ 0.4 kcal/mol. Taking into account the low ion-
exchange capacity of the membranes, these results suggest that
membranes with acceptable conductivity to be used as poly-
electrolytes in low temperature fuel cells could be obtained by
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2
Financial support from National Council for Science and Tech-
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