Polynorbornene with pentafluorophenyl imide side chain groups: Synthesis and sulfonation

Article abstract of DOI:10.1002/pola.24073

The mixtures of exo-endo-monomers and isomerically pure endo-monomers of N-pentafluorophenyl-norbornene-5,6-dicarboximide (2a) and N-phenyl-norbornene-5, 6-dicarboximide (2b) were synthesized and polymerized via ring opening metathesis polymerization usin

Full text of DOI:10.1002/pola.24073

Polynorbornene with Pentafluorophenyl Imide Side Chain Groups:
Synthesis and Sulfonation
3
ARLETTE A. SANTIAGO,1 JOEL VARGAS,1 SERGUEI FOMINE,2 RUBEN GAVINO, MIKHAIL A. TLENKOPATCHEV2
´
˜
1Facultad de Qu´ımica, Universidad Nacional Auto´ noma de Me´xico, CU, Coyoaca´n, Me´xico DF 04510, Me´xico
2Instituto de Investigaciones en Materiales, Universidad Nacional Auto´ noma de Me´xico, Apartado Postal 70-360,
CU, Coyoaca´n, Me´xico DF 04510, Me´xico
3Instituto de Qu´ımica, Universidad Nacional Auto´ noma de Me´xico, CU, Coyoaca´n, Me´xico DF 04510, Me´xico
Received 23 February 2010; accepted 14 April 2010
DOI: 10.1002/pola.24073
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The mixtures of exo-endo-monomers and isomeri-
cally pure endo-monomers of N-pentafluorophenyl-norbornene-
5,6-dicarboximide (2a) and N-phenyl-norbornene-5,6-dicarboxi-
mide (2b) were synthesized and polymerized via ring opening
metathesis polymerization using bis(tricyclohexylphosphine)
benzylidene ruthenium (IV) dichloride (I) and tricyclohexylphos-
phine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-
ylidene][benzylidene] ruthenium dichloride (II). Ring opening
metathesis polymerization of mixtures of exo-endo-monomers
(2a) and (2b) and pure endo-2b gave the corresponding high
molecular weights poly(N-pentafluorophenyl-norbornene-5,6-
dicarboximide) (3a) and poly(N-phenyl-norbornene-5,6-dicar-
boximide) (3b). The isomerically pure endo-2a did not polymer-
ize by I in these conditions, since I is the least active catalyst and
endo-2a is the least active monomer because of the intramolecu-
lar complex formation between the Ru active center and the fluo-
rine atom of ring-opened endo-2a on the one hand and steric
hindrances caused by the pentafluorinated ring on the other.
The quantitative hydrogenation of the polymer 3a, at room tem-
perature and 115 bar, was achieved by a Wilkinson’s catalyst.
The new polynorbornene bearing highly fluorinated sulfonic
acid groups (5) was obtained by the reaction of the hydrogen-
ated poly(N-pentafluorophenyl-norbornene-5,6-dicarboximide)
C
V
(4) with sodium 4-hydroxybenzenesulfonate dihydrate.
2010
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2925–
2933, 2010
KEYWORDS: fluorinated sulfonic acid polynorbornene dicarboxi-
mide; functionalization of polymers; ionomers; polynorbornene
with pentafluorophenyl pendant groups; ring opening metathe-
sis polymerization; ROMP
INTRODUCTION Fluorine containing polymers are important
specialty materials because of their high thermostability,
chemical inertness, and good hydrophobicity. These polymers
with low intermolecular and intramolecular interactions are
good candidates for membrane applications. Thus, the intro-
duction of fluorine atoms into polynorbornene dicarboxi-
mides decreased interchain interactions between polar imide
side chain groups and increased the gas permeability across
them without detriment to the selectivity.1–3 Compared with
polynorbornene dicarboximides with phenyl-, adamantyl-,
and cyclohexyl-side chain groups, polynorbornenes with phe-
nylfluorine imide pendant groups exhibit much higher gas
permeability.2,4,5 Thus, it was reported that the gas perme-
ability, diffusion, and solubility coefficients of polynorbor-
nene dicarboximides with trifluoromethylphenyl pendant
groups were up to an order of magnitude larger than those
of the nonfluorinated one.2,3
lysts is well established.6,7 Recently, we proceeded with the
synthesis and polymerizations of new norbornene deriva-
tives with various fluorine atom units using well defined
ruthenium alkylidene catalysts.2,8,9 We recently also reported
not only the synthesis but also the gas and ionic transport
properties of a nonfluorinated sulfonic acid polynorbornene
dicarboximide displaying ionic conductivity at low degree
of hydration.10,11 Hence, in this study we have envisioned
the synthesis via ROMP of polymers based on N-pentafluoro-
phenyl-norbornene-5,6-dicarboximide, their homogenous
posthydrogenation and even further sulfonation to obtain
new highly fluorinated sulfonic acid polymers. It is expected
that these kinds of new polymers will exhibit good ionic
properties resulting from a balanced chemical structure. On
one hand, the extremely hydrophobic domains such as fluo-
rophenyl side chain units and cyclopentane ring in the satu-
rated hydrocarbon main chain will control the mechanical
properties and proton diffusion across the membrane. On
the other hand, the hydrophilic domains arising from the
The ring opening metathesis polymerization (ROMP) of fluo-
rine containing norbornenes using classical metathesis cata-
Correspondence to: M. A. Tlenkopatchev (E-mail: tma@servidor.unam.mx)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2925–2933 (2010) 2010 Wiley Periodicals, Inc.
SYNTHESIS AND SULFONATION, SANTIAGO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis route of monomers 2a and 2b, respectively.
imide functionality and polar sulfonic pendant groups will
be responsible for the proton conductivity.
Reagents
Norbornene-5,6-dicarboxylic anhydride (NDA) was prepared
via Diels–Alder condensation of cyclopentadiene and maleic
anhydride according to literature.10 2,3,4,5,6-pentafluoro-
aniline, aniline, and sodium 4-hydroxybenzenesulfonate dihy-
drate were purchased from Aldrich Chemical and used
without further purification. 1,2-dichloroethane, dichlorome-
thane, p-dioxane, toluene, and N,N-dimethylacetamide
were dried over anhydrous calcium chloride and distilled
over CaH2. Bis(tricyclohexylphosphine) benzylidene ruthe-
nium (IV) dichloride (I), tricyclohexylphosphine [1,3-
bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]
[benzylidene] ruthenium dichloride (II), and ClRh(PPh3)3
were purchased from Aldrich Chemical and used as received.
EXPERIMENTAL
Techniques
1H NMR, 13C NMR, and 19F NMR spectra were recorded on a
Varian spectrometer at 300, 75, and 300 MHz, respectively,
in deuterated chloroform (CDCl3), N,N-dimethylformamide
(DMF)-d7, and dimethyl sulfoxide (DMSO)-d6. Tetramethylsi-
lane and trifluoroacetic acid (TFA) were used as internal
standards, respectively. Glass transition temperatures, Tg,
were determined in a DSC-7 Perkin–Elmer, at scanning rate
ꢀ
of 10 C/min under nitrogen atmosphere. The samples were
encapsulated in standard aluminum DSC pans. Each sample
was run twice on the temperature range between 30 C and
Synthesis and Characterization of N-Pentafluorophenyl-
Norbornene-5,6-Dicarboximide (2a)
ꢀ
300 ꢀC under nitrogen atmosphere. Onset of decomposition
temperature, Td, was determined using thermogravꢀimetric
analysis, which was performed at a heating rate of 10 C/min
under nitrogen atmosphere with a DuPont 2100 instrument.
FTIR spectra were obtained on a Nicolet 510 p spectrometer.
Molecular weights and molecular weight distributions were
determined with reference to pꢀolystyrene standards on a
Waters 2695 Alliance GPC at 35 C in tetrahydrofuran using
a universal column and a flow rate of 0.5 mL/min. Mechani-
cal properties under tension, Young’s modulus (E) and stress
(ru), were measured in a Universal Mechanical Testing
Machine Instron 1125-5500R using a 50 kg cell at a cross-
head speed of 10 mm/min according to the method ASTM
D1708 in film samples of 0.5 mm of thickness at room
temperature.
Monomer 2a was synthesized by reacting 2,3,4,5,6-penta-
fluoroaniline with NDA to the corresponding amic acid which
was cyclized to imide using acetic anhydride as dehydrating
agent (Scheme 1).12,13 NDA (5.0 g, 30.5 mmol) was dissolved
in 40 mL of CH2Cl2. An amount of 5.58 g (30.5 mmol) of
2,3,4,5,6-pentafluoroaniline in 20 mL of CH2Cl2 was added
dropwise to the stirred solution of NDA. The mixture was
boiled for 3 h and then cooled to room temperature. Solvent
removal gave a white solid of amic acid. The obtained amic
acid 1a (10.3 g, 29.7 mmol), anhydrous sodium acetate (2.50
g, 30.47 mmol), and acetic anhydride (21.0 g, 205.7 mmol)
were heated at 80 ꢀC for 24 h. The mixture was washed
with dilute HCl and extracted into ether. The ether layer was
washed with dilute HCl, saturated NaHCO3, and H2O. Solvent
was evaporated and pure monomer 2a was obtained after
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ARTICLE
SCHEME 2 ROMP of norbornene dicarboximides 2a and 2b, respectively.
twice recrystallization from hexane and dried in a vacuum
oven at 50 ꢀC overnight: yield ¼ 75%, m.p. ¼ 112–113 ꢀꢀC
exo(90%)–endo(10%) monomer mixture, m.p. ¼ 128–129 C
endo(100%) monomer.
1H NMR (300 MHz, CDCl3), d (ppm) ¼ 7.49–7.25 (5H, m),
6.33 (2H, s), 6.24 (2H, s), 3.38 (2H, s), 2.84 (2H, s), 1.62–
1.46 (2H, m). 13C NMR (75 MHZ, CDCl3): d (ppm) ¼ 176.8
(C¼¼O), 137.8 (C¼¼C), 134.4, 131.7 (CAN), 129.0, 128.4,
126.2, 47.7, 45,7, 42.8. FTIR (KBr, cmꢁ1): 3064, 2946 (CAH
asym str), 2877 (CAH sym str), 1770 (C¼¼O), 1594 (C¼¼C
str), 1454 (CAN), 1382, 1329, 1289, 1188, 975, 799.
1H NMR (300 MHz, CDCl3), d (ppm) ¼ 6.36 (1H, s), 6.25
(1H, s), 3.53 (1H, s), 3.42 (1H, s), 2.96 (2H, s), 1.70–1.54
(2H, m). 13C NMR (75 MHZ, CDCl3): d (ppm) ¼ 174.7 (C¼¼O),
147.8–139.6 (CAF), 137.8 (C¼¼C), 134.4 (C¼¼C), 107.1
(CAN), 52.1, 48.4, 45.8, 45.6, 42.9. 19F NMR (300 MHz,
CDCl3, ref. TFA [ꢁ77ppm]): d (ppm) ¼ ꢁ142.2, ꢁ142.4,
ꢁ150.1, ꢁ150.6, ꢁ160.1, ꢁ160.4. FTIR (KBr, cmꢁ1): 3076,
2949 (CAH asym str), 2880 (CAH sym str), 1782 (C¼¼O),
1724, 1644 (C¼¼C str), 1519, 1356, 1299 (CAF), 1172, 1157,
984, 793.
Metathesis Polymerization of Monomers
Polymerizations were carried out in glass vials under dry
nitrogen atmosphere. They were inhibited by adding a small
amount of ethyl vinyl ether and the solutions were poured
into an excess of methanol. The polymers were purified by
solubilization in chloroform containing a few drops of 1 N
HCl and precipitation into methanol. The obtained polymers
ꢀ
were dried in a vacuum oven at 40 C to constant weight.
Synthesis and Characterization of N-Phenyl-Norbornene-
5,6-Dicarboximide) (2b)
Polymerization of 2a
Monomer 2a (1.0 g, 3.04 mmol) and catalyst I (2.49 ꢂ
10ꢁ3g, 0.0030 mmol) were stirred in 4.3 mL of 1,2-dichloro-
ethane at 45 ꢀC for 2 h (Scheme 2). The obtained polymer
3a was soluble in chloroform and dichloroethane. Tg ¼ 171
Monomer 2b was synthesized according to literature
(Scheme 1).13 NDA (5.0 g, 30.5 mmol) was dissolved in
50 mL of toluene. An amount of 2.8 g (30.1 mmol) of aniline
in 10 mL of toluene was added dropwise to the ꢀstirred solu-
tion of NDA. The reaction was maintained at 50 C for 3 h. A
precipitate was filtered and dried to give 7.6 g (29.5 mmol)
of amic acid 1b. The amic acid obtained (7.6 g, 29.5 mmol),
anhydrous sodium acetate (3.0 g, 36.0 mmol), and acetic an-
hydride (21.0 g, 212.0 mmol) were heated at 90 ꢀC for 6 h
and then cooled. The solid crystallized on cooling was fil-
tered, washed several times with water and dried in a vac-
uum oven at 50 ꢀC overnight. Pure monomer 2b was
obtained after twice recrystallization from toluene: yield ¼
81%, m.p. ¼ 195–196 ꢀC exo(90%)-endo(10%) monomer
mixture.
ꢀ
ꢀC, Td ¼ 425 C, E ¼ 1226 MPa, ru ¼ 48.7 MPa.
1H NMR (300 MHz, CDCl3): d (ppm) ¼ 5.78 (1H, s, trans),
5.56 (1H, s, cis), 3.28 (2H, s), 2.88 (2H, s), 2.24 (1H, s), 1.70
(1H, s). 13C NMR (75 MHz, CDCl3): d (ppm) ¼ 174.7, 147.0,
146.1, 141.0, 135.3, 133.3 (cis), 131.9 (trans), 107.1, 51.4,
46.6, 41.9. 19F NMR (300 MHz, CDCl3, ref. TFA [ꢁ77ppm]): d
(ppm) ¼ ꢁ142.2, ꢁ142.5, ꢁ143.2, ꢁ150.0, ꢁ150.3, ꢁ159.8,
ꢁ160.2, ꢁ160.7. FTIR (thin film, cmꢁ1): 3002, 2930 (CAH
asym str), 2855 (CAH sym str), 1790 (C¼¼O), 1725, 1647
(C¼¼C str), 1513, 1356, 1297 (CAF), 1165, 1138, 984, 785,
767, 624.
SYNTHESIS AND SULFONATION, SANTIAGO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 3 Hydrogenation of poly(N-pentafluorophenyl-norbornene-5,6-dicarboximide) and further sulfonation of the polymer.
Polymerization of 2b
sium carbonate (0.52 g, 3.77 mmol) were mixed in a round
flask equipped with a Dean-Stark trap and stirred in 15 mL
of solvent (N,N-dimethylacetamide-toluene 2:1) at 120 C for
Monomer 2b (1.0 g, 4.18 mmol) and catalyst II (3.5 ꢂ
10ꢁ3g, 0.0041 mmol) were stirred in 4.2 mL of 1,2-dichloro-
ꢀ
ꢀ
ethane at 25 C for 1.4 h (Scheme 2). The obtained polymer
9 h (Scheme 3). Progressive precipitation overtime was
observed. The product was then filtered off, washed several
times with distilled water and dried in a vacuum oven at
3b was soluble in chloroform and dichloroethane. Tg
¼
ꢀ
ꢀ
222 C, Td ¼ 418 C, E ¼ 1560 MPa, ru ¼ 57.0 MPa.
ꢀ
40 C overnight. The resulting polymer 5, a pale-brown pow-
1H NMR (300 MHz, CDCl3), d (ppm) ¼ 7.42-7.21 (5H, m),
5.78 (1H, trans, s), 5.54 (1H, cis, s), 3.49 (2H, s), 3.14–2.86
(2H, m), 2.16 (1H, s), 1.61 (1H, s). 13C NMR (75 MHZ,
CDCl3): d (ppm) ¼ 177.1, 133.7 (cis), 131.8 (trans), 128.9,
126.3, 52.5, 50.9, 48.6, 46,0, 42.8, 40.5. FTIR (thin film,
cmꢁ1): 3034, 2930 (CAH asym str), 2869 (CAH sym str),
1775 (C¼¼O), 1590 (C¼¼C str), 1457 (CAN), 1385, 1323,
1290, 1165, 980, 790.
der, was soluble in DMF and DMSO: yield ¼ 94%, Tg
¼
228 ꢀC, Td1 ¼ 260 ꢀC (sulfonic group loss), Td2 ¼ 430 ꢀC
(main chain decomposition).
1H NMR (300 MHz, DMF-d7): d (ppm) ¼ 7.80 (2H, s), 7.18
(2H, s), 3.56 (2H, s), 2.73, 2.31, 1.83, 1.58, 1.91. 13C NMR
(75 MHZ, DMF-d7): d (ppm) ¼ 175.0 (C¼¼O), 145.5, 145.0,
140.4, 139.7, 128.2 (CAO), 115.1, 107.2, 49.0, 43.0. 19F NMR
(300 MHz, DMSO-d6, ref. TFA [ꢁ77ppm]): d (ppm) ¼
ꢁ141.9, ꢁ143.0, ꢁ153.1. FTIR (thin film, cmꢁ1): 2926 (CAH
asym str), 2860 (CAH sym str), 1787 (C¼¼O), 1726, 1636,
1509, 1406, 1356, 1295 (CAF), 1140 (ASO3H, asym str),
1132, 1039 (ASO3H, sym str), 981, 833, 698, 561.
Hydrogenation of 3a
A total of 0.5 g of 3a was added to 60 mL of solvent
(dichloromethane-p-dioxane 1:1) in a Schlenk tube. The cata-
lyst (5 wt %) was previously introduced into a Parr shaker
reactor. The solution was degassed and charged into the re-
actor under N2. Then, hydrogen was added. A 99% of hydro-
genation, determined by 1H NMR, for 4 was achieved using
Wilkinson’s catalyst, ClRh(PPh3)3, at room temperature and
115 bar (Scheme 3). The obtainedꢀpolymer 4 was soluble in
RESULTS AND DISCUSSION
Monomers 2a and 2b were prepared in high yields
(75–81%).12,13 2,3,4,5,6-Pentafluoroaniline and aniline
reacted with NDA to the corresponding amic acids which
were cyclized to imide using acetic anhydride as dehydrating
agent (Scheme 1). 1H, 13C, and 19F NMR spectra and ELEM.
ANAL confirmed monomers structure and purity.
ꢀ
chloroform and toluene. Tg ¼ 144 C, Td ¼ 448 C, E ¼ 1190
MPa, ru ¼ 43.1 MPa.
1H NMR (300 MHz, CDCl3): d (ppm) ¼ 3.06, 2.31, 2.17, 1.88,
1.62, 1.25. 13C NMR (75 MHZ, CDCl3): d (ppm) ¼ 175.6
(C¼¼O), 146.1, 144.7, 140.8, 135.8, 132.4, 107.2, 51.9, 44.6,
44.0, 42.2. 19F NMR (300 MHz, CDCl3, ref. TFA [ꢁ77ppm]): d
(ppm) ¼ ꢁ142.2, ꢁ143.1, ꢁ150.2, ꢁ159.9, ꢁ160.2. FTIR
(thin film, cmꢁ1): 2902 (CAH asym str), 2861 (CAH sym
str), 1794 (C¼¼O), 1720, 1502, 1460 (CAN), 1367, 1279
(CAF), 1161, 1147, 1000.
The polymerizations of 2a and 2b were carried out in 1,2-
dichloroethane using catalysts I and II (Scheme 2). Table 1
summarizes the results of the polymerizations of exo-endo-
and endo- monomers. It is seen that the pure endo-2a did
not polymerize by I (entries 6 and 7) whereas II led to the
formation of high molecular weight polymers in high yields.
The endo-2b polymerized by both catalysts (entries 9 and
10). It was shown that the reactivity difference between the
exo- and endo-isomers of norbornene derivatives is primarily
because of steric interactions between the propagating
Ru-center and the endo-ring of an incoming monomer.14
Sulfonation of 4
Hydrogenated
poly(N-pentafluorophenyl-norbornene-5,6-
dicarboximide) (4) (0.5 g, 1.51 mmol), sodium 4-hydroxy-
benzenesulfonate dihydrate (0.70 g, 3.02 mmol), and potas-
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ARTICLE
TABLE 1 Polymerization Conditions of N-Pentafluorophenyl-Norbornene-5,6-Dicarboximide (2a) and N-Phenyl-Norbornene-5,6-
Dicarboximide (2b)
Endo Isomer in
the Feed (%)a
Temperature
(ꢀC)
Cis Content in
Polymer (%)a
Entry
Monomer
Catalystb
Time (h)
Yield (%)c
Mnꢂ10ꢁ5 d
MWDd
1
2
2a
2a
2a
2a
2a
2a
2a
2a
2be
2be
25
25
I
45
65
45
45
45
45
70
45
70
25
2
16
18
53
19
51
–
80
91
96
49
81
–
1.21
1.81
3.07
0.83
1.61
–
1.30
1.23
1.62
1.74
1.27
–
I
0.10
0.66
19
1
3
25
II
I
4
49
5
49
II
I
6
100
100
100
100
100
24
108
1
7
I
–
–
–
–
8
II
I
43
17
45
72
56
75
1.80
0.41
0.58
1.60
1.82
1.96
9
11
1.4
10
a
II
Determined by 1H NMR.
GPC analysis in tetrahydrofuran with polystyrene calibration
d
b
Monomer/catalyst ¼ 1000, 1,2-Dichloroethane as solvent, Initial mono-
standards.
e
mer concentration [M0] ¼ 0.7 mol/L.
Initial monomer concentration [M0] ¼ 1.0 mol/L.
c
Methanol insoluble polymer.
There have been reports on the reactivity in the ROMP of
exo-endo-isomers of norbornene derivatives with polar
groups.15 It is assumed that compared with the exo-mono-
mer, where functional groups are far from the metal active
center, the polar groups of the endo-monomer may coordi-
nate to the metallacarbene active center inhibiting the poly-
merization. In the case of the endo-2a polymerization, the
intramolecular reaction between the Ru-center and the fluo-
roaryl moiety of the monomer is possible. Thus, molecular
complexes formed during the reaction of the endo-2a with
the 14-electron Ru-centers of I and II were optimized using
M06L functional implemented in Gaussian 09 suite of pro-
grams.16 M06L functional was designed to deliver superior
performance for organometallic systems and weak interac-
tions.17 6-31G(d) Basis set was used for non metallic atoms,
while for the Ru atom was used cc-pvtz basis set and
Stuttgart RSC 1997 ECP.18 The calculations show that the
Ru–fluorine distances for catalysts I and II in the formed
intramolecular complexes A and B are of 2.99 Å and 2.97 Å,
respectively, (Fig. 1). The nonfluorinated endo-2b does not
form these kinds of complexes (RuAH distances are of 4.33
and 4.47 Å for C and D, respectively). This is more than a
sum of Ru and H van-der Waals radii and clearly demon-
strates RuAF interactions for the endo-2a. The inspection of
charges on Ru atoms further confirms interactions between
fluorine and Ru atoms. Thus Mulliken charges on Ru atoms
in A, B, C, and D complexes (Fig. 1) with the endo-2a and
the endo-2b were found to be of ꢁ0.29, ꢁ0.15, ꢁ0.23, and
ꢁ0.09, respectively. As seen, there is a slight but observable
built up of electron density on Ru atom in fluorinated com-
pounds revealing a transfer of electron density from fluorine
to Ru-centers. In the case of an endo-chlorinated monomer
the ClARu distance in the intramolecular complex E (Fig. 1)
is even less than for the endo-2a (2.87 Å) demonstrating a
better interaction of Cl atoms with the Ru-center compared
with fluorine one. It was reported that chlorine atoms coor-
dinated better than fluorine atoms to the Ru atom.19 Ruthe-
nium–fluorine interactions have been observed in Ru-alkyli-
dene catalysts with fluorinated N-heterocyclic carbene
ligands.20 The intramolecular interactions between the
Ru-center and carbonyl-oxygen of olefinic esters have also
been studied.20 It is important to note that ruthenium–fluo-
rine interactions are weaker compared with Ru-carbonyl
intramolecular reactions. Thus, RuAO distances are typically
2.22–2.26 Å, compared with longer RuAF distances.21 On the
other hand, it is generally accepted that the activity of a
reactive intermediate decreases with its stability. Since, the
stability of metallacarbenes decreases with the charge at a
Ru-center, one can relate the reactivity of a metallacarbene
with the charge at a Ru atom.22 Thus, the Mulliken charges
at Ru atoms of intramolecular complexes A and B (Fig. 1)
for I and II are of ꢁ0.29 and ꢁ0.15, respectively, revealing
that the metallacarbene active center of the second genera-
tion Grubbs catalyst is more active compared with this of
the first generation. Experimental data demonstrated that
the second generation Ru-alkylidene catalyst is more active
than the first generation one.23 Computational modeling also
confirmed that the absolute activation energies of the me-
tathesis reactions are notoriously lower for the second gen-
eration catalyst.24 It is important to note that molecular vol-
umes of pentafluorophenyl and phenyl groups in 2a and 2b
were found to be of 85 and 71 Å3, respectively. We believed
that the least active catalyst I, the Ru–fluorine intramolecular
interaction and the steric effect of the pentafluorinated ring
in the endo-2a are factors which can impede the ROMP of
the endo-2a using I. In Table 1, the results obtained by GPC
analysis show that the number average molecular weights
(Mn) were between 41,000 and 307,000. Furthermore, the
molecular weight distribution of the polymers 3a and 3b
(entries 3, 5, 8, and 10) obtained by II is about Mw/Mn
¼
SYNTHESIS AND SULFONATION, SANTIAGO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 1 Optimized geometries of ru-
thenium intramolecular complexes
(A), (B), (C), (D), and (E).
1.27–1.96 which is broader compared with polymers pre-
pared by I (Mw/Mn ¼ 1.23–1.82). Changing the pendant moi-
ety did not affect the stereochemistry of the double bonds in
the polymer. Catalyst I gave polymers with predominantly
trans configuration of the double bonds (81–84%), whereas
catalyst II produced polymers with a mixture of cis and trans
double bonds (43–53% of cis structure).
signals corresponding to the methylene protons arise in the
region of d ¼ 2.33–1.28 ppm. A 99% of hydrogenation for
polymer 4 was achieved according to the methodology previ-
ously reported for this kind of polymers.11 Stress–strain
measurements in tension for the films of the synthesized
polymers were carried out. The experiments were stopped
at the maximum stress and indicate, on one hand, that in
spite of bearing the smaller substituent, 3b shows higher
elastic modulus (E) as well as stress in tension (ru), 1560
MPa and 57.0 MPa, respectively, in comparison with 3a
(1226 MPa and 48.7 MPa). The latter could be attributed to
the ability of polymer 3b to chain packing which results in
an increase of rigidity. On the other hand, the highest
Figure 2 shows the 1H NMR spectra of (A) hydrogenated
polymer 4 and (B) its unsaturated analogous polymer 3a.
The polymer olefinic signals are observed at d ¼ 5.78 and
5.56 ppm, which correspond to the trans and cis double
bonds of the polymer, respectively. After the hydrogenation
step, the signals mentioned above become weak and new
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ARTICLE
FIGURE 2 1H NMR spectra of (A) hydrogenated polymer 4 and (B) its unsaturated analogous polymer 3a.
conformational mobility of polymer chains in the saturated
backbone of polymer 4 was reflected in a lesser elastic mod-
ulus and stress in tension, 1190 MPa and 43.1 MPa, respec-
tively. Having improved the thermo-oxidative stability of
polymer 3a by hydrogenating, the polymer reactivity
towards the nucleophilic aromatic substitution in the penta-
fluorophenyl moiety was explored. Therefore, we reacted
polymer 4 with sodium 4-hydroxybenzenesulfonate dihy-
drate to obtain a quantitative film forming sulfonated poly-
mer 5. Progressive precipitation of the ionomer overtime
was observed and polymer recovery was quantitative. The
ionomer was soluble in DMF and DMSO for degrees of sulfo-
nation up to 60 mol %; however, as the degree of sulfonation
was increased, the polymer solubility became poor until only
DMSO was able to dissolve the fully sulfonated polymer. The
substitution reaction was monitored by 19F NMR spectros-
copy, and the degree of sulfonation was controlled both by
the nucleophilic agent amount and the time of reaction.
Figure 3 shows the19F NMR of (A) nonsulfonated polymer 4,
(B) partially sulfonated polymer 5, and (C) fully sulfonated
polymer 5. It is appreciated that as the pentafluorophenyl
moiety is sulfonated, the signal corresponding to the fluorine
atom in meta position of unsulfonated polymer 4 (A, ꢁ159.9
ppm) becomes weak and a new meta signal corresponding
to those pentafluorophenyl moieties which have already
been sulfonated become to grow (B, ꢁ154.8 ppm) until a
unique meta signal is observed at complete sulfonation of
polymer 4 (C, ꢁ153.2 ppm). At the same time, the signal
corresponding to the fluorine atom in para position (B,
ꢁ152.5 ppm) decreases until its complete disappearance
when a fully sulfonated polymer is obtained. From this anal-
ysis, we conclude that only the carbon in para position has
undergone the nucleophilic aromatic substitution. Prelimi-
nary measurements performed in membranes of polymer 5,
equilibrated with distilled water, indicate that the protonic
conductivity is slightly higher than 1.0 S mꢁ1 at room tem-
perature, comparable to that displayed by perfluorinated
acidic membranes such as Nafion in the same conditions. In
this regard, it is worth noting that hydrolysis stability plays
an important role in the long-term ionomer performance.
Sulfonated phthalic polyimides have been reported to display
lesser water stability in comparison with naphthalenic sulfo-
nated polyimides when they have been exposed in the same
tough conditions, both imide structures degrade and become
brittle in time mainly owing to the hydrolytic polymer chain
scission.25 Nevertheless, because the imide moiety of poly-
mer 5 is a side chain group, this polyelectrolyte does not
undergo severe degradations as those of linear polymers
bearing the imide moiety in the main chain so that dramatic
decreases in molecular weight as well as in dimensional sta-
bility and performance have not been observed when mem-
branes of polymer 5 have been subjected at 80 ꢀC in a full
hydration environment up to 48 h. Furthermore, the pres-
ence of a flexible linkage such as ether bond raises the con-
formational mobility of polymer chains which in turn
reduces the swelling stress when polymer 5 is in film form.
Moreover, as the electron-withdrawing sulfonic acid groups
are bonded to an aromatic ring other than the fluorine-stabi-
lized aminophenyl ring of polymer 5, a more basic amine
moiety is obtained improving the hydrolysis stability of the
SYNTHESIS AND SULFONATION, SANTIAGO ET AL.
2931

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 19F NMR of (A) nonsulfonated polymer 4, (B) partially sulfonated polymer 5, and (C) fully sulfonated polymer 5.
imide ring. This effect of the amine basicity on the hydrolysis
stability of the imide ring has also been observed in naph-
thalenic sulfonated polyimides synthesized via polycondensa-
tion reactions.26 An extensive research concerning the ionic
transport properties of this kind of ionomers is actually
being carried out by our group and it will be the subject of a
forthcoming article.
poly(N-pentafluorophenyl-norbornene-5,6-dicarboximide) (3a)
and poly(N-phenyl-norbornene-5,6-dicarboximide) (3b),
whereas the isomerically pure endo-2a did not polymerize by
I in these conditions. The steric effect of the pentafluorinated
ring in the monomer, the intramolecular complex formation
between the Ru active center and the fluorine atom of ring-
opened endo-2a and, compared with II, the least active I
were responsible for the ROMP inhibition of the endo-2a.
The hydrogenated poly(N-pentafluorophenyl-norbornene-5,6-
dicarboximide) (4) underwent a nucleophilic aromatic substi-
tution by reacting with sodium 4-hydroxybenzenesulfonate
dihydrate to give the corresponding functionalized polymer 5.
This new polymer bearing the sulfonic acid group is expected
to exhibit ionic conduction features.
CONCLUSIONS
ROMP of mixtures exo-endo-monomers and isomerically pure
endo-monomers of N-pentafluorophenyl-norbornene-5,6-dicar-
boximide (2a) and N-phenyl-norbornene-5,6-dicarboximide
(2b) 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) was studied. The mixtures of exo-
endo-monomers (2a), (2b), and pure endo-2b monomer poly-
merized to give the corresponding high molecular weights
The authors thank CONACyT and DGAPA-UNAM PAPIIT for
generous support with contracts 23432, ES-104307, and
IX227904. Financial support from National Council for Science
and Technology of Mexico (CONACyT) (PhD Scholarship to
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ARTICLE
15 Nishihara, Y.; Inoue, Y.; Nakayama, Y.; Shiono, T.; Takagi,
A.A.S.) is gratefully acknowledged. The authors are grateful to
Alejandrina Acosta, Gerardo Cedillo, Salvador Lo´pez Morales,
Miguel Angel Canseco, and Esteban Fregoso-Israel for their as-
K. Macromolecules 2006, 39, 7458–7460.
´
16 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.;
Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.;
Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.;
Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.;
Nakai, H.; Vreven, T.; Montgomery, J. A.; Peralta, J. E.; Ogliaro,
F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.;
Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.;
Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Far-
kas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, Revision A. 02; Gaussian: Wallingford, CT, 2009.
sistance in NMR, GPC, and thermal properties, respectively.
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