NEW TECHNIQUES AND PROCESSES FOR CROSSLINKING ION EXCHANGE MEMBRANES AND THEIR APPLICATIONS

NOUVELLES TECHNIQUES ET NOUVEAUX PROCEDES POUR LA RETICULATION DE MEMBRANES D'ECHANGE IONIQUE ET APPLICATIONS CONNEXES

English Abstract

Crosslinking sulfonated polymers through sulfonimide,
bis(sulfonyhmethane) or tris(sulfonylmethane) chains containing an
ionic charge.

Claims

CLAIMS
1) process for crosslinking sulfonated polymers, characterized in that at
least some of the bonds linking
the chains bears au ionic charge and involve, partially or in their totality,
the sulfonyl groups through
interchain linkage of the following type:
P~SO2Y(M+)SO2~P'
P~SO2(M+)Y-SO2Y-(M+)SO2~P,
P~SO2(M+)Y-SO2QSO2Y-(M+)SO2-P'
where:
P and P' represents two different strands of the polymer backbone.
Y represents:
- N (Nitrogen)
- CH, CCN, CR where R represents an alkyl or alkylene with 1 to 20 carbons,
halogenated or
not, possibly bearing aza or oxa subtituents, or T or an alkyl- or an alkylene-
sulfonyl group,
with 1 to 20 carbons, halogenated or not, possibly bearing aza or oxa
subtituents, including
TSO2.
Q represents a divalent, alkyl, oxaalkyl, azaalkyl, aryl or arylalkyl or
alkylalyl radical containing 1
(inclusive) to 20 (inclusive) carbon atoms, possibly halogenated, is
particular perfluorinated and
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optionally possibly including aza- or oxa- subtituents. When there is no
carbon atom, the
compound is a sulfamide or a sulfone
2) crosslinked sulfamide polymers, characterized in that at least some of the
bonds linking the chains
bears an ionic charge and involve, partially or in their totality, the
sulfonyl groups through interchain
linkage of the following type:
P~SO2Y-(M+)SO2~P
P~SO2(M+)Z-SO2-Z-(M+)SO2~P
P~SO2(M+)Z-SO2QSO2Z-(M+)SO2-P
3) process for crosslinking polymers according to claim 2 characterized in
that the sulfonated groups
are totally or partially under the form :
P~SO2L
where:
L = is a leaving group, like F, Cl, Br, au electrophilic heterocycle N-
imidazolyl, N-triazolyl,
R"SO3, R" being au organic radical, preferably halogenated, especially
fluorinated.
4) process for crosslinking polymers according to claim 2 characterized in
that the crosslinking agents
are of the general formula:
(M+)A2Z
(M+)AZSO2ZA(M+)
(M+)AZSO2QZA(M+)
5) process for crosslinking polymers according to claim 2 characterized in
that one of the following
reactions is used to form the crosslinks:
P~SO2L+(M+)A2Y + LO2S~P'~ P~SO2Z(M+)O2S~P'+2LA
P~SO2L+(M+)AYSO2ZA(M+) + LO2S~P' ~
P~SO2Z(M+)SO2Y(M+)SO2~P' + 2LA
P~SO2L + (NI+)AYSO2QZA(M+) + LO2S~P'~
P~SO2Y(M+)SO2QSO2Y(M+)SO2~P'+2LA
6) process for crosslinking polymers according to claim 3 characterized in
that the sulfonated groups
are totally or partially under the form:
P~SO2Y(M+)A
7) process for crosslinking polymers according to claim 4 characterized in
that one of the following
reactions is used to form the crosslinks:
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P~SO2Y(M+)A + LSO2L + A(M+)Y-P' ~
P~SO2Z(M+)SO2Z(M+)SO2~P' + 2LA
P~SO2Y(M+)A + LSO2QSO2L + A(M+)Y~P' ~
P~SO2Z(M+)SO2QSO2Z(M+)SO2~P' + 2LA
8) process for crosslinking polymers according to claim 3 and 4 characterized
in that either M+ or A or
both is a proton and the reaction is conducted in presence of a tertiary or
hindered organic base, an
organometallic reagent, a metal amide.
9) process for crosslinking polymers according to claim 4 characterized in
that A is a trialkylsilyl
group, especially trimethylsilyl.
10) process according to claim 4 characterized in that A is a tertioalkyl
group and the condensation
reaction is conducted in the presence of a tertialy or hindered organic base.
11) process for crosslinking polymers according to claim 8 and 10
characterized in that the tertiary base
is triethylamine) di-isopropylamine, quinuclidine), 1,4-
diazobicyclo[2,2,2]octane (DABCO); a
pyridine (for example pyridine, alkylpryidines, dialkylaminopyridine); an
imidazole (for example
N-alkylimidazoles, imidazo[1,1-a]pyridine); as amidine (for example 1,5-
diazabicyclo[4,3,0]non-
5-ene (DBN), 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU); a guanidine (for
example tetramethyl
guanidine) 1,3,4,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine (HPP).
12) process according to claim 3 characterized in that enter A or M+ or both
are solvated by
dialkylethers or oligo-ethylene glycols or permethylaled oligo-ethylendiamines
(ex tetramethyl-
ethylene diamine TMEDA).
13) crosslinked polymers derived from at least one of the following monomers:
<IMG>
-9-

<IMG>
where:
- X represents F, Cl or CF3
- a being comprised between 0 (included) and 10
- E represents an ether -O-, sulfide -S-, sulfone -SO2- or nothing (direct
=C(Z)~aryl link).
- Z is either F or H.
14) crosslinked polymers according to claim 13 characterized is that L = F or
Cl.
15) crosslinked polymers according to claim 13 characterized in that n = 0
(included) or 1.
16) process according to claim 4 characterized in that the crosslinking agent
are chosen between:
Li3N C3AI4 [(CH3)3Si]2NLi,Na, K
NH3 + 3DABCO CF3SO2C[(CH3)3Si][Li(TMEDA)]2 (CH3)3CNH2 + 3TEA
NH2SO2NH2 + 4TEA {[(CH3)3Si](Li)N]2SO2 [(TMEDA)(Mg)N]2SO2
CH3Li (CH3)3Al NH2Li, Na, K
{[Si(CH3)3](Li)NSO2]2CF ((Li)[Si(CH3)3]NSO2CF2)2CF2 [(Li)Si(CH3)3NSO2CF2]2
2
{(Li)[Si(CH3)3]NSO2CF2CF2}2O
17) process according to claim 6 characterized in that the crosslinking agent
are chosen between:
SO2Cl2 + 3DABCO SO2(imidazole)2 [FSO2CF2]2 + 3TEA
(FSO2CF2CF2)2O + 3DABCO
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18) sulfonated polymers according to claims 2 characterized in that the
uncrosslinked polymer
containing the P~SO2L is processed into its final shape and crosslinked in a
further step.
19) sulfonated polymers according to claims 2 characterized in that the
uncrosslinked polymer is
mechanically mixed with the cross-linking agent and pressed and heated,
preferably at temperatures
ranging from 0 to 200°C.
20) sulfonated polymers according to claims 2 characterized in that the
uncrosslinked polymer is
processed into its final shape and brought in contact with a solution of the
crosslinking reagent in
an inert solvent and reacted at temperatures ranging from -60 to 200°C.
21) sulfonate polymers according to claims 2 characterized in that the
crosslink density is controlled
by the immersion time, the temperature and the concentration of the reagent.
22) Method for preparing a membrane according to claim 20 characterized in
that the suitable solvent is
chosen among: lower aliphatic alcohols, polyhalocarbons, THF, the glymes,
tertiary alkylamides
including DMF, N-methyl-pyrrolidone, tetramethyl-urea and its cyclic analogs,
N-alkylimidazoles,
tetraalkyl sulfamides and mixtures thereof.
23) sulfonated polymers according to claims 2 characterized in that the
uncrosslinked polymer is is
processed into its final shape and brought in contact with the crosslinking
reagent and a non-crosslinking
ion-generating reagent to form ~SO3-(M+), or -[SO2YSO2R]-(M+) end groups, R"'
being an organic radical, preferably halogenated, especially perfluorinated.
24) sulfonated polymers according to claims 23 characterized in that the
uncrosslinked polymer is is
processed info its final shape and brought in contact sequentially wills the
crosslinking reagent and
the non-crosslinking ion-generating reagent.
25) sulfonated polymers according to claims 23 characterized is that the
uncrosslinked polymer is is
processed info its final shape and brought in contact simultaneously wish the
crosslinking reagent
and the non-crosslinking ion-generating reagent, the crosslink density being
controlled by the
immersion time, the temperature and the concentration of the reagents.
26) sulfonated polymers according to claims 23 characterized in that the non-
crosslinking
ion-generating reagent, is (CH3)3SiO-(M+) or [(CH3)3SiNSO2CF3]-(M+).
27) Method for preparing material according to claims 2 to 26 characterized in
that ion exchange to the
desired cation M+ is performed offer polymerization.
28) Material according to claim 2 to 26 characterized in that inorganic or
organic filler particles,
including fibers, filaments, woven or non woven cloth , are included in the
polymers while in the
processable form.
29) electrochemical cell characterized in that a membrane according to claims
1 to 28 is used as solid
electrolyte.
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30) electrochemical cell according to claim 29 characterized in that it is a
fuel cell, an/or a water
electrolyser, a chlor-alkali cell, an electrochemical acid or salt recovery
cell, an ozone production
cell.
31) electrochemical cell according to claim 29 characterized in that at least
one electrode is in contact
with the membrane.
32) electrochemical cell according to claims 30 characterized in that at least
one electrode containing a
conductive additive, optionally a catalyst, optionally a pore forming agent
and the un-crosslinked
sulfonated polymer is coated on the pre-crosslinked electrolyte membrane, then
crosslinked.
33) electrochemical cell according to claim 23 characterized in that at least
one electrode containing a
conductive additive, optionally a catalyst, and optionally a pore forming
agent and the monomers of
claims 1 to 6, is coated on, or co-extruded with, the un-crosslinked
electrolyte membrane then the
assembly crosslinked.
34) electrochemical cell according to claim 30 characterized in that it forms
the element of a fuel cell
where M+ is an hydrated proton and the positive electrode contains au oxygen
reduction catalyst an
the negative electrode either an hydrogen, methanol, dimethoxymethane,
trimethoxymethane,
trioxane or ammonia oxidation catalyst.
35) fuel cell according to claim 34 characterized in that the electrodes are
applied onto the membrane
using the process or either claims 32 or 34
36) Material according to claims 1 to 11 characterized in that it is used for
chlor-alkali electrolysis.
37) Material according to claim 29 characterized in that it is used as a
separator in the electrochemical
preparation of organic or inorganic substances.
38) Material according to claims 29 characterized in that it is used a
separator between an an aqueous
phase and an organic phase.
39) Material according to claims 1 to 11 and 12 characterized in that the M+
ions associated with the
non-nucleophilic anionic centers of the backbone confer catalytic properties.
40) Material according to claims 1 to 11 and 20 characterized in that it is a
catalyst for Diels & Alder
additions, Friedel & Craft reactions, aldol condensations, cationic
polymerization, esterifications,
acetal formation.
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Description

CA 02236197 1998-04-28
New '1'eclmiyues uud 1'ruc:esses tur Crussliulciul; lua
Lxhange IVIeuWraues and their Ahhlicaliuus
lnvention by Chrislophe Nlichot and Michel Armand
Previuus Art:
Owing to their chemical inertness, fluorinated or perfluorinated ion exchange
membranes have been
selected for the chlor-alkali process and fur fuel cells consuming either
hydrogen or' methanol. The
materials presently available under the commercial names Nafion " ) Flemion~)
Down or materials
developed by Ballard lnc. (WOy7/253Gy) arc copolymers of tetrafluoroethyleuc
('1'I~G) and of
perfluorovinylethers or trifluorovinylstryrene. The active monomers bear
chemical functionalities which
are the precursors of ionic groups of the sulfonate or carboxylate type.
'These precursors are for'instance
F2C=CF-O CF2- i F-O CF2-CF2-SOZF
X n
or:
or
F2C=CF- O CF2 i F-O (CF2~C02CH3
X n
F2C=CF --« J J-S02F
sulfonated polyaromatic insides or ether sulfones have also been considered as
candidates:
fo-o-c~-o-o-~~
sqv
where:
- X represents F) CI or CF3
- 0 <_ n <_ 10
-p=lor2
Once obtained the copolymer containing the precursors is processed into sheets
then transformed into the
ionic form by hydrolysis (-S02F ~ -S03-M+; -C02CH3 ~ -COZ-M+).
where:
- M+ represents a cation, with for example: H+, Li+) Na+, K+) 1/2Mg2+,
1/2Ca2+, 1/2Ba2+ and
other alkaline earth metals ions) 1/2Zn2+, 1/2Cu2+ and other transition metals
ions, 1/3A13+)
1/3Fe3+) 1/3Sc-~+) 1/3Y3+, l/3La3+ and other rare earth metals ions) or an
organic cation of the
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CA 02236197 1998-04-28
opium type, oxoniun, ammonium or pyridinium, guanidinium, amidinium)
sulfonium,
phosphoniunl, non sunsliluled) partially or totally substituted by organic
radicals, organometallic
canons, like metalloceniunls, arene-ferrocenium) alkylsilyl, alkylgermanyl,
alkyltin...
Such materials have however several important drawbacks which are suuun~u~ized
below:
1 ) the copolymers in their ionic form are unlraclable, yet are not
dimensionally stable and swell
appreciably in water and polar solvents. Only when heated al high temperature
in supercritical water-
lower alcools nlixlures they eau form inverse nlicelles which, upon
evaporation, leave the cnalerials as
films. However this recast marerial is in a form lacking mechanichal
cohesiveness.
2) handling of TFE is hazardous, as its polymerization is under pressure and
my lead to runaway
reactions) especially in the presence of oxygen; due to the difference in
boiling points',bf the two
monomers, it is difficult.to obtain of a statistical pulymer corresponding to
the monomer feed ratio.
3) the ionic groups tend to impart solubility to the polymer. To avoid this,
the concentration of ionic
groups is kept low by incorporating a large weight or mole fraction of 'TFE
monomer and / or
increasing the side chains length (n > 1), resulting in typically less than 1
milli-equivalent/gram of
ion exchangeable groups. Consequently) the conductivity is relatively low and
very sensitive to the
water content of the membrane, especially when in the acidic form for fuel-
cell applications.
4) the permeation of methanol and of oxygen through the membrane is high, as
the perfluorocarbon part
of the polymer allows facile diffusion of molecular species, resulting in
crossover chemical reaction
and a loss of faladaic efficiency, in particular for direct nletlnulol fuel
cells (DMFC's).
Non fluorinated systems like sulfonaled polyimides or polyethcr sulfones,
proposed as substitute for the
fluorinated material, suffer from the same difficulty in compromising between
the charge density, thus
conductivity and the solubility or excessive swelling.
Description of Invention:
While it is known from the person skilled in the art that perfluoropolymers
usually cannot be crosslinked
by the techniques usually employed with non fluorinated polymers) the present
invention describes a
novel general technique for creating crosslinks between sulfonyl groups
attached to polymers including
those having a perfluorinated backbone, as for example derived from the
monomer (I) and its
copolymers. Advantageously) the crosslinking eau be achieved after the polymer
has been shaped while
in the processable non ionic precursor form. The invention also relates to the
use of the crosslinked
material in the membrane form for applications including fuel cells, wafer
electrolysis, chlor-alkali
process, electrosynthesis) v~ialer treatment and ozone production.
The creation of stable crosslinks is achieved though the reaction of two -S02Y
from adjacent chains to
form the sulfoninlide, bis(sulfonylmelhane) or iris sulfonylmelhane
derivatives, schematized as:
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CA 02236197 1998-04-28
SOIL +LS02
A2Y_(M+)
t
S02 Z~-O2
M+
+ 2 LA
or
S02L L02S
L(M+)-YS02Y-(M+)L
i
0 0
S02 YS02Y-S02
M+ M+
+ 2 LA
or:
S02L + L02S
A(M+)-YS02QS02Y-(M+)A
o i o
S02 YS02QSOzY-S02
M+ M+
+ 2 LA
Where M has the above signification and
Y represents:
- N (Nitrogen)
- CH) CCN, CR where R represents au alkyl or alkylene with 1 to 20 carbons)
halogenated or
not) possibly bearing aza or oxa subtituents, or '1' or an alkyl- or an
alkylene- sulfonyl group,
with 1 to 20 carbons) halogenated or not) possibly bearing aza or oxa
subtituents, including
TS 02.
A = M or Si(R')3) Ge(R')3, Sn(R')3, (R' = alkyl from 1 to 18 carbon atoms)
Q = a divalent) alkyl) ~ oxaalkyl, azaalkyl) aryl or arylalkyl or alkylaryl
radical containning 1
(inclusive) to 20 (inclusive) carbon atoms, possibly halogenated, in p~u-
ticular perfluorinated and
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CA 02236197 1998-04-28
optionally possibly including aza- or uxa- sublilucnls. Wl~cu lherc is no
carbon atom, the
compound is a sulfamide ur a sulfune.
The M+ species may themselves be solvated or complexed form to increase their
solubility or reactivity.
For example, protons can be complexed by a strong nucleuphilic tertiary base
like trielhylamine (1'EA))
dimethylaminopyridine (DMAY), 1,4-diazabicyclo[2.2.2]octane or as nascent form
in the terliobulyl
radical disproportionaling readily into H and CI-12=C(CI-I3)3; metallic ions
are solvated ~y dialkylelhers
of oligo-ethylene glycols, or permelhylaled oligo-elhylendiamines (e.g.
letramelhylelhylene-diamine
TMEDA). Similarly, the A2Y-(M+) compound can be formed in situ in the presence
of stong bases like
0 organometallics reacting on labile protons attached to the Y radical.
Suitable reagents include organo-
lithium, -magnesium or -aluminium compounds compounds, which also serve as a
source of'carbon for
Y = CR, alkali metal amides as a source of nitrogen fur Y = N, dialkyl amides
like LDA (lithium
diisopropylanlide).
An advantage of the technique and materials of the invention is that the
crosslinking agent creates
5 ionophoretic, i.e. charged species, the negatively charges moieties being
auached to the polymer and used
as bridges between chains. It is known that the sulfonylinlide groups and di
or trisulfonylmethane groups
are strong electrolytes in most media and thus the crosslinking reaction, in
addition to improving the
mechanichal properties, has no detrimental effect on the conductivity and
often results in its enhancement.
The compounds whose formulae are given below are examples of suitable ionogen
crosslinking agents
!0 and are given to illustrate the principle of the invention but we not
limiting its the scope:
Li~N C3AI4 [(CI-13)3Si]2NLi,
Na) K
NH3 + 3DABC0 CF3S02C[(CH3)3Si][Li(TMEDA)]2(Cl-I3)3CN1-I2 + 3TEA
NH2S02NH2 + 4TEA ( [(CH~)~Si](Li)N ) 2S02 [(TMEDA)(Nlg)N]2S02
CH3Li (CH~)~A1 NH2Li) Na, K
{ [Si(CH3)~](Li)NS02 { (Li)[Si(CH3)3]NSOZCF2 [(Li)Si(CH3)3NS02CF2]2
) 2CFZ ) 2CF2
( (Li)[Si(CH~)~]NS02CF2CFz
}20
Alternatively, the cross linking reaction can take place with when the Y group
is already on the polymer
precursor, as for a substituted anode; the general scheme in this case is
schematized as:
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CA 02236197 1998-04-28
p p
S02YA AYSO
M+ M+
+ 2 LA LSOZL
pt O
SOZ YS02Y- 02
M+ M+
+ 2 LA
ur:
O O
S02YA AYOZS
M+ M+
LS02QS02L
o i o
S02 YS02QS02Y 02S
M+ M+
+ 2 LA
The compounds whose formulae we given below are examples of suitable ionogen
crosslinking agents
and are given to illustrate the principle of the invention buWu~e non
linuting:
S02C12 + 3DABC0 S02(inudazole)2 ~rsO2Cr2~2 +
3'1'EA
(IS02CP2CI=2)20 + 3DA13C0
The crosslinking reaction lay imply the totality of the sulfonyl groups or a
fraction of tHel. The
crosslinking reagents may be applied by different leclniiques which are known
to the man skilled is the
art. Conveniently) the processable thermoplastic or soluble material is shaped
to the desired final form
before crosslinking, e.g. membranes or Hollow tubes and the material in
brought in contact) by
immersion or coating with a solution of the crosslinking reagent in a solvents
which promotes the
coupling reaction but is not itself effected by tl~e reactants. Appropriate
solvents include but are not
limited to) polyHalocarbons) 'fl-iF, the glyles) tertiary alkylawides
including DMP) N-lethyl-
pyrrolidone, tetramethyl-urea and its cyclic analogs, N-alkylimidazoles,
tetraalkyl sulfalides. The
desired degree of crosslinkinbg may be controlled by several factors, like
tile of contact) temperature or
the concentration of the crosslinking reagent.
Alternatively, a latex of the processuble material is iutin~ately mixed with
the reagent in the solid form and
the mixture is pressed or Hot rolled, possibly is the presence of a non-
solvent fluids like au hydrocarbon.
This technique is applicable in particular to thin membrane and results in
high productivity) though
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CA 02236197 1998-04-28
possibly less homogeneous material is pruduced. ll is understood lhul fillers,
as powders, woven ur non-
woven fibers or filanlenls) eau be added lu the pulynlers before the
crosslinking reaction as reinforcing
agents.
if only a fraction of bridging bonds ure rcyuired, the remaining -SOZY eau be
transformed info the ionic
sulfonale furor by alkaline hydrulysis. Alternatively, in a preferred
CIllbOdlillelll, lllc -SO~M group or
the non crosslinking inside group -S02NS02Rt:M can be obtained is file same
conditions as for the
crosslinks by ionogenic reagents like respectively M[(Cl-f3)3SiOJ or
Ivl[(CH~)3SiNS02Rr]; such
compounds are examples given fur illustration but are not linliling the scope
of this methode. It may be
advantageous to treat the meu~braue eilller seyuenlially by the crosslinking
agent then by the non
crosslinking ionogenic reagents. Alternatively, the ionogenic crosslinking
agent and the non-crossliukiug
ionogelmixed together or co-dissolved in the solvent in predelernlined
proportions and react
simultaneously.
The crosslinked material of the invenliun eau be easily separated from the
reaction pruducls, which are
either volatile like (CH3)3SiF or (CH3)3SiC1 or eau be washed away is au
appropriate solvent like wafer
or an organic fluid. Also, well known lechniyues front the Luau skilled in the
art like ion exchange or
electrophoresis eau be applied to exchange the calion Nl+ obtained in the
crosslinking reaction and/or
front the non crosslinking ionogen reagents wish llle desired M'+ for the
final application) (e.g. H+).
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Representative Drawing