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

NOUVELLES TECHNIQUES ET NOUVEAUX PROCEDES POUR LA RETICULATION DE MEMBRANES ECHANGEUSES D'IONS, ET APPLICATIONS

English Abstract

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

Claims

-7-

CLAIMS:
1) Process for crosslinking sulfonated polymers, characterized in that at
least
some of the bonds linking the chains bear an ionic charge and involve,
partially or in their totality, 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' represent polymer backbones
Y represents:
- N (Nitrogen)
CH, CQ where Q represents a monovalent, possibly fluorinated
or perfluorinated alkyl, oxaalkyl, azaalkyl, aryl or arylalkyl or alkylaryl
radical containing 2 to 20 carbon atoms, SO2R CCN, CF
Q represents a divalent, alkyl, oxaalkyl, azaalkyl, aryl or arylalkyl or
alkylaryl radical containing 1 (inclusive) to 20 (inclusive) carbon atoms,
possibly halogenated, in particular perfluorinated.

2) Crosslinked sulfonated polymers, characterized in that at least some of the
bonds linking the chains bear 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+)Y-SO2Y-(M+)SO2~P'
P~SO2(M+)Y-SO2QSO2Y-(M+)SO2~P'
where Y, P and P' are as defined in claim 1.

3) Process for crosslinking polymers according to claim 1, characterized in
that the sulfonated groups are totally or partially in the form:
P~SO2L
where:
L = is a leaving group, like F, Cl, Br, an electrophilic heterocycle
N-imidazolyl, N-triazolyl, R"SO3, R" being an organic radical, preferably
halogenated, especially perfluorinated.




-8-
4) Process for crosslinking polymers according to claim 1, characterized in
that the crosslinking agents are of the general formula:
(M+)A2Y
(M+)AYSO2YA(M+)
(M+)AYSO2QYA(M+)

5) Process for crosslinking polymers according to claim 1, characterized in
that one of the following reactions is used to form the crosslinks:

P~SO2L + (M+)A2Y + LO2S~P' ~ P~SO2Y(M+)O2S~P' + 2LA
P~SO2L + (M+)AYSO2YA(M+) + LO2S~P' ~
P-SO2Y(M+)SO2Y(M+)SO2~P' + 2LA
P~SO2L + (M+)AYSO2QYA(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 in 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:
P~SO2Y(M+)A + LSO2L + A(M+)Y~P' ~
P-SO2Y(M+)SO2Y(M+)SO2~P' + 2LA
P~SO2Y(M+)A + LSO2QSO2L + A(M+)Y~P' ~
P~SO2Y(M+)SO2QSO2Y(M+)SO2~P' + 2LA

8) Process for crosslinking polymers according to claims 3 and 4,
characterized in that either M+ or A or both is a proton and the reaction is
conducted in the 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.







-9-
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 tertiary or
hindered organic base.

11) Process for cross-linking polymers according to claim 8 characterized in
that the tertiary base is triethylamine, di-isopropylamine, quinuclidine,
1,4-diazobicyclo[2,2,2] octane (DABCO); pyridines (for example pyridine,
alkylpyridines, dialkylaminopyridines); imidazoles (for example
N-alkylimidazoles, imidazo[1,1-a]pyridines, amidines (for example
1,5-diazabicyclo[4,3,0]non-5-ene (DBN), 1,8-diazabicyclo[5,4,0]undec-7-ene
(DBU); guanidines (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 either A or M+ or both
are solvated by dialkylethers or oligo-ethylene glycols or permethylated
oligo-ethylendiamines (e.g. tetramethyl-ethylene diamine TMEDA).

13) Crosslinked polymers derived from at least one of the following monomers:

Image

or
Image


or: Image



Image



or:




-10-
or: Image

- X represents F, Cl or CF3
- n 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 in that L = F or
Cl.

15) Crosslinked polymers according to claim 13, characterized in that n = O
included or 1.

16) Process according to claim 4, characterized in that the crosslinking agent
is
chosen between:


Image

17) Process according to claim 6, characterized in that the crosslinking agent
is
chosen between:

Image

18) Sulfonated polymers according to claim 2, characterized in that the
uncrosslinked polymer containing the P~SO2L is processed into its final
shape and crosslinked in a further step.




-11-
19) Sulfonated polymers according to claim 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 claim 2, characterized in that the
uncrosslinked polymer is processed into its final shape and brought into
contact with a solution of the crosslinking reagent in an inert solvent and
reacted at a temperature ranging from -20 to 200°C.

21) Sulfonated polymers according to claim 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 thin membrane according to claim 11, characterized
in that the suitable solvent is chosen among: lower aliphatic alcohols,
acetone, methyl-ethylketone, cyclic ketones, cyclic ethers, the glymes,
N-alkyl-pyrolidones, tetraalkylsulfamides, methylene chloride, chloroform,
1,2 dichloroethane, N-alkylimidazole, fluorinated hydrocarbons and
mixtures thereof.

23) Method for preparing material according to claims 3 to 6, characterized in
that ion exchange to the desired cation M+ is performed after
polymerization.

24) Method according to claims 3 to 6, characterized in that inorganic or
organic filler particles, including fibers woven or non woven cloth, are
added to the solution before polymerization.

25) Electrochemical cell characterized in that a membrane according to claims
1
to 11, 13 to 19 is used as solid electrolyte.

26) Electrochemical cell according to claim 20, characterized in that it is a
fuel
cell, and/or a water electrolyser, a chlor-alkali cell, an electrochemical
acid
or salt recovery cell.




-12-

27) Electrochemical cell according to claim 20, characterized in that at least
one
electrode is in contact with the membrane.

28) Electrochemical cell according to claim 22, characterized in that at least
one
electrode containing a conducting additive, optionally a catalyst, optionally
a pore forming agent and the un-crosslinked polymer of claim 2 is coated
on the pre-crosslinked electrolyte membrane, then crosslinked.

29) 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 are
coated on, or co-extruded with, the un-crosslinked electrolyte membrane,
then crosslinked.

30) Electrochemical cell according to claim 23, characterized in that it forms
the element of a fuel cell where M+ is an hydrated proton and the positive
electrode contains an oxygen reduction catalyst and the negative electrode
either an hydrogen, methanol, dimethoxymethane, trimethoxymethane,
trioxane or ammonia oxidation catalyst.

31) Fuel cell according to claim 26, characterized in that the electrodes are
applied onto the membrane using the process or either claims 23 or 24.

32) Material according to claims 1 to 11, characterized in that it is used for
chlor-alkali electrolysis.

33) Material according to claims 1 to 11 characterized in that it is used as a
separator in the electrochemical preparation or organic or inorganic
substances.

34) Material according to claims 1 to 11 and 18, characterized in that it is
used
as a separator between an aqueous phase and an organic phase.

35) Material according to claims 1 to 11 and 12, characterized in that the M+
ions associated with the non-nucelophilic anionic centers of the backbone
confer catalytic properties.




-13-
36) 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.

Description

CA 02228467 1998-O1-30
-1-
New Techniques and Processes for Crosslinking Ion
Exchange Membranes and their Applications
This invention relates to techniques and process for crosslinking ion exchange
membranes and their applications.
Prior Art
Owing to their chemical inertness, fluorinated or perfluorinated ion exchange
membranes have been selected for the chlor-alkali process and for fuel cells
consuming either hydrogen or methanol. The materials presently available under
the commercial names Nafion~, Flemion~, Dow~ or materials developed by
Ballard Inc. (W097/25369) are copolymers of tetrafluoraethylene (TFE) and of
perfluorovinylethers or trifluorovinylstryrene. The active monomers have
chemical functionalities which are the precursors of ionic groups of the
sulfonate
or carboxylate type. These precursors are:
FZC=CF-O CFz- iF-O CFZ-CF2-S02F
X n
or:
or
FZC=CF-O CFZ-GF-O (CFZ~COZR
IX n
FZC=CF ~S02F
Sulfonated polyaromatic imides or ether sulfones have also been considered as
candidates:
0 0-(~- So
S 02Y
- X represents F, Cl or CF3
- OLnL 10
-p=lor2
- R = alkyl, (ethyl or methyl).
Once obtained the copolymer containing the precursors is processed
into sheets then transformed into the ionic form by hydrolysis
(--S02F ~ -S03 M+; -C02R ~ - C02 M+)


CA 02228467 1998-O1-30
-2-
where:
- M+ represents a cation, with for example: H+, Li+, Na+, K+, l/2Mg2+,
1/2Ca2+, I/ZBa2+ and other alkaline earth metals ions, 1/2Zn2+, l/2Cu2+ and
other transition metals ions, 1/3A13+, 1/3Fe3+, 1/3Sc3+, 1/3Y3+, 1/3La3+, and
other rare earth metals ions, or an organic cation of the opium type,
oxonium, ammonium or pyridinium, guanidinium, amidinium, sulfonium,
phosphonium, non substituted, partially or totally substituted by organic
radicals, organometallic cations, like metalloceniums, arene-ferrocenium,
alkylsilyl, alkylgermanyl, alkyltin...
Such materials have however several important drawbacks which are
summarized below:-
1) the copolymers in their ionic form are untractable, yet are not
dimensionally
stable and swell appreciably in water and polar solvents. Only when heated
at high temperature in supercritical water-lower alcools mixtures they can
form inverse micelles which, upon evaporation, leave the materials as films.
However this recast material is in a form lacking mechanical cohesiveness;
2) handling of TFE is hazardous, as its polymerization is under pressure and
may lead to runaway reactions, especially in the presence of oxygen; due to
the difference in boiling points of the two monomers, it is difficult to
obtain
a statistical polymer 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 easy diffusion of
molecular species, resulting in cross over chemical reaction and a loss of
faradaic efficiency, in particular for direct methanol fuel cells (DMFC's).
Non fluorinated systems like sulfonated polyimides or polyether 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.


CA 02228467 1998-O1-30
-3-
Description of Invention
While it is known in that 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 can be achieved after the polymer
has been processed while in the processable non ionic precursor form. The
invention also relates to the use of the crosslinked shaped material in
membrane
form for applications including fuel cells, water electrolysis, chlor-alkali
process,
electrosynthesis, water treatment and ozone production.
The creation of stable crosslinks is achieved through the reaction of two -
S02Y
from adjacent chains to form the sulfonimide, bis(sulfonylinethane) or tris
sulfonylinethane derivatives, schematized as:
S02L + LS02
A2Y-(M+)
f
S02-~ S02
+ 2 LA
SOIL + LS02
L(M+)-YS02Y-(M+)L
i
0 0
S0 2 YSO 21f- SOZ
M+ M+
+ 2 LA
S02L + LS02
A(M+rYS02QS02Y-(M+~1
o i o
sot Yso2QSO2Y-sot
M+ M
+ 2 u~


CA 02228467 1998-O1-30
-4-
where M has the above meaning and
Y represents:
- N (Nitrogen)
- CH, CQ where Q represents a monovalent, possibly fluorinated
or perfluorinated alkyl, oxaalkyl, azaalkyl, aryl or arylalkyl or
alkylaryl radical containing 2 to 20 carbon atoms, S02R CCN, CF
A = M or Si(R)3, Ge(R')3, Sn(R')3, (R' = alkyl from 1 to 18 carbon
atoms)
Q = a divalent, preferably halogenated, especially perfluorinated
alkyl, oxaalkyl, azaalkyl, aryl or arylalkyl radical containing 0 to
20 carbon atoms when there is no carbon atom, the compound is
a sulfamide...
The M+ species may themselves be solvated or complexed to increase their
solubility or reactivity. For example, protons can be complexed by a strong
nucelophilic tertiary base like triethylamine (TEA), dimethylaminopyridine
(DMAP), 1,4-diazabicyclo[2.2.2~octane or as nascent form in the tertiobutyl
radical dispxoportionating readily into an ether, H and CH2=C(CH3)3, metallic
ions are solvated by dialkylethers or oligo-ethylene glycols or permethylated
oligo-ethylendiamines (e.g. tetramethyl-ethylene diamine TMEDA). Similarly,
the A2Y-(M+) compound can be formed in situ in the presence of strong bases
such as organometallic compounds with labile protons attached to the Y
radical.
Suitable reagents include organo lithium, magnesium or aluminium compounds,
especially their methyl derivatives which also serve as a source of carbon for
Y =
CH, alkali metal amides as a source of nitrogen for Y = N, dialkyl amides like
LDA (lithium diisopropylamide).
An advantage of the technique and materials of the invention is that the
crosslinking agent creates ionophoretic, i.e. charged species, the negatively
charged moieties being attached to the polymer and used as bridges between
chains. It is known that the sulfonylimide groups and di or trisulfonylmethane
groups are strong electrolytes in most media and thus the crosslinking
reaction,
in addition to improving the mechanical properties, has no detrimental effect
on
the conductivity and often results in its enhancement. The compounds whose
formulae are given below are examples only of suitable ionogen crosslinking
agents and are given to illustrate the principle of the invention:

O~~'Q + Oz(z3~Z3~ZOS3) -.


d3.1. + Z~Z~~ZOS3)Z(al~P~~)ZOS 0~8t~a + ZI~zOS



:uor~uanm a~ ~o adoos a~ ~~j o~ papua~m you aye ~nq uoRuanut
a~ ~o aldtouud a~ a~~.~sn~ o~ uann are pine s~ua~~ ~unjuijsso~a ua~ouoi
aiqu~ms ~o saldurexa a.ie nnojaq uann are a~ejnuuo~ asoc~nn spunodu~oa auZ
y~ Z +
+W +W
SOS OzOS~OS~ SOS
l Z OSOz OSl
+W +W
zOSJll1 VAzOS
O ~ _
~ Z+
+W +W
z OS _ ~zOS~ ?OS
___
l OSl
+W + +W
zOSO VO OS
ae pazu~emauas si as~a
snp m auiaqas le.~aua~ a~ 'aptuze a~n~usqns ~e ~o~ s~e '.~osmaa.~d .zaurAjod
a~ uo
~p~a.~ si dno.~ ~ act uaqnn aaejd axed u~a uoyaea.z ~unluqsso,~a ~
'~ijanr~euza~~
Oz{z3~z3~ZOSNI(H~)!Sl(!'I)?


zfz3~zOSN(H~)!S(!'I))z3~z{z~~zOSNI(H~)!Sl(!'I)}zdJz{zOSN(r1U(H~)!Sl}


}I '~N '!'7ZHN ft~(H~) rIH~
-


ZOSzfN($W)(da~l.lJ1zOSz{N(~'1)fiS(H~)l} ~3,L~+zHNZOSZHN


t''3.1.+zHN~(H~) zUdQ3W,IJ!'-I1I!S(H~)I~zOS~~OJBda+HN


X 'EN '!'INzIIS(H~)1rf'o'~ NrI


'S'
0~-i0-866l G9b8ZZZ0 ~a
y


CA 02228467 1998-O1-30
-6-
The crosslinking reaction may imply the totality of the sulfonyl groups or a
fraction of them. The crosslinking reagents may be applied by different
techniques which are known to one skilled in 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 is
brought
in contact, by immersion or coating with a solution of the crosslinking
reagent in
a solvent which is non reactive towards the reactants. Appropriate solvents
include but are not limited to polyhalocarbons, THF, the glymes, tertiary
alkylamides including DMF, N methyl-pyrrolidone, tetraethyl urea and its
cyclic
analogs, N-alkyl-imidazoles, tetraalkyl sulfamides. The desired degree of
crosslinking may be controlled by several factors such as time of contact,
temperature or the concentration of the crosslinking reagent.
Alternatively, a latex of the processable material is intimately mixed with
the
reagent in solid form and the mixture is pressed or hot rolled, possibly in
the
presence of a non-solvent fluid such as an hydrocarbon. This technique is
applicable in particular to thin membrane and results in high productivity
though
less homogeneous material is produced. It is understood that fillers such as
powders, woven or non-woven fibers or filaments, can be added to the polymers
before the crosslinking reaction as reinforcing agents.
If only a fraction of bridging bonds are required, the remaining -S02Y can be
transformed into the ionic sulfonate form by alkaline hydrolysis.
Alternatively,
the -S03M group or the non crosslinking imide group -S02NS02RFM can be
obtained in the same conditions as for the crosslinks by ionogen reagents like
respectively M+[{CH3)3Si0]- or M+[(CH3)3SiNS02RF]-; such examples are
given for illustration but are not limitative. It may be advantageous to treat
the
membrane either sequentially by the crosslinking agent than by the non
crosslinking ionogen reagents. Alternatively, the ionogen crosslinking agent
and
the non crosslinking ionogen are mixed together or codissolved in the solvent
in
predetermined proportions and react simultaneously.
The crosslinked material of the invention can be easily separated from the
reactant products, which are either volatile like (CH3)3SiF or (CH3)3SiC1 or
can
be washed away in an appropriate solvent like water. Also, well known
techniques from one skilled in the art like ion exchange or electrophoresis
can be
applied to exchange the cation M+ for the final application, (e.g. H+).