Note: Descriptions are shown in the official language in which they were submitted.
lZQ3501
Case 3-13636/CGM 260/ZFO
Semipermeable Membrane Consisting of Crosslinked Copolymer
Containing Maleimide Groups
The present invention relates to semipermeable membranes
consisting of crosslinked polymers, to a process for the
production thereof and to the use of said membranes, in
particular in reverse osmosis or ultrafiltration.
It is known to use semipermeable membranes in separation
methods such as reverse osmosis (also known as hyperfil-
tration) and ultrafiltration. An essential feature of these
separation methods using membranes is the selective per-
meability of the membrane, especially the retention capa-
city for the dissolved substance and the flux of the sol-
vent.
Membranes made of plastic, which are used e.g. for obtai-
ning potable water from seawater or brackish water, in
wastewater treatment, in working up galvanic baths, as
well as in the food industry and pharmaceutical industry,
must comply wlth stringent requirements not only in respect
of their separating capacity but also in respect of their
mechanical strength and chemical resistance. Chiefly mem-
branes made of cellulose esters, polyamides or acryloni-
trile copolymers are used; but these membranes are still
deficient in respect of their separating capacity or of
their resistance to solvents. There has consequently been
no lack of efforts to eliminate these deficiencies by mo-
difying the known polymers. For example, in German Offen-
legungsschrift 2 906 334, issued August 23, 1979 assigned
to Ciba-Geigy AG, it is proposed to use cellulose ester
derivatives which have been modified with cyclic ~-keto
acids, especially with succinylo-succinic acid, for the
production of membranes.
... .
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It has now been found that semipermeable membranes having
improved resistance to solvents while still keeping good
flux and good retentivity, may be obtained in more simple
manner by using photocrosslinkable copolymers based on
ethylenically unsaturated monomers for the production of
membranes.
Accordingly, the present invention provides semipermeable
membranes consisting of crosslinked polymers, which mem-
branes were obtained by irradiating a layer which ~ applied
to a suitable support and which contains photocrosslinkable
copolymers based on ethylenically unsaturated monomers,
said photocrosslinkable copolymers having a molecular
weight o~ 103 to 107 and containing in the side-groups of
the polymer chain at least 2 maleimide groups of the for-
mula I Q
/ \./ 1
-N \
~/ \R2
wherein each of Rl and R2 is methyl or Rl and R2, together
with the carbon atom to which they are attached, form a 5-
or 6-membered carbocyclic ring which may be substituted by
methyl, and with at least 10~ by weight of said monomers,
based on the total amount of the comonomers used for obtai-
ning the copolymers, containing acid and/or basic groups,
with electromagnetic waves.
The photocrosslinkable copolymers used for obtaining the
membranes of this invention are e.g. those which contain
the maleimide groups of the formula I in molecule chain
members of the formulae
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- CH - CR -
COO - Yl - MI
-CH - CR -
COO~ CH2~CH - CH2 - OOC - Y2 ~ MI
OH (x = 1 or 2 )
- CH - CR -
CONR - Y - MI
1 5 1R7
-- C -- C --
R6 - Y4 - MI
- CH - CH -
COOH COO-Y5-MI
- CH - CH
COOH CONRg- (Y6) -MI or
R5 R6
--C C--
OC/j ~CO
(Y )
17 q
MI (q = o or l)
wherein
MI is the maleimide group of the formula I and
Y2 is an aliphatic, cycloaliphatic, carbocyclic-aromatic,
araliphatic, heterocyclic-aliphatic or heterocyclic-
aromatic bridge member, each containing altogether at
most 18 carbon atoms,
Yl has the same meaning as Y2 or is the grouping of the
formula
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-- 4 --
(CH2)yC~ /R8
i!` ! (y = 1 to 4)
HOOC/ \.3~
Y3 has the same meaning as Y2 or Y3 is the grouping -CO-
2'
Y4 has the same meaning as Y2 or Y4 is preferably an ali-
phatic or carbocyclic-aromatic radical,
Y5 has the same meaning as Y2 or Y5 is the grouping of
the formula -CH2-8H-(CH2~ ( n = 1 or 2),
Y6 has the same meaning as Y2,
Y7 has the same meaning as Y2, while q is preferably 0,
R3 is hydrogen or alkyl, preferably methyl,
R4 is hydrogen or alkyl of 1 to 6 carbon atoms,
R5, R6 and R7, each independently of the other, are hydro-
gen, halogen, cyano, alkyl, aryl, aralkyl, with hydro-
gen being preferred,
R8 is hydrogen, -COOH or -COO(CH2)z CH3 (z = O to 18) and
Rg i9 hydrogen or alkyl of 1 to 6 carbon atoms.
The photocrosslinkable copolymers used for the production
of the membranes of this lnvention are known from German
Offenlegungsschrift 26 26 769 and may be obtained by the
methods descrlbed thexein, elther by introducing into an
existing polymer chain containing reactive side groups such
as -OH, -SH, -NH2, dicarboxylic acid anhydride or epoxy
groups, the light-sensitive maleimide groups by means of a
condensation or additlon reaction, or by copolymerising a
mixture of comonomers, in which at least 10% by weight of
the monomers already contain the light-sensitive maleimide
group. Such monomers containing maleimide groups are known
from German Offenlegungsschrift 26 26 795.
The membranes of this invention preferably consist of
lZQ3SOl
crosslinked copolymers which are obtained using photocross-
linkable copolymers prepared from
(1) a (meth)acrylate, (meth)acrylamide or vinyl ether
derivative which contains at least one maleimide group of
the formula I, or from a compound of the formula II
o
/ \ / 1
CH2=CH~Y2~;~ N~ li ( I I ),
o/ 'R2
wherein Rl, R2, Y2 and n have the meanings previously
assigned to them and n is preferably 1,
(2) at least 10~/o by weight, based on the total amount of the
comonomers, of an ethylenically unsaturated comonomer
containing acid and/or basic groups, and optionally
(3) at least one further ethylenically unsaturated comonomer
which differs from the comonomers (1) and (2).
referred comonomers (1) have the formulae III to V
CH = CR
11 12 ' (III)
CH = CR
C~R13 - Rll R12 (IV) or
R14 R16
C = C--O - Rll-R12 (V)
R15
wherein Rlo is hydrogen or methyl, Rll is straight chain or
branched alkylene of 1 to 12 carbon atoms or cycloalkylene of
5 or 6 carbon atoms, R12 is maleimide grouping of the
formula
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- 6 -
o O O
Il 11 11 CH
C~ ~CH3 C~ ~-~ ~C~ ~ 3
or -~
\C/ \CH \C/ \ / \C~ \ /
O ~ O
and R13 is hydrogen or alkyl of 1 to 6 carbon atoms, and
each of R14, R15 and R16 is hydrogen, halogen, cyano or
alkyl of 1 to 6 carbon atoms.
The comonomers of the formulae III and V are especially
preferred, in particular those of the formula V, e.g. the
compound of the formula
CH (H) O
~ 3 11
CH2 = ~C f~ ~ 3
COOCH2CH2~ i1
CH3
o
The content of these comonomers in the photocrosslinkable
copolymer determines the density of crosslinking of the
network formed by the action of light. If it is too low,
then the crosslinking and consequently the mechanical strength
of the membrane is insufficient.
In addition to the above described molecule chain members
which contain maleimide groups and which may comprise 10
to 90% by weight of the copolymers, the copolymers contain
molecule chain members in which maleimide groups are not
present and which contain acid and/or basic groups as well
as optionally in addition further chain members in which
maleimide groups are not present.
The acid chain members may be derived from the following
comonomers (2): a,~-unsaturated carboxylic acids, e.g.
acrylic acid, methacrylic acid, maleic acid, fumaric acid,
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itaconic acid, crotonic acidi monomers which contain sulfonic
acid groups, e.g. vinylsulfonic acid and salts thereof (e.g.
Na- or K-salt), 2-sulfoethylmethacrylate, styrenesulfonic
acid, or monomers which contain carboxyl groups and are
obtained by reaction of cyclic acid anhydrides (1 mole)
with hydroxyethyl(meth)acrylate (1 mole), e.g. mono-~-(meth)-
acryloxyethyl phthalate.
Chain members containing basic groups are introduced into
the copolymer using carboxylic acid derivatives which
preferably contain dialkylamino groups or alkylarylamino
groups, a,~-unsaturated carboxylic acids or nitrogen-
containing heterocyclic vinyl compounds as comonomers.
Examples of suitable basic comonomers are: comonomers of
the series of the vinylpyridine compounds such as 2-vinyl-
pyridine, 4-vinylpyridine, (dialkylamino)acrylates which
are substituted by basic groups, e.g. dimethylaminoethyl-
(meth)acrylate, diethylaminoethyl(meth)acrylate, dimethyl-
aminopropyl(meth)acrylate, diethylaminopropyl(meth)acrylate,
dimethylaminopropylmethacrylate or diethylaminopropyl-
methacrylate. The basic groups preferably consist of a vinyl-
pyridine or an alkyl ester of N,N-dialkylamino- or N,N-
alkylarylamino(meth)acrylic acid, in particular of N,N-
dialkylamino(meth)acrylic acid.
The comonomers (3) which contain no acid or alkaline groups
and which may be used concurrently for obtaining the photo-
crosslinkable copolymers are derived e.g. from the following
comonomers: olefins, especially alkenes, vinyl halides, e.g.
vinyl chloride, vinyl bromide, or vinyl fluoridei vinylidenes,
e.g. vinylidene chloride; nitriles of a,~-unsaturated acids,
e.g. (meth'acrylonitrilei esters of a,~-unsaturated acids
(acrylic and methacrylic acid), e.g. methylacrylate,
ethyl acrylate, propyl acrylate, butyl acrylate, octyl
acrylate, 2-ethylhexyl acrylate, methyl methac:ylate,
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ethyl methacrylate, isopropyl methacrylate, butyl methacrylate,
glycidyl acrylate, glycidyl methacrylate, chloromethyl meth-
acrylate; a ,~-unsaturated carboxamides and derivatives
thereof, e.g. acrylamide, methacrylamide; aromatic vinyl
compounds, e.g. styrene, methyl styrene, vinyl toluene,
a-chlorostyrene; vinyl ketones, e.g. methyl vinyl ketonei
vinyl esters, e.g. vinyl acetatei heterocyclic vinyl com-
pounds, e.g. vinyl pyrrolidone, vinyl carbazole or a vinyl
ether.
It is preferred that the copolymers contain as comonomer (3)
an alkene, a vinyl or vinylidene halide, a (meth)acrylo-
nitrile, an ester or amide of an -unsaturated acid, an
aromatic or heterocyclic vinyl compound, a vinyl ester or
ether or a vinyl ketone, in particular an alkyl- or hydroxy-
alkyl(meth)acrylate, and, most preferably, an alkyl(meth)-
acrylate. The photocrosslinkable copolymers may contain
from 0 to 80% by weight of repeating units which are derived
from the comonomers (3).
Of the possible copolymers, those are preferred which are
prepared from comonomers (2) containing free carboxyl groups,
e.g. in particular ,~-unsaturated acids such as methacrylic
acid, acrylic acid, maleic acid (maleic anhydride) and
mono-~-methacryloxyethylphthalate. The content of these
acids in the polymer may vary from 90% to 10% by weight,
preferably from 50% to 15% by weight.
Those photocrosslinkable copolymers which contain a basic
group are used in particular for the production of the
membranes of this invention, the comonomer consisting of a
vinylpyridine or an alkyl ester of N,N-dialkylamino- or
N,N-alkylarylamino(meth)acrylic acid. And in a preferred
embodiment the tertiary N-atoms contained in the basic
groups are quaternised in known manner with a quaternising
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agent, e.g. dimethyl sulfate.
Membranes which are prepared from photocrosslinkable
copolymers which contain both acid and basic groups like-
wise constitute a preferred embodiment.
The photocrosslinkable copolymers may be purified by
conventional known methods, e.g. by precipitation in a
solvent in which the polymer is insoluble, and subsequent
washing and drying.
The light-sensitivity of the photocrosslinkable copolymers
is very substantially increased by photosensitisers. The
sensitivity to the light of different commercially available
copying lamps, e.g. metal halide lamps, can be adjusted to
the maximum degree by appropriate choice of photosensitisers.
Suitable photosensitisers are in particular triplet sensitisers
in the use of which the crosslinking is effected by triplet
energy transfer of the excited photosensitiser to the non-
excited maleimide ester of the formula I. Reference is made
in this connection to N.J. Turro, "Mol. Photochemistry",
W.A. Benjamin Inc. [1965], page 107. The conditions for
effective sensitisation are such that the triplet sensitiser
has a maximum absorption which permits a virtually sufficient
light absorption in the range of more than 300 nm and that
the triplet energy transfer is exothermic.
Most suitable for light of 400-420 nm (metal halide) are
substituted thioxanthones, e.g. alkyl esters of 6-carboxy-2-
methylthioxanthone. The photosensitisers are preferably
used in amounts of 0.1 to 10% by weight, based on the weight
of the copolymer. Combinations of several different photo-
sensitisers may also be used.
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Suitable light sources for irradiating the polymeric material
are those which emit an effective amount of radiation in
the range of the absorption bands of the photosensitiser.
As many of the above mentioned photosensitisers have an
absorption in the range from 300 nm to 450 nm, light sources
are preferred which emit a high amount of radiation in this
range. Both point light sources and planar light sources
(light arrays). Examples are: carbon arc lamps, xenon arc
lamps, mercury vapour lamps which may be doped with metal
halide (metal halide lamps), fluorescent lamps with luminiscent
material which emits UV light, incandescent argon lamps,
electronic flash lamps and photographic floodlights. The
distance between lamp and the polymeric material can vary,
depending on the end use and the type or strength of lamp,
e.g. from 2 cm to 150 cm. In certain cases it may be
advantageous to irradiate with visible light using a photo-
sensitiser which is sensitive in the visible range of the
spectrum. In such cases, the irradiation source should emit
an effective amount of visible light.
Many of the light sources specified above emit the requisite
amount of visible light. It is also possible to crosslink
the polymers without photosensitisers. To this end, light
sources are necessary which emit light in the range of the
absorption bands of the maleimides of the formula (1), i.e.
in the range from 200 to 350 nm. Suitable light sources are
e.g. low or medium pressure mercury lamps.
The semipermeable membranes of this invention are obtained
in known manner by applying the photocrosslinkable copolymers
in a thin layer in the form of an organic solution or melt
to a suitable support, removing the solvent, if one is used,
by evaporation, and irradiating the resultant film. The most
suitable thickness of the layer in the individual case
depends on the particular utility of the membrane.
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-- 11 --
Preferred layer thicknesses are in the range from 0.1 to
100 um, preferably from 0.1 to 50 um.
As mentioned at the outset, the semipermeable membranes of
this invention have in particular improved resistance to
solvents. They are therefore used for the separation of
organic substances, in particular in hyperfiltration or
ultrafiltration.
The following Examples illustrate the invention in more
detail.
Preparation of the photocrosslinkable coPolYmers
ExamPle A: A sulfonating 1ask equipped with reflux cooler,
stirrer, nitrogen inlet and thermometer, is charged with
80 parts by weight of 2-~dimethylmaleimido) ethyl methacry-
late and 20 parts by weight of methacrylic acid as 15% solu-
tion in methyl ethyl ketone (MEK)/methyl cellosolve ~ (MCS)
~ratio of MEK:MCS = 1:1 parts by volume). The flask is eva-
cuated repeatedly and scavenged with nitrogen, whereupon
the contents are heated to 65C and 0.2% by weight of azo-
blsisobutyronitrile (AIBN), based on the sum of the mono-
mers, is added. A further 2 portions of 0.2% by weight of
AIBN are added at intervals of 4 hours. After a reaction
time of 24 hours the copolymer is precipitated in a 15-
fold excess of ether and the precipitate is dried in a high
vacuum at 40C. The copolymer is obtained in a yield of
94% of theory and has an inherent viscosity (rl inh.) of
0.21 dl/g, measured in a solvent mixture consisting of
equal parts of MEK and MCS at 25C.
Example B: 50 parts by weight of 2-(dimethylmaleimido)ethyl
methacrylate, 25 parts by weight of methacrylic acid and 25
parts by weight of butyl methacrylate are copolymerised
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- 12 -
in a manner similar to that described in Example A. Yield:
68% of theory; ~ inh = 0.22 dl/g.
Example C: 80 parts by weight of 2-(dimethylmaleimido)ethyl
methacrylate, 20 parts by weight of N,N-dimethylaminoethyl
methacrylate and 1% by weight of dodecyl mercaptan, based
on the sum of the monomers, are dissolved in a sulfonating
flask in accordance with Example A to give a 25% solution
in isopropanol. This solution is cooled to +10C and then
equimolar amounts of dimethyl sulfate, based on the amount
of N,N-dimethylaminoethyl methacrylate, are added. The
solution is then evacuated repeatedly, scavenged with
nitrogen and heated to 80C. Then 1.5% by weight of AIBN,
based on the sum of the monomers, is added. A further 1%
by weight of AI~N is added after 1~ hours and the reaction
solution is allowed to react for another 2 hours. The
precipitate is isolated by filtration and dried in a high
vacuum at 40C. The copolymer is obtained in a yield of
98.8% and has an inherent viscosity ~of 0.13 dl/g at 25C
in MEK/MCS (1:1).
Example 1: A solution of 1.42 g of the copolymer obtained in
Example A in 8.5 g of dioxane, which solution contains
0.075 g of thioxanthone-2-methyl carboxylate as photo-
sensitiser, is applied uniformly to a flat support, left to
dry overnight at room temperature, and then irradiated for
2 hours with a 2kW medium pressure mercury lamp to give a
12.4 /um film. Thîs film is used as membrane in a hyper-
filtration test. With pure water and at a pressure of 100 bar
the water flux is 9.8 1/m2d, whereas with a O.lN NaCl solution
under the same conditions the flux is 4.8 1/m2d (1 = litre
of permeated volume,m = membrane area, and d = day) and the
salt retention is 43.3%. The membrane is water-resistant and
insoluble in acetone, chloroform, tetrahydrofuran and
dimethyl sulfoxide.
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Example 2: A solution of 1.4 g of the copolymer obtained in
Example s in 8.5 g of dioxane, containing 0.075 g of
thioxanthone-2-methyl carboxylate as photosensitiser, is
poured onto a flat support, left overnight at room temperature
for evaporation of the solvent, and then irradiated for
% hour with a 2 kW medium pressure mercury lamp to give a
stable 25 ~m film which is used as membrane. In a hyper-
filtration test performed as described in Example 1, the
flux is 1.6 1/m2d with pure water and 2.01 1/m2d with a
O.lN NaCl solution. The salt retention is 63.4%. The membrane
is water-resistant and insoluble in acetone, chloroform,
tetrahydrofuran and dimethyl sulfoxide.
Example 3: 84 g of the copolymer obtained in Example C are
dissolved in 9 ml of a solvent mixture consisting of equal
parts of methyl ethyl ketone and ethylene glycol monomethyl
ester. The soluti~n contains 0.16 g of thioxanthone-2-methyl
carboxylate as photosensitiser and is poured onto a flat
support to give a 0.1 mm layer. The solvent is allowed to
evaporate at room temperature over 45 minutes and the layer
is then irradiated for 15 minutes as described in Example 1.
The 20 ~m thick film obtained is used as membrane in a
hyperfiltration test. Under the conditions described in
Example 1, the flux is 175.4 1/m2d with pure water and
157.2 1/m2d with a O.lN NaCl solution. The salt retention
is 93.9%. The membrane is water-resistant and insoluble in
acetone, chloroform, tetrahydrofuran and dimethyl sulfoxide.
