CA1119749A - Polymerisable disulphimide derivatives containing maleic imide groups and their use - Google Patents

Abstract

A semi-permeable membrane prepared from a copolymer consisting of copolymerized units of (A) 50 to 99% by weight of acrylonitrile, (B) 1 to 50% by weight of at least one monomer of the formula <IMG> where in Ar is a benzene or naphthalene group; R1 to R4 are identical or different and each is H, or lower alkyl; and X is H, Na, K or NH4; and (C) 0 - 30% by weight of at least one other olefinically unsatur ated monomer which is copolymerisable with acrylonitrile, the sum of the percentage contents of (A) to (C) being in all cases 100. The semi-permiable membrane is useful in reverse osmosis and ultra-filtra-tion techniques for separating substances in aqueous solution under pressure.

Description

~1~9~9 'rhis illVC'lltiOIl relates -to a sem.i-pcrme.lble mel1lbrallc~ clncl jts llse ir a reverse osmosis or ultra-filtration process.
This application is clivided from applicants copending Canadian Application Serial No. 322 885 filed on March 5, 1979 and directed in part to a compound corresponding to the general formula (I):
o Il / 2 N S02 ~ Ar R2 ~ C - C

wherein Ar denotes a benzene or naphthalene group;
Rl to R4 are identical or different and denote H, or lower alkyl, and X denotes H, Na, K or NH4.
In numerous synthetic polymer products, certain properties and com-binations of properties can be obtained or improved by incorporating strongly acidic components as comonomers in the polymer chain. Particularly important among these properties are the capacity to absorb basic triphenyl methane dyes, anti-electrostatic properties, acceptability to the skin in the case of synthetic fibres and the wetting power o:E glass fibres and of pigments.
Although a broad range of polar monomers is available, e.g. acrylic acid, maleic acid, acrylamide or hydroxyethyl acrylate, the effects obtained by chemical incorporation of these monomer units are frequently insufficient so that it is necessary to resort to highly polar systems, preferably with acidic components.
However, only a small number of comonomers which introduce strongly acidic groups into synthetic resins polymerised by radical polymerisation ~.

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has hitherto been avail.llle. Virtually the only comonolllers of thi; type whJch are of any teclmical interest are mcthal]yl sulpilollic acid and vinyl sulpllonic acid, and even these have certain disadvantages. Methallyl sulphonic acid is particularly disadvantageous owing to its high transfer constant, i.e. the quantity in which these monomers can be incorporated in synthetic resins is limited, and in addition the overall reaction velocity is reduced and the molecular weights of the resulting polymers are correspondingly reduced.
Vinyl sulphonic acid can only be handled in the form of an aqueous solution on account of its instability, and this entails additional costs, e.g. for transport and storage.
Furthermore, it has been disclosed, inter alia in British Patent No. 867,006, that ~meth)acryloyl amino-benzene-benzene disulphimides can be prepared by the reaction of halides of (meth)acrylic acid with amino-benzene-benzene-disulphimides and can be used as comonomers for radical polymerisa-tion. From the general formula on page 1 of the said specification, it is also possible, by a mosaic-like juxtaposition, to construct 3-carboxy (meth) acryloyl-aminoaryl-aryl-disulphimide (i.e. ~hyl )maleic acid monoamidoaryl-aryl-disulphamide) corresponding to the following formula:

H(CH3) o o HOOC-CH=C-C-NH-arylene-S-NH-S-aryl ,. .. ..
O O O
which is used as a sta:rting material for the preparation of the monomers ac-cording to the invention or formed as an intermediate product. In the general information given in the aforesaid British Patent Specification on page 2, lines 34 to 41, it is recommended to prepare such compounds by the reaction of maleic acid anhydride with disulphimides which contain primary amino groups.
'~he British Patent Specification contains no further details about the reaction ` 1119~9 conditions or any practical examples. If the reaction of maleic acid anhy-dride with aminobenzene-benzene-disulphimides is carried out by the usual methods, for example according to United States Patent No. 3,018,290, column 5, lines 42 - 47, i~e. in suitable solvents, using the reactants in approxi-mately equimolar proportions, the N-substituted maleic amido acids are not only obtained in very poor yields but are also highly contaminated.
~ It is also known that the N-substituted maleic amido acids may be - converted into the corresponding maleic imide derivatives by cyclodehydration in organic solvents at 0 - 100C in the presence of acetic acid anhydride and ; 10 catalysts such as nickel salts and tertiary amines (see German Offenlegungs-schrift No. 2,040,094), or in anhydrides of lower fatty acids such as acetic acid anhydride at temperatures above 25C in the presence of catalysts such as tertiary amines ~see United States Patents Nos. 3,018,290 and 3,018,292).
However, no N-substituted maleic imides in which the N-substituent is a diaryl sulphimide have yet been disclosed.
i The present invention provides a semi-permeable membrane prepared from a copolymer consisting of copolymerized units of ~A) 50 to 99% by weight of acrylonitrile, ~B) 1 to 50% by weight of at least one monomer of the formula 11 \ N - Ar - SO2 - N - SO2 - Ar

2 C ,C, R3 X R4 . O
wherein Ar is a benzene or naphthalene group;
Rl to R4 are identical or different and each is H, or lower alkyl; and ,~

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X is H, Na, K or NH4; and ~C~ 0 - 30% by weight of at least one other olefinically unsaturated `.monomer which is copolymerizable with acrylonitrile, the sum of the percentage contents of (A) to (C) being in all cases 100.
In another aspect, the invention provides in a reverse osmosis or ultra-filtration process comprising passing a solution under pressure over the - surface of a semi-permeable membrane to separate solvent and solute, the im-provement comprises the semi-permeable membrane being prepared from a copoly-mer consisting of copolymerized units of 5~ h ~
.~ 10~A) 1 ~ by weight of acrylonitrile, (B) 1 to 50% by weight of at least one monomer of the formula : O

. 1 C C
¦¦N - Ar - S02 - N - S02 - Ar R2 ~ C - CR3 X R4 .~

wherein ~ Ar is a benzene or naphthalene group; .
Rl to R4 are identical or different and each is H, or lower alkyl; and : X is H, Na, K or NH4; and (C) 0 - 30% by weight of at least one other olefinically unsaturated monomer which is copolymerisable with acrylonitrile, the sum of the percentage contents of (A) to (C) being in all cases 100.
The process claimed in copending application Serial No. 322,885 from which this application is divided is a process for the preparation of a compound corresponding to the general formula (I) as defined above, which comprises reacting maleic acid anhydride, or a maleic acid anhydride which is ;- :. . . - .

.. :-. ,, . . i , :'. ' ' . ~. : ` .

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substituted by CH3, with an aminoaryl-aryl-disulphimide solvent-free with or without a catalyst, the maleic acid anhydride or substituted maleic acid an-hydride being used in a 1 to 5 times molar excess over the amino-aryl-aryl-; disulphimide; and cyclodehydration of the resulting N-substituted maleic amido acid in an anhydride of a saturated fatty acid having a maximum of 5 C-atoms, : in the presence of a catalyst.
` The aforementioned process takes place in accordance with the fol-.~ lowing reaction scheme, in which the various symbols have the meaning indicated for formula ~

O
~A) (2 to 6 mol) Rl - C - C \

/ 2 ,r S02 ,N S02 lAr R2 ~ C - C R3 X R4 C ~a) solvent-free, .~ ~ ~catalyst) .
~B) HOOC-C=C-CONH-Ar-S02-N-S02-Ar + ~1 to 5 mol) RlR2 R3 4 0 ~b) Rl - C - C~
Il ~O
;' R2 - C - C
., O
.1l cyclodehydration ;
O catalyst Rl - C - C \ ~ saturated fatty acid anhydride ,, ¦¦ ~N - Ar - S02 _ ~ - S02 - Ar + H20 R2 ~ C - C R3 4 , O
The aminoaryl-aryl-disulphimides ~a) used as starting materials for reaction ~A) ~see reaction scheme) are either known in the literature . :: :

11~9~749 ~see Methoden der Organischen Chemi, Houben-Weyl, Volume 11/1, (1957), page 368) or can be prepared by known methods (see German Patent No. 757,262, German Auslegeschrift No. 1,249,259 and United States Patent No. 2,374,934).
The reaction with the substituted or unsubstituted maleic acid ar.hydride citraconic acid anhydride may also be used) is carried out solvent-free, i.e.

. , ~'; at temperatures of about 60 to 180C, preferably 100 to 140C, using from 2 to 6 mol, preferably from 3 to 5 mol of anhydride to one mol of the disul-phimide. The excess of anhydride can easily be removed subsequently by distillation under vacuum or by extraction with a suitable solvent.
As catalysts for reaction (A) there may be used tertiary amines corresponding to the following formula:

Rl - N - R3 wherein Rl, R2 and R3 may be identical or different and denote alkyl groups having from 1 to 4 C-atoms. Cyclic tertiary amines such as pyridine, N-Cl-~; C4-alkylated morpholines, piperidines, piperazines and triethylene diamine ~Dabco) may also be used.

, The above-mentioned catalysts are preferably used in quantities of from 0.2 to 2% by weight, based on the quantity of substituted or unsubsti-` tuted maleic acid anhydride put into the process.
Cyclodehydration of the maleic acid monoamidoaryl-aryl-disulphimides ~b) may be carried out by known methods, for example the methods according to United States Patents Nos. 3,018,290 and 3,018,292 or German Offenlegungs-schrift No. 2,040,094. It is preferably carried out by the method disclosed in United States Patent No. 2,444,536, i.e. in an anhydride of a saturated fatty acid having from 2 to 5 C-atoms, such as acetic acid anhydride, in the presence of alkali metal salts of these fatty acids having from 2 to 5 C-atoms, ' ~ . . .- - . . . .

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such as sodium acetate, at temperatures ranging from about 25C to below the decomposition point of the reactants or of the maleic amido acid-disulphimide formed, in particular at 60 to 100C. The anhydride of the fatty acid having from 2 to S C-atoms is preferably used in a 1 to 10 times molar quantity, in particular a 5 to 8 times molar quantity, based on 1 mol of maleic amido acid ,2 disulphimide. The quantities of alkali metal salts of the aforesaid C2 - C5 ' fatty acids added, in particular of sodium acetate, preferably amount to from 5 to 20% by weight of the quantity of anhydride of the fatty acid anhydride put into the process. The excess of anhydride used and the fatty acid formed may be distilled off after cyclodehydration, optionally in a vacuum, and the maleic`~mido disulphimide may be isolated after crystallization or it may be ` obtained by the addition of a suitable precipitating agent, such as a lower alcohol (Cl-C4 carbon atoms), water (pH = 7), acetone, etc. before distilla-!~ ~ tion.
The maleic imido-disulphimides according to the invention can easily ,;i be copolymerised by radical copolymerisation, they are easily handled and stored as solid powders and they are also distinguished by being obtainable ~- by exceptionally simple methods of preparation.
`~ The monomers polymerised by radical polymerisation. A particularly preferred variation of such polymerisation is the copolymerisation with mono-.
mers such as (meth)acrylic acid, (meth)acrylamide, (meth)acrylic acid esters having from 1 to 12 C-atoms, preferably from 1 to 4 C-atoms in the alcohol component, butadiene, styrene, maleic acid, fumaric acid, vinyl chloride, vinylidene chloride, vinyl acetate, maleic imidesj vinyl pyrrolidone, vinyl carbazole, vinyl pyridine, vinyl caprolactam or acrylonitrile.
, The copolymers with acrylonitrile may be used for the production ~3~, of fibres if they contain the compounds according to the invention in ; ~ -7-., .
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1119~9 proportions of, preferably, from 1 to 5% by weight. These fibres are distin-guished from the known polyacrylonitrile products by their improved dye absorption with basic dyes; they are also more acceptable to the skin.
Reverse osmosis and ultra-filtration are methods of separating sub-stances, This separation takes place by passing an aqueous solution under pressure over the surface of a semi-permeable membrane so that the solvent and possibly a proportion of the dissolved substances pass through the membrane while the other components of the solution are held back by the surface of the membrane and can be concentrated in the solution.
Technically the most important of these membranes are those made of cellulose derivatives, in particular cellulose acetate. In spite of their efficiency in allowing water to pass through and separating substances, they have various disadvantageous properties which limit their general usefulness.
These include their lack of chemical resistance, in particular their sensiti-vity to hydrolysis at high and low pH values, and their sensitivity to degrad-ation by microorganisms. This causes deterioration of the membrane properties in the course of time.
Membranes of polyacrylonitrile have already been produced for reverse osmosis. These membranes have a certain capacity to retain salts but a low permeability to water ~S.W. Saltonstall Jr. et al., OSW R0s. Der. Progr.
Report No. 220 (1966)). Ionic acrylonitrile copolymers have been described in German Auslegeschr~ften Nos. 2jl45,183 and 2,346,011. Although these sub-stances have a high permeability to water, they are only suitable for the filtration of solutions of macromolecular substances, i.e. for the separation of relatively high molecular particles.
No membranes are therefore as yet available which have both a high permeability to water and a high selectivity for substances in the range of :, ., :::

..

`' 11197~.9 - medium molecular weights without ths disadvantages described above of the usual cellulose acetate membranes.
It has now been found that membrianes which do not have the disad-vantageous properties of conventional membranes based on cellulose acetate can be obtained from maleic-imido aryl-aryl-disulphimide/acrylonitrile co-polymers. These membranes have a low separation limit of about 500 and permeability to water, but still one which is considerably greater than, for example, that of membranes produced from pure polyacrylonitrile.
The following are mentioned as further examples of olefinically ` lO unsaturated monomers ~III) which are copolymerisable with acrylonitrile:
(meth)acrylic acid, ~meth)acrylamideJ ~meth)acrylic acid alkyl esters having . . .
from 1 - 12, preferably from 1 - 4 C-atoms in the alcohol componentJ hydroxy-alkyl-(meth)acrylates having from 2 - 4 C-atoms in the alkyl group, sul-s~ phoalkyl-(meth)acrylates having from 2 - 4 C-atoms in the alkyl group, maleic / ~ acid, vinyl chloride and vinylidene chloride. The above-mentioned monomers , ..
are preferred; further examples include butadiene, styrene, fumaric acid, maleic acid semi-amide optionally mono or di-substituted by Cl - C4 alkyl groups on the nitrogen; maleic imide optionally substituted by Cl - C4 alkyl or l by; phenyl on the nitrogen; vinyl pyrrolidone, vinyl pyridine or methacrylic .;~! 20 acid salicylate (salicylic acid-0-methacrylate).

~ Preparation of the copolymers from monomers (I) to (III) is carried i out by conventional methods, for example the method described in Cerman Patent No. 1,089,548.
:j ~ The monomer units are built into the resulting copolymers in a sub-`1I stantially statistical distribution. Although it is possible in principle i to vary the molecular weights of the polymers according to the invention with-in wide limits by known methods, polymers having relative viscosities in the ~ _ g _ `
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rallge of abollt l.(~ to ~.6 are ~articularly sllitrll)le ~`or tnc ~roduction of membranes .
The membranes according to the in~ention m.-ly be prepared, for ex-ample, as follows: A homogenous solution of the copolymer obtained from monomers (I) to (III) (= polymer) is prepared in a suitable solvent, prefer-ably a solvent of the amide type. From 5 - 35% by weight of the polymer, based on the total quantity of polymer and solvent, are dissolved in a polar aprotic solvent with the addition of from 1 - 10% by weight of an alkali metal salt or alkaline earth metal salt, preferably LiCl, LiBr, LiN03, MgC12, CaC12 or CaBr2, or an organic amine such as triethylamine, tripropylamine, pyridine, ethanolamine or triethanolamine. The following solvents are preferred: di-methyl formamide, dimethyl acetamide, N-methyl pyrrolidone~ hexamethyl phos-phoric acid triamide, dimethyl sulphoxide, and mixtures of these solvents.
Heating may be employed to accelerate the solution process.
This casting solution is used for the production of a film by applying the solution to a glass or metal surface or any other suitable substrate, e.g. a continuously moving belt or a drum, to form on it a layer of from 150 - 500 ~ in thickness.
The solvent is partly evaporated off by heat treatment. The film 20 is dried at a temperature of from 40 - 150C for 2 - 60 minutes. This step may be omitted, depending on the desired membrane properties of the film.
After a cool:ing phase of several minutes, the film is immersed in a precipitation bath and left therein for about 60 minutes. The liquids used for precipitation may be solvents which are miscible with the organic solvent of the casting solution and possibly also capable of dissolving the salt, but are non-solvents for the polyamide. Water, methanol, ethanol and i-propanol, with the optional addition of salts such as CaC12, are suitable for this ~119749 purpose. Water i5 the preferred precipitating agent. The temperature of the precipitation bath may be in the region of from 0 - 50C and is preferably from 0 - 25C.
The membranes according to the invention may be used in the form of foils, pipes, flexible tubes or hollow fibres. The techniques employed for ; the manufacture of tubes, pipes and hollow fibres accord with the processes described above. The methods known to the expert for the production of pipes, tubes and hollow fibres of polymer solutions are employed.
The membranes may be used for concentrating or recovering usable substances and removing unwanted substances, e.g. in the treatment of ef-fluents from the dyestuff, paper and textile industry.
The membranes produced from the polymers used according to the . invention are preferably asymmetric membranes which are characterised by the ~ following structure: The selective separating layer proper is extremely thin - and merges almost continuously into an underlying layer of the same material which has a porous structure and serves as a substrate or supporting layer.
One advantage of such membranes is that all the substances are separated on . the surface of the membrane, where they can be removed by the stream of solut~supplied. The life of the membranes is thereby increased since the membranes cannot so readily become blocked.
To determine the membrane properties, the completed membrane is applied to a porous sintered plate of metal on which a filter paper is placed, and the whole arrangement is inserted in a pressure filtration apparatus in which various solutions of test substances in water are pumped over the mem-brane surface at room temperature and at various pressures. The pump output is 21.5 litres per hour and the effective membrane surface about 40 cm2.
The throughput of water, in terms of litres/m2 per day ~= 1/m2d) ,. ~ . . ... .. . .

~' - ' - -, -is a measure of the filtration power of the membrane. The percentage reten-tion is normally defined as follows:
Concentration of dissolved , substance in filtrate '~ Retention = 1 - x 100.
Concentration of dissolved ' substance in starting solution '. The membranes according to the invention have a high permeability . ~
: to water but at the same time they are capable of separating substances having 10 a molecular weight of 500 from substances having molecular weights in the 2 region of 100. The molecular weight of the dissolved component of components ! iS to be regarded as a measure of the retention or separation.
These membranes are used for the concentration, removal or recovery '~
of various substances from aqueous solutions by reverse osmosis, ultrafiltra- '' tion or similar processes. The present invention also relates to the use of the membranes.
,~.
,, The percentages given in the Example are percentages by weight un-less otherwise3indicated.
~, Example 1 i.
' 20 2.2 kg of 3- amino-N-~phenylsulphonyl)-benzene sulphonamide and 2.8 ,, kg of maleic acid anhydride are heated to about 110 to 120C and 2 ml of tri-ethylamine are added as catalyst. After about 2 hours, the temperature is t slowly raised to 150C and excess maleic acid anhydride is distilled off , ''under'vacuum. The reaction mixture is then cooled to 110C (an isolated sample of 3-maleic acid-amonoamidebenzene-benzene-disulphimide melts at 185C) and 4.5 kg of acetic acid anhydride and 490 g of sodium acetate (an-hydrous) are added. After about 40 minutes at 100C, acetic acid and anhy-dride are distilled off at 20 Torr so that the crude product crystallizes.

~. -' , ~- ~ ,,,:

~ 9749 ':
The residue i5 then treated with about 5 litres of isopropanol and suction-filtered, The yield of 3-maleic imido-benzene-benzene-disulphimide is 2.3 kg, corresponding to 84% of the theoretical yield;
Mp 157 - 160C.
IR: VcO = 1720 (s)/1785 (w) cm ' The yields in Examples 1 and 2 are based on the quantity of 3-amino-N-(phenylsulphonyl)-benzene sulphamide put into the process.
:` Example 2 . .
40 g of 3-amino-N-(phenylsulphonyl)-benzene sulphonamide and 25 g of methyl maleic acid anhydride are heated to 120 - 130C, and a small quan-tity of triethylamine is added as catalyst. After about 2 hours, the tempera-ture is raised to 175C and excess methyl maleic acid anhydride is distilled off under vacuum. When distillation is completed (an isolated sample of 3-methyl-maleic acid-monoamido benzene-benzene-disulphimide melts at 165C), 94 g of acetic acid anhydride and 9 g of sodium acetate are added at about 90C. The reaction mixture is cooled after about 30 minutes and the solid product is suction-filtered and washed with isopropanol. Yield of 3-methyl-maleic-imidobenzene-benzene-disulphimide: 44 g, corresponding to 90% of the theoretical yield;
Mp(isopropanol) = 171C.
IR: VcO = 1720 ~s) : 1775 (w) cm Example 3 5 g of 3-maleic-imidobenzene-benzene-disulphimide from Example l and 20 g of methacrylic acid are dissolved in 30 ml of methanol and heated under reflux after the addition of 0.5 g of azodiisobutyronitrile. Poly-merisation is stopped after 80 minutes and the viscous solution is added dropwise to acetone to precipitate a polymer product. The product is , .
- , -:~: :.

11~9749 ~ `
purified by redissolving it in methanol and precipitating it from acetone. A
copolymer consisting of 15% by weight of 3-maleic-imidobenzene-benzene-di-sulphimide units and 85% by weight of methacrylic acid units is obtained. The ! amounts incorporated were determined in each case from the S-analysis data.
. ~
~ Example 4 ,.
`~ 5 g of 3- maleic-imidobenzene-benzene-disulphimide and lOg of meth-acrylic acid are copolymerised in the same way as in Example 3. The copolymer contains 24% by weight of 3-maleic-imidobenzene-benzene-disulphonimide units and 76% by weight of methacrylic acid units.
` 10 Example 5 A.) Copolymers of 3-maleic-imidobenzene-benzene-disulphimide (sodium salt) with acrylonitrile 53 g of acrylonitrile and 5.9 g of a compound corresponding to the .,~
~ J following formula:
~ .
O

~, are heated to 60C in 760 ml of water. The pH is then adjusted to 3 with dilute sulphuric acid and polymerisation is started by the addition of 0.7 g i~ of potassium peroxodisulphate and 2.9 g of sodium sulphite. After 5 hours, ~~.
, the precipitated copolymer is suction-filtered, washed until neutral and .. i . .
drled. The copolymer contains about 94.6% by weight of acrylonitrile units and 5.4% by weight of built-in units of 3-maleic-imido-benzene-benzene-di-' sulphimide (sodium salt) determined by sulphur analysis.
, ~
'~ nrel 2.70 ~0.5 g/100 ml in N-methyIpyrrolidone) l The sodium salt of maleic-imidobenzene-benzene-disulphimide is obtained '4 ~'~ from the aqueous solution of the disulphimide by the addition of aqueous ~3 .~., ~t , ~` :.: ~ ,.

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sodiu~ ydroxide alld concelltratioll o~` thc a(lucous solutio~l I)y evaporatior~
followed by crystallizatio B.) Production of membrane A solution was prepared from 15 g of the polymer described above, 4.5 g of CaC12 and 130.5 g of N-methyl pyrrolidone by stirring and heating to 60C. A casting solution ready for use was obtained by filtration and re-moval of any remaining air bubbles.
A film 250 ~ in thickness was applied to a glass plate and then heated to 50C on a hot plate for 20 minutes. After a cooling phase of 10 minutes~ the film was immersed in an ice/water bath and left therein for 30 minutes. During this time, the film became detached from the glass plate.
The finished membrane was stored in water at room temperature.
The results obtained from examination of the membrane are shown in the following Table:

Substance Concentration Retention Through-% % flo~
l/m d NaCl 1 0 Sodium lauryl sulphate 1 73 3100 Congo red 0.1 99.9 3400 Pressure: 20 bar Example 6 A) Co olymerisation of 3-maleic-imidobenzerie-benzene-disulphimide with acryl-P
onitrile 53 g of acrylonitrile and 13.25 g of 3-maleicimide benzene-benzene-disulphimide are dissolved in 760 ml of water. The pH is adjusted to 3 with 1~9~

dilute su]plluric acid .Illd pOlylllC'risatiOIl i'; st.lrtecl ~It 60( by tile addition of 0.7 g of potassium peroxodisulphate .~nd 2.9 g of sodium sulphite. ~ftcr 5 hours, the precipitated polymer is suction-~iltered, washed and dried. It contains approximately 91.8% by weig}lt of built-in acrylonitrile units and 8.26 by weight of built-in Lmits of 3-maleic-imidobenzene-benzene-disulphimide.
n 1: 2.65 ~0.5 g/100 ml in N-methyl pyrrolidone).
B) Production of membrane 10 g of the polymer described above, 3 g of CaC12 and 87 g of N-methyl pyrrolidone were used to prepare a casting solution. The casting so-lution was cast to form a film 250 LI in thickness which was dried at 60C
for 20 minutes.
The membrane is found to have a retention of 99.9% ~Congo red, 0.1%)and a permeability to water of 2,100 1/m2/d at a pressure of 20 bar.
Example 7 A.) Copolymerisation of 3-maleic-imidobenzene-benzene-disulphimide with .
acrylonitrile and methyI methacrylate 53 g of acrylonitrile, 3.12 g of methyl methacrylate and 6.25 g of

3-maleic-imidobenzene-benzene-disulphimide are dissolved in 780 ml of water under nitrogen at 60C and the pH is adjusted to 3 with dilute sulphuric acid.
After the addition of 0.7 g of potassium peroxodisulphate and 2.9 g of sodium sulphite, the reaction mixture is stirred for 5 hours at 60C, suction-fil-tered, washed until neutral and dried.
el: 1.98 ~0.5 g/100 ml in N-methyl pyrrolidone) B.) Production of membrane 20 g of the polymer described above and 6 g of CaC12 were dissolved in 174 g of N-methyl-pyrrolidone. A 250 LI film was prepared from this cast-ing solution and dried at 60C for 10 minutes.

11~ 9 At a pressure of 2Q bar, the membrane was found to have a through-flow rate of 3,5Q0 1/m2/d and a retention to Congo red (0.1%) of 99.9%.
Comparison Example :`
12 g of a homopolymer of acrylonitrile are dissolved in 84.4 g of N-methyl pyrrolidone with the addition of 3.6 g of CaC12. A film 250 ~ in thickness was formed from this casting solution on a glass plate and the sol-:~ `
.,1i vent was then evaporated off by heating to 70C for 20 minutes, and the film . was immersed in a precipitation bath (ice/water). The rate of throughflow of water at 20 bar was found to be only l,lO0 l/m2/d, and the retention of Congo ~^~ lO red was 99.9%.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A semi-permeable membrane prepared from a copolymer consisting of copolymerized units of (A) 50 to 99% by weight of acrylonitrilel (B) 1 to 50% by weight of at least one monomer of the formula wherein Ar is a benzene or naphthalene group;
R1 to R4 are identical or different and each is H, or lower alkyl; and X is H, Na, K OT NH4; and (C) 0 - 30% by weight of at least one other olefinically unsatur-ated monomer which is copolymerisable with acrylonitrile, the sum of the percentage contents of (A) to (C) being in all cases 100.

2. A semi-permeable membrane as claimed in claim 1 wherein component (B) is 3-maleic-imidobenzene-benzene-disulphimide.

3. A semi-permeable membrane as claimed in claim 1 wherein component (B) is 3-methyl maleic-imidobenzene-benzene-disulphimide.

4. In a reverse osmosis or ultra-filtration process comprising passing a solution under pressure over the surface of a semi-permeable membrane to separate solvent and solute, the improvement comprises the semi-permeable membrane being prepared from a copolymer consisting of copolymerised units of (A) 50 to 99% by weight of acrylonitrile, (B) 1 to 50% by weight of at least one monomer of the formula wherein Ar is a benzene or naphthalene group;
R1 to R4 are identical or different and each is H, or lower alkyl; and X is H, Na, K or NH4; and (C) O - 30% by weight of at least one other olefinically unsatur-ated monomer which is copolymerisable with acrylonitrile, the sum of the percentage contents of (A) to (C) being in all cases 100.

5. The process according to claim 4 wherein component (B) of said copolymer is 3-maleic-imidobenzene-benzene-disulphimide.

6. The process according to claim 4 wherein component (B) of said co-polymer is 3-methyl maleic-imidobenz.ene-benzene-disulphimide.

FEATHERSTONHAUGH ? CO.
OTTAWA, CANADA
PATENT AGENTS