AU618032B2 - Separating water soluble polymers - Google Patents

Description

I I i r 1 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE USE Class 6180V Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name of Applicant: ALLIED COLLOIDS LIMITED 0 "Address of Applicant: t

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44* t Actual Inventor(s) t «Address for Service: It I I I It P.O. Box 38, Low Moor, Bradford, West Yorkshire, BD12 OJZ,

ENGLAND.

DAVID FARRAR MALCOLM HAWE DAVIES COLLISON, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Complete specification for the invention entitl.ed: "SEPARATING WATER SOLUBLE POLYMERS" The following statement is a full description of this invention, including the best method of performing it known to us 1 -la- "SEPARATING WATER SOLUBLE POLYMERS" It is well known that low molecular weight water soluble polymers, and especially such polymers containing acidic groups that may have been partially or completely neutralised, are of value as pigment dispersants (including grinding aids). The polymers generally have a molecular weight (weight average molecular weight, Mw) of 1,000 to 10,000. However, the polymer will always consist of a blend of molecules of differing molecular weights, according to the number of monomeric units in each molecule. In practice, each conmercial polymer is a mixture of molecules having a very wide variation in chain length. For instance a polymer having Mw 5,000 will generally contain significant amounts of molecules of molecular weight below 1,000 and above 6,000. The extent to which any particular product is formed of molecules of a range of chain lengths is measured by its 20 polydispersity. The polydispersity (PD) of a product is 0a 0 0 the weight average molecular weight (Mw) divided by the o number average molecular weight (Mn) If PD 1 then the polymer consists entirely of molecules of a single 'chain length. In practice PD is always much higher, "o 25 generally above 2.

British Specification No. 1414964 describes certain 0: vinyl acetate copolymers for dispersing chalk. In example 2, the polymers are described as having a number average molecular weight of 1,200 to 2,300 and fractional 30 precipitation of the polymer is said to give fractions having number'aerrage molecular weight of 150 to 4,000.

Slightly different process conditions in Example 3 are said to give a narrower molecular weight distribution and fractions of from 960 to 3,000. The range of molecular weight within each fraction is not quoted. The specification does not disclose the use or properties of any of these fractions but it does attempt to show the polymer of Example 3 (that is a blend of fractions having average molecular weights of 960 to 3,000) has better properties than the product of Example 2 and attributes this to the "effect of optimising the molecular weight distribution". Since the polymers of Examples 2 and 3 could be split into polymer fractions having such a wide range of molecular weights, it is clear that the polymers of Examples 2 and 3 both had high polydispersity values, probably of the order of 2. It is impossible to predict what the polydispersity values would have been of the polymer fractions, as this can vary according to the method of fractionisation, but it was probably in excess of 1.7. There is no suggestion to use the polymer fractions for any purpose.

The products that commercially are most successful as dispersants are polyacrylic acid and acrylic acid S2-acrylamido 2-methyl propane sulphonic acid (AMPS) copolymers. A widely used polyacrylic acid (as the S°4 sodium salt) is our product Dispex N40 (Dispex is a trade ao mark). The products we sell generally have o polydispersity values above 1.8 and indeed most products that are commercially available have polydispersity values above 2. We have regarded it as uneconomic and unnecessary to strive for lower polydispersity values and 904, although batches of polymer having polydispersity o slightly below 1.8 are sometimes made by us, during storage they always become blended with batches having 30 higher polydispersity.

It is standard practice to make water soluble acidic polymers, such as polyacrylic acid, by solution polymerisation in which event the solvent may be a blend of water and an organic liquid such as isopropanol. The

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product of the polymerisation is a solution of polymer together with some oligomer and unreacted monomer.

One process that we have used for removing th unwanted low molecular weight components, i.e. the oligomers and monomer, has involved adding excess sodium hydroxide to the solution so as to neutralise all the acidic groups, and allowing the mixture to separate into an upper isopropanol fraction containing the unwanted low molecular weight components and a lower aqueous fraction containing the desired polymer. This fractionation has been regarded merely as a way of separating the useful polymer from the unwanted by-products. The useful polymer is a blend of molecules of various molecular weight' and the PD values quoted above are of the purified polymer.

A particular process for separating unwanted by-products is described in European Patent Publication 46573. In this it is said that an aqueous solution of polyacrylic acid may be neutralised and that the neutralised polymerisate may then be treated in the usual S 20 way with polar solvents, fethanol, ethanol, propanol, isopropanol, acetone and tetrahydrofuran being mentione,.

In the examples 80 grams fully neutralised sodium polyacrylate is fractionated in solution in 500 grams water with 400 grams methanol or 40 grams isopropanol.

In each instance the lighter, organic, phase is rejected.

This therefore seems to be a conventional fractionation I I, Ito remove oligomers and the product would therefore be a I conventional blend of molecular weights. If the starting polymer mixture is conventional the Mw, Mn and PD values 30 of the extracted polymer will also be conventional, e.g.

PD above 1,8.

The same patentees have published in their later British Patent Specification 2109363 a generally similar p:o disclosure of treating the aqueous polymerisate with polar solvents except that no process details are given yl li-.lr---i^ii-i-111and in this example the organic fraction is said to be a useful product having a molecular weight distribution ranging between 400 and 1,200 and the aqueous fraction is said to have a molecular weight ranging between 1,200 and 12,000.

Whenever a water soluble acidic polymer is made it is generally used in the form of a fully neutralised salt although in some instances a partially neutralised salt or the free acid may be used. The polymer may be supplied to the user as a solution, for instance as a solution in which it was made initially, optionally after distilling any organic solvent from the solution, or the polymer may be separated from the solution, for instance by precipitation by the addition of an insolubilising material, such as excess acetone.

It is well recognised that minor variations in the polymerisation 4,o conditions used for making the polymer can greatly affect the activity of the product for any particular purpose, and so manufacturers exercise great care in optimising their process conditions to make a product that has optimum 15 activity for its intended purpose.

The invention provides a method for separating a water soluble polymer containing acid groups into higher and lower molecular weight fractions, 0" 0 preferably at least one of which has polydispersity below 1.5. The method comprises forming a solution of the polymer in a blend of a polar organic solvent, water and base in an amount sufficient to neutralise at least 10% but not more than 90% molar of the said acid groups and the solvent, the base 9 4 and the amount of base and/or the amount of solvent are selected to cause phase separation of the solution into an aqueous phase containing a higher molecular weight fraction and an organic phase containing a lower S4 910827Csdat.122,28es 0IO molecular weight fraction and subsequently both these fractions are used.

The precise split between the lower and higher molecular weight fractions can be selected by altering the process conditions, and in particular the degree of neutralisation, and so the method provides, for the first time, a simple process by which an acidic, water soluble, polymer can be fractionated into preselected molecular weight fractions. Unlike prior processes where the organic fraction is usually rejected, in the invention both fractions of polymer are commercially useful and so are recovered and used, the fraction in the organic phase being useful where lower molecular weights are desired and the fraction in the aqueous phase being useful where higher molecular weights are desired.

Additionally we have surprisingly found that the polymer in each fraction generally has at least one activity that is very much improved compared to the activity of the starting polymer. Often the polymer of one fraction has one type of greatly improved activity (for instance as a viscosifier) while the polymer: in the other fraction may have a different type of greatly improved activity (for instance as a dispersant). The method is of particular value for making polymeric dispersing agents as described in our parent application 35611/84.

The polymer in each fraction will have lower polydispersity (weight average molecular weight divided by number average molecular weight) than the starting polymer. For instance the initial value is almost always above 1.6, and often is above 2, but the fractions obtained may both have values of below 1.5, often 1.05 to 1.45 and most preferably 1.1 to 1.4.

Each of the polymer solutions can be used in the form in which it is obtained by phase separation, for

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instance simply by mixing the solution into the water or other liquor to be treated, or the polymer can be recovered from the solution by evaporation, precipitation or other conventional recovery techniques. The polymer in each of the separated solutions is generally in a partially neutralised state and can be acidified or fully neutralised in conventional manner if desired.

The process conditions that can be altered to affect the split between lower and higher molecular weight fractions include the choice of solvent, the choice of base, the amount of solvent and the amount of base. Once one has appreciated the novel concept that it is possible to fractionate usefully provided the acidic groups are partially neutralised, as opposed to full neutralisation in the prior art, it is possible to obtain any particular desired split or fractionation by appropriate selection of solvent, base, and amounts of each.

The particular solvent may have to be selected having regard to the nature of the polymer, and in 20 particular its molecular weight. For instance the polar solvents are generally selected from C 1 5 alcohols and

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3 8 (generally C 3 or C 4 aliphatic ketones, most preferably isopropanol or acetone. Although the alcohols are very suitable for a wide range of polymers they are of particular value for the lower molecular weight polymers, molecular weight preferably below 100,000, most preferably below 30,000 and, especially, below 10,000.

In contrast, the ketones are primarily of value for fractionating higher molecular weigit polymers, for instance having average molecular weight above 50,000, generally above 100,000 and preferably above 200,000 or even 500,000.

In one preferred process of the invention a solution is formed in a blend of water and a polar solvent of a water soluble polymer containing neutralised acid groups Y 4 4 -7 and the solution is separated into an aqueous phase containing a higher molecular weight fraction of the polymer and an organic phase containing a lower molecular weight fraction of the polymer, and in this process the polar solvent is a C 1 to C s alcohol, the acid groups are neutralised with cations selected from sodium, potassium, lithium and ammonium and the molar proportion of neutralised acid groups is 10 to 55% when the cation is selected from sodium and potassium, 10 to 70% when the cation is ammonium and to 90% when the cation is lithium.

The polymer may have been made by any conventional polymerisation process and may have then been isolated, for instance as a solid, from any liquid phase in which it was formed, and then redissolved in the aqueous organic solution containing base used in the invention. Generally however the process of the invention is conducted on a solution of the polymer obtained by solution polymerisation of the appropriate monomers. The preferred solution 15 polymerisation medium is an aqueous solution containing appropriate initiators or other polymerisation promoters, for instance water soluble peroxides and persulphates, or redox catalysts or catalysts for photopolymerisation and will generally include an organic solvent, for instance as a molecular weight 4 SC: regulator. Other known molecular weight regulators that provide terminal -COOM, -OH or C 13 alkyl groups) may be included in the solution if desired.

C 06 Preferably the acidic polymer is a polymer obtained by polymerising monomers selected from acrylic acid, 2-acrylamido-2-methyl propane sulphonic acid, 2-acry!amido-2-phenyl propane sulphonic acid, methacrylic acid, itaconic acid, vinyl sulphonic acid, vinyl sulphuric acid, allyl sulphonic acid, maleic acid, 4 .fumaric acid and crotonic acid.

The solution polymerisation may be conducted in the presence of the amounts of solvent, base and water required for the fractionation provided the polymerisation is conducted with sufficient agitation to prevent separation during polymerisation, the polymerisation mixture then being allowed to stand to allow separation to occur. Generally however the 910826,casdat122,25080-3

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7 hi I ii Ne.l:;;LU; polymerisation is conducted in the presence of amounts of solvent, base and water such that separation will not occur and these amounts are then adjusted after polymerisation to cause separation.

In one process the solution of polymer is made by polymerisation in a mixture of water and organic solvent and this organic solvent may serve as the organic liquid for use in the invention. Generally this solvent should be fully miscible with the aqueous polymer solution, e.g.

an alcohol or acetone. A very common solvent in solution polymerisations is isopropanol and blends of water and isopropanol are often very suitable in the invention. When polymerisation is conducted in the presence of the chosen solvent fractionation can then be brought about by appropriate adjustment of the amount of cation in the solution. With many monomers the polymerisation is generally conducted on the free acid o o form of the monomers in which event the base adjustment .is effected by adding the appropriate amount of alkali or 20 other source of cation. If the polymerisation is carried out on a wholly neutralised form of monomer (e.g.

I "in the polymerisation of sodium vinyl sulphate) then the cation adjustment can be brought about by adding sufficient free acid to partially acidify the neutralised groups, thereby forming a polymer having the desired degree of neutralised groups. The free acid must be sufficiently strong to acidify the neutralised polymer acid groups. Often it is a mineral acid such as hydrochloric or sulphuric acid. The free acid may be the free acid form of the acidic polymer or it may be a water insoluble acidic polymer, preferably an anionic (generally sulphonic or other strong acid) ion exchange resin.

In another process the polymerisation is conducted in the presence of base in an amount sufficient to iarr.rPislr*ur;xr;r ih neutralise 10 to 90% of the acid groups and then the phase separation is caused by adding the polar solvent in the required amount. If the amount cf cation in the polymerisation mixture is not the optinum for the phase separation then additional base for acid) may be added with the polar solvent to achieve the desired degree of neutralisation.

Irrespective of whether the solution is made by blending preformed polymer, water, organic solvent and base or by adding base to the reaction product of polymerisation in aqueous organic liquid, or in any other manner, the process of the invention requires that phase separation should be brought about between aqueous and organic phase in the presence of the specified solvents and the required amounts of the cations.

The bases are preferably basic compounds of nonovalent cation is such as sodium, potassium, lithium and ammonium, preferably in the amounts quoted above since in general we find that with most solvents amounts 20 outside these ranges give less satisfactory fractionation. Lower alkyl amines ethylamine) may *be suitable for some polymers, as may basic compounds of multivalent cations (provided the amount and type of cations does not result in precipitation of the polymer).

Suitable multivalent cations include Ca, Zn, Cu, Mg and Al. The basic compounds may be, for example, oxides, hydroxides, carbonates, bicarbonates, alkoxides, phosphates, hydrogen phosphates, phosphonates, polyphosphates or organic carboxylic salts where the organic acid is weaker than the polymeric acid, e.g.

sodium acetate, adipate or citrate when the polymeric acid is a sulphuric or sulphonic acid.

The degree of neutralisation of the acid groups controls the fractionation. The results obtained in any particular process will depend upon, inter alia, the T 17 i i concentrations, the polymer type and the solvent but there is a mininum degree of neutralisation below which substantially no fractionation occurs and the system may instead remain as a homogeneous solution. When the cation of the base is sodium, potassium or lithium the degree of neutralisation will normally be at least 10%, often at least 15% and preferably at least whilst if the cation is lithium the degree of neutralisation will normally have to be at least about 30%, preferably at least 40% and generally at least 50%. If the degree of neutralisation is too high the size of the lower molecular weight fraction is unacceptably low. When the cation of the base is sodium or potassium the degree of neutralisation will normally be below 55%, preferably below 50% and most preferably below 40%. When the cation of the base is ammonium the degree of neutralisation will normally be below preferably below 60% and most preferably below 50%. When the cation of ~the base is lithium the degree of neutralisation will normally be below 15 90%,and preferably below S* In any particular process the size of, for instance, the higher molecular weight fraction can be increased (with consequential reduction in its average molecular weight and consequential reduction in the size and the average molecular weight of the lower molecular weight fraction) by increasing the amount of base and conversely the size of the low molecular weight fraction r. can be increased by reducing the amount of base.

The process conditions are preferably selected such that each fraction contains from about 10 to 90%, more preferably about 20 to 80%, and most preferably 30 to 70%, by weight of the starting polymer.

The partial neutralisation of the acidic polymer is normally achieved by adding a hydroxide or other base that will provide the chosen cation in the selected amount to the dissolved polymer. Mixtures of two or more cations may be utilised, in which event the proportions will be selected such that they have the same effect as suitable amounts of the individual cations.

For any partkiular polymer, the degree of fractionation is dependent not only on the degree of neutralisation and the type of cation but also upon the coincentration of the polymer and the choice and amount of the alcohol or A f" 0 ,o w o CA.

o" .".,910826,as dat,122;2S0.re ,3 t 1 -11other solvent. The alcohol is preferably isopropanol but propanol and other alcohols, especially C to C s alcohols, may be used. The proportion water:alcohol or other solvent be weight is preferably from 1:0.2 to 1:5, most preferably 1:0.5 to 1:2 with best results generally being achieved, especially when the solvent is isopropanol and the cation is sodium, when the j. I~ rtion is about 1:1. The proportions should preferably be selected such that, having regard to the degree and nature of neutralisation, each of the phases will have a polymer concentration of at least more preferably at least 10% and most preferably at least 15% by weight of the phase.

The amount of the polymer (measured as the acid polymer) is normally I at least 5% by weight based on the weight of polymer, solvent and water (including water introduced with the alkali) and preferably is at least The concentration is preferably not so high that the system is so viscous that mixing and phase separation is significantly impeded and so is preferably below 15 30%. More preferably the concentration is 15 to 25% by weight, The phase separation may also be affected by the temperature at which the process is conducted. This is preferably between 15 and 80 *C but more b preferably is between 30 and 70 OC.

The process may be conducted by combining the essential components of the solution in any convenient manner, for instance by adding aqueous alkali to the C. I aqueous organic reaction product obtained by polymerisation of the monomer or monomers in aqueous organic solution. The process may be conducted continuously or batchwise. Depending upon the degree of neutralisation, and type and strength of base, the concentration of the polymer, the amount of solvent and the temperature the phase separation may occur rapidly or slowly. For instance it may occur substantially instantaneously or it may be necessary to leave the system to stand for periods of, for instance, 5 minutes to 2 hours, typically 30 minutes to 1 hour. The separation may be conducted batchwise or continuously.

with the mix being fed through a conventional separation column or separation reactor.

The two phases are kept separate, may be fully neutralised with the same or different alkali and organic solvent may be stripped from the organic phase by distillation.

Each of the polymer fractions is recovered for subsequent commercial use.

Very low molecular weight fractions obtained by this technique have a particular value as agents for inhibiting the build-up of scale, and settlement of scale, and in particular as antiscalants. For instance we have established that the maxim'm level of alkalinity that can be maintained in solution is increase PD is reduced. Thus best results are achieved if Mw ±I from 350 to 1,000 and PD is below 1.5, most preferably 1.05 to Si 1.3.

EXAMPLE 1 A 23% by weight solution of polyacrylic acid in a blend of equal parts by weight isopropanol and water was prepared by polymerisation of acrylic acid using ammonium persulphate as initiator, in conventional manner.

Samples of the product were extracted while other samples ^I -"ltlwere neutralised by the addition of varying amounts of sodium hydroxide, introduced as a 46% by weight aqueous solution. Each of the samples, after the addition of sodium hydroxide, was allowed to stand for sufficient time for an aqueous phase to separate from an organic phase (that probably contained some water) and these phases were then separated from one another in conventional manner. Each phase was then fully neutralised with sodium hydroxide and the residual alcohol was removed by distillation. The yield of polymer in each of the phases was recorded.

EXAMPLE 2 A 20% solution of polyacrylic acid having Mw of 3131 and PD (polydispersity) of 1.677 was dissolved in 50/50 w/w isopropanol/water was neutralised with various basic compounds and the two layers separated. The amount and molecular weight of the polymer in each layer was 0oo determined. The results are shown in Table 1.

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0 4 4 a, SE It t #4 t TABLE 1 Aqueous layer Organic layer Base Neutralisation Extracted Mw P.D. Extracted Mw P.D.

NaOH NH 4OH LiO1 LiOH KOH1- NaOF NacOi NaOH 75. 2 3833 55.6 4025 NO SEARATION~ 50.2 3957 63.5 3649 20.6 3976 95.7 3688 99.3 3376 1.30 1,*30 1.427 1.56 1.49 1.51 1.53 24.8 44.4 49.8 36.5 79.4 4.3 0.7 1452 1689 1.402 1.34 1783 1.44 1402 1.49 2027 1.63 Very lowq Very low~ EXAMPLE 3 The products obtai4ned in Example 1 were adjusted to I active solids and compared as marble grinding aids as described in Example 11 of British Patent Specification No. 1,414,964. The results are set out in Table 2.

20 TABLE 2 Percent Yield Percent Aqueous Layer Neutralisation Organic Aqueous Milling indiex 10 87.2 12.8- 79.3 2.0.7 23.1 76.9 1 .94 4.0 96.0 2.33 0.7 99.3 1.22 100 0.5 99.5 0.37 In the described test a milling index value of around 0.5 is generally satisfactory as it indicates acceptable properties for preventing gel~ation of the marble dispersion.

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r a 'I *9r 9 90 4951 *4 I;

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It is apparent from the table that after full neutralisation almost all the polymer is in the aqueous phase but that substantial amounts of polymer go into the organic phase at low degrees of neutralisation. It is also very notable that the milling index is greatly improved even when the amount of polymer that is in the organic phase, instead of the aqueous phase, is quite low. For instance at 50% neutralisation the amount of polymer in the organic phase is low but the milling index is about 5 times what would be considered to be commercially adequate. At higher degress of neutralisation only a very low amount of polymer goes into the organic phase.

EXAMPLE 4 A polymer was prepared by conventional polymerisation technique as a 23% solution of acrylic acid in equal amounts of isopropanol and water was neutralised to 25% with aqueous sodiuz hydroxide after polymerisation. This caused the reaction mixture to 20 separate into two phases. These were separated and the polymer present in such phase was recovered after removal of the isopropanol by distillation. The samples were fully neutralised with sodium hydroxide solution and adjusted to 40% active as sodium polyacrylate.

An unfractionated control polymer was also prepared from the original unneutralised polymer in isopropanol/water by removing the isopropanol by distillation and fully neutralising with sodium hydroxide and adjusting to 40% active as sodium polyacrylate.

The products were evaluated as dispersants for titanium dioxide, having particle size 97% below 2 4m, at w/w slurry solids content by recording the slurry viscosity (cP) at 0.6, 0.8 and 1% dry polymer based on dry pigment. The results are given in Table 3.

'--C-Fl~llll -3 ll~ 111119Ll~lC~3 s i 6CI--.

TABLE 3 Neutralisa- Mw Mn PD Slurry Viscosity (cP) tion 0.6 0.8 100 Control 3161 2019 1.565 1320 1380 Aqueous 4236 2795 1.515 2600 phase Organic 1795 1367 1.314 3500 700 340 phase EXAMPLE Other polymers are prepared by the general technique described in Example 1 but using different monomers.

SWhen the monomer consisted solely of methacrylic acid neutralisation with sodium hydroxide fractionated the 0, product into a lower molecular weight isopropanol phase that was useful as a dispersant for china clay and a oo higher molecular weight aqueous phase.

c 20 S, When the monomer consist of equal parts by weight S; itaconic acid and methacrylic acid 25% neutralisation with sodium hydroxide results in fractionation into a higher molecular weight aqueous phase and a lower molecular weight isopropanol phase.

When the monomer consisted of sodium vinyl sulphonate the initial polymer is in the sodium form and this can be part neutralised by acidic ion exchange resin I and then fractionated using isopropanol.

Claims (9)

1. A process for separating a water soluble polymer containing acid groups into higher and lower molecular weight fractions the method comprising forming a solution of the polymer in a blend of a polar organic solvent, water and base in an amount sufficient to neutralise at least 10% but not more than molar of the said acid groups and in which the solvent, the base and the i amount of at least one of the base and the solvent being selected to cause phase separation of the solution into an aqueous phase containing a higher molecular weight fraction and an organic phase containing a lower molecular weight fraction, allowing phase separation to occur, separating both fractions and subsequently using both fractions. retr

2. A process according to claim 1 comprising the preliminary step of q i S.forming the solution in the blend by polymerising water soluble acidic monomer in the blend and then adding sufficient base to partially neutralise the polymer.

3. A process according to claim 1 comprising the preliminary step of forming an aqueous solution of water soluble polymer by aqueous solution S, polymerisation of polymerisable monomers including acidic monomers in the presence of base in an amour. sufficient to neutralise from 10 to 90% of the acid groups and then adding the polar solvent.

4. A process according to any one of claims 1 to 3 in which the acidic J polymer is a polymer obtained by polymerising monomers selected from acrylic acid, 2-acrylamido-2-methyl propane sulphonic acid, 2-acrylamido-2-phenyl propane sulphonic acid, methacrylic acid, itaconic acid, vinyl sulphonic acid, vinyl sulphuric acid, allyl sulphonic acid, maleic acid, fumaric acid and crotonic acid. A process according to any one of claims 1 to 4 in which at least one of /i .l v 910827,msdat.122,25080.res,5 'T va a. I +v a r e +a I t -I 1L--l -18- the molecular weight fractions has a polydispersity below

6. A process according to claim 5 in which the polymer initially has polydispersity above 1.6 and in which both fractions have a polydispersity below

7. A process according to any one of claims 1 to 6 in which the concentration of polymer (by weight of the acid polymer based on polymer, water and solvent) is at least 10%, and each phase contains from 20 to 80% by weight of the polymer. oil 8, A process according to any one of claims 1 to 7 in which the polar solvent is a C 15 alcohol and the polymer has molecular weight below 10,000. I t S0 9. A process according to claim 8 in which the cation is selected from sodium, potassium, lithium and ammonium and the molar proportions of neutralised groups are 10 to 55% when the base is a compound containing a "1 cation selected from sodium and potassium, 10 to 70% when the base is a compound containing ammoinium and 30 to 90% when the base is a compound containing lithium. *I, A process according to claim 9 in which the solvent is isopropanol.

11. A process according to claim 10 in which the blend is a blend of 1 part water to 0.5 to 2 parts isopropanol, the polymer is present in a concentration of 10 to 30% by weight of the blend, the polymer is a polymer formed from monomers comprising acidic monomers selected from acrylic acid and 2- acrylamido-2-methyl propane sulphonic acid, and from 10 to 50% by weight of the acid groups are present as a salt with sodium, the remainder of the acid groups being free acid groups.

12. A process according to any one of claims 1 to 7 in which the polar 0t.-rS Vat 91027* -19- solvent is a C 3 8 aliphatic ketone and the polymer has a molecular weight above 50,000.

13. A process for separating a water soluble polymer containing acid groups into higher and lower molecular weight fractions, substantially as hereinbefore described with reference to the examples. *aa a 99a V II a a *g .bat stat a. a .9 9.b S I Dated this 26th day of August, 1991. DAVIES COLLISON Patent Attorneys for ALLIED COLLOIDS LIMITED Sb Sb ~t Vt a. 5 54 lb a S Sb V 4 bq5* V. ba S *4 bb bj 91GWcmsdat.122ZWxes,7