CA1265635A - Water soluble polymers - Google Patents

Abstract

ABSTRACT
WATER SOLUBLE POLYMERS
A water soluble polymer containing acid groups can be fractionated into higher and lower molecular weight fractions by partial neutralisation of the polymer as a solution in a blend of water and a low molecular weight alcohol and separating the resultant aqueous and organic phases.
Pigment dispersions contain, as dispersing agent novel water soluble polymers containing acid groups, preferably polyacrylic acid or copolymers of polyacrylic acid with AMPS, having polydispersity below 1.5 and molecular weight in the range about 1,000 to about 5,000.

Description

~26563S

This application claims a process for separating a water soluble polymer into ~ig~er and lower molecular I weight fractions. Divisional application S.N. ~9J,/~/
filed 30 May 1989 has claims directed to a dispersion of pigment, an aqueous dispersion paint and a polymeric. - -~ - dispersing agent.

It is well known that low molecular weight water soluble polymers, and especially such polymers coDtaining 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, MwJ
of 1~000 to 10,000~ ~owever, the polymex will always consist of a blend of mol~cules of diffe~ing molecular weights, according to the number of momomeric units in each molecule. .In practice, each commercial 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 amou~ts of ~olecules 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 polydispersity. The polydispersity (PD) of a product is the -weight average molecular weight (Mw) divided by the number avexage molecular weight (Mn). If PD - 1 then the polymer consists entirely of molecules of a single chain length. In practice PD is always m~ch higher, ~- generally above 2.
British Specification No. 141496~ describes certain 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 precipitation of tpe polymex is said to give fractions :~L26S635 1 (a~

having .number average molecular weight of 150 to 4, 000 .
Slightly different process conditions in Example 3 are said to give a narrower molecu.lar weight distribution and frac~ions of from ~60 to 3,00Q. The range of molecular weight within each fraction is not quoted. The specification does not disclose the_ use or properties of ~6S63~

any of these ~ractions 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 bo-th 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 -

2-acrylamido 2~methyl propane sulphonic acid (AMPS) copolymers. A widely used polyacrylic acid is our product Dispex N40 (Dispex is a *rade mark). The products we sell generally have 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 although batches of polymer having polydispersity slightly below 1.8 are sometimes made by us, during storage they always become blended with batches having 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 product of the polymerisation is a solution of polymer together with some oligomer and unreacted-monomer.

1265~i35 One process that we have used for removing the unwanted low molecular weight components, i.e. the oligomers and monomer, has invo:Lved 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 weights 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 way with polar solvents, methanol, ethanol, propanol, isopropanol, acetone and tetrahydrofuran being mentioned.
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 to remove oligomers and the product would therefore be a conventional ~lend of molecular weights. If the starting polymer mixture is conventional the Mw, Mn and PD values of the extracted polymer will also be conventional, e.g.
PD above 1.8.
Certain sulphide, sulphone or sulphoxidè terminated oligomers are described in US Patent Specification 3759860 for use as, for instance, emulsifiers. There is no suggestion that they should be used for dispersing pigments. It is said that they may have PD less than 2 "and frequently as low as 1.4 to 1.5". Apart from this ~65~

disclosure, we are unaware of anyone ever having proposed the commercial use of low polydispersity water soluble polymers for any purpose and in particular there has been no suggestion that they would be of use in pigment dispersions. Indeed since it is much easier to make polymers having high PD values than low PD values the possibility of trying to make them on a commercial scale has probably never occurred to anyone previously as no one has ever previously recognised that there is any particular value in them.
Insoluble low molecular weight polymers having low polydispersity values are described in European Patent Specification 68887 but since such polymers are insoluble they cannot be used as pigment dispersants.
We have now found that low molecular weight water soluble polymeric dispersants have greatly improved pigment dispersing properties if the polymer has a much narrower range of molecular weight than has previously been used, that is to say if PD is reduced substantially below the conventional values of 1.8 and above to a value below 1.5. Thus we have found that for any particular purpose optimum results are ob~ained if the polymer consists of molecules of very limited range of chain lengths. The prese~ce of molecules of other chain lengths is disadvantageous for two reasons. First, and most important, these other molecules counteract the beneficial effects of the preferred molecules, presumably because of preferential absorption of some other deleterious or antagonistic mechanism. Secondly, these other molecules dilute the polymer so that it contains less than the theoretical maximum of the preferred molecules.
The presen-t invention provides a new way of making polymers having improved properties, as well as particular uses of certain polymers. In the invention a ~6S635 solution is formed in a blend of water and a polar solvent of a water soluble polymer containing neutralised acid groups 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 Cl to C5 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 30 to 90~ when the cation is lithium.
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 invention 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).

1265~i35 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 in the invention often 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 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.
In the invention a dispersion of pigment in an aqueous medium contains a dispersing agent for the pigment which is a water soluble polymer formed from one or more ethylenically unsaturated monomers and contains acid groups selected from carboxyl and sulphonic groups, or is a water soluble salt thereof, and has a polydispersity of below 1.5 and has a low molecular weight. Mw is normally at least about 1,000 and can be up to about 6,000 but preferably it is up to about 5,000.
Particularly preferred products are those having PD below 1.4 and Mw 1,000 to 4,000.
Generally PD = 1.05 to 1.45 and in particular from 1.1 to 1.4. The best results are obtained with PD below 1.4 and preferably below 1.35. Although it is desirable for the value to be as close to 1 as possible it is generally acceptable for it to be above 1.25.
The polymer is preferably acrylic acid or copolymer thereof with AMPS (2-acrylamido-2-methyl propane sulphonic acicl). Throughout this specification it must ~21~56;~S

be understood that any acid polymer can be present in the form of a partial or complete salt with an alkali metal, often sodium, or ammonia or an amine or other cation that yields a water soluble salt. For instance the polymer may be a copolymer of acrylic acid with a salt of AMPS or it may be a complete salt of acrylic acid AMPS copolymer or a partial or complete salt of acrylic acid. All molecular weights herein are measured as the full sodium salt.
Although these are the pr~eferred polymers, other water soluble polymers can be used in the invention, generally being polymers obtained by polymerisation of an ethylenically unsaturated monomer that contains acid groups either alone or with other ethylenically unsaturated monomeric material. Oligomers formed from the corresponding monomers may be used in place of the monomers. The acid groups are generally carboxylic acid or sulphonic acid groups. The monomers are often acrylic monomers and therefore preferred acidic monomers include one or more of methacrylic acid or, especially, acrylic acid or 2-acrylamido-2-methyl propane sulphonic acid, but a wide range of other polymerisable acidic monomers can be used, for instance maleic a~id or vinyl sulphonic acid. Any comonomers that can be copolymerised, in the amounts present, with the acidic monomer or monomers to form a water soluble polymer can be used and include monomers such as acrylamide, acrylonitrile and acrylic esters. ~enerally at least 50% by weight and often at least 80~ by weight of the monomers from which the polymer is formed are acidic monomers. The polymer is generally a linear polymer.
Within the broad inventive concept defined above there are certain areas of particular value.
As mentioned above certain low molecular weight vinyl acetate copolymers are mentioned in British Specification ~26S6;~5 No. 1414964 for dispersing pigments and as grinding dispe~sants for pigments. In practice however these have not made any significant commercial impact and the dispersants normally used are the low molecular weight polyacrylic acids having PD generally above 1.8.
According to one aspect of the invention a dispersion in water of a pigment includes, as dispersing agent, a polyacrylic acid having PD below 1.5 and Mw in the range about 1,000 to about 3,300, preferably 1,000 to 3,000 and most preferably in the range about 1,800 to about 2,200, with best results generally being achieved at values of around 2,000. PD preferably is in the range 1.05 to 1.4, most preferably 1.1 to 1.3 or 1.35.
These dispersions can conveniently be made simply by blending particulate pigment with water in the presence of the dispersing agent, the amounts of pigment and dispersing agent being conventional. For instance the amount of dispersing agent is often from 0.05 to 0.3% by weight dry polymer based on dry pigment. The amount of pigment is often from 10 to 90% by weight of the dispersion, most preferably 50 or 60 up to 80~ by weight.
The pigment will be chosen having regard to the intended use of the dispersion. Often the dispersion is used in the paper industry, for instance for paper coating, and suitable pigments include china clay, talc, titanium dioxide and precipitated calcium carbonate. The particle size is generally in the range 0.5 to 100 microns, preferably 1 to 50 microns.
It is well recognised that there is a particular problem in making concentrated pigment dispersions by grinding calcium carbonate in water, particularly if very fine particle sizes are required. This is discussed in our European Patent Specification 108842 and in the literature to which that refers. We describe in that how sodium polyacrylate Mw 2,800 is conventionally used but ~6563~;i that improved results can be obtained using acrylic acid-AMPS copolymers, the best result (lowest viscosity) being shown at Mw around 5,700.
According to a second aspect of the invention a dispersion of calcium carbonate in water is made by grinding calcium carbonate in water in the presence of a dispersing agent that is a polyacrylic acid having PD
below 1.5 and Mw in the range ab~ut 2,500 to about 4,500, most preferably in the range 3,300 to 3,900.
According to a third aspect of the invention a dispersion of calcium carbonate in water is made by grinding calcium carbonate in water in the presence of a dispersing agent that is a copolymer of acrylic acid and AMPS having PD below 1.5 and Mw in the range about 1,500 to about 3,500, most preferably about 2,250 to about 2,750.
The preferred molecular weight for the homopolymer is about 3,600 and the preferred molecular weight for the copolymer is about 2,500. The proportions by weight of acrylic acid to AMPS are preferably 99:1 to 50:50.
When grinding calcium carbonate in accordance with either of these aspects of the invention PD is preferably from 1.05 to 1.4, most preferably 1.1 to 1.3.
The grinding is preferably by sand grinding and the resultant particle size of the calcium carbonate (marble~
is preferably mainly below 2 microns. The amount of pigment in the resultant dispersion is preferably above 70~ and most preferably is above 75%. For more description of suitable grinding techniques, particle sizes and concentrations reference should be made to European Patent Publication 108842 and to the literature referred to therein.
In US Patent Specification 3840487 and in British Patent Specification 1505555 various aqueous dispersion paints comprising of pigment and a low molecular weight ~21Ei563S

polymeric dispersing agent are described. For the purposes described in those specifications particular polyacrylic acid-ester copolymers are used but in many other instances polyacrylic acid homopolym~r, and in particular Dispex N40 is generaLly regarded as entirely satisfactory. We now find better results are obtained using the novel polymer defined herein. In particular, according to a fourth aspect of the invention an aqueous dispersion paint comprises a pigment, a binder for the paint and a dispersing agent for the pigment, the dispersing agent being polyacrylic acid having PD below 1.5 and Mw in the range about 1,500 to about 6,000. PD
is preferably from 1.05 to 1.4, most preferably 1.1 to 1.3 and the molecular weight` is preferably in the range 1,500 to 4,500. The aqueous medium of the paint may be water or a mixture of water with a polar solvent, generally a glycol.
The pigment generally is titanium dioxide, china clay, or calcium carbonate and generally has a particle size of 0.1 to 50 microns, preferably 0.2 to 25 microns.
The amount of pigment in ~he paint may be conventional, typically from 5 ~o 50% by weight of the paint. The binders and other components in the paint may be conventional, for instance as described in US Patent Specification 3840487 and British 1505555.
The low polydispersity values required in the invention can be obtained by various techniques. For instance, a polymer can be made by a conventional polymerisation technique, for instance, solution polymerisation, to obtain a product having a high polydispersity value (typically 2 or higher) and may then be subjected to careful fractional precipitation so as to obtain fractions each having a polydispersity below 1.5.
The conditions for conducting the fractional precipitation must be such as to give this low ~26563~;

polydispersity and so must consist of i~othermal non solvent addition as detailed in Chapter B1 of "Polymer Fractionation" Ed. Manfred Cantow.
Another way of obtaining the desired polymer is to conduct its synthesis under conditions that lead to its formation. For instance the polymer may be made by solution polymerisation in the presence of isopropanol as chain regulator. The process must be carried out under very uniform and closely monitored conditions, for instance controlled feeds of monomer~ and initiator and uniform temperature throughout. If the product tha* is obtained has a polydispersity above the desired value it must be rejected or treated in such a manner as to reduce its polydispersity.
Another way of obtaining the desired polymer is to make an insoluble acrylate polymer having the desired PD
and Mw valuesl for instance as described in Example 40 of European Patent Specification 68887 and then to hydrolyse the acrylate to the free acid, ~or instance by reaction with sodium hydroxide at 85~C for 6 hours or as long as is necessary to achieve hydrolysis, the reaction generally being conducted in the presence of methanol as a diluent.
The preferred method is the method described above.
~5 This may be conducted on any of the polymers discussed above.
The average molecular weight of the polymer that is to be fractionated can vary widely provided the value is not so high that the polymer is insoluble. Generally it is 500 to 1 million and the most valuable advantages are found when the average molecular weight is below 100,000, generally bel~w 30,000 and especially between 1,000 and 10,000 for instance around 1,500 to 4,500.
The polymer may have been made by any conventional polymerisation process and may have ~hen been isolated, 12~i56~S

for instance as a solid, from any liquid phase in which it was formed, and then redissolved in the aqueous organic alkaline solution used in the in~ention.
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 polymerisation medium is an aqueous solution containing appropriate initiators or other polymerisation promotors, 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 regulator. Other known molecular weight regulators may be included in the solution if desired.
When the solution of polymer is made by polymerisation in a mixture of water and organic solvent this organic solvent may serve as the organic liquid for use in the invention. A very common solvent in solution polymerisations is isopropanol and blends of water and isopropanol are suitable for many processes according to the invention.
Irrespective of whether the solution is made by blending preformed polymer, water, organic solvent and alkali or by adding alkali 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 specified amounts of the specified-cations. If other solvents, other cations or other amounts of the specified cations are used the process generally will not give the variable fractionation of the invention but instead will either give no useful results or will merely strip oligomer and monomer from the product, For instance it is not possible to select the degree of ~2651~3~;

fractionation if the organic solvent is acetone or tetrahydrofuran or if the cation is provided by an amine such as ethylamine.
The degree of neutralisation of the acid groups controls the fractionation~ The results obtained in any particular process will depend upon, inter alia, the concentrations, the polymer type and the solvent but there is a minimum degree of neutralisation below which substantially no fractionation occurs and the system may instead remain as a homogeneo~s solution. When the cation is sodium, potassium or lithium the degree of neutralisation will normally be at least 10%, often at least 15~ and preferably at least 25~ 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 is sodium or potassium the degree of neutralisation will normally be below 55%, preferably below 50~ and most preferably below 40%. When the cation is ammonium the degree of neutralisation will normally be below 70%, preferably below 60% and most preferably below 50%. When the cation is lithium the degree of neutralisation will normally be below 90~, and preferably below 70~.
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 alkali and conversely the size of the low molecular weight fraction can be increased by reducing the amount of alkali.

~2656~5 The process conditions are preferably selected such that each fraction contains from 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 compound that will provide the chosen cation, the compound usually being a hydroxide, in the selected amount to the dissolved polymer. Mixtures of two or more of the four cations may be utilised, in which event the proportions will be selected such that they have the same effect as the amounts specified for the individual cations.
For any particular polymer, the degree of fractionation is dependent not only on the degree of neutralisation and the type of cation but also upon the concentration of the polymer and the choice and amount of the alcohol. The alcohol is preferably isopropanol but propanol and other alcohols, especially C2 to C5 alcohols, may be used. The proportion water:alcohol by 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 alcohol is isopropanol and the cation is sodium, when the proportion is about 1:1. The proportions should 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 5%, generally at least 10% and preferably at least 15% by weight of the phase.
The amount of the polymer (measured as the acid polymer) is normally at least 5% by weight based on the weight of polymer, alcohol and water (including water introduced with the alkali) and preferably is at least 10%. The concentration must not be so high that the system is so viscous that mixing and phase separation is significantly impeded and so is generally below 30~.
Preferably the concen~ration is 15 to 25~ by weight.

~2~5~i3~;

The phase separation may also be affected by the temperature`at which the process is conducted. This may be between 15 and 80C but preferably is between 30 and 70C.
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 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.
The 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 desalination aids. For instance we have established that the maximum level of alkalinity that can be maintained in solution is increased if PD is reduced. Thus best results are ~26~5 achieved if Mw is from 350 to 1,000 and PD is below 1.5, most preferably 1.05 to 1.3.
In the following examples, Example l demonstrates how a polymer may be made to the desired PD and Mw values by careful polymerisation, and Examples 2 and 3 demonstrate how the polymer may be obtained by partial neutralisation and fractionation.

To a 700 cm3 resin pot equipped with thermometer, stirrer and external heating, three separate mixtures were continuously added over a 6 hour period.
Feed 1 consisted of: ~ 340 g glacial acrylic acid in 226 g water Feed 2 10.5 g 100 vol. hydrogen peroxide and 57~1 g water Feed 3 28 g thioglycollic acid and 38.6 g water.
The pot contents were maintained at reflux temperature throughout the addition and then for a further hour before being cooled. The percentage unpolymerised acrylic acid was determined by Gas Liquid Chromatrography and shown to be 0.3% of the amount added.
The remaining polymer was fully neutralised by the addition of 46.6~ sodium hydroxide and the final product diluted to give a 40~ w/w sodium polyacrylate solution.
The viscosity of the product at 25~ was 12.1 cS
(suspended level viscometer, No. 2, 25C~. GPC analysis showed Mw = 1740, Mn = 1321, Polydispersity = 1.32.

A 23% by weight solution of polyacrylic acid in a blend of e~ual 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 were neutralised by the addition of varying amounts of 12@i5~i~S

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.

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 determined. The results are shown in Table 1.

Aqueous layer Organic layer Base ~ %
Neutralisation Extracted Mw P.D. Extracted M~ P.D.
NaOH 25 75.2 3833 1.30 24.8 1452 1.402 NH40H 25 55.6 4025 1.30 44.4 1689 1.34 LiOH 25 NO SEP~RA~ION
LiOH 50 50~2 3957 1.427 49.8 1783 1.44 K~l 25 63.5 3649 1.56 36.5 1402 1.49 NaOH 15 20.6 3976 1.49 79.4 2027 1.63 NaOH 50 95.7 3688 1.51 4.3 Very low

3 NaOH 75 99.3 3376 1.53 0.7 Very low The products o~tained in Example 2 were adjusted to 40% active solids and compared as marble grinding aids as ~2~5635 described in Bxample ll of British Patent Specification No. 1,414,964. The results are set out in Table 2.

5 PercentYield Percent Aqueous Layer Neutralisation Organic Agueous Milling index 87.2 12.8 79.3 20.7 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 *This product is made in conventional manner by full neutralisation followed by removal of the organic phase by distillation, and so there is no fractionation.
In the described test a milling index value of around 0.5 is generally satisfactory as it indicates commercially acceptable properties for preventing gelation of the marble dispersion.
It is apparent $rom 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.

~265~i~S

A polymer was prepared ~y conventional polymerisation technique as a 23% solution o.E acrylic acid in equal amounts of isopropanol and water was neutralised to 25%
with aqueous sodium hydroxide after polymerisation. This caused the reaction mixture to 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 ~m, at 75% w/w slurry solids content by recording the slurry viscosity (cP~ at 0.6, 0.8 and 1% dry polymer based ~n dry pigment. The results are given in Table 3.

Neutralisa- Mn PD Slurry Viscosity (cP) 25tion 96 0.60.3 1.0 100 Control 3161 20191.565 _ 1320 1380 Apquaesoeus 4236 27951.515 _ _ 2600 30 2S Organi~ 1795 13671 314 3500 70D 340 Samples of narrow polydispersity sodium polyacrylates of decreasing molecular weight were evaluated as 1~i5~i3~

disper~ant for china clay at 64% w/w slurry ~olids content at p~ 6.~-7.0 and at various dosages, as in Example 4. The results are gi~en in Table 4.

. _ ~ , Mw Mn PD SlurrY Visoosit~ (cP~
0.100.12 0.14 0.16 0.18 -0.~20 0.2 _ _ _ 5543 4817 1.15 _ _ 1567 359 290 321 376 4876 3907 1.25 _ 1483 643 285 296 330 405 4447 35~2 1.24 _ 933 423 255 269 312 361 4053 3273 1.24 _ 703 263 225 249 284 3202 2709 1.18 234 198 211 233 271 2144 1901 1.13533 183 190 207 231 266 065 334 1.28637 226 199 201 213 230 The results show that the most effective sodium polyacrylates for china clay dispersants lie between a molecular weight of 1000--3000. Preference been given to a molecular weight of approximately 2000.
EX~MPLE 7 Four samples of sodium polyacrylate of similar moleculaL
weight but varying polydispersity were evaluated as marble milling aids.
Each of the moleculaL weights (and all the other molecula~
weights quoted herein) were determined by GPC (gel peLmeation chcomotography). It involves permeation of the polymer unde~ test through a GPC column (Ultragel Ac~ 54, Scm diameter and 31cm length) when being eluted with O.lM sodium chloride at 3ml/min at a temperature of 30C, the eluate being analysed with a W
detector. The column will previously have been calibrated between upper and lower moleculae weights by use of fractions of a polymer of the same chemical type ti.e., polyacrylic acid) but in which ~. ii 126S63~i each fraction i6 a laboratory reagent grade ~f ~hat polymer having a di~ferent molecular weight. The ueper and lower limits of the calibration range are defined by markers of known molecular weight, for instance lO,O00 at the upper end and below l,000 at the lower end.
Mw and Mn values for each polymer that is being te6ted can thus be determined in conventional manner and PD can then be calculated as described above. The results expressed as Milling Index using a test method as desceibed in Example 11, British Patent No. 1,414,964 are shown in Table 5.

TABLE S
Mw PD Milling Index 3225 1.38 2.54 3105 1.52 1.23 3229 1.63 0.29 3358 2.01 <0.20 The results show that the effectiveness of sodium polyacrylate on marble milling is depenaent on polydispersity. The lower the polydispersity the more effective the product.

It can be shown that the interrelationship between molecular weight and polydispersity of a sodium AMPS/sodium acrylate (20/80 wfw) copol~mer has a crucial effect when the product is evaluated as a marble grinding aid according to Example 11 of British Patent Specification No. 1,~14~964. The interrelationship between these parameters is shown in Table 6.

12~i563S

MW --~g Low mole~r weight low polydis~ity 2351 1.26 2.6 2630 1.34 2.4 Low molea~r weight high polydi~sity 2834 1.6 0.38 3151 1.55 0.44 Hi~h mDleo~r weight low polydispersity 7193 1.40 0.67 9625 1.47 0.81 High m~Kl~dr weight high polydispersity 6265 1.64 0.64 . 5836 1.53 0.77 , _ _ _ ._ The results show that polymers of low molecular weight with narrow polydispersity are the most effective marble grinding aids~ The optimum molecular weight lies between 1500 and 3500 with preference given to polymers with a molecular weight of 2500.

Samples of sodium polyacrylate of similar molecular weight but varying polydispersity were evaluated as in Example 4 as dispersants for precipitated calcium carbonate at 70~ w/w slurry solids content. The results are given in Table 7.

MW ED __ Br ~ cf eld Visoosit~
_ 0.150 0.175 0.~00 0.225 0.250 0.275 ~.300 32~6 1.38 117 114 130 177 114 107 1~4 3105 1.52 120 134 167 ` 1~8 164 130 127 1265~83S

SUPPLEMENTARY-~ISCL~SU~E

W~ aescribe in the Princi~al Disclosure ~revi~usly known ways Of separating diffeLent molecul.ar weight comeonents feo~ ~ater soluble poly~ers.
We describe in that Prin~Fal Dis¢~e our p~K~S in which a solution in a blend of water and a Cl to 5 alcohol of a water soluble polymer conta;ning acid ~roups is separated into an aqueous phase contai~ling a higher molecular weight fraction and an organic phase containing a lower molecular weigh~ fraction and we descri~e that the acid groups are neutralised with a catlon selected from sodium, potassium, l;thium and ammoniu~ and the molar proportion of neutralised acid groups is from 10 to 55~
when the cation is selected from sodium and potassium, 10 to 70~ when the cation is ammonium and 30 to 90~ when the cation is lithium The preferred polymers are polymers formed from acidic monomers selected from ~crylic acid and 2-acrylamido-2-methyl propane sulphonic acid. The preferred way of forming the solution that is to be phase sepaxa~ed comprises polymerising ~he acidic monomer in the ~ree acid form as a solution in water and the alcohol and ~hen ad~ing the appropriate amount of cation, al~hough the specification does say that other methods can be use~. -.We have now. ound tha~ a solut-ion can be -formed o a ~~ water soluble polymer containing acid groups in a blend .

~ -23-~.~

~2~;S63~i of a polar solvent, water and base in an amount sufficient to neutralise at least l0~ but not more than 90% molar of ~he said acid groups and the solvent, the base and the amount of base and/or t:he amount of s~lvent are selected to cause phase separa1:ion of the solution into an aqueous phase containing a higher molecular weight polymeric fraction and an organic pha~e containing a lower molecular weight polymeric fraction.
In one preferred aspect the solution of water soluble polymer in the blend of water, polar solvent and base if formed by polymerisation of a water soluble monomer containing acid groups in aqueous solution in the presence ~f the base, and if necessary then adjusting the amount of base and/or solvent so as to cause the desired phase separation.
In ano~her preferred aspect the polar solvent is an aliphatic ketone and the polymer has a molecular weight above 50,000.
In another preferred aspect the polymer is formed from one or more monomers comprising allyl sulphonic acid. For instance such a polymer can be fractionated in a manner as described in the Principal Disclosure using a Cl to C5 alcohol as polar solvent and using lO to 55~ molar neutralisation with sodium or potassium, l0 to 70~ molar neutralisation with ammonium or 30 to 90% molar neutralisation with lithium.
The process condiSions that can be altered to affect the selit between lower and higher molecular weight ~ractions as referred to in the Princieal Disclosure include the choice of solvent. the choice o~ base, the amount of solvent and ~he amount of base.
Once one has appreciated the novel concept that it is possible ~o `i ~
! 24 12Çi5635 fractionate usefully, provided the acidic groups are partially neutralised, as o~po~ed to full n~utralisation in the prior art, it is possible to obtain any paeticular desired split or fractionation by appropriate selection of solvent, base, and amounts of each.
The particular solvent ~ay have to be selected having regard to the nature of the polymer, and in particular its molecular weight. For instance the polar solvents are gene~ally selected from Cl 5 alcohols as already disclosed and C3-8 (generally C3 or C4) 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 weight polymers, for instance having average molecular weight above 50,000, generally above 100,000 and preferably above 200,000 ox even 500,000.
As already disclosed, the polymer can be any water soluble p~lymer containing acidic groups and may have been made by any suitable polymerisation technique. The polymer is generally obtained by polymerisation of an ethylenically or other unsaturated monomer that contains acid groups either alone or with other ethylenically unsaturated monomeric material. Oligomers formed from the corresponding monomers may be used in place of the monomers. The acid groups are generally carboxylic acid or sulphonic acid or sulphuric acid groups. The monomers are of~en acrylic monomers and therefore i ~ -25-~L2~5~3S

preferred acidic monomers include one or more o~acrylic acid, 2-acrylamido-2-methyl propane sulphonic acid (AMPS), 2-acrylamido-2-phenyl propane sulphonic acid, methacrylic acid, itaconic acid, crotonic acid, vinyl sulphonic acid, vinyl sulphuric acid, allyl sulph~nic acid, maleic acid and fumaric acid, the preferred monomers being acrylic acid and AMPS. As already disclosed in the Principal Disclosure, any comonomers that can be copolymerised, in the amounts p~esent, with the acidic monomer or monomers to form a water soluble polymer can be used ancl include monomers such as acrylamide, acrylonitrile and acrylic esters. Generally at least 50% by weight and often at least 80% by weight of the monomers from which the polymer is formed are acidic monomers. The polymer is generally a linear polymer.
Preferred polymers for use in the invention are polyacrylic acid homopolymers but other very valuable polymers that may be treated in the invention are acrylic acid copolymers, especially copolymers with 2-acrylamido-2-methyl propane sulphonic acid or its salts, methacrylic acid homopolymer, itaconic acid methacrylic acid cop~lymers, vinyl sulphonic acid homopolymer and allyl sulphonic acid homopolymer and polyvinyl sulphuxic acid.
Also, as disclosed in the Principal Disclosure, the average molecular weight of the polymer that is to be fractionated can vary widely provided the value is not so high that the polymer is insoluble Ol forms a solution that has such a high viscosity that it cannot be frac~ionated into two phases or that forms, upon fractionation, a phase that has such a high viscosity that it cannot conveniently be separated feom the other phase. Generally the molecular weight is 500 to 1 million and the most valuable advantages are found when the average molecular weight is below 100,000, generally below ~0,000 and especially between 1,000 and 10,000, for instance a~ound 1,500 to 4,500.
. .
G i~ :

~656~5 As referred to in the Principal Disclo~ure, the polymer may have been made by any conventional polymeri~ation p~ocess and may have then been isolated, for ins~ance as a solid, from any liquid phase in which it wa~ formed, and then redi6solved 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 pol~mer obtained by solution polymerisation of the appropriate monomers, The preferred solution polymerisation medium is an aqueous solution containing appropriate initiators or other polymerisation promotors, ~or 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 regulator. other known molecular weight regulators (e.g. that provide terminal -COOH, -OH or Cl 3 alkyl groups) may be included in the solution if desired.
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 mixtur~ then being allowed to stand to allow separation to occur. Generally however the 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.

~2~S~i3S

an alcohol or acetone~ A very common solvent in solution polymerisa~ions is isopropanol and blends o~
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 form of the monomers in which event the base adjustment is effected by adding the appropriate amount of alkali or other source of cation. If the polymerisation is carried out on a wholly neutralised form of monomer (e.g.
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 neutralise 10 to 90% of the acid groups and then the phase separatîon is caused by adding some or all of the polar solvent, to the required amount. If the amount of cation in the polymerisation mixture is not the optimum for the phase separation then additional base (or acid) may be added with the polar solvent to achieve the desired degree of neutralisation.

-2~-~2~563S

As referred to in the Principal Di~closure, irrespective of whether the solution i8 made by blending preformed polymer, water, orqanic solvent and base or by adding base to the raction produ~t 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 ~equi~ed amount~ of the cations.
The bases are preferably basic compounds of monovalent cations such as sodium, potassium, lithium and ammonium, p~eferably in the amounts quoted previously in the Principal Disclosure herein since in geneeal we ~ind that with most solvents amounts outside these ranges give less ~atisfactory fractionation. Lower alkyl amines (e.g. 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 co~pounds 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. ~odium ace~ate, adipate or cit~ate when the polymeric acid is a sulphuric or sulphonic acid.
As set out in the Principal Disclosure, the degree of neutralisation of the acid groups controls the fractionation. The results obtained in any particular process will depend upon, inter alia, the concentrations, the polymer type and the solvent but there is a minimum degree of neutralisation below which substantially no fractionation occurs and the system may instead remain as a homogeneous solu~ion. 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 25~ whilst if ! ~i ' ~ -29-~S63~;

the cation is lithium the degree of neutralisation will normally have to be at least about 30g, preferably at least 40% and generally at least 50%. If the degree of neutralisation is too hiqh 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 prefera~ly below 40~. When the cation of the base is ammonium the degree of neutralisation will normally be below 70~, preferably below 60~ and most preferably below 50~. When the cation of the base is lithium the degree of neutralisation will normally be below 90~, and preferably below 70~.
Other conditions set out in the Principal Disclosure aeply equally well here afi, for example, the weight of starting polyme~
in each flaction, achieving partial neutralisation, degree of fractionation proprortion of solvent, concentration of polymer.
tempe~ature, and the like.
~arn p I f, 10 Other polymers are prepared by the general technique described in Example 2 but using different monomers.
When the monomer consisted solely of methacrylic acid 25%
neutralisation with sodium hydroxide fractionated the product into a lower molecula~ weight isopropanol phase that was useful as a dispersant for china clay and a higher molecular weight aqueous phase.
When the monomers consist of equal parts by weight 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 and then fractionated using isopropanol.
~, ~

~1 26S635 A solu~ion of acrylic acid monomer containing sufficient sodium hydroxide to neutralise 25% of the acrylic acid groups was polymerised by thermally initiated polymerisation in isopropanol. The product fractionated into organic and aqueous phases containing, respectively, 8.g and 91.1% by weight of the polymer.
When the process was repeated with 20% neutralisation and with 15~ neutralisation the organic and aqueous phases fractionated with polymer contents as shown in Table 7.

~CABLE: ?
_ .
% Neutra~sation% of Polymer Mw Mu PD

32 - organic 1284 1012 1.27 68 - aqueous 3616 2515 1.44 44.6 - organic 2268 1620 1.40 56.4 - aqueous 4447 3245 1.37 -The process of Examplell was repeated except that the solvent that was added was acetone and the degree of neutralisation 20~. The aqueous and organic phases respectively contaîned 49.1 and 50.9~ by weight of the polymer and the polymer iD each phase had a~ intrinsic viscosity of 0.919 dl/g (aqueous phase) and 0.652 dl/g forganic phase). The aqueous phase was tending towards a gel.

When the process was repeated with methanol and 25%
neutralisation the aqueous and organi~ phases respectively contained 57.8 and ~2.2% by weight of the polymer and the polymer in each phase had an intrinsic viscosity of 0.423 dl/g ~aqueous phase) and 0.32 dl/g : (organic phase).

A blend of 85 parts acrylic acid and 15 parts sodium allyl sulphonate was polymerised by continuous addition to isopropanol and water using ammonium persulphate, as initiator, giving a final reaction mass containing 29%
polymer, 36% isopropanol and 35% water.
This was divided into two portions. One portion was fully neutralised with 46~ NaOH, allowed to separate into two layers and the lower aqueous layer stripped of isopropanol by distillation, titrated for strength and molecular weight determined by GPC. This produced a control polymer.
To the second portion sufficient 46% sodium hydroxide was added to neutralise lS~ of the carboxyl groups present in the polymer, the reaction mass was allowed to phase separate into both aqueous and isopropanol layers, both layers were stripped of isopropanol, fully neutralised and analysed for molecular weight. The analysis of each fraction is shown in Table 8.
TAsLE 8 M~ Mn PolydispersitY
Control polymer 3612 2146 1.683 15% neutralised aqueous phase 4210 2600 1.619 15% neutralised isopropanol phase 2580 1631 1.582 , ~, ~ 32-

Claims (17)

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

1. A process in which a solution in a blend of water and a polar solvent of a water soluble polymer containing neutralised acid groups is separated into an aqueous phase containing a higher molecular weight fraction and an organic phase containing a lower molecular weight fraction characterised in that the polar solvent is a C1 to C5 alcohol, the acid groups are neutralised with a cation selectee from. sodium, potassium, lithium or ammonium and the molar proportion of neutralised groups is from 10 to 55% when the cation is selected from sodium and potassium, 10 to 70% when the cation is ammonium and 30 to 90% when the cation is lithium.

2. A process according to claim 1 in which the alcohol is isopropanol and the proportion water:alcohol is from 1:0.5 to 1:2.

3. A process according to claim 1 in which the concentration of polymer (by weight of the acid polymer based on polymer, water and alcohol) is at least 10%, and each phase contains from 20 to 80% by weight of the polymer.

4. A process according to any of claims 1 to 3 comprising the preliminary step of forming the solution in the blend by polymerising water soluble acidic monomer in the blend and then adding sufficient alkali to partially neutralise the polymer.

5. A process according to any of claims 1 to 3 in which the cation is selected from sodium and potassium and the proportion of neutralised groups is from 15 to 40% or the cation is ammonium and the proportion neutralised groups is from 15 to 50%.

6. A process according to claim 1 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.

7. A process according to claim 6 comprising the preliminary step of forming the polymer, in free acid form, as a solution in the blend by polymerisation of polymerisable monomers including the said acidic monomers in the blend and then converting 10 to 50% of the acid groups to the sodium salt form by adding sodium hydroxide.

CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE

8. A process in which a solution is formed of a water soluble polymer containing acid groups in a blend of a polar solvent, water and base in an amount sufficient to neutralise at least 10%
but not more than 990% molar of the said acid groups and in which the solvent, the base and the amount of at least one of the base and the solvent are selected to cause phase separation of the solution into an aqueous phase containing a higher molecular weight polymeric fraction and an organic phase containing a lower molecular weight polymeric fraction.

9. A process according to claim 8 in which the solution of the water soluble polymer is the blend of water, polar solvent and base is formed by polymerisation of water soluble monomer containing acid groups in aqueous solution in the presence of the base, and if necessary then adjusting the amount of base and/or solvent so as to cause the phase separation.

10. A process according to claim 9 in which the polymerisation is conducted in the presence of substantially the desired amount of base to cause the phase separation.

11. A process according to claim 9 in which the polymerisation is conducted in the presence of an amount of base greater than is required for the phase separation and mineral acid is then added in an amount sufficient to cause phase separation.

12 A process according to any of claims 9, 10 and 11 in which some or all of the polar solvent is added after the polymerisation to cause the phase separation.

13. A process according to claim 1 or 8 in which the polymer is a polymer of allyl sulphonic acid.

14. A process according to claim 8 in which the polar solvent is a C1 to 5 alcohol, the base contains a cation selected from sodium, potassium, lithium and ammonium and the amount of the base is such that the molar proportion of neutralised groups is from 10 to 55% when the cation is selected from sodium and potassium, 10 to 70% when the cation is ammonium and 30 to 90% when the cation is lithium.

15; A process according to claim 14 in which the molecular weight of the polymer is below 100,000.

16. A process according to claim 8 in which the polar solvent is a C3 to 8 aliphatic ketone and the polymer has a molecular weight above 50,000.

17. A process according to claim 16 in which the polar solvent is acetone and the polymer has a molecular weight above 100,000.