WO2014091209A2

WO2014091209A2 - Polymeric thickeners and production processes with reduced environmental impact

Info

Publication number: WO2014091209A2
Application number: PCT/GB2013/053231
Authority: WO
Inventors: Paul Edward HUNT; Mark Thomas STANION
Original assignee: Scott Bader Company Ltd
Priority date: 2012-12-10
Filing date: 2013-12-06
Publication date: 2014-06-19
Also published as: GB201222190D0; WO2014091209A3; GB2508672A

Abstract

A method for making a pH responsive thickener composition particularly effective under acidic conditions comprises a step of hydrolysing, at a temperature between 30ºC and 75ºC, a copolymer obtainable by emulsion copolymerisation of the following monomer components: A. ethyl acrylate, in an amount greater than 30% by weight, based on the total weight of monomer components A + B + C + D; B. from 0·1% to less than 69·0% by weight, based on the total weight of monomer components A + B + C + D, of at least one ethylenically unsaturated carboxylic acid monomer containing 15 one C=C double bond capable of free radical copolymerisation with component A and at least one carboxylic acid (CO2H) group; C. from 1% to 20% by weight, based on the total weight of monomer components A + B + C + D, of at least one associative monomer, being a (meth)acrylate ester of an alkoxylated alcohol; and 20 D. from 0% to 15% by weight, based on the total weight of monomer components A + B + C + D, of one or more non-ionic ethylenically unsaturated monomers other than those defined above as A, B or C; wherein the total monomer components A + B + C + D together add up 25 to 100%. There is also provided an emulsion copolymer latex comprising a copolymer obtainable via the emulsion copolymerisation of the following monomer components A' and B' with C and D as above: A'. ethyl acrylate, in an amount greater than 80% by weight and less than 97·5% by weight( based on the total weight of 30 monomer components A' + B' + C' + D'); and B'. from 0·1% to 19% by weight of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A' and at least one carboxylic acid (CO2H) group, wherein the 35 at least one ethylenically unsaturated carboxylic acid monomer comprises acrylic acid in an amount greater than 30%, up to 100%, of the total weight of B'.

Description

POLYMERIC THICKENERS AND PRODUCTION PROCESSES WITH REDUCED

ENVIRONMENTAL IMPACT

INTRODUCTION

The invention relates to acrylic/methacrylic emulsion copolymers useful for the thickening of a variety of aqueous systems and processes for producing thickeners. In particular the invention is concerned with thickeners effective under acidic conditions and processes for producing those thickeners.

Various forms of acrylic/methacrylic copolymers have been used as thickeners for many decades. An early form of the technology is disclosed in US Patent No. 2,798,053, in which a poly [acrylic acid] is prepared by copolymerising acrylic acid with a small amount of diallyl sucrose. Whilst the copolymers of US' 053 may be prepared via polymerisation in water, they are too water-soluble to give an aqueous solution/dispersion that is easy to handle, and the preferred method of preparation involves dispersion polymerisation in an inert organic solvent such as heptane or benzene, followed by isolation of the copolymer as a solid powder prior to use. Even when the copolymers are prepared in water, isolation as a powder is still deemed necessary. The main problem with using such copolymers in powder form is the difficulty in dispersing the powder into the aqueous medium to be thickened. Often the grains of powder clump together when added to water, and the resulting lumps are difficult to disperse evenly, even with the aid of high levels of mechanical shearing, such as with a high shear dispersion mixer. Acrylic/methacrylic copolymer thickeners handleable as aqueous dispersions are taught by British Patent No. 870,994. These are prepared as emulsion copolymers of 25% to 70% by weight of

methacrylic acid with lower alkyl acrylate or methacrylate esters, and are used to thicken aqueous systems at pH = 7-0 or above.

GB870,994 also discusses, at page 1 lines 28 to 43, the preparation of polyacrylate/polymethacrylate-type thickeners by the alkaline hydrolysis of esters, amides or nitriles of acrylic acid. This hydrolysis process was clearly part of the common general knowledge in November 1956 (the priority date of the patent) , and products of this nature have been commercially available from Scott Bader

Company Limited for many years, under the trade name Texigel®. The Texigel® products are primarily hydrolysed copolymers of >80%wt (based on polymer) of methyl acrylate with a small amount of acrylic or methacrylic acid, methyl acrylate being preferred for ease of hydrolysis at ambient temperatures. Although, however, GB870,994 discusses this hydrolysis process, none of its example thickeners are subjected to that process; typically these examples are used after neutralisation with only an equivalent amount of NaOH, at pHs generally in the range 7-6 to 8-6. Another class of acrylic/methacrylic copolymer thickeners is the so- called HASE thickeners, an acronym for Hydrophobically modified, Alkali Swellable (or Soluble) Emulsions. Such thickeners are described in, for example, European Patent Application EP-A- 0,013,836, which discloses copolymer dispersions obtainable by aqueous emulsion copolymerxsation of the following monomer types.

(i) 20% to 69 -5% by weight, based on the total weight of

monomers, of methacrylic acid or acrylic acid

(ii) 0-5% to 25% by weight, based on the total weight of

monomers, of acrylic or methacrylic ester monomers of general formula

H₂C=CR-C (0) -0- (CH₂-CH₂0) n-R°

in which R = H or methyl, n is at least 2 and R° is a hydrophobic group, such as an alkyl, alkylaryl or polycyclic alkyl group, having 8 to 30 carbon atoms.

(iii) At least 30% by weight, based on the total weight of

monomers, of a (Ci to C₄) alkyl acrylate or alkyl

methacrylate, preferably ethyl acrylate, butyl acrylate or methyl methacrylate, most preferably ethyl acrylate. (iv) Optionally, up to 1 -0% by weight of a polyethylenically

unsaturated monomer.

Like the thickeners of GB870,994, the examples of EP-A-0, 013, 836 are used in non-hydrolysed form, being neutralised with one equivalent of sodium hydroxide. This would suggest an end-use pH in the range 7-0 to 9-0.

US Patent No. 4,138,381 also discloses acrylic/methacrylic copolymer latex thickeners, although these are prepared as dispersions in glycols (especially propylene glycol) or aqueous glycols, rather than in purely aqueous carriers. The polymers themselves are prepared from the following monomers.

(i) About 10% to 98% by weight (most preferably 30 to 88%) of polymer of at least one unsaturated carboxylic acid of 3 to

6 carbon atoms .

(ii) About 1% to 50% by weight (most preferably 2 to 30%) of

polymer of at least one alkyl acrylate or alkyl methacrylate wherein the alkyl group has from 1 to 30 carbon atoms.

(iii) About 1% to 85% by weight (most preferably 10 to 40%) of

polymer of at least one ester of general formula

H₂C=CR-C (0) -O- (CH₂-CH (R²) O) x (CH₂) y-R¹

in which R and R² are hydrogen or methyl, x is a positive integer of 5 to 80 y is 0 or a positive integer of 1 to 20, and R¹ is a (Cx to C₂o) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms.

These thickeners are also used without being hydrolysed first. They are used to thicken paints whose pH, where it is stated, is generally given as 9-5. The preferred acid component (i) is methacrylic and the preferred alkyl acrylate or methacrylate ester, - component (ii) - is clearly stearyl methacrylate.

One document which does disclose polyacrylate/polymethacrylate species effective as thickeners at acidic pHs is US Patent No.

4,384, 096. This discloses aqueous emulsion copolymers of the following monomers.

(i) About 15% to 60% weight, based on total monomers, of at

least one C₃ to C₈ a, β-ethylenically unsaturated carboxylic acid monomer (for example, acrylic or methacrylic acid) . (ii) About 15% to 80% weight, based on total monomers, of at

least one non-ionic, copolymerisable C₂ to C₁₂ α, β- ethylenically unsaturated monomer, including Ci to C₈ alkyl acrylates or methacrylates .

(iii) About 1% to 30% weight, based on total monomers, of at least one so-called non-ionic vinyl surfactant ester of general formula

H₂C=CR-C (0) -0- (CH_Z-CH(R' ) O) m (CH₂-CH₂0) n-R"

in which R is H or methyl, R' is methyl or ethyl, R" is C₈ to C₂o alkyl or C₈ to Ci₆ alkylphenyl, n is an average number from about 6 to about 100 and m is an average number from 0 to about 50.

This patent claims effective thickening down to pH = 5-5, although the thickeners described therein are normally used in ammonium salt form (i.e. neutralised with ammonia solution), and for the examples for which a pH is stated, this figure is of the order of 9-0. The patent discusses possible presolubilisation of the thickeners with aqueous alkali, but hydrolysis before use is not taught. The vast majority of the example copolymers are derived from methacrylic acid as component (i) and ethyl acrylate as component (ii) . European Patent EP-B-0, 705, 854 discloses

polyacrylate/polymethacrylate emulsion copolymer thickeners prepared from the following monomers.

(i) About 15% to 60% weight, based on total monomers, of at

least one C₃ to C₈ a, -ethylenically unsaturated carboxylic acid monomer (for example, acrylic or methacrylic acid) .

(ii) About 15% to 80% weight, based on total monomers, of at

least one non-ionic, copolymerisable C₂ to C12 , β- ethylenically unsaturated monomer, including Ci to C₈ alkyl acrylates or methacrylates.

(iii) About 1% to 30% weight, based on total monomers, of at least one so-called ethylenically unsaturated biphilic monomer. The biphilic monomer of this particular invention is an acrylate or methacrylate ester of a polyethoxylated hydrophobic alcohol, namely a tristyrylphenol . (The methacrylate ester of the 25-mole ethoxylate of behenyl (C22) alcohol is shown as a comparative example) . The example copolymers are derived from methacrylic and or methacrylic anhydride as component (i) and ethyl acrylate as component (ii) . The thickeners are used after neutralisation with sodium hydroxide, but are not hydrolysed. Thickening is demonstrated at pHs from "about 1" up to 9-36. At these alkaline pHs, superior thickening is obtained with the copolymers incorporating the tristyrlphenol- derived monomer.

US Patent no. 5,703,176 teaches alkaline hydrolysis of aqueous dispersions of ethyl acrylate copolymers. Example thickener preparations are derived from 99 parts methyl acrylate with 1 part methacrylic acid and 99 parts ethyl acrylate with 1 part methacrylic acid. The compositions of this patent, however, require severe hydrolysis conditions. Temperatures between 170°F and 200°F (76-7°C and 93-3°C), preferably 190°F (87-8°C), for times between 4 hours and 24 hours, using a huge excess of hydroxide (more than 60 equivalents), are taught. Use of these compositions and the associated method is therefore, in practice, not attractive.

Furthermore, this US document is silent as to the effectiveness or otherwise of its thickeners in acidic media. United Kingdom patent application no. 1120022.7 discloses aqueous dispersions of methyl acrylate copolymers which are subsequently hydrolysed under alkaline conditions to give polymeric thickeners effective at acidic pH, in some cases at pH values below 5-0. A drawback with these compositions is that the alkaline hydrolysis liberates methanol, which is toxic. There is therefore a requirement in the commercial application of this technology to mitigate the risks associated with potential exposure to methanol during the hydrolysis step, particularly when carrying out that process on a large scale.

There remains, therefore, a need for a process for producing waterborne thickeners for aqueous media that requires only mild conditions without the evolution of hazardous volatiles such as methanol, which thickeners are effective at acidic pH, for example at pH 6 or below and especially at pH below 5-5, as well as at alkaline pH. SUMMARY OF INVENTION

Surprisingly, the applicants have found that the above objectives can be addressed by conducting alkaline hydrolysis, at specified conditions, of an emulsion copolymer latex comprising a copolymer obtainable from monomer components comprising ethyl acrylate, an ethylenically unsaturated acid component and a (meth) acrylate surfactant ester component. The combination of a specific alkaline hydrolysis step with the specific latex composition has been found to provide access to a range of useful polymeric thickeners which perform very well at acidic H, suitably at pH below 5.5.

In particular, the applicants have found that the objectives discussed above may be addressed by the alkaline hydrolysis, at a temperature between 30°C and 75°C, of an emulsion copolymer latex comprising a copolymer obtainable via the emulsion copolymerisation of the following monomer components:

A. ethyl acrylate, in an amount greater than 30% by weight, based on the total weight of monomer components A + B + C + D; B. from 0-1% to less than 69-0% by weight, based on the total

weight of monomer components A + B + C + D, of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A and at least one carboxylic acid (C0₂H) group;

C. from 1% to 20% by weight, based on the total weight of monomer components A + B + C + D, of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol, preferably an alkoxypoly (alkyleneoxy) ethyl (meth) acrylate, suitably of general formula (I)

R-O- (CH₂-CH₂-0) x (CH₂-CH (R¹ ) 0) y-C (0) -CR²=CH₂ (I)

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20; and D. from 0% to 15% by weight, based on the total weight of monomer components A + B + c + D, of one or more non-ionic

ethylenically unsaturated monomers other than those defined above as A, B or C; wherein the total monomer components A + B + C (and D if present) together should add up to 100%.

Thus, the applicants have found that a process of alkaline

hydrolysis conducted under specific conditions provides a valuable and very practical route to useful thickeners. In particular, the applicants have created a process that (a) is adapted for effective alkaline hydrolysis of an emulsion copolymer latex by virtue of a defined temperature range; (b) does not produce hazardous volatiles such as methanol; and (c) produces a polymeric thickener that is useful at acidic conditions, suitably at pH below 5.5, as well as at alkaline conditions.

Experimental studies have shown that a clear thickener solution is achieved at low pH, with no cloudiness and without the formation of visible lumps that can be observed with prior art processes. A yet further advantage demonstrated by embodiments of the invention is that the thickening behaviour is reversible in the sense that even if the pH is dropped to an extremely low level (e.g. below pH 5.0) such that viscosity is no longer at the desired level, the viscosity may nevertheless be recovered by raising the pH. This reversible pH- viscosity function permits storage/supply/transfer of a low viscosity acidic solution and subsequent adjustment of pH to restore a desired viscosity when required. The applicants have also found that particularly good levels of thickener performance at acidic pH, suitably at pH below 5.5, can be achieved if the latex comprises, as part of the ethylenically unsaturated acid component, at least a substantial quantity of acrylic acid. Furthermore, not only is low pH thickener performance achieved, but the alkaline hydrolysis of the latex can be performed at ambient temperature.

More specifically, the applicants have found that an aqueous polyacrylate/polymethacrylate composition, effective in thickening aqueous media at acidic pH, suitably at pH below 5 -5, may be obtained by the alkaline hydrolysis at ambient temperature of an emulsion copolymer latex comprising a copolymer obtainable via the emulsion copolymerisation of the following monomer components:

A' . ethyl acrylate, in an amount greater than 80% by weight and less than 97 -5% by weight, based on the total weight of monomer components A' + B' + C + D' ;

B' . from 0 -1% to 19% by weight, based on the total weight of monomer components A' + B' + C + D' , of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A' and at least one carboxylic acid (CO₂H) group, wherein the at least one ethylenically unsaturated carboxylic acid monomer comprises acrylic acid in an amount greater than 30%, up to 100%, of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' ;

C . from 1% to 20% by weight based on the total weight of monomer components A' + B' + C + D' of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol, preferably an

alkoxypoly (alkyleneoxy) ethyl (meth) acrylate, suitably of general formula (I)

R-O- (CH₂-CH₂-0) x (CH₂-CH (R¹) 0) y-C (0) -CR²=CH₂ (I)

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20; and D' . from 0% to 15% by weight, based on the total weight of

monomer components A' + B' + C + D' , of one or more non- ionic ethylenically unsaturated monomers other than those defined above as A' , B' or C ; wherein the total monomer components A' + B' + C (and D' if present) together should add up to 100%.

Thus, the applicants have found that alkaline hydrolysis of specific latexes, even at ambient temperature, provides a valuable and very practical route to useful low pH thickeners. The applicants have created an emulsion copolymer latex that is (a) adapted for use with the alkaline hydrolysis process at very mild conditions; (b) does not produce hazardous volatiles such as methanol; and (c) produces, after alkaline hydrolysis, a polymeric thickener that is useful at acidic conditions, suitably at pH below 5.5.

The provision of a novel process comprising alkaline hydrolysis at mild conditions of a specific class of emulsion copolymer latexes, and the provision of a specially adapted sub-class of emulsion copolymer latexes that permits ambient temperature alkaline hydrolysis, all without the production of hazardous volatiles such as methanol, represents a valuable contribution to the art.

In a first aspect, the invention provides a method for making a thickener composition which comprises a step of hydrolysing, suitably at a temperature between 30 °C and 75°C, a copolymer obtainable by emulsion copolymerisation of components A to C, and optionally D, as defined herein. The method may comprise a preliminary step of obtaining the copolymer by emulsion copolymerisation of components A to C, and optionally D, prior to hydrolysis. The copolymer may be in the form of a latex, the latex comprising the copolymer in an aqueous phase. The latex may be formed by the above-mentioned preliminary step of obtaining the copolymer by emulsion copolymerisation of components A to C, and optionally D, prior to hydrolysis. Alternatively, the latex may be formed in a separate latex-forming process .

Typically the method may include a preliminary step of diluting a latex with water in order to provide a content of up to 10% by weight of copolymer, preferably up to 7 % by weight and more preferably up to 5% by weight, prior to the hydrolysis step.

Suitably the hydrolysis is alkaline hydrolysis.

Preferably the hydrolysis step comprises the addition of a water soluble alkali typically selected from potassium hydroxide, sodium hydroxide and ammonium hydroxide. Conveniently alkali is added in an amount sufficient to provide a pH of at least 10 and preferably at least 12. Preferably sodium hydroxide is employed.

Typically the hydrolysis step uses at least 3, preferably at lea 5, equivalents of hydroxide relative to the acid content of the copolymer. Suitably no more than 15, preferably no more than 10, equivalents are used. Preferably 3 to 10 equivalents, more

preferably 5 to 10 equivalents, most preferably 5 -5 to 8 -5

equivalents are used.

Suitably hydrolysis is carried out at a temperature in the range 30°C to 75°C, preferably 30°C to 65°C, more preferably 30°C to 60°C, more preferably 35°C to 60°C, more preferably 35°C to 55°C and most preferably 38°C to 52°C. Naturally, for the sub-class of copolymer obtainable from A' to D' , hydrolysis can occur at ambient

temperature .

Hydrolysis of the copolymer is indicated by gel formation and an increase in the viscosity of the composition. Preferably the hydrolysis product exhibits a viscosity of at least 10,000

centipoise (when measured using a Brookfield RVT instrument at 25°C using spindle 6, speed 5 rpm) at a solids content of no more than 10%, and preferably no more than 7%, and at a pH of at least 9.5, preferably at least 10.

Typically the composition is held at a temperature in the range 30 °C to 75 °C for a period sufficient to promote the hydrolysis reaction. Conveniently a time period of less than 4 hours, preferably less than 3 hours, more preferably less than 2½ hours, most preferably about 2 hours, is appropriate. Generally a time period of at least 1 hour, preferably at least 1½ hours, is appropriate.

Typically, for example, following the period at temperature in the range 30°C to 75°C, the composition is allowed to stand at ambient temperature for a period sufficient to allow adequate gel formation. Conveniently a time period of less than 30 hours, preferably less than 24 hours, more preferably between 16 hours and 24 hours and especially between 16 hours and 21 hours is appropriate.

Preferably the method includes a subsequent step of reducing the pH of the hydrolysis product with acid in order to reduce the pH to 6 or less, and especially to 5-5 or less. Preferably the process employs a weak acid, especially a weak organic acid such as citric acid, acetic acid, oxalic acid ascorbic acid, tartaric acid, malic acid and lactic acid, for example. pH reduction with citric acid as a weak acid is preferred.

In a second aspect the invention provides a composition suitable for use as a pH responsive thickener, which composition comprises a hydrolysis product of a copolymer obtainable by emulsion

copolymerisation of components A to C, and optionally D, as defined herein, or a latex comprising the copolymer. Suitably the hydrolysis product is the hydrolysis product of the method of the first aspect. Suitably the thickener composition is a thickener composition obtainable via hydrolysis according to the method of the first aspect . In a third aspect the invention provides the use of a thickener composition obtainable via hydrolysis of a copolymer obtainable by emulsion copolymerisation of components A to C, and optionally D, as defined herein, or a latex comprising the copolymer, as a thickener for an aqueous system.

The present inventors have surprisingly found that the combination of an alkaline hydrolysis step applied to a defined class of emulsion copolymer permits the formation of thickener compositions without evolution of methanol and without requiring severe

conditions, the thickener compositions being effective at both alkaline and acidic pH. In particular, the hydrolysis product is surprisingly effective for thickening at low pH.

This combined technical effect of high and low pH thickening performance, no production of hazardous volatiles such as methanol and use of only mild conditions, is surprising and is not disclosed in the prior art discussed above. Indeed, there is no hint in the prior art discussed above that alkaline hydrolysis as described herein should be applied to emulsion copolymers or latexes obtained from components A to C, let alone in anticipation of good thickening performance at low (and high) pH.

The first aspect of the invention therefore represents a valuable contribution to the art not only because of the excellent thickening performance achievable by the hydrolysis product but because the potentially costly and difficult steps required to mitigate risks associated with hazardous volatiles such as methanol are not necessary, and also because the challenging reaction and process conditions required by the prior art processes can be avoided.

As noted above, the copolymer that is the subject of hydrolysis in accordance with the first aspect can be in the form of a latex. The latex may contain additional optional components selected from surfactants, defoamers, biocide preservatives and antioxidants, for example. Preferably the latex comprises an anionic or non-ionic surfactant. Preferably the latex comprises up to 50% and typically up to 45% by weight of the copolymer.

Suitably the copolymer is present in the latex as particles having an average particle size in the range of 50 to 500 nm, especially 50 to 300 nm, more preferably 80 to 200 nm, as measured by a photon correlation spectroscopy method as described later.

Conveniently the latex exhibits a viscosity in a range of 7 to 45 centipoise, especially 20 to 40 centipoise when measured using a Brookfield RVT instrument at 25°C using spindle 2, speed lOOrpm.

According to the above aspects of the invention the copolymer is generally derived from an amount greater than 30% by weight, based on the total weight of monomer components A + B + C + D, of ethyl acrylate. Preferably the ethyl acrylate component A is present in an amount of at least 40% by weight, more preferably at least 50% by weight, more preferably at least 55% by weight, more preferably at least 60% by weight, more preferably at least 65% by weight, more preferably at least 70% by weight, more preferably at least 75% by weight, more preferably at least 78% by weight, and most preferably at least 80% by weight, based on the total weight of monomer components A + B + C + D. In some embodiments the ethyl acrylate component A is present in an amount selected from: at least 82% by weight, at least 85% by weight, and at least 90% by weight, based on the total weight of monomer components A + B + C + D.

Suitably the ethyl acrylate component A is present in an amount of up to 98% by weight, preferably up to 96% by weight, more preferably up to 94% by weight and most preferably up to 92% by weight, based on the total weight of monomer components A + B + C + D. In some embodiments the ethyl acrylate component A is present in an amount selected from: up to 90% by weight, up to 88% by weight, and up to 86% by weight, based on the total weight of monomer components A + B + C + D.

In embodiments, the upper and lower limits disclosed above for component A both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits.

Preferred ranges include any one of: 50% to 98% by weight, 50% to 94% by weight, 60% to 94% by weight, 70% to 94% by weight, 75% to 94% by weight, based on the total weight of monomer components A + B + C + D.

Preferably the ethylenically unsaturated carboxylic acid component B is provided in an amount of from 0.1% by weight, more preferably from 0.5% by weight, more preferably at least 1.5% by weight, more preferably at least 2% by weight, and most preferably at least 5% by weight, based on the total weight of the monomer components A + B + C + D. In some embodiments the ethylenically unsaturated carboxylic acid component B is provided in an amount selected from: at least 7% by weight, at least 8% by weight, and at least 10% by weight, based on the total weight of the monomer components A + B + C + D.

Suitably the ethylenically unsaturated carboxylic acid component B is provided in an amount of up to 65% by weight, preferably up to 60% by weight, more preferably up to 55% by weight, more preferably up to 50% by weight, more preferably up to 45% by weight, more preferably up to 40% by weight, more preferably up to 35% by weight, more preferably up to 30% by weight, more preferably up to 25% by weight, more preferably up to 20% by weight, and more preferably up to 17% by weight, and most preferably up to 15% by weight, based on the total weight of the monomer components A + B + C + D. In some embodiments the ethylenically unsaturated carboxylic acid component B is provided in an amount selected from: up to 15% by weight, up to 14% by weight, up to 13% by weight, up to 12.5% by weight, up to 12% by weight, up to 11.5% by weight, up to 11% by weight, up to 10.5% by weight, up to 10% by weight, and up to 9.5% by weight, based on the total weight of the monomer components A + B + C + D. In embodiments, the upper and lower limits disclosed above for component B both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits.

Preferred ranges include any one of: 2% to 50% by weight, 2% to 40% by weight, 2% to 30% by weight, 2% to 20% by weight, 2% to 17% by weight, 5% to 20% by weight and 5% to 17% by weight, based on the total weight of monomer components A + B + C + D.

Various ethylenically unsaturated carboxylic acid monomers are suitable for use as component B, as discussed in more detail below. Preferred examples include C₃ to C₈ acid monomers including acrylic acid, methacrylic acid, carboxyethyl acrylate, itaconic acids and mixtures thereof. Preferably component B comprises at least 30% by weight, more preferably at least 40% by weight, more preferably at least 45% and even more preferably at least 50% by weight of one or more C₃ to Ce ethylenically unsaturated acid monomers, preferably acrylic acid, based on the total weight of component B.

The associative monomer component C is provided in an amount of at least 1% by weight, preferably at least 1.5% by weight, more preferably at least 2% by weight, and most preferably at least 2.5% by weight, based on the total weight of monomer components A + B + C + D. In some embodiments, the associative monomer component C is provided in an amount selected from: at least 3% by weight, at least 5% by weight, at least 7% by weight, and at least 9 % by weight, based on the total weight of monomer components A + B + C + D. Suitably the associative monomer component C is provided in an amount of up to 18% by weight, preferably up to 15% by weight, preferably up to 13% by weight, preferably up to 11% by weight, preferably up to 10% by weight, preferably up to 9% by weight and most preferably up to 8% by weight, based on the total weight of monomer components A + B + C + D. In some embodiments, the

associative monomer component C is provided in an amount selected from: up to 7% by weight, up to 5% by weight, up to 3% by weight. and up to 2% by weight, based on the total weight of monomer components A + B + C + D.

In embodiments, the upper and lower limits disclosed above for component C both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits.

Preferred ranges include any one of: 1% to 18% by weight, 1% to 15% by weight, 2% to 15% by weight, 2% to 10% by weight, 2.5% to 10% by weight, and 2.5% to 8% by weight, based on the total weight of monomer components A + B + C + D.

According to preferred embodiments of the invention the associative monomer C of formula (I) contains a substituent R which is a C₈ to C30 alkyl group, especially a C10 to C25 alkyl group, more preferably a Ci2 to C₂₃ alkyl group and most preferably a C_i2 to C22 alkyl group. In further prepared embodiments component C comprises an associative monomer of formula (I) having a value X in the range of from 20 to 25.

Most preferably the associative monomer of component C contains a substituent R² which is methyl.

Example associative monomers C, including those of formula (I), employed in embodiments of the invention are described in more detail below.

One or more components D_r if present, may provide up to 15% by weight of the monomer components, preferably no more than 10% by weight and most preferably no more than 5% by weight.

Example optional monomers D are described in more detail below.

Particularly preferred emulsion copolymers used in the method of the first aspect {in terms of components A to D) are discussed in more detail below. These preferred arrangements apply equally to the second and third aspects of the invention. As noted above, the second aspect of the invention provides a composition suitable for use as a pH responsive thickener, which composition comprises a hydrolysis product of a copolymer or a latex as defined herein. Suitably the composition is made according to the method of the first aspect.

Typically the composition ready for use as a thickener exhibits a viscosity of at least 5,000 centipoise when measured at pH 6 using a Brookfield RVT instrument (spindle 6, speed 5 rpm) . Embodiments of the composition may exhibit a viscosity of at least 10,000, preferably at least 20,000 centipoise, when measured at pH 6.

Embodiments may exhibit a viscosity of at least 4,000, preferably at least 5,000, more preferably at least 6,000, and most preferably at least 8,000 centipoise, when measured at pH 5.5. As discussed herein, the composition suitably also provides excellent thickening performance at alkaline pH. Suitably the composition ready for use as a thickener exhibits a viscosity of at least 20,000, preferably at least 30,000, and most preferably at least 40,000 centipoise, when measured at pH 12.5.

As noted above, the third aspect of the invention provides the use of a thickener composition obtainable via hydrolysis of a copolymer or a latex as defined herein, as a thickener for an aqueous system. Preferably this aspect of the invention concerns the use of a thickener composition obtainable by (i) hydrolysing of the copolymer or the latex and (ii) adjusting the pH of the hydrolysis product to 6 or less.

Especially in cases where the pH of the thickener composition is 6 or less, it may be stirred into the aqueous composition to be thickened. Alternatively components of the proposed aqueous composition may be stirred into the thickener composition.

Further aspects of the invention relate to the inventors' findings that particularly good levels of thickener performance at acidic pH, suitably at pH below 5.5, can be achieved if the latex comprises, as part of the ethylenically unsaturated acid component, at least a substantial quantity of acrylic acid.

Thus, in a fourth aspect the invention provides a copolymer obtainable by emulsion copolymerisation of components A' , B' and C , and optionally D' , as defined herein.

In a fifth aspect the invention provides a latex comprising an emulsion copolymer in accordance with the fourth aspect in an aqueous phase.

In a sixth aspect the invention provides a method of making a thickener composition which comprises a step of hydrolysing an emulsion copolymer of the fourth aspect or a latex of the fifth aspect of the invention. Suitably the step of hydrolysis is carried out at less than 30°C, preferably less than 28°C, and more

preferably 25°C or less. In embodiments, hydrolysis is carried out at ambient temperature. In a seventh aspect the invention provides a composition suitable for use as a pH responsive thickener, which composition comprises a hydrolysis product of an emulsion copolymer in accordance with the fourth aspect or a latex in accordance with the fifth aspect. In an eighth aspect the invention provides the use of a thickener composition, obtainable via hydrolysis of an emulsion copolymer in accordance with the fourth aspect or latex in accordance with the fifth aspect, as a thickener for an aqueous system. As discussed above, the present inventors have surprisingly found that an emulsion copolymer derived from a defined amount of ethyl acrylate in combination with an ethylenically unsaturated carboxylic acid monomer component comprising a significant proportion of acrylic acid and further in combination with a selected type of associative monomer is a suitable precursor for a thickener effective at both alkaline and acidic pH. In particular, a hydrolysis product of this emulsion copolymer is surprisingly effective for thickening at low pH.

This technical effect is surprising and is not disclosed in the prior art discussed above. Indeed, as a refinement of the preceding aspects, it provides a specific and comparatively narrow sub-class of copolymer, obtainable by emulsion copolymerisation of components A' to D' , which can be formed into useful pH responsive thickeners via a readily accessible, low cost and efficient ambient temperature process step, without generating hazardous volatiles such as methanol .

This represents a further valuable contribution to the art. If desired the copolymer of the fourth aspect of the invention may be isolated as a solid by spray drying or evaporation or by other processes known in the art.

The fifth aspect of the invention concerns a latex comprising a copolymer in accordance with the fourth aspect in an aqueous phase. The latex may be as defined above in respect of the preceding aspects, for example the latex may contain additional optional components as discussed above in respect of the preceding aspects. According to the fourth and subsequent aspects of the invention the emulsion copolymer is generally derived from above 80% up to 97.5% by weight, based on the total weight of monomer components A' to D' , of ethyl acrylate. Preferably the ethyl acrylate component A' is present in an amount of at least 80.5% by weight, based on the weight of the monomer components A' to D' . In some embodiments the ethyl acrylate component A' is present in an amount selected from: at least 81% by weight, at least 82% by weight, at least 84% by weight, at least 86% by weight, at least 88% by weight, at least 89% by weight, and at least 90% by weight, based on the weight of the monomer components A' to D' . Suitably ethyl acrylate component A' is present in an amount up to 95% by weight, preferably up to 93% by weight, more preferably up to 91% by weight, more preferably up to 89% by weight, and most preferably up to 86% by weight, based on the weight of the monomer components A' to D' . In some embodiments the ethyl acrylate component A' is present in an amount selected from: up to 85% by weight, up to 84% by weight, up to 82% by weight, and up to 81% by weight, based on the weight of the monomer components A' to D' . In embodiments, the upper and lower limits disclosed above for component A' both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits.

Preferred ranges include any one of: above 80% up to 93% by weight, above 80% up to 89% by weight, and 80.5% to 86% by weight, based on the total weight of monomer components A' + B' + C + D' .

Preferably the ethylenically unsaturated carboxylic acid component B' is provided in an amount of at least 0.5% by weight, more preferably at least 1% by weight, more preferably at least 1.5% by weight, more preferably at least 2% by weight, and most preferably at least 5% by weight, based on the total weight of the monomer components A' + B' + C + D' . In some embodiments the ethylenically unsaturated carboxylic acid component B' is provided in an amount selected from: at least 7% by weight, at least 8% by weight, and at least 10% by weight, based on the total weight of the monomer components A' + B' + C + D' .

Suitably the ethylenically unsaturated carboxylic acid component B' is provided in an amount of up to 17% by weight, more preferably up to 15% by weight, more preferably up to 13% by weight, more preferably up to 12.5% by weight, and most preferably up to 12% by weight, based on the total weight of the monomer components A' + B' + C + D' . In some embodiments the ethylenically unsaturated carboxylic acid component B' is provided in an amount selected from: up to 11% by weight, up to 10% by weight, up to 9% by weight, up to 8% by weight, and up to 7% by weight, based on the total weight of the monomer components A' + B' + C + D' .

In embodiments, the upper and lower limits disclosed above for component B' both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits.

Preferred ranges include any one of: 5% to 12.5% by weight, 8% to 12.5% by weight, and 10% to 12% by weight, based on the total weight of monomer components A' + B' + C + D' .

As for the amount of acrylic acid, suitably acrylic acid is present in an amount of at least 40% of the total weight of the

ethylenically unsaturated carboxylic acid monomer component B' , preferably at least 45%, more preferably greater than 50%, more preferably at least 50.5%, more preferably at least 55%, more preferably at least 60%, and more preferably at least 65% of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' . In some embodiments the acrylic acid is present in an amount selected from: at least 70%, at least 80%, and at least 90% of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' .

Suitably the acrylic acid is present in an amount of up to 99% and preferably up to 95% of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' . In some

embodiments the acrylic acid is present in an amount selected from: up to 90%, up to 85%, up to 80%, up to 77.5%, up to 75%, up to 70%, up to 65%, and up to 60% of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' .

In embodiments, the upper and lower limits disclosed above for acrylic acid content both apply. Indeed, any one of the upper limits may be combined with any one of the lower limits. Preferred ranges include any one of: above 50% up to 95%, above 50% up to 80%, 60% to 80%, and 65% to 77.5% of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' . Preferred amounts for the associative monomer component C are the same as for the associative monomer component C discussed above with respect to the first aspect. For completeness, the preferred ranges are repeated here: 1% to 18% by weight, 1% to 15% by weight, 2% to 15% by weight, 2% to 10% by weight, 2.5% to 10% by weight, and 2.5% to 8% by weight, based on the total weight of monomer components A' + B' + C + D' .

As for component D' , the optional and preferred features are the same as for component D discussed above with respect to the first aspect.

Particularly preferred embodiments of the various aspects of the present invention are described below, by way of example.

Embodiments described in relation to the first aspect of the invention i.e. the emulsion copolymer apply equally to the other aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION In considering the invention in detail, it should be understood that the term (meth) acrylate refers to acrylate and/or methacrylate, an abbreviation commonly used by those skilled in the art. Therefore, the expression "methyl acrylate" refers to a compound of formula H₂C=CH-C (0) -O-CH₃, and the term "methyl methacrylate" refers to a compound of formula H₂C=C (CH₃) -C (0) -0-CH₃, whereas the term "methyl

(meth) acrylate" refers to either a compound of formula H₂C=CH-C (O) -0- CH₃ or a compound of formula H₂C=C (CH₃) -C (0) -0-CH₃ or, indeed, a mixture of the two. The terms " (meth) acrylic" and

"poly (meth) acrylate" may also be understood in the same light.

A method of hydrolysis according to the invention is preferably carried out on an emulsion copolymer latex, suitably at a temperature between 30°C and 75°C, the latex preferably comprising a poly (meth) acrylate copolymer obtainable by free radical emulsion copolymerisation of the following three monomer components: A. ethyl acrylate, in an amount greater than 30% by weight, based on the total weight of monomer components A + B + C + D;

B. from 0-1% to less than 69-0% by weight, based on the total

C. from 1% to 20% by weight, based on the total weight of monomer components A + B + C + D, of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol, preferably an alkoxypol (alkyleneoxy) ethyl (meth) acrylate, suitably of general formula (I)

R-O- (CH₂-CH₂-0) x (CH₂-CH (R¹ ) 0) y-C (O) -CR²=C¾ ( I )

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20; and

D. from 0% to 15% by weight, based on the total weight of monomer components A + B + C + D, of one or more non-ionic

A copolymer suitable for hydrolysis at ambient temperature according to the invention preferably comprises a poly (meth) acrylate copolymer obtainable by free radical emulsion copolymerisation of the following three monomer components: ethyl acrylate, in an amount greater than 80% by weight and less than 97 -5% by weight, based on the total weight of monomer components A' + B' + C + D' ; from 0 -1% to 19% by weight, based on the total weight of monomer components A' + B' + C + D' , of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A' and at least one carboxylic acid (C0₂H) group, wherein the at least one ethylenically unsaturated carboxylic acid monomer comprises acrylic acid in an amount greater than 30%, up to 100%, of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' ; from 1% to 20% by weight based on the total weight of monomer components A' + B' + C + D' of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol, preferably an

alkoxypoly (alkyleneoxy) ethyl (meth) acrylate, suitably of general formula (I)

R-O- (CH₂-CH₂-0) x {CH₂-CH (R¹) 0) y-C (O) -CR²=CH₂ (I)

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is

0 or a positive integer with an average value from 1 to 20; and

D' . from 0% to 15% by weight, based on the total weight of

monomer components A' + B' + C + D' , of one or more non- ionic ethylenically unsaturated monomers other than those defined above as A' , B' or C ; wherein the total monomer components A' + B' + C (and D' if present) together should add up to 100%. Preferred example monomer components are as follows, noting that references to component B also apply to component B' , likewise references to component C also apply to component C , and references to component D also apply to component D' .

Component B - Ethylenically unsaturated carboxylic acid monomer

The ethylenically unsaturated carboxylic acid monomer (component B) may be any ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical

copolymerisation with component A and at least one carboxylic acid (C0₂H) group. Possible non-limiting examples of ethylenically unsaturated carboxylic acid monomers having more than one carboxylic acid (CO₂H) group are itaconic acid, maleic acid or fumaric acid. Possible non-limiting examples of ethylenically unsaturated carboxylic acid monomers having only one carboxylic acid (C0₂H) group are acrylic acid, methacrylic acid and β-carboxyethyl acrylate (sometimes referred to as acrylic acid dimer) . The monoalkyl esters of dicarboxylic acids such as itaconic, maleic or fumaric acids may also be used as examples of ethylenically unsaturated carboxylic acid monomers having only one carboxylic acid (C0₂H) group. Mixtures of ethylenically unsaturated carboxylic acid monomers may also be used .

The use of ethylenically unsaturated carboxylic acid monomers having only one carboxylic acid (C0₂H) group is preferred. Preferred examples of such ethylenically unsaturated carboxylic acid monomers (component B) are acrylic acid, methacrylic acid, β-carboxyethyl acrylate, and mixtures thereof.

Especially preferred examples of ethylenically unsaturated

carboxylic acid monomers (component B) are acrylic acid, methacrylic acid, and mixtures thereof. Naturally, in respect of component B' , at least 30% of the total weight of monomer component B' is acrylic acid . Where a mixture of two or more ethylenically unsaturated carboxylic acid monomers is used, the amount of acrylic acid present within the mixture to facilitate adequate hydrolysis at ambient temperature should be greater than 30% by weight of the total weight of monomer component B, more preferably greater than 40%, and most preferably greater than 50% by weight of the total weight of monomer component B. Typically the amount of acrylic acid within the mixture does not exceed 98%, more typically 95%. Preferably, the amount of acrylic acid within the mixture should be at least 50%, up to 95% by weight of the total weight of monomer component B. More preferably, the amount of acrylic acid within the mixture should exceed 50%, up to 80% by weight of the total weight of monomer component B. Most preferably, the amount of acrylic acid within the mixture should lie between 60% and 80% by weight of the total weight of monomer component B, most especially preferably between 65% and 77 -5% by weight of the total weight of monomer component B. In embodiments, monomer component B is monomer component B' .

In embodiments, the sole ethylenically unsaturated carboxylic acid monomer of component B is acrylic acid. That is, component B is 100% acrylic acid.

If performing the hydrolysis of the emulsion copolymer latex at mild but above-ambient (30°C to 75°C) temperature, it is still the case that the use of ethylenically unsaturated carboxylic acid monomers having only one carboxylic acid (C0₂H) group is preferred. Preferred examples of such ethylenically unsaturated carboxylic acid monomers (component B) are acrylic acid, methacrylic acid, β-carboxyethyl acrylate, and mixtures thereof, whilst especially preferred examples of ethylenically unsaturated carboxylic acid monomers (component B) are acrylic acid, methacrylic acid, and mixtures thereof. However, if performing the hydrolysis of the emulsion copolymer latex at elevated temperature (i.e. between 30°C and 75°C), the relative amounts of different ethylenically unsaturated carboxylic acid monomers within any mixture constituting the total of ethylenically unsaturated carboxylic acid monomer component B are not critical. In such cases it is, for instance, quite possible for 100% of the ethylenically unsaturated carboxylic acid monomer component B to be made up of methacrylic acid alone.

For completeness, it is re-iterated that optional and preferred features in respect of component B also apply to component B' .

Component C - Associative Monomer

The associative monomer component C generally makes up from 1% by weight to 20% by weight of the total of monomer components A + B + C + D (if D is present) and is typically a compound of general formula (I)

R-0- (CH₂-CH₂-0) x (CH₂-CH (R¹) 0) y-C (O) -CR²=CH₂ (I)

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20. The above general formulae of monomer component C may be viewed as consisting of three distinct segments C{i), C(ii) and C(iii), bonded together into the associative monomer C (i) -C (ii) -C (iii) , wherein: C(i) is the residue from a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms,

C(ii) is a poly [alkylene oxide] polyether chain i.e. a poly [ethylene oxide] polyether chain or a poly [ethylene oxide -co-propylene oxide] polyether chain, and

C(iii) is an acrylate ester or methacrylate ester group.

Preferably R in formulae (I) and (II) is a C₈ to C32 alkyl group.

Such associative monomer components C may therefore, in principle, be prepared by reacting a monof nctional alcohol R-OH, in which R⁴ is a linear or branched (C₈ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, with either ethylene oxide, or both ethylene oxide and propylene oxide

sequentially in either order (giving a block copolymer) , or a mixture of ethylene oxide and propylene oxide together (giving a random copolymer) , and the subsequent conversion of the resultant alkoxylated alcohol into its acrylate or methacrylate ester. Suitable alcohols R⁴-OH may be any linear or branched monofunctional alcohol whose alkyl group R⁴ has from 8 to 32 carbon atoms, or any alkylphenol whose alkyl group may be linear or branched and has from 1 to 20 carbon atoms. Preferred alcohols R⁴-OH are the linear or branched monofunctional alcohols with an alkyl group R⁴ having from 8 to 32 carbon atoms, non-limiting examples of which are 2-ethyl-l- hexanol, 1-nonanol, 2-nonanol, 3, 7-dimethyl-l-octanol, 3 , 7-dimethyl- 3-octanol, l,decanol, 2-decanol, isodecanol, 1-undecanol, 2-butyl-l- octanol, 1-dodecanol, lauryl alcohol, 2-dodecanol, 1-tridecanol, 1- tetradecanol, myristyl alcohol, 2-tetradecanol , pentadecanol, 1- hexadecanol, cetyl alcohol, palmityl alcohol, 2-hexadecanol, 1- heptadecanol, margaryl alcohol, 1-octadecanol, stearyl alcohol, 1- nonadecanol, 2-octyl-l-decanol , eicosanol, arachidyl alcohol, heneicosanol, 1-docosanol, behenyl alcohol, tricosanol, 2-decyl-l- tetradecanol, tetracosanol, lignoceryl alcohol, pentacosanol, hexacosanol, heptacosanol, octacosanol, nonacosanol, triacontanol , melissyl alcohol, hentriacontanol, dotriacontanol and mixtures of any of the above.

More preferred alcohols R⁴-OH are the linear or branched

monofunctional alcohols with an alkyl group R⁴ having from 10 to 25 carbon atoms, including 3, 7-dimethyl-3-octanol , l,decanol, 2- decanol, isodecanol, 1-undecanol, 2-butyl-l-octanol, l-dodecanol, lauryl alcohol, 2-dodecanol, 1-tridecanol, 1-tetradecanol, myristyl alcohol, 2-tetradecanol, pentadecanol, 1-hexadecanol , cetyl alcohol, palmityl alcohol, 2-hexadecanol, 1-heptadecanol, margaryl alcohol, 1-octadecanol, stearyl alcohol, 1-nonadecanol, 2-octyl-l-decanol, eicosanol, arachidyl alcohol, heneicosanol, 1-docosanol, behenyl alcohol, tricosanol, 2-decyl-l-tetradecanol, tetracosanol,

lignoceryl alcohol, pentacosanol, and mixtures of any of the above.

Particularly preferred alcohols R-OH are the linear or branched monofunctional alcohols with an alkyl group R⁴ having from 12 to 22 carbon atoms, including 1-dodecanol, lauryl alcohol, 2-dodecanol, 1- tridecanol, 1-tetradecanol , myristyl alcohol, 2-tetradecanol, pentadecanol, 1-hexadecanol, cetyl alcohol, palmityl alcohol, 2- hexadecanol, 1-heptadecanol , margaryl alcohol, 1-octadecanol, stearyl alcohol, 1-nonadecanol , 2-octyl-l-decanol, eicosanol, arachidyl alcohol, heneicosanol, l-docosanol, behenyl alcohol, and mixtures of any of the above.

Especially preferred are lauryl alcohol and behenyl alcohol. Most especially preferred is behenyl alcohol.

Examples of alcohols R⁴-0H, in which R⁴ is an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, are octylphenol, nonylphenol and dodecylphenol . The use within the invention of associative monomers (component C) derived from alcohols R-OH in which R⁴ is an alkylphenyl group is, however, not preferred.

The poly [alkylene oxide] polyether chain that makes up the middle segment C(ii) of the associative monomer component C has the general formula (II)

- (CH₂-CH₂-0) x (CH₂-CH (R¹) 0) y- (II)

in which R¹ is methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20.

When propylene glycol is present in the poly [alkylene oxide] polyether chain, it is preferred to use only small amounts of it, i.e. average values of y ranging from 1 to 5. However, the avoidance of propylene glycol is most preferred, i.e. y = 0 in the above general formula.

The average value of x may range from 3 to 80, preferably from 10 to 60, more preferably from 20 to 30, most preferably from 20 to 25. As will be readily understood by those skilled in the art, the ethoxylation/propoxylation of alcohols typically produces a mixture of products differing in the lengths of their alkylene oxide chains. Hence the reaction of, say, 1 mole of 2-ethyl-l-hexanol with 10 moles of ethylene oxide will not produce a uniform product in which each molecule of 2-ethyl-l-hexanol is bonded to a polyether chain consisting of exactly 10 molecules of ethylene oxide, but will actually produce a mixture of products in which any given molecule of 2-ethyl-l-hexanol is bonded to a polyether chain that could be any length from perhaps 2 or 3 ethylene oxide units up to perhaps 15 or more ethylene oxide units. Within any individual molecule of product, the number of ethylene oxide units will be an integer, but that the value of that integer will vary from one molecule of product to the next. The average chain length across the bulk product, however, will be 10 ethylene oxide units. The same principle applies if the alcohol is reacted with propylene oxide as well as with ethylene oxide, so the reaction of 1 mole of 2-ethyl-l- hexanol with, say, 5 moles of propylene oxide and 10 moles of ethylene oxide will produce a mixture of products in which any individual molecule could contain anywhere between 1 or 2 and 6 or more propylene oxide units, and anywhere between 2 or 3 and 15 or more ethylene oxide units. The average chain length across the bulk product, however, will be 5 propylene oxide and 10 ethylene oxide units. The discussion of the values of x and y in the associative monomer component C used in the invention, having the general formulae ( I ) :

R-O- (CH₂-CH₂-0) x (CH₂-CH (R¹ ) 0) y-C (0) -CR=CH₂ ( I )

should be viewed in this light.

As will also be clear from the above discussion, the notation - (CH₂- CH₂-0) x (CH₂-CH (R¹) O) y- in formula (I) is intended to cover block copolymers, alternating copolymers and random copolymers wherein the (CH₂-CH₂-0) and (CH₂-CH (R¹) 0) units are present in any order, provided the numerical limitations for x and y are satisfied.

In cases in which the poly [alkylene oxide] polyether segment C(ii) of the associative monomer component C contains some propylene oxide units (i.e. y ≠ 0) and the poly [alkylene oxide] polyether chain is a block copolymer, associative monomers are preferred in which the (meth) acrylate ester group C(iii) is bonded to the ethylene oxide terminus of the polyether chain.

It has already been observed above that associative monomers useful in the invention may be obtained via the conversion of alkoxylated, preferably ethoxylated, alcohols, into their acrylate or

methacrylate esters. As is well known to those skilled in the art, numerous alkoxylated, especially ethoxylated, alcohols are

commercially available, their primary use being as non-ionic surfactants. Such surfactants are available from a variety of suppliers, examples being the Brij™ and Synperonic™ ranges offered by Croda Europe of Goole, UK, the Serdox™ range offered by Elementis Specialties of Delden, The Netherlands, the Tergitol™ range offered by Dow Chemical Company, the Empilan™ range offered by Huntsman Performance Products and the Rhodasurf™ range offered by Rhodia

Novecare. Illustrative examples of these surfactants include Serdox™ NSL 30 (described as a 30-mole ethoxylate of stearyl alcohol) and Synperonic 13/9, understood to be a 9-mole ethoxylate of tridecyl alcohol. Illustrative examples of surfactants that include some propylene oxide units, (CH₂-CH (R¹ ) O) , as well as ethylene oxide units, (CH₂-CH₂-0) , within their structures include the Croda product Synperonic™ LF/26 and the Rhodia product Antarox® FM33. Many surfactant products are obtained by ethoxylation/propoxylation of mixtures of alcohols of different carbon chain lengths. Illustrative examples of these materials are Tergitol™ 15-S-30, which is understood to be a 31-mole ethoxylate of a mixture of Cn-Cis secondary alcohols and Serdox™ NBS 6.6/90, which is understood to be a mixture of C₉-Cn alcohols ethoxylated with, on average, 6 -6 moles of ethylene oxide per mole of alcohol. In principle, the conversion of any of these alkoxylated alcohol surfactants to their

(meth) acrylate esters would give associative monomers useful as monomer component C in the preparation of emulsion copolymer latexes of the instant invention. The (meth) acrylate ester segment C(iii) may be attached to the alkoxylated alcohol by any chemical process known to those skilled in the art. Non-limiting examples of such processes include esterification with (meth) acrylic acid, or reaction with the appropriate (meth) acrylic anhydride or (meth) acryloyl chloride.

Preferred examples of associative monomer component C are those monomers of general formula -0- (CH₂-CH₂-0) x-C (0) -CR²=CH₂ in which R is a linear or branched (Cio to C25) alkyl group, the average value of x lies in the range from 10 to 60, R² is H or methyl and especially methyl More preferred examples of associative monomer component C are those monomers of general formula R-O- (CH₂-CH₂-0) x-C (0) -CR²=CH₂ in which R is a linear or branched (C_i2 to C₂₂) alkyl group, the average value of x lies in the range from 20 to 30, R² is H or methyl and especially methyl .

Even more preferred examples of associative monomer component C are those monomers of general formula R-O- (CH₂-CH₂-0) x-C (O) -CR²=CH₂ in which R is a linear or branched (Ci₂ to C₂₂) alkyl group, the average value of x lies in the range from 20 to 25, R² is H or methyl and especially methyl.

Suitably the associative monomer component C comprises one or more of the active ingredients in the commercial products Sipomer® BEM, Sipomer® HPM-100 and Sipomer® HPM-400, the methacrylate ester of the 11-mole ethoxylate of a C16-C18 fatty alcohol and the methacrylate ester of the 25-mole ethoxylate of a C16-C18 fatty alcohol.

Preferably the associative monomer component C comprises one or more of the active ingredients in the commercial products Sipomer® BEM and Sipomer® HPM-400.

For completeness, it is re-iterated that optional and preferred features in respect of component C also apply to component C . Component D - Optional additional non-ionic ethylenically

unsaturated monomer

The optional non-ionic, ethylenically unsaturated monomer (component D) may comprise one or more additional non-ionic ethylenically unsaturated monomers copolymerisable with both the ethyl acrylate of component A and the other copolymerisable monomer components B and C. Furthermore, ethyl acrylate makes up at least 80-1% by weight of the total of monomers A to D. Thus, when the total weight percentage of monomer components B + C together add up to 19 -9% of the total monomers making up the copolymer, the whole of the remaining 80 -1% of the .total monomer composition making up the copolymer should preferably be ethyl acrylate. If, however, the total weight percentage of monomer components B + C together add up to only 15% of the total monomers making up the copolymer, the remaining 85% of the total monomer composition making up the copolymer should preferably comprise from 80 -1% to 85% of ethyl acrylate and from 0% to 4 -9% by weight of additional non-ionic ethylenically unsaturated monomer D .

The optional, additional non-ionic ethylenically unsaturated monomer making up component D is not particularly limited and may be any non-ionic ethylenically unsaturated monomer copolymerisable with ethyl acrylate A and the other monomer components B and C. Possible additional non-ionic ethylenically unsaturated monomers are the linear, branched, cycloaliphatic or arylaliphatic esters of acrylic or methacrylic acids, such as methyl methacrylate, ethyl

methacrylate, the various isomers of butyl (meth) acrylate, the various isomers of hexyl (meth) acrylate, n-octyl (meth) acrylate, 2- ethylhexyl (meth) acrylate, 1-decyl (meth) acrylate, 2-decyl

(meth) acrylate, isodecyl (meth) acrylate, the various isomers of dodecyl (meth) acrylate including lauryl (meth) acrylate, myristyl (meth) acrylate, cetyl (or palmityl) (meth) acrylate, stearyl

(meth) acrylate, also cyclohexyl (meth) acrylate, isobornyl

(meth) acrylate, benzyl (meth) acrylate, and the like. Other optional, additional non-ionic ethylenically unsaturated monomers making up part of component A may be vinylaromatic monomers such as styrene, a-methylstyrene, vinyltoluene and the like, or amide or nitrile derivatives of (meth) acrylic acids such as acrylamide, acrylonitrile and the like.

It is also possible for a small proportion of monomer component D to comprise a small amount (up to 0 -5% of the total amount of

components A to D) of a polyethylenically unsaturated monomer such as methylene-bis-acrylamide, divinylbenzene, ethylene glycol di (meth) acrylate or other di (meth) acrylate ester (s) of di-or- polyfunctional alcohols such as 1 , 3-butanediol , 1, 4-butanediol, 1,6- hexanediol, diethylene glycol, trimethylolpropane, pentaerythritol and the like. The use within the invention of a polyethylenically unsaturated monomer is, however, not preferred.

Where an optional, additional non-ionic ethylenically unsaturated monomer is used (monomer component D) , preferred examples of such monomers are the Ci-C₈ alkyl esters of (meth) acrylic acid (such as methyl methacrylate, ethyl methacrylate, butyl acrylate, 2- ethylhexyl acrylate and the like), styrene or acrylonitrile.

It is most preferred, however, to avoid the use of an additional non-ionic ethylenically unsaturated monomer D, although trace amounts may be included as impurities present in the commercial supplies of any monomer.

In addition to the ethylenically unsaturated components A, B, C, and D, a chain transfer agent may also be included with the monomer components making up the copolymer of the invention. Chain transfer agents may be used to adjust, suitably improve, hydrolysis. This may be achieved through a reduction in the weight average molecular weight (Mw) of the copolymer as compared to a copolymer made in an otherwise identical process using the same monomers in the absence of chain transfer agent. Lower molecular weight polymer chains may be more readily hydrolysable as compared to higher molecular weight chains. In some cases the use of chain transfer agent, whilst facilitating hydrolysis, may, because of the lower proportion of higher molecular weight species, reduce the thickening properties of the hydrolysis product. Nevertheless, embodiments of the invention advantageously permit the use of chain transfer agents, typically to adjust hydrolysis performance, whilst maintaining useful low pH thickening performance. Thus, in some embodiments a chain transfer agent is used; and in other embodiments a chain transfer agent is not used. Common chain transfer agents are halocarbons or sulphur containing species, though some alcohols and some compounds containing an allylic C—H bond will also behave as chain transfer agents in emulsion polymerisation reactions. Examples of halocarbon chain transfer agents are carbon tetrachloride, bromoform and bromotrichloromethane . Possible sulphur containing chain transfer agents include thioesters and thiols, the latter often being known as mercaptans . Examples of suitable thioesters include butyl thioglycolate (butyl mercaptoacetate ) , isooctyl thioglycolate, isooctyl mercaptopropionate, dodecyl thioglycolate and

pentaerythritol tetrakis (3-mercaptopropionate) . Examples of suitable thiols (mercaptans) include n-dodecyl mercaptan, t-dodecyl

mercaptan, octyl mercaptan, tetradecyl mercaptan and hexadecyl mercaptan. When a chain transfer agent is used, it is preferable to use a sulphur containing chain transfer agent, more preferable to use a thiol (mercaptan) and most preferable to use n-dodecyl mercaptan.

For completeness, it is re-iterated that optional and preferred features in respect of component D also apply to component D' . Preparation of the emulsion copolymer latex

The emulsion copolymer latex may be prepared by a conventional aqueous emulsion copolymerisation process familiar to those skilled in the art. In such a process, the monomers are first emulsified into an aqueous pre-emulsion in which the continuous phase is the aqueous phase, emulsification being facilitated by the use of appropriate surfactants. These surfactants may be anionic or non- ionic in nature.

Examples of non-ionic surfactants are alkylene oxide adducts (i.e. ethoxylates and/or propoxylates) of long chain (C₈-C₃o, linear or branched) alcohols or long chain (C₈-C3o, linear or branched) alkylphenols . Preferred non-ionic surfactants are the ethoxylates of secondary CIO to C16 alcohols. Preferred anionic surfactants are the sodium or ammonium sulphate salts, either of ethoxylated long chain (C₈-C₃o, linear or branched) alcohols, or of ethoxylated long chain (C₈-C₃₀, linear or branched) alkylphenols. Sodium or ammonium salts of ethoxylated alcohol sulphates are especially preferred.

In a typical emulsion copolymerisation process for preparing copolymer latexes of the invention, employing a thermal initiator it is preferable to first charge a part of the aqueous phase to the reactor and heat this to reaction temperature (70° to 90°C, preferably 75° to 85 °C, most preferably 80° to 85 °C) and then add part of a pre-prepared aqueous solution of a free radical initiator before commencing a drip-feed of the monomer emulsion described above. The polymerisation process is exothermic, so the feed rate of the monomer emulsion is carefully controlled in order to maintain reaction temperature while avoiding exceeding it. The remainder of the pre-prepared initiator solution may be fed concurrently with the monomer emulsion, throughout the whole of the monomer emulsion feed or only part of it. Preferred thermal initiators are alkali metal persulphate salts or ammonium persulphate, ammonium persulphate being most preferred.

The pH of the reaction mixture during polymerisation is likely to be in the range of 1 to 5, more typically 2 to 4. As an alternative to the use of thermal initiators the

polymerisation process may employ a pair of redox initiators which would generally be said to react together but as separate feeds. One is an oxidant initiator (such as a persulphate salt, tertiary butyl hydroperoxide, hydrogen peroxide or potassium bromate) and the other a reductant initiator (such as sodium metabilsulphite, sodium formaldehyde sulfoxylate, sodium hydrosulphite, tartaric acid, ascorbic acid or a ferrous salt such as ferrous sulphate) .

In the case where a redox initiation system is used a lower polymerisation temperature may be employed (such as 60°C or down to 40°C) . In this case the polymerisation pH is expected to be below 7

After apparent completion of the polymerisation reaction, a "chaser" initiator solution may be added to ensure polymerisation of any lingering unreacted monomer, reducing the free monomer content of the finished latex down to below lOOOppm. Redox couple initiators are preferred for this process, such as a combination of tert-butyl hydroperoxide and sodium formaldehyde sulfoxylate, or a combination of hydrogen peroxide and ascorbic acid.

The finished emulsion polymer latex is normally filtered before packaging or use, in order to remove any coagulum, often referred to as grit. This mainly consists of copolymer particles of diameters much larger than the dispersed copolymer particles making up the bulk of the latex, and its presence in the final product is most undesirable. If, for instance, the latex were to be used to thicken a printing paste, the presence of grit could lead to blocking of the inkjet nozzles used in the printing process. Filtration is usually performed through a screen of 60μ or 100μ mesh size. Although the grit may be removed by filtration, the presence of too much grit in the latex before filtration can block or partially block the filter, leading to an unacceptably slow filtration time. For this reason, it is preferred that the amount of grit present in the latex before filtration is less than 0 -01% by weight of the total latex.

The following experiments illustrate the present invention and the principles on which it is based; EXPERIMENTS

Materials and Methods SURFACTANT A is a solution (approx. 25% active content) of a sodium fatty alcohol ether sulphate, CAS No. 68585-34-2. It is commercially available as Kemsurf ESD from Lankem Ltd., of Dukinfield, Cheshire, UK, or as Empicol ESC3/G2 from Univar of Bradford, West Yorkshire, UK.

ACTICIDE MBS is a proprietary biocide, commercially available from Thor Specialties UK, of Northwich, Cheshire, UK.

E-CHEM DF 1315 is a proprietary defoamer, commercially available from eChem Ltd. of Leeds, UK.

Sipomer® BEM is the methacrylate ester of the 25-mole ethoxylate of behenyl (C22) alcohol. It is manufactured by Rhodia-Novecare as a solution of ~50% active content that also includes ~25% methacrylic acid, and may be obtained in the UK via Melrob Ltd., of Crawley, Sussex, UK.

HPM-100 is the active ingredient in the commercial product Sipomer® HPM100 available from Rhodia-Novecare. The chemical nature of the associative monomer is not publicly available but it is thought to be a 22 mole ethoxylate of a Cll alcohol.

HPM400 is the active ingredient in the commercial product Sipomer® HPM400 available from Rhodia-Novecare. Again, the exact chemical nature of the associative monomer is not publicly available but it is believed to be a 20 mole ethoxylate of a C13 alcohol.

C1618-11MA is a solution of the methacrylate ester of the 11-mole ethoxylate of a C16-C18 fatty alcohol. This solution contains approximately 50% of the active ingredient in a 1:1 mixture of methacrylic acid and water, i.e. similar to the composition of commercial Sipomer® BEM. C1618-25MA is a solution of the methacrylate ester of the 25-mole ethoxylate of a C16-C18 fatty alcohol, also ~50% active content in aqueous methacrylic acid.

C1618-50MA is a solution of the methacrylate ester of the 50-mole ethoxylate of a C16-C18 fatty alcohol, also ~50% active content in aqueous methacrylic acid. Solids contents are measured by weighing a small sample of the latex into an aluminium foil dish of 2-3cm in diameter, placing this in an oven at 110°C for one hour, cooling and weighing the amount of solid remaining. The sample size of latex used for this test is typically 0 -75-1 -00g. pH is measured at ambient temperature with a Hanna pH meter, model HI 9125.

Particle size is measured via a photon correlation spectroscopy method using a Zetasizer 1000 instrument, manufactured by Malvern Instruments Limited of Malvern, Worcestershire, UK.

Viscosities are measured by a Brookfield RVT instrument at 25°C. Viscosities of the Latex Formulations are measured using spindle 42 speed lOOrpm and are measured in centipoise (mPa.s).

Preparation of Emulsion Copolymer Latexes

Latex Formulation 1

Firstly, 195 -05g of deionised water was charged to a beaker. 30 -0g of Surfactant A and 30 -25g of acrylic acid were then added with gentle stirring, until the surfactant dissolved. In a separate beaker, 60 -0g of Sipomer® BEM-25 was dissolved into 312 -75g of ethyl acrylate, and this solution gradually added to the surfactant solution with vigorous stirring. Stirring was continued for a further 15 minutes to form Monomer Emulsion 1. The actual emulsion polymerisation was carried out in a 2-litre glass reactor which could be heated or cooled by means of a water jacket. This reactor was fitted with a lid incorporating inlet ports for a gaseous nitrogen feed and feeds of liquid reactants, the shafts of both a stainless steel turbine-style stirrer and an electronic thermometer, and the mounting for a water-cooled condenser. Into this reactor was charged 314 -OOg of deionised water, which was heated, with stirring, up to 83-85°C while maintaining a sub-surface nitrogen purge for at least 15 minutes. Thereafter, nitrogen flow was continued throughout the remainder of the process, but at a much reduced rate.

In another beaker, 0 -15g of sodium bicarbonate and 0.20g of ammonium persulphate were dissolved in 30 -00g of deionised water to make the initiator solution. Once the water in the reactor had reached temperature and had been nitrogen-purged at temperature for at least 15 minutes, 22 -76g of the initiator solution (i.e. 75% of the total amount of initiator solution) was added to the reactor and a feed of Monomer Emulsion 1 commenced at a rate slow enough to control the temperature in the reactor at between 83° and 85°C. As the volume of liquid in the reactor increased, the rate of addition of monomer emulsion could also be increased, such that the addition was completed in approximately 3 hours without exceeding a reactor temperature of 85 °C. After an addition time of 2 hours, a drip feed of the remaining initiator solution into the reactor was started, to run concurrently with the remaining hour of the monomer emulsion feed. On completion of the two feeds, the vessel from which the monomer emulsion had been fed was flushed into the reactor with 12 -50g deionised water and the contents then stirred for a further 30 minutes at 83-85°C before cooling to 70°C and adding 2 -00g of a solution of hydrogen peroxide (50% concentration) dissolved in 2 -00g of deionised water. After a further 15 minutes' stirring, a solution of 1 -00g of ascorbic acid B.P. in 4 -00g deionised water was added and stirring continued for a further 30 minutes. The reactor contents were then cooled, with continued stirring, down to a temperature of 40°C and 1 -50g Acticide MBS and 0'60g Surfactant A added. Finally, a solution of 0 -50g DF 1315 in 1 '50g deionised water was added, flushed into the reactor with a further 2 -0g deionised water .

The product emulsion copolymer latex was Latex Formulation 1. After cooling to room temperature, it was filtered through a nylon filter bag of mesh size 60μ to remove any coagulum (grit) . The theoretical composition of the polymer, calculated from the weights of monomers used, is 80 -6% ethyl acrylate, 7 -8% acrylic acid, 3 -9% methacrylic acid and 7 -7% methacrylate ester of the 25-mole ethoxylate of behenyl alcohol.

The theoretical composition of this polymer, along with the liquid properties of the latex, are set out in Table 1. The same procedure was also used to prepare Latex Formulations 2 to 5, adjusting the weights of the raw materials employed to give the polymer compositions shown in the Table. The theoretical

compositions of the polymers in Latex Formulations 2 to 4 are also set out in Table 1. Latex Formulation 5 was made with the same raw material quantities as Latex Formulation 2, with 0 -lg of n-dodecyl mercaptan chain transfer agent also included in the Monomer

Emulsion, the mercaptan being added to the ethyl acrylate + Sipomer® BE solution prior to emulsification .

(% )

PH 2 -46 2 -01 2 -08 2 -70 2 -73

Particle size 90 72 106 96 80 (nm)

Table I

* the %wt of BEM active agent in the Table is the %wt of the alkoxylated alcohol methacrylate ester, understood to be ~50% of the Sipomer® BEM as supplied.

# Latex Formulation 5 was prepared with 0 -lg chain transfer agent.

Using the same process as that used to prepare Latex Formulation 1, Latex Formulations 6 to 11 were also prepared, being aqueous dispersions of copolymers having the theoretical compositions set out in Table II. Latex Formulations 6 to 10 were prepared in accordance with the teaching of the prior art discussed above. Latex Formulation 11 does not contain any associative monomer C. Latex Formulation 12 was also prepared by the method of Latex formulation 1. This employed the same monomer proportions as Latex formulation 1, but with the ethyl acrylate monomer replaced by n- butyl acrylate. A further formulation, Latex Formulation 13, comprises a

reproduction of Thickener B from Table 1 of Example 1 of

US5,703,176, being one of the prior art documents discussed above. The latex is formed from 99% ethyl acrylate and 1% methacrylic acid, with no associative monomer C.

Acrylic 10 ·0 5 ·0 10 ·5 7 ·8 acid (%wt)

ethacrylic 25 -0 15 -0 5 ·0 10 ·0 5 ·0 3 ·9 1 · ο acid (%wt)

BE active 10 -0 10 -0 10 ·0 10 · ο 10 · ο 7 ·7 agent (%wt)

LATEX PROPERTIES

Viscosity 26 36 34 30 30 40 30 34 (cps)

Solids 39 -0 37 -1 38 -7 37 ·4 37 ·8 39 ·5 37 -6 39 ·3 content (%)

PH 2 -08 2 ·30 2 -30 2 -47 2 -22 2 -04 2 -58 2 -91

Particle 96 67 176 76 97 115 177 121 size (nm)

Table II

Further formulations prepared by the method of Latex Formulation were Latex Formulations 14 to 17. These all employed the same monomer proportions as Latex Formulation 2 (84-7% ethyl acrylate, 7-7% acrylic acid, 2-51 methacrylic acid and 5-1% alkoxylated alcohol (meth) crylate associative monomer), but in each case a different associative monomer was used instead of the BEM. The properties of these latexes are shown in Table III.

Table III The latex formulations described above were subjected to hydrolysis steps at mild temperatures. Further experiments were conducted to ascertain whether or not the prior art teaching of a neutralisation (i.e. not hydrolysis) step would provide acceptable thickening performance. This established that those formulations that are used in accordance with the hydrolysis process of the invention provide the desired, and demanding, thickening performance, whereas those used according to the neutralisation process of the prior art do not. The hydrolysis and thickening tests further demonstrate that the specific sub-class of latexes (obtained via emulsion

copolymerisation of A' + B' + C + D' ) described herein provides excellent levels of thickening performance even when hydrolysed at ambient temperature.

Hydrolysis of the Emulsion Copolymer Latexes at 40°C

Latex Formulations were subjected to hydrolysis at 40°C to ascertain whether useful low pH thickeners could be obtained using mild process conditions. The same test was applied to the Formulations according to the prior art to ascertain whether similar levels of thickening performance at low pH was obtainable.

Hydrolysis of the emulsion copolymer latexes at elevated temperature was accomplished via the following test method. 10 -06g of latex was diluted with 84 -47g deionised water in a 250ml round bottomed flask containing a magnetic stirrer bar, and 5 -46g of 32% aqueous sodium hydroxide solution was swirled into it. The flask was then loosely stoppered with a rubber septum cap and mounted on a magnetic stirrer hotplate having shaped depressions in its surface to take the curvature of the flask. (The hotplate was of a size designed to take five flasks. at a time, so five tests could be carried out

simultaneously.) The flask (s) on the hotplate were then heated, with stirring, to 40°C and maintained at this temperature for two hours before being left to cool naturally back to ambient temperature and stand at ambient temperature overnight. The next day, the contents of the flask (usually a gel) was transferred to a beaker and diluted with 255 -86g deionised water before measuring the viscosity with a Brookfield RVT instrument (spindle 6 speed 5 rpm) . The pH of the mixture was then progressively reduced with 50% aqueous citric acid solution, measuring the viscosity at each downward pH step until thickening effect was no longer perceptible.

The emulsion copolymer Latex Formulations 6 to 10 (taught as HASE thickeners for use under neutralisation conditions by the prior art) were subjected to these test conditions and the results are set out in Table IV.

Table IV

Note: Vise. = viscosity in centipoise. These data show that, although the emulsion copolymer latex compositions taught by the prior art as thickeners when used in neutralised form have negligible thickening effect under acidic conditions when used as previously taught (see below for discussion of neutralisation experiments) , when subjected to the mild

temperature hydrolysis process of the invention they will function as thickeners under acidic conditions, below pH 5 -5, and even below pH 5.0, in some cases.

Emulsion copolymer Latex Formulations 1 to 4, illustrating the presently claimed invention, were also hydrolysed at 40°C to assess subsequent behaviour under acid conditions. The results of these tests are set out in Table V (viscosities again being in

centipoise) , and show the effectiveness of these compositions also as thickeners for aqueous acidic media when first hydrolysed according to the inventive process.

Table V

Latex Formulation 11 (having no component C) performed poorly, giving post-hydrolysis viscosities of only 2,000 centipoise and 3,000 centipoise at pHs 12-8 and 12-7 respectively. It was not considered worthwhile to reduce the pH of this sample, given the low starting viscosities. This demonstrates that the absence of component C is very significant.

Latex Formulation 12, comprising butyl acrylate instead of ethyl acrylate, was hydrolysed at 40 °C for 2 hours under the same conditions as used for the other formulations. The alkaline dispersion remained cloudy and the viscosity at pH = 12-8 was too low to measure, indicating that hydrolysis did not occur. This shows that copolymers of (meth) acrylate esters of higher alcohols

(homologues >C2 alcohols) such as n-butanol are not suitable for the preparation of thickeners under the specific mild hydrolysis conditions of the invention.

Latex Formulation 13, Thickener B from Table 1 of Example 1 of US5,703,176 and lacking component C, was also hydrolysed at 40°C for 2 hours under the same conditions as used for the other

formulations. Once more, the alkaline dispersion remained cloudy and the viscosity at pH = 12 -8 was too low to measure, indicating that hydrolysis did not occur. This shows that the prior art composition (99% ethyl acrylate; 1% methacrylic acid; no component C) is not viable for the preparation of thickeners under the specific mild hydrolysis conditions of the invention.

In contrast, the formulations described herein in respect of the inventive method are adapted so as to provide good thickening performance.

Latex Formulations 14 to 17, which illustrate the presently claimed invention, were hydrolysed at 40°C to assess subsequent behaviour under acid conditions. The results of these tests are set out in Table VI, and show the effectiveness of these compositions also as thickeners for aqueous acidic media when first hydrolysed according to the inventive process.

Table VI

The above results show that thickeners made in accordance with the invention provide a viscosity at pH 5.6 of at least 3,600

centipoise, in some cases at least 7,000 centipoise, in some cases at least 10,000 centipoise and even 15,000 centipoise or more for some embodiments.

Not only is excellent low pH thickening performance achieved, but alkali thickening behaviour is also good, with viscosities of at least 20,000 centipoise achieved at pH 12.7, in some cases at least 50,000 centipoise and even 100,000 centipoise or more for some embodiments . As noted above, the viscosity of the compositions formed in accordance with the invention can be reversibly adjusted by control of the pH. Thus, a low viscosity solution can be formed by "over acidifying" the composition, permitting convenient

storage/supply/transfer, with the desired viscosity being recovered by raising the pH at a desired time and place.

Hydrolysis of the Emulsion Copolymer Latexes at 50 °C The hydrolysis and pH reduction test previously described for a hydrolysis temperature of 40°C was repeated on Latex Formulations 3, 7, 8 and 9, except that a temperature of 50°C was now employed for the hydrolysis step. The results of these tests are set out in Table VII, viscosities being in centipoise, as before.

Table VII

Again, impressive low pH viscosities were achieved, with some embodiments providing a viscosity of at least 10,000 centipoise at pH 5.5. For all of the experiments, good thickening at alkali pH was also demonstrated, with 15,000 centipoise or more achieved at pH 12.5.

Neutralisation of the Emulsion Copolymer Latexes at Ambient

Temperature

The normal method of use of the HASE thickener compositions according to the prior art (such as those of EP-A-0, 013, 836, discussed above) is to neutralise the copolymer with one equivalent, or thereabouts, of an alkali (such as aqueous sodium hydroxide solution) or other base to effect thickening of an aqueous medium in the pH range of approximately 7 to approximately 9-5. Some of the emulsion copolymer Latex Formulations described above were therefore tested for thickening under acidic conditions following

neutralisation, rather than hydrolysis.

In this case, 28g of the emulsion copolymer latex was diluted with 235g of deionised water. To this dispersion was then added an amount of 32% aqueous sodium hydroxide solution calculated to neutralise the copolymer and bring the pH of the dispersion into the range 7 to 9-5. This mixture was left to stand at ambient temperature overnight before being diluted with 711 -8g of deionised water. The viscosity was then measured in the usual way. When a measurable viscosity was recorded, the pH of the neutralised dilution was reduced by means of small additions of 50% aqueous citric acid solution until the viscosity dropped to below measurable range.

This test was performed on Latex Formulations 6 to 10, and the results are set out in Table VIII.

Table VIII

Note: Vise. = viscosity in centipoise.

The data in Table VIII show that when the compositions of the prior art are used in the manner taught by the prior art, i.e. neutralisation to pH between 7 and 9 -5, thickening falls away markedly if the pH of the thickened medium is subsequently reduced to acidic values. This is even the case with Latex Formulation 6, which gives outstanding thickening at pH 6 -9 or above, but for which effective thickening disappears below pH 6-6. The prior art neutralisation process is therefore inadequate for achieving effective thickening at acidic pH, especially pH below 6 -0 and most especially below pH 5-5. In contrast the specific hydrolysis process according to the invention achieves thickening under such acidic (and alkaline) conditions.

Hydrolysis of the Emulsion Copolymer Latexes at Ambient Temperature

The Latex Formulations of the invention were subjected to ambient temperature hydrolysis to ascertain whether useful low pH thickeners could be obtained using not just mild temperatures but ambient temperature, an even more challenging proposition. The same test was applied to the Formulations according to the prior art to ascertain whether similar levels of thickening performance at low pH was obtainable.

As in the neutralisation test, 28 -0g of emulsion copolymer latex was diluted with 235 -0g of deionised water. 15 -2g of 32% aqueous sodium hydroxide solution was stirred into the mixture, which was then left to stand overnight at ambient temperature. The next day, the mixture (which was by now considerably higher in viscosity) was further diluted with 711 -8g of deionised water, using a Silverson mixer to ensure homogeneity. The pH and viscosity (Brookfield RVT, spindle 6 at 5 rpm) were measured and the pH then reduced with a 50% aqueous solution of citric acid. It was generally found that lOg of this solution would bring the pH down into the region 5-5 to 6 -3, giving a polymer content of the order of 1-1%. Where necessary, further additions of citric acid solution were used to reduce the pH still further, until the viscosity dropped below 500 centipoise, often becoming too low to register a value under these measurement conditions . The behaviour of Latex Formulations 1 to 5 (from Table I) as the of the hydrolysed dispersions is reduced is set out in Table IX.

Table IX

The results in Table IX show that not only is excellent performance achieved at alkali pH (viscosity at pH 12.5 of at least 45,000 centipoise) but also impressive performance at acid pH (viscosity at pH 5.5 of at least 8,000 centipoise, in most cases at least 10,000 centipoise; and viscosity at pH 5.3 of at least 2,000 centipoise). Indeed, even when a chain transfer agent is used, in Latex

Formulation 5, good thickening over a very wide pH range is achieved.

As noted above, Latex Formulations 6 to 10 are compositions formulated according to the teaching of the prior art. These were subjected to the same ambient temperature hydrolysis test as Latex Formulations 1 to 5, and the results of these tests are set out in Table X. All viscosities are, once again, in centipoise.

- - - - - - - - 5 ·3 1, 000

Table X

Note: Vise. = viscosity in centipoise.

The data in Table X show the prior art latexes (Formulations 6 to 10) to be less effective, when hydrolysed at ambient temperature, in thickening at high pH (e.g. pH 12.5) and also at low pH, especially at pHs of 5 -5 or below, as compared to the latexes of the invention (Formulations 1 to 5) . Latex Formulation 11, which contains no associative monomer component C, hydrolysed poorly at ambient temperature, the

hydrolysis product having a viscosity of 1,200 centipoise at pH 12-3. It was not considered worthwhile to reduce the pH when testing Latex Formulation 11. This demonstrates once again that the absence of component C is significant.

Latex Formulation 12 employs butyl acrylate in place of ethyl acrylate. The hydrolysis of this latex also failed at ambient temperature, again illustrating that ethyl acrylate is required as described herein for effective thickening performance. pH reduction using various weak acids

Latex Formulations 3 and 7 were hydrolysed by means of the same 40°C hydrolysis methodology described above, only in these tests the citric acid used to reduce the pH of the diluted, alkaline solutions was replaced first by acetic and then by ascorbic acid. The data in Table XI below show the effectiveness of the invention when these alternative acids are used for the pH reduction steps.

- - 6 -54 49, 000 6 -50 15,200 - -

- - 5 -96 54, 400 - - 6 -06 9, 000

- - - - 5 -84 5, 600 - -

- - - - - - 5 -65 2, 600

- - 5 -53 24, 400 - - 5 -51 ~0

5 -36 29, 800 5 -36 16, 800 5 -00 1, 200 - -

5 -21 20, 000 5 -20 8, 800 - - - -

5 -05 9, 000 5 -00 ~0 - - - -

4 -92 2, 800 - - - - - -

4 -82 1, 400 - - - - - -

4 -71 1, 200 - - - - - -

4 -55 100 - - - - - -

Table XI

Hydrolysis using potassium hydroxide

The usual 40°C hydrolysis method, as described above in relation to Tables IV and V, was also adapted to hydrolyse the emulsion copolymer latexes with potassium hydroxide instead of sodium hydroxide, maintaining the molar concentration of the potassium hydroxide in this test at the same level as that of the sodium hydroxide in the usual test. In this case, therefore, 10 -06g of latex was diluted with 82 -28g deionised water in the 250ml round bottomed flask, and 7 -65g of 32% aqueous potassium hydroxide solution was swirled into it. The remainder of the test was conducted as previously described. Latex Formulations 3 and 7 were tested in this way and the results are shown in Table XII below.

5 -85 57, 000 5 -92 11,400

- - 5 -66 1, 400

5 -47 30, 000 5 -47 200

5 -21 16, 600 - -

4 -93 1, 600 - -

4 -71 ~0 - -

Table XII

The data demonstrate that an alternative base to sodium hydroxide can be used to perform the inventive process to good effect. Latex Formulation 3, in which the copolymer is derived from both acrylic and methacrylic acid, is particularly effective at very low pH.

Recovery of Viscosity Following Acidification

Latex Formulation 3 was hydrolysed at ambient temperature via the methodology discussed above in relation to Table IX. However, having reduced the pH down to below 5 -0 with citric acid in the normal way, the pH was then raised again by dropwise addition of the 32% aqueous sodium hydroxide solution. The Table XIII below shows that, as the pH climbs back to values greater than 5 -0 once again, the viscosity also increases again, to quite substantial values.

Table XIII To compare this behaviour with that of a neutralised HASE thickener of the prior art, 28 -0g of Latex Formulation 7 was dispersed into 247 -76g of deionised water, and 2 -44g of 32% aqueous sodium hydroxide solution stirred in to neutralise the latex. As with the method described above, used to create the data in Table VIII, the pH was then reduced with small additions of citric acid solution. The viscosity of the dispersion swiftly dropped to below measurable values. The pH was reduced down to 3-6 and then raised again by dropwise addition of 32% aqueous sodium hydroxide solution. The viscosity, however, remained below measurable values, even when the pH was raised back to above 10-0. The data are set out in the Table XIV below. They demonstrate the benefit of thickening according to the inventive process, showing that thickening via the inventive process can be recovered from highly acidic conditions simply by raising the pH once again, whereas once a thickened

solution/dispersion of the prior HASE art has been over-acidified, its thickening remains lost.

Table XIV The demonstration was repeated for hydrolysis at elevated

temperature by hydrolysing Latex Formulations 3 and 7 at 40 °C via the usual methodology. As before, the pH was reduced with citric acid solution and then raised again by dropwise sodium hydroxide addition. These data are set out in the Table XV below. Latex Formulation 3 Latex Formulation 7

PH Viscosity (cps) H Viscosity (cps)

13 -52 78, 000 13 -76 27, 000

6 -72 66, 000 - -

- - 6 -18 12, 600

5 -65 42, 000 5 -55 4, 600

5 -45 23, 000 - -

5 -16 13, 000 5 -23 ~0

4 -97 3,200 - -

4 -88 ~0 - -

5 -40 32, 800 - -

- - 6 -17 7,200

- - 7 -03 9,200

7 -70 40, 000 - -

12 -40 47, 000 12 -75 10, 000

Table XV

The data show that thickening via the inventive process performed at elevated temperature can also be recovered after over-acidification simply by addition of small quantities of alkali to raise the pH once again.

Non-ionic ethylenically unsaturated monomers D

Latex Formulation 18 was based on Latex Formulation 3, but with the 88-3% of ethyl acrylate replaced by 85-0% ethyl acrylate and 3-3% styrene, to show the effect of an additional non-ionic ethylenically unsaturated monomer (Component D) within the invention.

Viscosity (cps) 18

Solids content (%) 38 -9

pH 2 -88

Particle size (ran) 98

Table XVI

Hydrolysis of the Emulsion Copolymer Latexes at 40°C

Latex Formulation 18 was hydrolysed at 40°C according to the method used to generate the data in Tables IV, V and VI. The viscosities of the hydrolysed polymer as the pH was reduced are set out in the table below.

Table XVII

The data show that when a small amount of optional additional non- ionic ethylenically unsaturated monomer (component D) is included in the preparation of the latex formulation, the product still, upon hydrolysis, functions effectively as a thickener for aqueous acidic media .

Hydrolysis of Emulsion Copolymer Latexes at Ambient Temperature

Latex Formulation 18 was hydrolysed at ambient temperature with sodium hydroxide solution and the effectiveness of the product demonstrated as a thickener for aqueous acidic media by reducing the pH with citric acid by using the same test procedure used to generate the data in Tables IX and X. The changes in viscosity upon pH reduction are displayed in the table below. Latex Formulation 18

pH Viscosity (cps)

13 -30 96,000

7 -80 75, 000

6 -25 61, 000

5 -91 40, 000

5 -64 18, 000

5 -50 11, 400

5 -33 3,000

5 -22 <400

Table XVIII

As was the case at 40°C (Table XVII above) , the data show that when a small amount of optional additional non-ionic ethylenically unsaturated monomer (component D' ) is included in the preparation of the latex formulation, the product still, upon hydrolysis, functions effectively as a thickener for aqueous acidic media.

Latex Formulation 18 was hydrolysed at ambient temperature, again using the method described above in relation to Tables IX and X (28 -0g of latex in 235 -0g of deionised water plus 15 -2g of 32% aq. Sodium hydroxide) , except that on these occasions the pH reduction part of the test was performed using acetic acid instead of citric acid, and again using ascorbic acid instead of citric acid. These results are tabulated below.

5 -17 ~0 5 -25 ~0

Table XIX

The data show that when alternative acids to citric are used to reduce the pH of the hydrolysed copolymer solution, it is still possible to achieve adequate thickening effect under acidic conditions.

Hydrolysis of Emulsion Copolymer Latexes at 75 °C

The hydrolysis and pH reduction test previously described in relation to Table IV for a hydrolysis temperature of 40 °C was repeated on Latex Formulations 13 (formulated according to the prior art, US Patent no. 5,703,176 previously referred to), 3 and 7, except that a temperature of 75°C was now employed for the

hydrolysis step. It was found that the prior art formulation, Latex Formulation 13, still could not be hydrolysed with sodium hydroxide solution at this concentration. Even at this higher temperature of 75 °C, the contents of the round bottomed flask remained very mobile, even after 24 hours. By contrast. Latex Formulations 3 and 7 behaved normally, forming viscous gels within their round bottomed flasks after two hours at 75 °C and cooling back to ambient temperature. Their viscosity data after dilution and pH reduction according to the normal test method can be seen in the table below.

Table XX These tests clearly show the prior art formulation (Latex

Formulation 13) to be ineffective as a thickener when subjected to the milder hydrolysis conditions of the process according to the invention. The prior art formulation evidently requires the more severe hydrolysis conditions taught within US Patent no. 5,703,176 in order to function adequately, whereas latex formulations within the compositional ranges claimed under the invention are seen to be effective as hydrolysable thickeners when subjected to the milder, inventive process.

Latex Formulation 3, in which the copolymer is derived from both acrylic and methacrylic acid, is particularly effective at very low _PH.

Claims

1. A method for making a thickener composition which comprises a step of hydrolysing, at a temperature between 30°C and 75°C, a copolymer obtainable by emulsion copolymerisation of the following monomer components :

A. ethyl acrylate, in an amount greater than 30% by weight, based on the total weight of monomer components A + B + C + D;

B. from 0 -1% to less than 69 -0% by weight, based on the total

C. from 1% to 20% by weight, based on the total weight of monomer components A + B + C + D, of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol; and

ethylenically unsaturated monomers other than those defined above as A, B or C; wherein the total monomer components A + B + C + D together add up to 100%.

2. A method according to claim 1, wherein the step of hydrolysing comprises the addition of a water soluble alkali selected from potassium hydroxide, sodium hydroxide and ammonium hydroxide.

3. A method according to claim 1 or claim 2, wherein the step of hydrolysing comprises adjusting the pH to at least 10.

4. A method according to any one of claims 1 to 3, wherein the step of hydrolysing comprises adding 3 to 10 equivalents of

hydroxide relative to the acid content of the copolymer.

5. A method according to any one of the preceding claims, wherein the step of hydrolysis is conducted at a temperature in the range 35°C to 55°C.

6. A method according to any one of the preceding claims, wherein the method includes, after the hydrolysis step, a step of reducing the pH of the hydrolysis product with acid in order to reduce the pH to 6 or less.

7. A method according to claim 6, wherein the step of reducing the pH employs a weak acid selected from citric acid, acetic acid, oxalic acid ascorbic acid, tartaric acid, malic acid and lactic acid .

8. A method according to any one of the preceding claims, wherein the ethyl acrylate component A is present in an amount selected from

50% to 98% by weight, 50% to 94% by weight, 60% to 94% by weight, 70% to 94% by weight, and 75% to 94% by weight, based on the total weight of monomer components A + B + C + D.

9. A method according to any one of the preceding claims, wherein the ethylenically unsaturated carboxylic acid component B is provided in an amount selected from: 2% to 50% by weight, 2% to 40% by weight, 2% to 30% by weight, 2% to 20% by weight, 2% to 17% by weight, 5% to 20% by weight and 5% to 17% by weight, based on the total weight of monomer components A + B + C + D.

10. A method according to any one of the preceding claims, wherein component B is selected from: acrylic acid, methacrylic acid, β- carboxyethyl acrylate, and mixtures thereof.

11. A method according to any one of the preceding claims, wherein component B comprises at least 30% by weight, suitably at least 40% by weight, of acrylic acid, based on the total weight of component B.

12. A method according to any one of the preceding claims, wherein the associative monomer component C is provided in an amount selected from: 1% to 18% by weight, 1% to 15% by weight, 2% to 15% by weight, 2% to 10% by weight, 2.5% to 10% by weight, and 2.5% to 8% by weight, based on the total weight of monomer components A + B + C + D.

13. A method according to any one of the preceding claims, wherein the associative monomer component C is an

alkoxypoly (alkyleneoxy) ethyl (meth) acrylate of general formula (I) R-O- (CH₂-CH₂-0) x(CH₂-CH (R¹) 0) y-C (0) -CR²=CH₂ (I)

in which R is a linear or branched (C₇ to C₃₂) alkyl group or an alkylphenyl group whose alkyl group has from 1 to 20 carbon atoms, R¹ is methyl, R² is hydrogen or methyl, x is a positive integer with an average value from 3 to 80 and y is 0 or a positive integer with an average value from 1 to 20.

14. A method according to claim 13, wherein R is a linear or branched (Ci₂ to C₂₂) alkyl group, the average value of x lies in the range from 20 to 30, and R² is H or methyl, suitably methyl.

15. A method according to any one of the preceding claims, wherein the associative monomer component C comprises one or more of the active ingredients in the commercial products Sipomer® BEM, Sipomer® HPM-100 and Sipomer® HPM-400, the methacrylate ester of the 11-mole ethoxylate of a C16-C18 fatty alcohol, and the methacrylate ester of the 25-mole ethoxylate of a C16-C18 fatty alcohol.

16. A method according to any one of the preceding claims, wherein the non-ionic ethylenically unsaturated monomer component D is present in an amount of no more than 5% by weight based on the total weight of monomer components A + B + C + D.

17. A method according to any one of the preceding claims, wherein the non-ionic ethylenically unsaturated monomer component D is selected from linear, branched, cycloaliphatic or arylaliphatic esters of acrylic or methacrylic acids.

18. A composition suitable for use as a pH responsive thickener, which composition comprises a hydrolysis product of a copolymer obtainable by emulsion copolymerisation of components A to C, and optionally D, as defined in any one of the preceding claims, or a latex comprising the copolymer.

19. A composition according to claim 18, wherein the hydrolysis product is the hydrolysis product of the method of any one of claims 1 to 17.

20. The use of a thickener composition obtainable via hydrolysis of a copolymer obtainable by emulsion copolymerisation of components A to C, and optionally D, as defined in any one of claims 1 to 17, or a latex comprising the copolymer, as a thickener for an aqueous system.

21. The use of claim 20, wherein the use as a thickener includes use as a thickener for an aqueous system at acidic pH.

22. An emulsion copolymer latex comprising a copolymer obtainable via the emulsion copolymerisation of the following monomer

components :

B' . from 0-1% to 19% by weight, based on the total weight of monomer components A' + B' + C + D' , of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A' and at least one carboxylic acid (C0₂H) group, wherein the at least one ethylenically unsaturated carboxylic acid monomer comprises acrylic acid in an amount greater than 30%, up to 100%, of the total weight of the ethylenically unsaturated carboxylic acid monomer component

B' ;

C . from 1% to 20% by weight based on the total weight of monomer components A' + B' + C + D' of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol; and

D' . from 0% to 15% by weight, based on the total weight of

monomer components A' + B' + C + D' , of one or more non- ionic ethylenically unsaturated monomers other than those defined above as A' , B' or C ; wherein the total monomer components A' + B' + C + D' together add up to 100%.

23. An emulsion copolymer latex according to claim 22, wherein ethyl acrylate component A' is present in an amount selected from: above 80% up to 93% by weight, above 80% up to 89% by weight, and 80.5% to 86% by weight, based on the total weight of monomer components A' + B' + C + D' .

24. An emulsion copolymer latex according to claim 22 or claim 23, wherein the ethylenically unsaturated carboxylic acid component B' is provided in an amount selected from: 5% to 12.5% by weight, 8% to 12.5% by weight, and 10% to 12% by weight, based on the total weight of monomer components A' + B' + C + D' .

25. An emulsion copolymer latex according to any one of claims 22 to 24, wherein component B' , other than the acrylic acid component, is selected from: methacrylic acid, β-carboxyethyl acrylate, and mixtures thereof.

26. An emulsion copolymer latex according to any one of claims 22 to 25, wherein acrylic acid is present in an amount selected from: above 50% up to 95%, above 50% up to 80%, 60% to 80%, and 65% to 77.5% of the total weight of the ethylenically unsaturated

carboxylic acid monomer component B' .

27. An emulsion copolymer latex according to any one of claims 22 to 26, wherein the associative monomer component C is present in an amount selected from: 1% to 18% by weight, 1% to 15% by weight, 2% to 15% by weight, 2% to 10% by weight, 2.5% to 10% by weight, and 2.5% to 8% by weight, based on the total weight of monomer

components A' + B' + C + D' .

28. An emulsion copolymer latex according to any one of claims 22 to 27, wherein the associative monomer component C is as defined for component C in any one of claims 13 to 15.

29. An emulsion copolymer latex according to any one of claims 22 to 28, wherein the associative monomer component D' is as defined for component D in any one of claims 16 and 17.

30. A method of making a thickener composition which comprises a step of hydrolysing an emulsion copolymer latex of any one of claims 22 to 29.

31. A method according to claim 30, wherein the step of hydrolysis is carried out at ambient temperature.

32. A composition suitable for use as a pH responsive thickener, which composition comprises a hydrolysis product of an emulsion copolymer latex of any one of claims 22 to 29.

33. The use of a thickener composition, obtainable via hydrolysis of an emulsion copolymer latex of any one of claims 22 to 29, as a thickener for an aqueous system.

34. A copolymer obtainable via the emulsion copolymerisation of the following monomer components: ethyl acrylate, in an amount greater than 80% by weight and less than 97 -5% by weight, based on the total weight of monomer components A' + B' + C + D' ; from 0 -1% to 19% by weight, based on the total weight of monomer components A' + B' + C + D' , of at least one ethylenically unsaturated carboxylic acid monomer containing one C=C double bond capable of free radical copolymerisation with component A' and at least one carboxylic acid (C0₂H) group, wherein the at least one ethylenically unsaturated carboxylic acid monomer comprises acrylic acid in an amount greater than 30%, up to 100%, of the total weight of the ethylenically unsaturated carboxylic acid monomer component B' ; from 1% to 20% by weight based on the total weight of monomer components A' + B' + C + D' of at least one associative monomer, being a (meth) acrylate ester of an alkoxylated alcohol; and from 0% to 15% by weight, based on the total weight of monomer components A' + B' + C + D' , of one or more non- ionic ethylenically unsaturated monomers other than those defined above as A' , B' or C ; wherein the total monomer components A' + B' + C + D' together add up to 100%.