WO2009090204A1

WO2009090204A1 - Associative thickeners

Info

Publication number: WO2009090204A1
Application number: PCT/EP2009/050403
Authority: WO
Inventors: Franco Federici; Gianmarco Polotti; Andrea Buzzoni; Thierry Bossi; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2008-01-16
Filing date: 2009-01-15
Publication date: 2009-07-23
Also published as: ITVA20080005A1

Abstract

Crosslinked associative polymeric thickeners for use in aqueous compositions, especially in cosmetics and personal care products, are prepared by polymerization of: a) from 20 to 70% by weight of at least one monoethylenically unsaturated monomer containing a carboxylic group; b) from 20 to 70% by weight of at least one monoethylenically unsaturated nonionic monomer; c) from 1 to 20% by weight of at least one nonionic associative monomer obtained from i) a diisocyanate, ii) a monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality, iii) a compound comprising a linear carbon atoms chain of at least 6 carbon atoms and a polyoxyalkylene chain; d) from 0.01 to 3% by weight of at least one polyethylenically unsaturated monomer

Description

ASSOCIATIVE THICKENERS Technical field

The present invention relates to crosslinked associative polymeric thickeners for use in aqueous compositions, especially in cosmetics and personal care products. The crosslinked associative polymeric thickeners of this invention: possess high thickening capability, even in the presence of surfactants and electrolytes; - give good performances in terms of shear thinning index increase; their aquoeus solution are homogeneous and clear. Background art

It is known that a technical problem often encountered in the cosmetic industry is to obtain stable high viscous homogeneous formulations comprising surfactants, dispersed solid particles and electrolytes.

Thickeners employed in cosmetics shall manifest their thickening capability without negatively altering the other properties of the formulations, such as hair and/or skin compatibility.

Most often, thickeners are also asked to control the whole rheology of cosmetics, imparting them the desired viscosity in each step of their life, from packaging to application.

In the specialised literature many methods are reported to regulate the rheological properties of different formulations, often including the use of anionic polymers performing as thickeners at neutral and basic pHs. We cite as an example:

- GB 870,994, disclosing copolymers of methacrylic acid and CrC₄ alkyl acrylate in aqueous emulsion.

- EP 13836 (Rohm & Haas), describing thickeners based on copolymers of (meth)acrylic acid, d-C₄ (meth)acrylic esters, selected (meth)acrylic esters comprising oxyethylene units, and optionally polyethylenically unsaturated monomers; the thickeners are said to be less sensitive to electrolytes than prior art synthetic thickeners that are prepared without the use of the selected (meth)acrylic esters. - EP 1272159 (Noveon), describing the use of crosslinked acrylate copolymers generally free from, i.e. containing less than about 1% by weight, associative monomers.

Some synthetic thickeners, originally designed for use in other industrial fields, such as latex paints and coatings, also proved to be useful in cosmetics. As an example, we cite the alkali soluble latex thickeners of US 4,514,552 (DeSoto), which essentially are aqueous emulsion copolymers of: (A) about 20-70 weight percent of an alpha, beta-unsaturated carboxylic acid, typically methacrylic acid; (B) about 20-80 weight percent of a monoethylenically unsaturated monomer lacking surfactant characteristics, typically ethyl acrylate; (C) about 0.5-60 weight percent of a nonionic urethane monomer which is the reaction product of a monohydric nonionic surfactant with a monoethylenically unsaturated monoisocyanate; in US 6,228,348 (L'Oreal) describes a composition for cosmetic use which comprises at least one acrylic terpolymer based on the same monomers of US 4,514,552.

US 5,015,711 (Coatex) describes associative thickening copolymers used particularly in charged and/or pigmented aqueous compositions generating rheological characteristics close to the Newtonian behaviour. The Newtonian behaviour is pursued by the joint incorporation of a surfactant monomer having at least one urethane function and by the very low molecular weight of said copolymer.

Crosslinkers are absent and the copolymer is almost linear; the molecular weight is maintained low by means of known systems, such as the presence of an alkylmercaptan transfer agent, and the resulting upper BrookfieldOviscosity of the copolymers of US 5,015,71 1 is 220 mPa*s (spindle 1 to 3, RVT, 100 rpm, 2% by weight, pH 9 and 20 ⁰C). Disclosure of the Invention

In accordance with the present invention crosslinked associative thickeners are produced providing high viscosity to their aqueous solutions and possessing a pseudoplastic rheologic behaviour which renders them particularly suitable for use in cosmetics and personal care products, especially those comprising suspended particles. The crosslinked associative thickeners are obtained by polymerization of: a) from 20 to 70% by weight of at least one monoethylenically unsaturated monomer containing a carboxylic group; b) from 20 to 70% by weight of at least one monoethylenically unsaturated nonionic monomer; c) from 1 to 20% by weight of at least one associative monomer obtained from i) a diisocyanate, ii) a monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality, iii) a compound comprising a linear carbon atoms chain of at least 6 carbon atoms and a polyoxyalkylene chain; d) from 0.01 to 3% by weight of at least one polyethylenically unsaturated monomer.

An advantage of the thickeners of the invention is their general insensitiveness to electrolytes and surfactants.

With the expression "cosmetics and personal care products" we mean the products normally used for personal care, such as shampoos, skin and body cleansers, body and face creams and lotions, hair gels and lotions, hair colouring and bleaching creams, sunscreen compositions, make-up products, moisturizing and perspiring fluids, nail varnishes and other products for similar applications. Acrylic acid, methacrylic acid, itaconic acid and mixture thereof are examples of monoethylenically unsaturated monomer containing a carboxylic group that are useful for the preparation of the associative thickeners. Examples of useful monoethylenically unsaturated nonionic monomer are (meth)acrylic esters, such as methyl, ethyl, propyl, butyl, 2-ethylhexyl, lauryl (meth)acrylates; acrylonitrile; acrylamide; styrene; methylstyrene; mixture thereof.

Preferably the monoethylenically unsaturated nonionic monomer is a (meth)acrylic ester, more preferably ethyl acrylate, ethyl methacrylate or mixture thereof. The addition of the polyethylenically unsaturated monomer, acting as polymer crosslinker, is a key point in the preparation of the thickener of the present invention. The polyethylenically unsaturated monomer can be any of the known polyfunctional derivatives that are known to undergo radical polymerization with (meth)acrylic monomers.

Among the useful polyethylenically unsaturated monomer we cite diallylmaleate, allyl methacrylate, diallylphthalate, N-methylene-bis- acrylamide, pentaerithritol ether triacrylate, triallylcianurate. A further key point in the preparation of the thickener of the present invention is the presence in the polymer backbone of a specific associative monomer, having the structure detailed here below. As previously described, the associative monomer is obtained from the reaction of i) a diisocyanate, ii) a monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality, iii) a compound comprising a linear carbon atoms chain of at least 6 carbon atoms and a polyoxyalkylene chain Preferably, the monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality is allyl alcohol, which may be optionally 1 to 3 moles ethoxylated and/or propoxylated.

Due to their reactivity, the most preferred unsaturated compounds comprising a -NCO reactive hydroxyl functionality are allyl alcohol, monoethoxylated allyl alcohol and mixture thereof.

The compound comprising a linear carbon atom chain and a polyoxyalkylene chain may be any nonionic compound having an hydrophobic portion (linear carbon atom chain) and a hydrophilic portion (polyoxyalkylene chain). Preferably, the compound comprising a linear carbon atom chain and a polyoxyalkylene chain is an ethoxylated long chain fatty alcohol derived from artificial or natural source.

The long chain fatty alcohol can be linear or branched and shall contain at least ten carbon atoms and not more than 36 carbon atoms, preferably from 12 to 22 carbon atoms. The ethoxylated groups are introduced by standard ethoxylation technique and the ethoxyl number is statistically distributed around an average value that, for our purposes, is preferably in the range from 20 to 25. The lenght of the polyoxyethylene chain is important since it influences the water solubility of the whole polymeric chain, when the monomer is tide off in the polymer backbone.

The diisocyanates used in the preparation of the nonionic associative monomer can be any aliphatic or aromatic diisocyanate, such as isophorone diisocyanate, 1 ,6-hexamethylenediisocyanate, 4,4'-dicyclohexyl methane diisocyanate, toluene diisocyanate and mixture thereof.

Aliphatic diisocyanates are preferred and, among them, isophorone diisocyanate is particularly preferred because of the different reactivity of its two -NCO groups.

The presence of the diisocyanate backbone imparts additional hydrophobic properties to the monomer (beside those due to the presence of the carbon atoms chain) and also some rigidity to the structure, that it is thought may help the associative monomer to extend away from the polymer backbone. The associative monomer is prepared by two reaction steps, that are carried out with the use of catalysts that can be mantained in the final product, since they are not active in the further monomer radical reactivity.

As further detailed in the examples, the preparation of the associative monomer tipically starts with the dehydration of a fatty polyethoxylated alcohol in a close vessel under vacuum.

This is done prior to the addition of the diisocyanate, that is very water sensitive.

The molar ratio between the fatty ethoxylated alcohol and the diisocyanate is about 1. Due to the different molecular weight of the two species it is expected that only one of the NCO group per molecule of diisocyanate reacts with the fatty ethoxylated alcohol.

Some phosphoric acid may be added to neutralise the basic catalysts used in the preparation of the fatty polyethoxylated alcohol. After completion of the first stap of the reaction, the monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality is added. The reactivity of these species is normally very high, but, however some butyl tin dilaurate is prefarably previously added, as a catalyst for the addition reaction.

A careful addition of some radical inhibitors (not excessive, in order to avoid problem in the subsequent copolymerization), such as hydroquinone monomethyl ether, may be done to prevent the radical polymerization.

The monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality is added in a slight molar excess.

Alternatively, the associative monomer con be prepared by addition of the diisocyanate to the monoethylenically unsaturated compound comprising a -

NCO reactive hydroxyl functionality and subsequent reaction with the compound comprising a linear carbon atoms chain and a polyoxyalkylene chain.

The associative thickeners of the present invention are obtained by radical polymerization of monomers a) to d).

The polymerization starts thanks to the use of a radical initiator. Common initiators are chosen, depending on the polymerization process and reaction temperature.

Utilizable common initiators are: sodium, ammonium or potassium persulphate, with or without sodium methabisulphite, in order to make the well known redox couple; 2,2'-azobis(2-amidinopropane)-dihydrochloride, hydrogen peroxide and t-butyl-hydroperoxide.

Since high molecular weights are pursued, no chain transfers are added in the polymerization. The associative thickeners of the invention have high Brookfield® viscosity, i.e. have Brookfield® viscosity (spindle 6, RVT, 100 rpm, 2% by weight, pH 9 and 20 ⁰C) of at least 2,000 mPa-s.

Moreover, they possess a remarkable pseudoplastic behaviour which is illustrated in the following examples. The associative thickeners of the present invention are generally prepared and supplied in their acidic form; as they contain acidic groups, they need to be neutralized to the salt form to develop optimal viscosity increase in the aqueous compositions or cosmetics or personal care products. Surfactants, which are typical ingredients of cosmetics and personal care products, can be added before or after neutralization; a subsequent acidification of the obtained thickened composition may also take place, when needed, without significant impairment of the viscosity level. For the neutralization, high diffusion alkalis are commonly used, such as sodium or potassium hydoxyde, ethanolamine, ethylamine, methylamine, etc.. For back acidification typically weak organic acids, such as citric acid, salicylic acid and the like may be used. Example 1 Preparation of an associative monomer (AM1 )

In a 1 litre glass reactor with mechanical stirrer, condenser, thermometer and nitrogen purging line, 430 g (0.3171 mol) of 25 moles ethoxylated Ci_6-Ci₈ alcohol (MW = 1 356 dalton) were added . With gentle warming, the temperature is increased up to 135°C. Then a vacuum distillation (at 20 mmHg) was run for 1 hour to strip out all the possible water. After cooling to 90⁰C, 0.075 g of phosphoric acid (85% water solution) were added followed by 70.5 g (0.3171 mol) of isophorone diisocyanate (MW = 222.3 dalton). After 20 minutes, 0.2 g of dibutyl tin dilaurate were added to the reactor. The temperature was maintained at 90⁰C till NCO% equal to 2.3% (about 30 minutes). The reactor is then cooled to 60°C and , with a slow inflow of air, 20.3 g (0.3494 mol) of allyl alcohol (MW = 58.1 dalton) were added together with 0.2 g of hydroquinone monometyhl ether (MEHQ). Thanks to the exothermic reaction the internal temperature of the reactor raises to 65°C. This temperature is maintained till no NCO is present, as detected by the IR spectrum. Example 2

Preparation of an associative monomer (AM2)

In a 1 litre glass reactor with mechanical stirrer, condenser, thermometer and nitrogen purging line, 530 g (0.3908 mol) of 25 moles ethoxylated Ci_6-Ci₈ alcohol (MW = 1356 dalton) were added. Under gentle warming, the temperature is increased up to 135°C. Then a vacuum distillation ( at 20 mmHg) was run for 1 hour to strip out all the possible water. After a cooling to 90⁰C, 0.075 g of phosphoric acid (85% water solution) were added followed by 96 g (0.4318 mol) of isophorone diisocyanate (MW = 222.3 dalton). After 20 minutes, 0.2 g of dibutyl tin dilaurate were added to the reactor. The temperature is maintained at 90⁰C till NCO% equal to 2.61 % (about 30 minutes). The reactor is then cooled to 60⁰C and, with a slow inflow of air, 75 g (0.4688 mole) of 1.6 moles propoxylated allyl alcohol (MW = 160 dalton) were added together with 0.2 g of MEHQ. Thanks to the exothermic reaction the internal temperature of the reactor raises to 65°C. This temperature is maintained till no NCO is present, as detect by the IR spectrum. Example 3 Preparation of an associative monomer (AM3)

In a 1 litre glass reactor with mechanical stirrer, condenser, thermometer and nitrogen purging line, 43O g (0.3171 mol) of 25 moles Ci₆-Ci₈ ethoxylated alcohol (MW = 1356 dalton) were added. Under gentle warming, the temperature is increased up to 135°C. Then a vacuum distillation ( at 20 mmHg) was run for 1 hour to strip out all the possible water. After a cooling to 90⁰C, 0.075 g of phosphoric acid (85% water solution) were added followed by 77.5 g (0.3486 mol) of isophorone diisocyanate (MW = 222.3 dalton). After 20 minutes, 0.2 g of dibutyl tin dilaurate were added to the reactor. The temperature is maintained at 90°C till NCO% equal to 2.62% (about 30 minutes). The reactor is then cooled to 60⁰C and, with a slow inflow of air, 38.9 g (0.3809 mole) of 2-allyloxyethanol (MW = 102.13 dalton) were added together with 0.2 g of MEHQ. Thanks to the exothermic reaction the internal temperature of the reactor raises to 65°C. This temperature is maintained till no NCO is present, as detect by the IR spectrum. Example 4

Preparation of an associative thickener according to the invention In a one litre glass bottle with mechanical stirrer, an emulsion is made from: 429.47 g of water 9.15 g of a 30% aqueous solution of sodium lauryl sulphate, 216.55 g of ethyl acrylate, 139.11 g of methacrylic acid, 33.02 g of 1 % diallylmaleate solution in ethyl acrylate and 7.54 g of the associative monomer AM1.

In the same reactor of the Example 1 , 294.07 g of water, 9.12 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82⁰C the reaction is started by addition of a solution made of 2.94 g of water and 0.0598 g of ammonium persulphate. The temperature in the reactor raises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and an aqueous solution of 59.45 g of water and 0.5954 g of ammonium persulphate are added in 1 hour at 88-90⁰C. The system is left for 30 minutes more at 88-90°C, then it is cooled down at 65°C. At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a third termination is run at 40⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a fourth termination is run at 30⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes the reactor is discharged and the emulsion is filtered under a 150 micron polythene filter. Example 5

Preparation of a comparative associative thickener. For comparison, Example 4 was repeated by using, instead of AM1 , a commercial monomer commonly used in the production of associative acrylic thickeners (methacrylic ester of an ethoxylated (25 mol EO) C₁6-C₁8 fatty alcohol, 15% in methyl methacrylate, trade name PLEX® 6877-0 by Rohm GmbH). In a one litre glass bottle with mechanical stirrer, an emulsion is made from: 429.47 g of water 9.15 g of a 30% aqueous solution of sodium lauryl sulphate, 197.93 g of ethyl acrylate, 139.11 g of methacrylic acid, 33,02 g of 1 % diallylmaleate solution in ethyl acrylate and 26.16 g of PLEX 6877-0. In the same reactor of the Example 1 , 294.07 g of water, 9.12 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82⁰C the reaction is started by addition of a solution made of 2.94 g of water and 0.0598 g of ammonium persulphate.

The temperature in the reactor rises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and a water solution of 59.45 g of water and 0.5954 g of ammonium persulphate are added in 1 hour at 88- 90⁰C. The system is left for 30 minutes more at 88-90°C, then it is cooled down at 65°C.

At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a third termination is run at 40⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a fourth termination is run at 30⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes the reactor is discharged and the emulsion is filtered under a 150 micron polythene filter. Example 6-9 Preparation of more associative thickeners according to the invention.

More polymers were prepared following the procedure of Example 4, but varying the amount of associative monomer and the amount and kind of polyethylenically unsaturated monomer. These tests were made to assess if the changes in the two parameters could affect the thickening capability of the new polymers.

Although the crosslinker amount affects the absolute viscosity values, the thickeners of the invention always show an increase of viscosity and of its slope versus shear rate (bilogarithmic scale), as it is apparent from the following table (Table 1 ), where the viscosity data of 1.5% aqueous solution of the thickeners from the Examples 4-9 at different shear rates are reported (values are in pascal). Table 1

^**comparative

Example 6

In a one litre glass bottle with mechanical stirrer, an emulsion is made from:

429.47 g of water 9.15 g of a 30% aqueous solution of sodium lauryl sulphate, 208.38 g of ethyl acrylate, 139.1 1 g of methacrylic acid, 41 .28 g of a 1 % diallylmaleate solution in ethyl acrylate and 7.54 g of the associative monomer AM1.

In the same reactor of the Example 1 , 294.07 g of water, 9.12 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82⁰C the reaction is started by addition of a solution made of 2.94 g of water and 0.0598 g of ammonium persulphate. The temperature in the reactor rises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and a water solution of 59.45 g of water and 0.5954 g of ammonium persulphate are added in 1 hour at 88- 90⁰C. The system is left for 30 minutes more at 88-90⁰C, then it is cooled down at 65°C. At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a third termination is run at 40°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a fourth termination is run at 30⁰C by charging each time 0.32 g of ascorbic acid U. A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes the reactor is discharged and the emulsion is filtered under a 150 micron polythene filter. Example 7

In a one litre glass bottle with mechanical stirrer, an emulsion is made from: 429.47 g of water 9.15 g of a 30% aqueous solution of sodium lauryl sulphate, 208.38 g of ethyl acrylate, 139.1 1 g of methacrylic acid, 41 .28 g of a 1 % diallylmaleate solution in ethyl acrylate and 8.67 g of the associative monomer AM1.

In the same reactor of the Example 1 , 294.07 g of water, 9.12 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82°C the reaction is started by addition of a solution made of 2.94 g of water and 0.0598 g of ammonium persulphate. The temperature in the reactor rises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and a water solution of 59.45 g of water and 0.5954 g of ammonium persulphate are added in 1 hour at 88- 90⁰C. The system is left for 30 minutes more at 88-90°C, then it is cooled down at 65°C. At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a third termination is run at 40⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a fourth termination is run at 30⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes the reactor is discharged and the emulsion is filtered under a 150 micron polythene filter.

Example 8

In a one litre glass bottle with mechanical stirrer, an emulsion is made from: 433.07 g of water 9.23 g of a 30% aqueous solution of sodium lauryl sulphate,

218.29 g of ethyl acrylate, 140.28 g of methacrylic acid, 21.46 g of a 1% allyl methacrylate solution in ethyl acrylate and 7.6 g of the associative monomer

AM1.

In the same reactor of the Example 1 , 296.54 g of water, 9.2 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82⁰C the reaction is started by addition of a solution made of 2.96 g of water and 0.06 g of ammonium persulphate.

The temperature in the reactor rises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and a water solution of 59.95 g of water and 0.6 g of ammonium persulphate are added in 1 hour at 88-

90⁰C.

The system is left for 30 minutes more at 88-90⁰C, then it is cooled down at 65°C.

At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water.

After 30 minutes, a third termination is run at 40⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water.

After 30 minutes, a fourth termination is run at 30°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water.

After 30 minutes the reactor is discharged and the emulsion is filtered under a

150 micron polythene filter. Example 9

In a one litre glass bottle with mechanical stirrer, an emulsion is made from: 429.47 g of water 9.15 g of a 30% aqueous solution of sodium lauryl sulphate, 197.93 g of ethyl acrylate, 139.11 g of methacrylic acid, 33.02 g of 1 % diallylmaleate solution in ethyl acrylate, 18.62 g of methyl methacrylate and 7.54 g of the associative monomer AM1.

In the same reactor of the Example 1 , 294.07 g of water, 9.12 g of a 30% aqueous solution of sodium lauryl sulphate are loaded and the temperature is increased to 80-82⁰C. 4.7% of the previously prepared emulsion is charged in the reactor and at 80-82⁰C the reaction is started by addition of a solution made of 2.94 g of water and 0.0598 g of ammonium persulphate. The temperature in the reactor rises up to 84-86°C and then begins to lower (end of the exothermic reaction). At the end of the exothermic reaction, a continuous feed of the remaining pre-emulsion and a water solution of 59.45 g of water and 0.5954 g of ammonium persulphate are added in 1 hour at 88- 90⁰C. The system is left for 30 minutes more at 88-90°C, then it is cooled down at 65°C.

At 65°C a termination is run by charging 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, one more termination is run at 65°C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a third termination is run at 40⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes, a fourth termination is run at 30⁰C by charging each time 0.32 g of ascorbic acid U.A. and 5.2 g of water and a solution of 0.92 g of hydrogen peroxide 130 vol in 5.2 g of water. After 30 minutes the reactor is discharged and the emulsion is filtered under a 150 micron polythene filter.

Claims

1 . Crosslinked associative thickeners obtained by polymerization of: a) from 20 to 70% by weight of at least one monoethylenically unsaturated monomer containing a carboxylic group; b) from 20 to 70% by weight of at least one monoethylenically unsaturated nonionic monomer; c) from 1 to 20% by weight of at least one nonionic associative monomer obtained from i) a diisocyanate, ii) a monoethylenically unsaturated compound comprising a -NCO reactive hydroxyl functionality, iii) a compound comprising a linear carbon atoms chain of at least 6 carbon atoms and a polyoxyalkylene chain; d) from 0.01 to 3% by weight of at least one polyethylenically unsaturated monomer.

2. Crosslinked associative thickeners according to claim 1 having Brookfield® viscosity (spindle 6, RVT, 100 rpm, 2% by weight, pH 9 and 20 ⁰C) of at least 2,000 mPa-s.

3. Crosslinked associative thickeners according to claim 2 wherein: a) the monoethylenically unsaturated monomer containing a carboxylic group is acrylic acid, methacrylic acid, itaconic acid or mixture thereof; b) the monoethylenically unsaturated nonionic monomer is a (meth)acrylic ester, acrylonitrile, acrylamide, styrene, methylstyrene or mixture thereof ; c) the associative monomer is obtained from i) isophorone diisocyanate, 1 ,6-hexamethylenediisocyanate, 4,4'-dicyclohexyl methane diisocyanate, toluene diisocyanate or mixture thereof; ii) allyl alcohol, 1 to 3 moles ethoxylated and/or propoxylated allyl alcohol, or mixture thereof; iii) a 20 to 25 moles ethoxylated linear or branched

CiO-C₃₆ fatty alcohol; d) the polyethylenically unsaturated monomer is diallylmaleate, allyl methacrylate, diallylphthalate, N-methylene-bis- acrylamide, pentaerithritol ether triacrylate, triallylcianurate, or mixture thereof.

4. Crosslinked associative thickeners according to claim 3, wherein: b) the monoethylenically unsaturated nonionic monomer is a (meth)acrylic ester; c) the non-ionic associative monomer is obtained from i) isophorone diisocyanate; ii) allyl alcohol, monoethoxylated allyl alcohol or mixture thereof; iii) a 20 to 25 moles ethoxylated linear or branched C12-C22 fatty alcohol.

5. Crosslinked associative thickeners according to claim 4 wherein b) the monoethylenically unsaturated nonionic monomer is ethyl acrylate, ethyl methacrylate or mixture thereof.

6. Cosmetics and personal care products comprising a crosslinked associative thickener according to any of claims from 1 to 5.