GB1592203A

GB1592203A - Non-ionic surfactants

Info

Publication number: GB1592203A
Application number: GB4660377A
Authority: GB
Original assignee: BASF Wyandotte Corp
Current assignee: BASF Corp
Priority date: 1976-11-10
Filing date: 1977-11-09
Publication date: 1981-07-01
Also published as: DE2748126A1; FR2370788A1; BE860691A; FR2370788B3

Description

(54) NON-IONIC SURFACTANTS (71) We, BASF WYANDOTTE CORPORATION, a corporation organized under the laws of the State of Michigan, United States of America, of 1609 Biddle Avenue, Wyandotte, Michigan, United States of America, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: This invention relates to non-ionic surfactants, and in particular to nonionic surfactants which are polyoxyalkylated fatty alcohols, preferably those which are derived by reacting C2 to C4 alkylene oxides with C8 to C18 fatty alcohols to form homopolymers, heteric polymers or block polymers, usually having an average molecular weight of 300 to 1500.

Such fatty-alcohol alkoxylates are well known and are commercially available. For some purposes, it is desirable to make nonionic surfactants of this type which exhibit a low cloud point and a low tendency to foam.

Various measures are known to those skilled in the art for obtaining a low cloud point and a low tendency to foam. One approach is to include more units of a relatively hydrophobic alkylene oxide in the molecule, i.e., replace some of the ethylene oxide with propylene oxide and/or butylene oxide. This has the drawback that the higher alkylene oxides are relatively more expensive; moreover, a change of this sort may affect other properties of the product in undesirable ways.

Another known approach for obtaining the material of low cloud point is that of reacting the terminal hydroxyl groups of the surfactant with a compound such as ethylvinyl ether to form an acetal. This ordinarily yields a product which retains most of the properties of the starting material but has a cloud point which is lower by about 20 to 300C than the starting material. The reaction between alkylvinyl ether and hydroxyl groups to form acetals is well known - see, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 21, p.145.

It has now been found that by reacting a monofunctional polyalkoxylated fatty-alcohol nonionic surfactant with certain difunctional coupling agents it is possible to make nonionic surfactants with very substantially lowered cloud points and substantially lower foaming tendency. In a broad aspect of the invention, various kinds of difunctional coupling agents may be used, so that the surfactant molecules are joined by in pairs by a carbonyl group (providing a carbonate linkage) or an optionally alkyl-substituted methylene group (providing an acetal linkage). In one particular aspect of the invention, it is found that the polyalkoxylates may be conveniently coupled by causing them to react with ethylvinyl ether under conditions such that a transacetalization reaction takes place, causing the formation of the desired coupled surfactant and a simple acetal, which latter can be readily separated because of its far lower boiling point. This last approach has proved exceedingly effective when applied to a fatty alcohol which has been'ethoxylated to the extent that ethylene oxide units comprise approximately 80% of the molecule; this yields a product having a cloud point of approximately 100"C lower than the starting material, a product which exhibits a water-solubility at room temperature of less than 0.1%, despite the high content of ethylene oxide units in the product. The product is also stable in aqueous alkaline media.

The starting polyalkoxylate, in accordance with the present invention, is preferably a product derived from the treatment of a C8 to C18 straight-chain fatty alcohol with some proportion of a lower (C2 to C4) alkylene oxide, to obtain a polymer having an average molecular weight of from 300 to 1500, and more usually from 800 to 1500. As is known to those skilled in the art, it is possible to produce a variety of such materials, depending upon the particular ingredients, proportions, and reaction conditions chosen. The materials may be block polymers or heteric polymers or homopolymers, speaking with respect to the moiety of the molecule which is of polymeric nature. If a solid polymer is desired, relatively more of the alkylene oxide is used and/or conditions are chosen to achieve a polymer of higher average molecular weight. If a less hydrophilic product is desired, a relatively greater proportion of propylene oxide or butylene oxide is used. These considerations apply as well to the making of coupled polyalkoxylate surfactants in accordance with the present invention as they do to the starting polyalkoxylates of the prior art.

In particular, the surfactants based upon a mixture of C16 to C18 fatty alcohols and ethylene oxide, with average molecular weights in the range of 770 to 1500, are relatively high in both tendency to foam and cloud point. The ones of higher molecular weight (containing more oxyethylene units) are more hydrophilic. It has not been apparent to those skilled in the art how they can be modified to have greatly lower cloud points.

It is necessary to select a coupling agent. Depending upon the kind of agent selected, linkages of different kinds may be obtained.

One possibility is the production of carbonate diesters, by reacting the starting material with a lower-alkyl (C1 to C3) carbonate diester, for example diethyl carbonate or dimethyl carbonate; in the reaction, a lower alkanol is eliminated and a coupled product results.

Another possibility is the use of an alkylene dihalide, usually contaning up to 3 carbon atoms, in which the halogen atoms are attached to the same carbon atom. This is reacted with the sodium alcoholate of the starting surfactant and it yields acetal linkages.

Alternatively, it is possible to create acetal linkages with the use as a coupling agent of a lower-alkyl (C1 to C4 vinyl ether, such as ethylvinyl ether. This may be illustrated by the following equations.

where R is the residue of an ethoxylated C8 to C18 fatty alcohol, e.g.

C17H35-(OCH2CH2)n-, and n is an integer indicating a proper degree of polymerization, preferably one yielding a molecular weight for the oxyalkylated fatty-alcohol radical of 300 to 1500.

When ethylvinyl ether was used with a starting material comprising a mixture of C16 to Cl8 fatty alcohols ethoxylated to an average molecular weight of approximately 1420, a somewhat surprising result was obtained. Frequently, the reaction of ethylvinyl ether with a monofunctional polyalkoxylate nonionic surfactant causes only the formation of an acetal cap, and it is usual for the acetal-capped compound to have a cloud point which is lower than that of the starting material by approximately 20 to 30"C. It was surprising to find that with this starting material, when an attempt was made to use ethylvinyl ether as before, there resulted a material having a cloud point approximately 100"C lower than that of the starting material; moreover, there was obtained a material having very. greatly reduced solubility in water (0.1% at room temperature as compared with greater than 25 percent for the starting material).

When appropriate conditions of temperature, absolute pressure, and time are used, the reaction proceeds beyond a first (capping) stage in which an alkyl vinyl ether produces an acetal cap upon the monofunctional polyol, and proceeds to a coupling or transacetalization stage. Thus, where the capping yields a 10 to 25"C decrease in the cloud point, the coupling effects a lowering of about 50"C or more. The extent to which the cloud point is changed can, to some extent, be controlled by the selection of reaction conditions. For example, where the use of a temperature of 54"C, atmospheric pressure, and a reaction time of three or four hours may yield a substantially fully coupled product with a hydroxyl number of 0.5, the use of milder conditions, such as 35 to 400C, same pressure, reaction time about 1 hour, yields a product that remains about 10% uncoupled.

To be somewhat more specific about the conditions of temperature, absolute pressure, and time used to effect coupling, these will depend, of course, upon the coupling agent selected.

In the case of using the alkyl vinyl ether and transacetalization, the reaction time may be 10 minutes to 12 hours, preferably 1 to 2 hours; the final pressure is usually a reduced pressure, 0 to 50 torr, and preferably 10 torr or less; the temperature is usually 60 to 1200C.

In the case of the alkyl carbonate reaction, atmospheric pressure may be used and usually is preferred. The reaction may be conducted at lower or higher absolute pressures if desired. The temperature to be used depends upon the boiling point of the alcohol to be removed at the absolute pressure involved. A temperature sufficiently high to cause the alcohol to be vaporized must be used. The temperature to be employed also depends upon the boiling point of the carbonate coupling-agent selected, and is at least somewhat thereabove.

In the case of coupling with the use of a carbonate, preferably the temperature is preferably from 125 to 1750C, though temperatures of 80 to 200"C may be used. Preferably, atmospheric pressure is used, because this requires less equipment. The time when a carbonate is used is usually somewhat longer, e.g. 1 to 24 hours; more usually, it is 2 to 10 hours.

The extent of the coupling reaction is indicated by the quantity of distillate recovered, and it is possible to make a material of predetermined cloud point or other desired properties by regulating the quantity of distillate recovered.

In still other work, a similar starting material was coupled with the use of diethyl carbonate, and the cloud point was reduced from 73"C to approximately 19.5 to 20.50C.

In another instance, diethyl carbonate was used to couple a different starting material, reducing its cloud point from 59"C to approximately 1"C.

These novel, modified, coupled, oxyalkylated fatty alcohols have a large number of potential applications. These include the use of them as emulsifiers for oil-based and water-based emulsions, as defoaming agents, as low-foaming surfactants, and as agents for demulsification. They are stable in concentrated alkali solutions, and thus are useful in various applications such as in textile-treating baths, bottle-washing compositions, etc., especially where low foam is desired.

Thus it can be said that there is made in accordance with the invention a nonionic surfactant which is one having the formula

where each R independently is an alkyl radical containing 8 to 18 carbon atoms; R' is hydrogen, methyl or ethyl, the entities R' in different oxyalkylene being identical or different with the proviso that 50% or more of the R' entities are hydrogen; n and m are integers such that the molecular weight attributable to oxyalkylene groups equals 30 to 95 percent of the molecular weight of the whole molecule; and A is

or an optionally allyl-substituted methylene group, preferably

in which R2 is an alkyl group containing 1 to 4 carbon atoms the molecular weight of the surfactant being 450 to 5500.

Preferably R' is hydrogen and m and n are integers such that the molecular weights of the moieties R-O-(CH2-CH2-O),- and R-O-(CH2-CH2-O),- are each in the range 300 to 1500, and over 60% of the surfactant is made up of oxyethylene units. In one embodiment R is formed from a mixture of fatty alcohols of 16 to 18 carbon atoms and m and n are each about 27.

The invention described above is more particularly illustrated by the following illustrative specific examples.

Example I To a two-liter flask equipped with a stirrer, a thermometer, and an additional funnel, there was added 1095 grams (0.75 equivalent) of a surfactant made by reacting a mixture of C16 to C18 fatty alcohols with approximately 27 units of ethylene oxide to produce a material having an average molecular weight of approximately 1420. Such material is sold by us as PLURAFAC A-38 surfactant. (PLURAFAC is a Registered Trade Mark). The material in the flask was heated to 1200C and subjected to a 4mm. of mercury absolute pressure to remove moisture. Hydrogen chloride was added (2.5 grams), and then 81 grams of ethylvinyl ether (1.1 mole) was added at a temperature of 54"C over a period of 25 minutes.

The heating was continued for three hours after the addition of the ethylvinyl ether, and then, 8 grams of sodium bicarbonate was added. The reaction mixture was permitted to stand overnight, and then the product was vacuum-distilled for 1 hour at up to 1200C, filtered, and poured onto aluminum foil to solidify and be broken up into chips. There was thus produced a light-yellow solid, weighing 1083 grams. The hydroxyl number of the product was less than 0.5. The product was tested for solubility in water at room temperature (25"C) and found to be soluble to the extent of less than 0.1%. The cloud point of an aqueous solution containing 1 percent by weight of the product was 5"C.

It must be understood that these nonionic surfactants, unlike many other substances, tend to become more sparingly soluble in water as the temperature of the water increases. It is usual and convenient to indicate the degree of compatibility between the surfactant and water by determining the temperature at which (starting from a low temperature, one at which a substantial proportion of the surfactant is soluble in water), when a mixture of 1 weight percent of the surfactant in water is heated, cloudiness or turbidity begins to develop. It is entirely possible and consistent for it to happen, as reported above, that at room temperature, (approximately 25"C) the solubility of a product of this sort in water is 0.1%, yet, for water at very close to 0 C, the solubility of the product in question in water is very much greater, such that it would, with water at that temperature, be relatively easy to dissolve as much as 1.0 weight percent of the product in water. Thus, it is not impossible to report, for such substance, a cloud point for a 1 weight percent solution of 5"C; this merely means that at, for example, 3"C, an aqueous solution containing 1 weight percent of the product in question is entirely soluble, and a clear solution results.

In this field of nonionic surfactants, the importance of the cloud point and of the properties which are related to it, such as the value obtained in a Dynamic Foam Height test, can scarcely be overemphasized. Often, a product which, if liquid, is not a clear liquid, or a product which, whether liquid or flake, does not yield, when dissolved in water at the concentration of intended use, a clear solution, is not a composition which is of any commercial interest. Moreover, the cloud point is, to a substantial extent, related to the result which is obtained in a Dynamic Foam Height test, a test indicative of the tendency of solutions containing the nonionic surfactant to generate foam. The Dynamic Foam Height test is adequately described in an article by H.E. Reich in the April, 1961 issue of Soap and Chemical Specialties, vol. 37, page 55. Ordinarily, foaming is more severe when the temperature of the liquid is lower; a surfactant which, in a Dynamic Foam Height test at 1200F exhibits a foam height of greater than 600 mm., is a nonionic surfactant of relatively great foaming tendency, and it is certainly to be expected, if the same composition is tested at 77"F, that the observed foam height would be at least as great, if not greater.

For some purposes, a nonionic surfactant which generates a cinsiderable amount of foam is not only tolerable but even desirable, for example, formulating compositions for use in the washing of dishes by hand.

There are, however, numerous applications for nonionic surfactants in which it is particularly desirable that the nonionic surfactant involved, while displaying adequate surface activity and detergency for the use intended, be one that also does not readily generate a large volume of foam. This consideration is more important, for example, in the formulation of materials for use in household and commercial dishwashing and laundry equipment, and in other places where any substantial accidental generation of foam would be a disadvantage. It will thus be understood that the present invention, whereby it becomes possible conveniently to lower substantially the cloud point of a non-ionic surfactant composition, is one which has numerous applications which will be well understood by those skilled in the art.

It is to be noted, in particular, that in the present instance, there is obtained a material which consists approximately of 80 weight percent of ethylene oxide units and yet is, at the same time, only 0.1 weight percent soluble in water. This is unusual and unexpected, because the ability, in most instances, of ethylene-oxide units to make a composition water-soluble and relatively hydrophilic is well known. How to achieve nonionic surfactant compositions which are relatively low-foaming and hydrophobic, with use of relatively inexpensive ethylene oxide, has not hereto been well known.

Example II A flask having a capacity of two liters was charged with 1077 grams (1 mol) of a different starting material, namely, a nonionic surfactant comprising essentially a mixture of fatty alcohols, alkoxylated with a mixture of ethylene oxide and propylene oxide to an average molecular weight of 1050. Such material is sold by us as PLURAFAC B-26 surfactant. To remove moisture, the flask was subjected to vacuum distillation conditions: 103"C and 3 mm. of mercury absolute pressure. Thereafter, the contents of the flask were cooled to 40"C, and 2.15 grams of methanesulfonic acid was added as catalyst, and then 79.3 grams (1.1 mol) of ethylvinyl ether was added at 400C over a period of 30 minutes. The reaction mixture was stirred for an additional 30 minutes at 360C, and then 3.3 grams of calcium carbonate was added, to neutralize the catalyst. Then, over a period of two hours, the reaction mixture was subjected to vacuum distillation, starting at a temperature of 32"C and 130 mm. of mercury absolute pressure and ending at a temperature of 98.5"C and an absolute pressure of 2 mm. of mercury. A distillate, comprising 57.6 grams was collected, and after the reaction mixture was cooled to 48"C, 10.8 grams (1 weight percent) of N,N,N',N',-tetrakis (2-hydroxypropyl) ethylene diamine was added as a stabilizer. The final weight of the reaction mixture was 1107.4 grams. The hydroxyl number of the final reaction mixture was determined and was adjusted for changes therein caused by the addition of the stabilizer; the result was a hydroxyl number of 3.3, as compared with an original hydroxyl number of 52.1.

Under the relatively milder reaction conditions used in this Example II, in comparison with those used in Example I, there was not so thorough a conversion of the acetal-capped compound to a coupled final product. Tests indicate that the ratio by weight of capped product to coupled product was 11:89.

The cloud point of a 1 weight percent aqueous solution was determined; it was found to be 10 to 250C, as compared with the value of 73"C for the starting material.

Example III To a flask having a capacity of 1 liter, there were charged 754 grams of a starting material which is the same as that used in Example II, and also 125.1 grams of diethyl carbonate, 2.0 grams of potassium carbonate, and 3 grams of a 20 weight percent solution of potassium hydroxide and methanol. This reaction mixture was heated to a reflux temperature under a fractional distillation column having a length of 0.61 meters (2 feet) and equipped with a distillation take-off head. Over a period of approximately 10 hours, a total of 37.8 grams of ethanol were collected overhead. As bottoms, there remained the reaction mixture, which was then subjected to vacuum distillation under conditions ranging to the use of 125"C at 6 mm. of mercury absolute pressure. This yielded 780.1 grams of a cloudy, crude product, and after the addition of 8 grams of a suitable filter aid (exceptionally pure diatomaceous silica of a kind yielding a high flow rate) and subsequent filtration, there was obtained, as a product, 736.5 grams of a clear, yellowish filtrate. This material had a hydroxyl number of 3.3. A 0.1 weight percent solution in water was clear, and it had a pH of 8.74, as compared with a pH of between 6 and 7 for the starting material at the same concentration in water.

The cloud point of a 1 weight percent solution of this product was 19.5 to 20.50C, as compared to 73"C for the starting material.

Both the starting material and the product according to Example III were subjected to a Draves sink time test, using a solution containing 0.1 weight percent of surfactant. The Draves sink test is adequately described in an article by C. Z. Draves and R. G. Clarkson, vol. 20, American Dye Reporter, pages 201-8 (1931). The values reported are the length of time, in seconds, that it takes a 5-gram skein of cotton rope, weighted with a 3-gram hook and placed into the solution to be tested, to sink. Solutions containing 0.1 weight percent of superior wettting agents usually exhibit values on the order of 60 seconds or less. In this case, the starting material had a Draves sink time of 58.2 seconds, and the derived carbonate, the coupled product of Example III, had a Draves sink time of 24 seconds.

The starting material and the derived, coupled product had, respectively, surface tensions, for a 0.1 weight percent solution, of 36.3 and 34.3 dynes per centimeter.

In a Dynamic Foam test at 400 ml. per minute flow, the starting material, a useful material but never one particularly noted for being low-foaming, exhibited a foam height in excess of 600 mm., and that was in a test conducted in a test at 1200F; in contrast, at the same temperature, the product coupled surfactant of Example II exhibited a foam height of only 22 mm., and even when the temperature of the test was reduced to 77"F, the foam height was only 75 mm.

Example IV Using a procedure very similar to that described above in reference to Example III, 738 grams (0.75 mol) of a different oxyalkylated fatty alcohol nonionic surfactant, one having an average molecular weight of 950, was reacted with diethyl carbonate to produce a coupled carbonate product. The cloudy, crude product weighed 755.5 grams, and after the addition of 8 grams of filter aid as above and suitable filtration, there was obtained 709.8 grams of a clear, yellowish filtrate, having a hydroxyl number of 2.2, as compared with an original value of 57.

Both the starting material and the product, as an aqueous solution containing 0.1 weight percent of the material in question, were clear, and such a solution had, for the starting material, a pH of between 6 and 7, and for the product material a pH of 5.74. An aqueous solution containing 1 weight percent of the starting material had a cloud point of 59"C, whereas the cloud point of the similar solution of the product was approximately 1"C, a decrease of 58"C. The starting material had a Draves sink time for the 0.1% solution of 40 seconds, and the product had a Draves sink time for the similar solution of 51.2 seconds.

The starting material had a surface tension for the 0.1 weight percent solution of 34.3 dynes per centimeter, and the product had a surface tension, for a similar solution, of 33.5 dynes per centimeter. The starting material is a commercially produced nonionic surfactant, and in a Dynamic Foam Height test at 400 ml. per minute in 1200F, it exhibits values of over 600 mm. of foam height. In respect to the product of Example IV, it was not necessary to conduct a foam-height test, because of the low solubility of the material in water.

WHAT WE CLAIM IS: 1. A surfactant comprising two polyoxyalkylated fatty alcohol surfactant molecules linked together through their polyoxyalkylene chains by means of a carbonate or acetal linkage.

2. A.surfactant as claimed in claim 1 wherein the polyoxyalkylated fatty alcohol surfactant molecule is the homopolymeric, hetericpolymeric or block polymeric reaction product of one or more C2 to C4 alkylene oxides with a C8 to C18 fatty alcohol and has a molecular weight of from 300 to 1500.

3. A surfactant having the formula

where each R independently is alkyl of 8 to 18 carbon atoms, R' is hydrogen, methyl or ethyl, the entities R' in different oxyalkylene moieties being identical or different with the proviso that 50% or more of the R' entities are hydrogen, n and m are integers such that the molecular weight attributable to oxyalkylene groups equals 30 to 95 percent of the molecular weight of the whole surfactant, and A is C=O or an optionally alkylsubstituted methylene radical, the molecular weight of the surfactant being 450 to 5500.

4. A surfactant as claimed in claim 3 wherein A is

where R2 is alkyl of 1 to 4 carbon atoms.

5. A surfactant as claimed in claim 3, wherein A is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. only 22 mm., and even when the temperature of the test was reduced to 77"F, the foam height was only 75 mm. Example IV Using a procedure very similar to that described above in reference to Example III, 738 grams (0.75 mol) of a different oxyalkylated fatty alcohol nonionic surfactant, one having an average molecular weight of 950, was reacted with diethyl carbonate to produce a coupled carbonate product. The cloudy, crude product weighed 755.5 grams, and after the addition of 8 grams of filter aid as above and suitable filtration, there was obtained 709.8 grams of a clear, yellowish filtrate, having a hydroxyl number of 2.2, as compared with an original value of 57. Both the starting material and the product, as an aqueous solution containing 0.1 weight percent of the material in question, were clear, and such a solution had, for the starting material, a pH of between 6 and 7, and for the product material a pH of 5.74. An aqueous solution containing 1 weight percent of the starting material had a cloud point of 59"C, whereas the cloud point of the similar solution of the product was approximately 1"C, a decrease of 58"C. The starting material had a Draves sink time for the 0.1% solution of 40 seconds, and the product had a Draves sink time for the similar solution of 51.2 seconds. The starting material had a surface tension for the 0.1 weight percent solution of 34.3 dynes per centimeter, and the product had a surface tension, for a similar solution, of 33.5 dynes per centimeter. The starting material is a commercially produced nonionic surfactant, and in a Dynamic Foam Height test at 400 ml. per minute in 1200F, it exhibits values of over 600 mm. of foam height. In respect to the product of Example IV, it was not necessary to conduct a foam-height test, because of the low solubility of the material in water. WHAT WE CLAIM IS:

1. A surfactant comprising two polyoxyalkylated fatty alcohol surfactant molecules linked together through their polyoxyalkylene chains by means of a carbonate or acetal linkage.

3. A surfactant having the formula

4. A surfactant as claimed in claim 3 wherein A is

where R2 is alkyl of 1 to 4 carbon atoms.

5. A surfactant as claimed in claim 3, wherein A is

6. A surfactant as claimed in claim 3, wherein A is

7. A surfactant as claimed in claim 5 wherein R' is hydrogen and m and n are integers such that the molecular weight of moieties R-O-(CH2-CH2-O),- and R-O (CH2-CH2-O),- are each in the range 300 to 1500, and over 60% of the surfactant is made up of oxyethylene units.

8. A surfactant as claimed in any of claims 3 to 7 wherein R is alkyl of 16 to 18 carbon atoms.

9. A surfactant as claimed in any of claims 1 to 8 having a solubility of 0.1 weight percent or less in water at 25"C and a cloud point (for a 1 weight percent solution) at least 50"C lower than that of a corresponding monofunctional polyoxyalkylated fatty alcohol surfactant.

10. A method of decreasing the cloud point of a monofunctional polyoxyalkylated nonionic surfactant starting material having an average molecular weight of 300 to 1500 and resulting from the oxyalkylation of a fatty alcohol containing 8 to 18 carbon atoms, which method comprises reacting said nonionic surfactant with a C1 to C3 alkyl carbonate diester to form a coupled surfactant in which the two surfactant moieties are linked by a carbonyl group or reacting said nonionic surfactant with a C1 to C4-alkyl vinylether to form a coupled surfactant in which the two surfactant moieties are linked by an ethylidene group.

11. A method as claimed in claim 10, wherein the non-ionic surfactant is reacted with ethylvinyl ether, and conditions of temperature, pressure, and time are used such that the reaction proceeds beyond the acetal-capped stage to a coupling stage.

12. A method as claimed in claim 10 or 11, wherein the monofunctional surfactant is one having at least 60% of its molecular weight accounted for by oxyethylene units, the coupled surfactant having a water-solubility at 25"C of 0.1 weight percent or less.

13. A method as claimed in any of claims 10 to 12, wherein the monofunctional surfactant comprises a mixture of fatty alcohols containing 16 to 18 carbon atoms, oxyethylated with approximately 27 oxyethylene units.

14. A method as claimed in claim 10 carried out substantially as hereinbefore specifically described or exemplified.

15. A surfactant of decreased cloud point when obtained by a method as claimed in any of claims 10 to 14.

16. The use of a surfactant as claimed in any of claims 1 to 9 or 15 as an emulsifier for an oil-based or water-based emulsion, as defoaming agent, or as an agent for demulsification.

17. A concentrated alkali solution containing a surfactant as claimed in any of claims 1 to 9 or 15.