POLYMERIC SURFACTANTS

Abstract: Crosslinked, star-shaped polymeric surfactants in particular those having at least two unsaturated moieties in the hydrocarbon chain, one forming a terminal group or a group derived thereof containing a methyl or ethyl group at the terminal carbon atom, whilst the polar group of the surfactant is connected to the last carbon atom at the other end of the hydro­ carbon chain. The polymeric surfactants can be prepared by polymerizing a monomeric surfactant as hereinbefore described in a polar solvent, wherein said surfactant is present in a concentration higher than its critical aggregate concentration, at the temperature of polymerization.

Description: The invention relates to polymeric surfactants, to a process for the preparation of the polymeric surfactants, to derivatives thereof and to the use of the polymeric surfactants and their derivatives. Many reactions are subject to significant rate and selectivity effects when carried out in the presence of surfactant aggregates such as micelles. A widespread application of these effects however, is thwarted by the often large amounts of surfactants needed to achieve these results and also by the problematic work-up of such reaction mixtures. Moreover, such surfactant aggregates are very sensitive to changes in solvent, temperature and to the presence of salts and other substances. A further restriction in their applicability is the limited number of solvents wherein such surfactant aggregates are formed. Hence, a considerable improvement would be achieved when, in reactions as hereinbefore described, large amounts of surfactants or high surfactant concentrations would not be required, and also when such surfactant aggregates would be less sensitive to environmental conditions such as solvent type and temperature or to the presence of salts and other substances. A method for providing surfactant aggregates which can be expected to be less sensitive to the environmental conditions, has been described in J. Polym. Sci., Polym. Lett. Ed., 17(12) 749-51(1979). Said method comprises the radiation-induced polymerization of sodium 10-undecenoate in an aqueous solution, wherein said compound was present in a concentration which exceeded its critical micelle concentration. Although the poly (sodium 10-undecenoate) thus obtained will probably adopt a micellar-like structure when dissolved in an aqueous medium, it can be expected that with this product the micellar-like structure will disappear when e.g. the carboxylate groups are replaced with other groups or when the poly (sodium 10-undecenoate) is dissolved in a different solvent. The problem underlying the present invention is to provide surfactant aggregates which do not suffer from one or more of the disadvantages hereinbefore described. There is surprisingly found that this problem can be solved by crosslinked, polymeric surfactants, wherein the starting monomeric surfactants have at least two unsaturated moieties in the hydrocarbon chain forming the hydrophobic part of the surfactant molecule, one of the unsaturated moieties forming a terminal group or containing a methyl or ethyl group at the terminal carbon atom, whilst the polar group of the surfactant molecule is connected to the last carbon atom at the other end of the hydrocarbon chain. Preferably the monomers contain conjugated unsaturated moieties, whereby the unsaturation is preferably alkynic rather than alkenic. Said crosslinked polymeric surfactants are novel compounds. It is believed that in these polymeric surfactants, typically linkages are present which connect the monomer derived surfactant groups and which do not, or only partly form linear structures. Instead, or in addition thereto, the polymeric surfactants contain crosslinking bonds which contribute to stabilizing the structure of the crosslinked polymeric surfactants. Such crosslinked polymeric surfactants are thus products having a crosslinked hydrocarbon centre from which hydrocarbon chains protrude carrying a polar group. The polar group of the surfactant molecules may conveniently comprise an anionic, a cationic, a nonionic or a zwitterionic group. Preferred monomeric surfactants containing conjugated alkynic moieties are surfactants of general formula R-C≡C-C≡C-(CH₂) m -C(H)X-(CH₂) n -R¹ I wherein R is H, CH₃ or C₂H₅; R¹ represents an anionic, a cationic, a nonionic or a zwitterionic group; X is H, Cl, Br, I or PR²R³ wherein R² and R³ are the same or different and represent an alkyl or an aryl group which may optionally be substituted; m and n are integers from 0 to 12 included and m+n has a value from 4 to 12 included, with the proviso that the number of carbon atoms in the surfactant molecules of general formula I, including R but excluding R¹, does not exceed 17 when X is H. The present invention further relates to a process for the preparation of crosslinked, polymeric surfactants, wherein a monomeric surfactant as hereinbefore described is polymerized in a polar solvent wherein said surfactant is present in a concentration which is higher than its critical aggregate concentration, as hereinafter defined, at the temperature of polymerization. In the context of the present invention the term critical aggregate concentration is defined as the concentration of a given surfactant in a given solvent at a given temperature above which concentration said surfactant forms aggregates. The nature of the aggregates formed is governed amongst others by the type of solvent and the type and concentration of the surfactant, but is as such not critical. The solvents which may conveniently be employed in the process of the present invention are polar solvents wherein a surfactant of general formula I will form aggregates. Aggregate formation and the critical aggregate concentration can conveniently be established e.g. via lightscattering or conductometric methods. Suitable solvents include water, lower mono-and polyhydric alcohols, dimethyl sulfoxide, dimethyl formamide and the like, or mixtures thereof. Water is a preferred solvent. It is generally accepted that such an aggregate comprises a lipophilic core consisting of the hydrocarbon chains of the surfactant molecules, which core is separated from the solvent phase by an interface in which the hydrophylic groups of the surfactant molecules are located. It is expected that such a selective orientation of the surfactant molecules in the aggregates, i.e. one wherein the hydrocarbon chains carrying the polymerizable groups are in close contact with one another in the core of the aggregate, will have a beneficial effect on the polymerization of said surfactants. The polymerization of the surfactants within the aggregates can be effected by conventional polymerization techniques such as in the presence of a free-radical initiator system. When such a free-radical initiator system is used there is a preference for employing an initiator which is insoluble or only partly soluble the solvent used. Such an initiator system can conveniently be introduced into the solvent system together with the surfactant. A preferred method for the preparation of the polymeric surfactants hereinbefore described, is to employ a surfactant of general formula I and to conduct the polymerization via a photochemically-induced polymerization procedure, for which a ⁶⁰Co source or UV irradiation is frequently used. Preferred anionic groups R¹ of the surfactants of general formula I are selected from the group comprising CO₂Y, SO₃Y, OSO₃Y, (OCH₂CH₂) p OSO₃Y wherein p is an integer in the range of from 1-10, and CON(CH₃)CH₂CH₂SO₃Y, wherein Y represents an alkalimetal atom or NH₄. Especially preferred are such anionic group containing surfactants wherein Y is a sodium atom. Examples of suitable cationic groups R¹ are quarternary ammonium groups of general formula -N⁺(R⁴)₃Z⁻ (III) wherein each R⁴ is the same or different and represents a lower alkyl, aryl or an alkaryl group, and Z represents a halogen atom or OH. Examples of suitable nonionic groups R¹ are oligomers of ethylene oxide or propylene oxide as well as oligomers based on mixtures of ethylene oxide and propylene oxide. Examples of suitable zwitterionic groups R¹ are groups of general formula -N⁺(R⁴)₂(CH₂) r Q⁻ (IV) wherein R⁴ has the same meaning as in general formula III, r is an integer in the range of from 1 to 5 and Q is a CO₂Y or SO₃Y group, wherein Y has the same meaning as hereinbefore described. Preferred surfactants are those of general formula I wherein R¹ represents an anionic group. Should the surfactant molecules of general formula I carry a group X, which X ≠ H, it is preferred that said group X is carried by the alpha-C atom of the molecule, i.e. a surfactant of general formula I wherein n is o. Sodium 10,12-tetradecadiynoate is an especially preferred anionic group-containing surfactant. For certain applications it may be advantageous to conduct the polymerization of the surfactants of general formula I in the presence of one or more cosurfactants. In addition to a polymerizable group it is preferred that such a cosurfactant should have a more or less similar molecular structure as the surfactants of general formula I in order to obtain mixed aggregates. Suitable cosurfactants include surfactants of general formula R⁵-(CH₂) m 1-C(H)X-(CH₂) n 1-R¹ II wherein R¹ and X have the same meaning as in general formula I; R⁵ is CH₂=CH, CH≡C, CH₃-C≡C, C₂H₅-C≡C or CH₂=CH-CH=CH; m¹ and n¹ are integers from 0 to 12 included and m¹+n¹ has a value in the range of from 6 to 12 included, with the proviso that the number of carbon atoms in the surfactant molecules of general formula II, including R⁵ but excluding R¹, does not exceed 17, when X is H. When in the practice of the present invention the polymerization of the surfactants of general formula I is conducted in the presence of one or more surfactants of general formula II, it is preferred that the molar fraction of the surfactants of general formula I comprises at least 50 % mol of the total surfactant composition. Upon completion of the polymerization, the polymeric surfactants may be isolated by known methods. Suitable methods include evaporation of the solvent medium or precipitation in a non-solvent after first having removed the excess of solvent wherein the polymerization had been conducted. With the latter procedure it may be advantageous to employ a solvent wherein the polymeric surfactant is insoluble while any non-polymerized surfactant and/or the relatively low molecular weight polymeric surfactants are soluble. An alternative method for isolating such polymeric surfactants having anionic polar groups is one wherein the polymeric surfactant is obtained as the acid derivative thereof. With said method, the solvent medium containing the polymeric surfactant is acidified before being evaporated to dryness. Subsequently the relatively low molecular weight species may, if required, be extracted from the residue using e.g. a hydrocarbon solvent. Finally the residue is dissolved in a solvent system which will enable the removal of the inorganic salts e.g. via filtration, which may be followed by evaporation of the solvent to obtain the polymeric surfactant in the acid form. The crosslinked polymeric surfactants may be used as such or they can be modified before use. With the anionic group-containing polymeric surfactants for example, one or more of the alkalimetal or ammonia groups may be replaced with different metals or alternatively the anionic group can be converted e.g. into the corresponding acid chloride or in an ester group. These modifications can be conducted via known methods. The crosslinked polymeric surfactants or their derivatives as hereinbefore described, can be used in chemical and physical processes e.g. as phase transfer catalysts. The invention will be further illustrated with the following examples for which the following information is provided: Sodium 10,12-tetradecadiynoate solution. A 500 ml 0.075 M solution of sodium 10,12-tetradecadiynoate was prepared by introducing into a 1 l three-necked flask the appropriate amounts of sodium hydroxide, freshly recrystallized (from n-hexane) 10,12-tetradecadiynoic acid and demineralized water and allowing the solution to stand in an argon atmosphere in the dark for 72 hours. The 10,12-tetradecadiynoic acid was prepared via the coupling of 1-bromopropyne and 10-undecynoic acid following the method as described by G. Englinton and W. McCrae in Adv.Org.Chem. Vol.4, p252-274. Example I Preparation of poly (sodium 10,12-tetradecadiynoate) The three-necked flask containing the 500 ml 0,075 M solution of sodium 10,12-tetradecadiynoate prepared as hereinbefore described, was connected to a falling film photo reactor [Applied Photophysics TFQ 15, equipped with a 15 W low pressure mercury lamp (Applied Photophysics model 3020) and a quartz filter]. The solution was irradiated for 240 hours without applying external cooling to the solution, in the course of which the temperature increased from 20 °C to 30 ± 5 °C. The resulting reddish-brown solution was acidified with 1 N HCl solution and subsequently evaporated to dryness using a rotary film evaporator at 50 °C and 1.33 mbar. The residue was treated with 200 ml boiling hexane to remove any unconverted monomer and subsequently dissolved in 50 ml of a 1:10 v/v blend of methanol and dichloromethane and filtered to remove the inorganic salts. The product was isolated by evaporating the solvents at 50 °C and 1.33 mbar. The isolated poly (10,12-tetradecadiynoic acid) was obtained in a > 90 % wt yield, based sodium 10,12-tetradecadiynoate intake. The corresponding poly (sodium 10,12-tetradecadiynoate) was obtained by neutralisation of the acid via titration with 0.1 N aqueous NaOH followed by drying. The product was found to be soluble in: Molecular weight determination of the methylester of poly (10,12-tetradecadiynoic acid) via gel permeation chromatography, using polystyrene as reference, gave the following results M n = 4930 M w = 6950 The outcome of NMR (¹H, ¹³C) analysis in different solvents as well as in in the solid state, in combination with negative results of the tests for unsaturation via Br₂ and O₃, confirm that the products prepared by the process of the present invention are crosslinked compounds. Example II Wacker oxidation of 1-hexene in the presence of poly (sodium 10,12-tetradecadiynoate) 0.5 mmol PdCl₂, 5 mmol CuCl₂, 0.5 mmol of poly (sodium 10,12-tetradecadiynoate) as prepared in example I, 12.5 mmol of 1-heptene, 4.2 mmol n-undecane (as internal standard) and 11 ml water were introduced into a two-necked reactor, equipped with a reflux condensor, and stirred (magnetically) at high speed. The mixture was covered with an oxygen blanket, which was made up by a slow stream of oxygen which entered the reactor just above the surface of the mixture. The reactor was placed in a thermostated oil bath (70° ± 5 °C) and the reaction was allowed to proceed for 4 hours. Subsequently the oxygen stream was stopped, 2.5 ml pentane was added to the reactor via the reflux condensor and the mixture was allowed to reflux for 1 minute followed by cooling to 20 °C. The product was analysed by gas liquid chromatography and the resulting data are given in Table I. Comparative experiments A and B. Following the procedure of example II and simultaneously with this example, two comparative experiments were carried out which only differed from example II in that in experiment A no poly (sodium 10,12-tetradecadiynoate) was used while in experiment B the poly (sodium 10,12-tetradecadiynoate) was replaced with an equal amount of sodium 10,12-tetradecanoate. The results of these experiments are also given in Table 1. It can be seen that the presence of poly (sodium 10,12-tetradecadiynoate) has a beneficial influence on the conversion of 1-heptene and the formation of 2-heptanone vis à vis the reaction wherein no phase transfer catalyst is used, but is also more effective than the sodium 10,12-tetradecanoate.

Claims: Crosslinked, polymeric surfactants, wherein the starting monomeric surfactants have at least two unsaturated moieties in the hydrocarbon chain forming the hydrophobic part of the surfactant molecule, one of the unsaturated moieties forming a terminal group, or containing a methyl or ethyl group at the terminal carbon atom, whilst the polar group of the surfactant molecule is connected to the last carbon atom at the other end of the hydrocarbon chain. Polymeric surfactants as claimed in claim 1, wherein the unsaturated moieties are conjugated unsaturated moieties. Polymeric surfactants as claimed in claim 1 or 2, wherein the unsaturated moieties are alkynic unsaturated moieties. Polymeric surfactants as claimed in claim 1-3, wherein the alkynic unsaturated moieties containing surfactants are monomeric surfactants of general formula R-C≡C-C≡C-(CH₂) m -C(H)X-(CH₂) n -R¹ I wherein R is H, CH₃ or C₂H₅; R¹ represents an anionic, a cationic, a nonionic or a zwitterionic group; X is H, Cl, Br, I or PR²R³ wherein R² and R³ are the same or different and represent an alkyl or an aryl group, which may optionally be substituted; m and n are integers from 0 to 12 included and m+n has a value in the range of from 4 to 12 included, with the proviso that the number of carbon atoms in the surfactant molecules of general formula I, including R but excluding R¹, does not exceed 17, when X is H. A process for the preparation of crosslinked, polymeric surfactants as claimed in any one of claims 1-4, wherein the monomeric surfactant is polymerized in a polar solvent, wherein said surfactant is present in a concentration which is higher than its critical aggregate concentration, at the temperature of polymerization. A process as claimed in claim 5, wherein the solvent is water. A process as claimed in claims 5 or 6, wherein a surfactant of general formula I is used, and a photochemically-induced polymerization procedure is employed. A process as claimed in any one of claims 5 to 7, wherein in general formula I R¹ represents an anionic group. A process as claimed in any one of claims 5 to 8, wherein the anionic groups R¹ are selected from the group consisting of CO₂Y, SO₃Y, OSO₃Y, (OCH₂CH₂) p OSO₃Y wherein p is an integer in the range of from 1-10 and CON(CH₃)CH₂CH₂SO₃Y wherein Y represents an alkalimetal atom or NH₄. A process as claimed in claim 9, wherein Y represents a sodium atom. A process as claimed in any one of claims 5-10, wherein in general formula I n is 0 when X ≠ H. A process as claimed in any of claims 5 to 11, wherein the surfactant is sodium 10,12-tetradecadiynoate. A process as claimed in any one of claims 5-12, wherein the polymerization of the surfactant of general formula I is conducted in the presence of one or more surfactants of general formula R⁵-(CH₂) m 1-C(H)X-(CH₂) n 1-R¹ II wherein R¹ and X have the meaning as hereinbefore defined; R⁵ is CH₂=CH, CH≡C, CH₃-C≡C, C₂H₅-C≡C or CH₂=CH-CH=CH; m¹ and n¹ are integers from 0 to 12 included and m¹+n¹ has a value in the range from 6 to 12 included, with the proviso that the number of carbon atoms in the surfactant molecules of general formula II, including R⁵ but excluding R¹ does not exceed 17 when X is H. Use of crosslinked polymeric surfactants as claimed in any one of claims 1-4, as phase transfer catalyst.

Inventors: DE JONG, BARTELE SYBREN, STAPERSMA, JOHAN, TOMASSEN, HENRICUS PAULUS MARIA
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: C08F38
IPC codes: C08F38, C07C57, B01F17, C08F2