Aqueous microemulsions comprising functional perfluoropolyethers

Abstract: Perfluoropolyether microemulsions of the oil-in-water or water-in-oil type, consisting of perfluoropolyethers having an average molecular weight of from 1,500 to 10,000, the end groups of which are at least partially of the func­ tionalized type, optionally containing peroxide bridges in the chain and consisting of mixtures of products having different molecular weights, of a perfluorinated surfactant and/or a co-surfactant of the alkanol type having 1 to 12 carbon atoms and of an aqueous liquid optionally comprising an electrolyte.

Description: IT-A-20 910 A/86 and 19,494 A/87, both in applicant's name, disclose microemulsions comprising perfluoropolyethers (PFPE) having perfluoroalkyl end groups, obtained by using fluorinated surfactants and, optionally, fluorinated or non-fluorinated co-surfactants , such as alkanols and fluoroalkanols and, optionally, electrolytes. Generally, in the abovesaid microemulsions the maximum amount of solubilized PFPE in the aqueous phase depends on the utilized amounts of surfactant and of co-surfactant, as the maximum PFPE/water interphase obtainable can be considered as lower than, or at the most equal to the sum of the areas of the surfactant and co-surfactant polar heads. Therefore it would be very advantageous, for example for use in the polymerization of fluorinated monomers, as is described in IT-A-20,909 A/86 in the name of the Applicant, to have available a microemulsion characterized by the presence of a water-soluble surfactant and co-surfactant in an amount lower than the one which is required for the microemulsions of PFPE having perfluoroalkyl end groups. It has now surprisingly been found that it is possible to prepare microemulsions characterized by a lower concentration of surfactant and co-surfactant and even free from added water-soluble perfluorinated surfactant, if a PFPE having end groups at least partially of the non-perfluoroalkyl type is used. Accordingly, the present invention provides a microemulsion of the oil-in-water (o/w) or water-in-oil (w/o) type, comprising (i) an aqueous dispersion of a liquid (per)fluoropolyether having an average molecular weight of from 1,500 to 10,000 and end groups (R f , R' f ) which are at least partially of the functionalized (non-perfluoroalkyl) type, said functionalized end groups being represented by the formula: -(B) n T m wherein n = 0 or 1, B is a linking divalent or polyvalent hydrocarbon group, in particular an alkylene, cycloalkylene or arylene group having up to 20 and preferably up to 8 carbon atoms, m ranges from 1 to 3 and preferably is equal to 1, and T is selected from -H, -COOH, -SO₃H, -OH, polyoxyalkylene-OH and ester, amidic, aminic and quaternary ammonium groups; (ii) a perfluorinated surfactant and/or a co-surfactant; and, optionally, (iii) one or more water-soluble electrolytes. By "microemulsion" there are usually meant products macroscopically consisting of a single liquid, transparent or opalescent and optically isotropic phase, comprising two immiscible liquids and at least a surfactant, in which products one of the two immiscible liquids is dispersed in the other in the form of droplets having diameters ranging from about 5 to 200nm (50 to 2,000 Å). In principle it cannot be excluded that particles having higher or lower sizes up to the limit of the molecular dispersion may be present. Furthermore, structures may be present, in which both liquids, interdispersed as bicontinuous tridimensional immiscible films, are co-solubilized at a molecular level. Such products spontaneously form by simple mixing of the components and are indefinitely stable in a certain temperature range, defined lateron as existence range. Whenever used herein, the term "microemulsion" has a broader meaning, comprising also non optically isotropic systems (i.e. birefractive), characterized by an orientation of the liquid-crystalline type of the components. The (per)fluoropolyethers employed in the present invention are characterized in that they can be a mixture of components of different molecular weights, comprising a (per)fluoropolyether chain in which a few end groups do not consist of perfluoroalkyl groups but of functional groups. Such end groups may be monovalent or polyvalent. Furthermore, the functional groups can be present on branches of the (per)fluoropolyether chain, as is described in IT-A-20,346 A/86. The preferred average functionality of the molecules is in the range from 0.1 to 4, preferably from 0.1 to 2 and most preferably from 0.3 to 1. The functional groups present in the PFPE chains are representable by the formula : -(B) n -T m as defined above. The preferred end groups are : -COOH, -OH, -polyoxyalkylene-OH, quaternary ammonium groups. The acid end group is preferably salified. As starting products it is possible to use also perfluoropolyethers with -COF or -SO₂F end groups which, in the preparation of the microemulsion, hydrolize to -COOH and -SO₃H groups. The average viscosimetric molecular weight of the (per)fluoropolyether chain ranges from 1,500 to 10,000, and preferably from 2,000 to 6,000. Generally, aqueous microemulsions comprising (per)fluoropolyethers having end groups with hydrophilic functionality (for example COOH, polyoxyalkylene-OH, etc.) exhibit the property of requiring, for being formed, a lower surfactant amount with respect to corresponding microemulsions of PFPE having perfluoroalkyl end groups, because the hydrophilic groups co-operate in the formation of an interphase film, which renders the (per)fluorooxyalkylene chains compatible with the aqueous solution, although the functionalized PFPE molecules are substantially insoluble. At the limit, it is possible to prepare functional PFPE microemulsions with hydrophilic functionaly even in the total absence of added surfactant and only in the presence of a co-surfactant, which should be preferably hydrogenated. Preferred (per)fluoropolyethers for the preparation of the microemulsions according to the invention, having R f , R' f end groups of the functionalized type and optionally in part also of the perfluoroalkyl type, as pointed out above, are the ones comprising fluorooxyalkylene units selected from the following : (CF₂CF₂CH₂O) and in particular belonging to the following classes : 1) with a random distribution of the perfluorooxyalkylene units, where n, m, p have such average values as to meet the above requirements regarding the indicated molecular weight; 2) R f O(CF₂CF₂O) n (CF₂O) m R' f with a random distribution of the perfluorooxyalkylene units, wherein m, n have such values as to meet the above molecular weight requirements; 3) wherein m, n, p, o have such values as to meet the above molecular weight requirements; 4) wherein n has such a value as to meet the above, molecular weight requirements; 5) R f O(CF₂CF₂O) n R' f wherein n has such an average value as to meet the above molecular weight requirements; 6) R f O(CF₂CF₂CF₂O) n R' f or R f O(CH₂CF₂CF₂O) n R' f wherein n has such a value as to meet the above molecular weight requirements. Perfluoropolyethers of class (1) are known on the market under the trade-mark Fomblin® Y, those of class (2) under the trade-mark Fomblin® Z, all of them being manufactured by Montedison. Commercially known products of class (4) are Krytox® (DuPont) products. The products of class (5) are described in US-A-4,523,039; those of class (6) are described in EP-A-148,482. The ones of class (3) are prepared according to US-A-3,665,041. Suitable are also the perfluoropolyethers described in US-A-4,523,039 or in J. Am. Chem. Soc. 1985 , 107, 1195-1201. The products of classes 1, 2, 3, which are obtained through photochemical oxidation processes, are utilizable as crude products of the photo-oxidation process, which contain peroxide groups (-OO-)in the chain, said groups being inserted between the perfluorooxyalkylene units. Perfluoropolyethers suited for the preparation of the microemulsions according to the invention are also the ones disclosed in IT-A-20,346 A/86, which comprise functional groups of the above-indicated type arranged along the chain and functional or perfluoroalkyl end groups. The fluorinated surfactants to be used according to the present invention may be ionic or non-ionic. In particular, the following ones can be cited : (a) perfluorocarboxylic acids with 5 to 11 carbon atoms and the salts thereof; (b) perfluorosulphonic acids with 5 to 11 carbon atoms and the salts thereof; (c) the non-ionic surfactants disclosed in EP-A-51526 consisting of a perfluoroalkyl chain and of a polyoxyalkylene hydrophilic head; (d) mono- and di-carboxylic acids derived from perfluoropolyethers having mean molecular weights not higher than 1000, and the salts thereof; (e) the non-ionic surfactants consisting of a perfluoropolyether chain bound to a polyoxyalkylene chain; (f) perfluorinated cationic surfactants or those derived from perfluoropolyethers having 1, 2 or 3 hydrophobic chains. As co-surfactant it is possible to use a hydrogenated alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms. The following examples are given merely to illustrate the present invention and are not to be considered as a limitation of the possible embodiments thereof. Example 1 16.992 g of a raw perfluoropolyether belonging to class 1, with -COF end groups, having an average functionality equal to 0.57 and an average viscosimetric molecular weight equal to 4,000, containing peroxide bridges (PO = 1.02% by weight) and consisting of a mixture of polymers having a different molecular weight, were neutralized with 0.3 ml of an ammonia solution at 30% by weight of NH₃. 3.74 ml of t.butanol were added to the system, thereby obtaining a limpid, transparent solution, which was indefinitely stable in the temperature range of from 25 to 75°C. The weight composition of the system was as follows: - aqueous phase : 1.48% - alcohol : 14.75% - raw perfluoropolyether : 83.77%. The obtained microemulsion was of the water-in-oil (w/o) type. Example 2 Following the modalities described in the preceding example 1, a solution was prepared, whereto 2.2 ml of bidistilled water were added under gentle stirring. The resulting system was still composed of a single limpid, transparent phase, which was indefinitely stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 11.12% - alcohol : 13.31% - raw perfluoropolyether : 75.57%. The obtained microemulsion was of the w/o type. Example 3 Following the modalities described in the preceding example 2 a solution was prepared, to which 1.2 ml of bidistilled water were added under gentle stirring. The resulting system was still composed of a single limpid, transparent phase, which was indefinitely stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 15.63% - alcohol : 12.63% - raw perfluoropolyether : 71.74%. The obtained microemulsion was of the w/o type. Example 4 1.26 g of a raw perfluoropolyether belonging to class 1, with -COF end groups, having an average functionality of 0.46 and an average viscosimetric molecular weight equal to 4,600, containing peroxide bridges (PO = 1.02%) and consisting of a mixture of polymers having different molecular weights, were neutralized with 0.3 ml of an ammonia solution at 10% by weight of NH₃ and 1 ml of bidistilled water was added thereto. To such mixture there were added, under gentle stirring, 0.05 ml of a surfactant consisting of an acid having a perfluoropolyether structure belonging to class 1 and exhibiting an average equivalent weight equal to 668, and 0.6 ml of tert-butanol corresponding to a fluorinated surfactant/alcohol weight ratio equal to 0.18. A microemulsion did form, which, macroscopically, was in the form of a limpid, transparent liquid, that was indefinitely stable at room temperature. By heating the product to temperatures higher than 35-40°C, the system tended to separate into two phases and the product became turbid. By cooling to room temperature, the system spontaneously regained the characteristics of a microemulsion. The weight composition of the system was as follows: - aqueous phase : 41.53% - alcohol : 15.34% - fluorinated surfactant : 2.87% - raw perfluoropolyether : 40.26%. Example 5 To 2.65 ml of the system described in example 4, 2 ml of bidistilled water were added at room temperature. The resulting system was in the form of a single limpid and transparent phase, which was stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 64.10% - alcohol : 9.55% - fluorinated surfactant : 1.75% - raw perfluoropolyether : 24.60%. The obtained microemulsion was of the oil-in-water (o/w) type. Example 6 0.7 g of a raw PFPE belonging to class 1 having an average equivalent weight of 6250 with respect to the acid end groups and an average viscosimetric molecular weight of 3500, containing peroxide bridges (PO = 1.01%) and consisting of a mixture of polymers having different molecular weights, were neutralized with 0.2 ml of an ammonia solution at 10% by weight of NH₃ whereafter 1.8 ml of bidistilled water were added. To the resulting system there were added, under gentle stirring, 0.16 ml of a surfactant consisting of an acid having a perfluoropolyether structure belonging to class 1 composed of a mixture of components having different molecular weights and with an average equivalent weight equal to 668, and 0.54 ml of isopropanol. Obtained was a system macroscopically composed of a single limpid and transparent phase, which was stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 58.82% - alcohol : 15.88% - fluorinated surfactant : 4.71% - raw perfluoropolyether : 20.59%. The resulting microemulsion was of the o/w type. Example 7 0.7 g of a raw perfluoropolyether belonging to class 1, having an average equivalent weight of 6250 with respect to acid end groups and an average viscosimetric molecular weight of 3,500, containing peroxide bridges (PO = 1.02%) and consisting of a mixture of polymers with different molecular weights, were neutralized with 0.2 ml of an ammmonia solution at 10% by weight of NH₃ whereafter 1.8 ml of KNO₃ 0.1 M were added thereto. To the resulting system there were added 0.16 ml of a surfactant consisting of an acid with perfluoropolyether structure belonging to class 1 and having an average equivalent weight equal to 668, as well as 0.54 ml of isopropanol. Obtained was a system macroscopically composed of a single limpid, transparent phase, which was stable in the temperature range of 25-75°C. The weight composition of the system was equal to the one of example 6. Example 8 1.5 ml of bidistilled water and 0.51 ml of ter.butanol were added to 1.0 g of a raw perfluoropolyether belonging to class 1, hydrolized by heat-treatment with H₂SO₄, having an average functionality in -COOH of about 0.57 and an average viscosimetric molecular weight equal to 4,000, containing peroxide bridges (PO = 1.01%) and consisting of a mixture of polymers with different molecular weights, neutralized with 0.1 ml of an ammonia solution at 10% by weight of NH₃. Obtained was a solution macroscopically consisting of a single limpid phase, which was stable in the temperature range of 25-65°C. The weight compositon of the system was as follows: - aqueous phase : 42.02% - alcohol : 10.71% - raw perfluoropolyether : 47.27%. Example 9 1.8 g of a raw perfluoropolyether belonging to class 1, hydrolized by heat-treatment with H₂SO₄, having an average equivalent weight of 7,000 with respect to the acid groups and an average viscosimetric molecular weight of 4,000, containing peroxide bridges (PO = 1.01%) and consisting of a mixture of polymers having different molecular weights, were neutralized with 0.2 ml of an ammonia solution at 10% by weight of NH₃. Under gentle stirring there were added 0.18 g of a fluorinated alcohol having formula CHF₂(CF₂)₆CH₂OH, 0.18 g of a 5 M aqueous solution of a surfactant consisting of the ammonium salt of an acid having perfluoropolyether structure belonging to class 1 and an average equivalent weight equal to 367, and 0.15 ml of ter.butanol. A system macroscopically consisting of a single limpid phase which was stable at room temperature (25-30°C) was obtained. The weight composition of the system was as follows : - aqueous phase : 9.51% - hydrogenated alcohol + fluorinated alcohol : 4.23 + 11.42% - fluorinated surfactant : 11.42% - raw perfluoropolyether : 63.42%. The obtained microemulsion was of the w/o type. Example 10 0.72 g of a raw perfluoropolyether belonging to class 1 having an average functionality of 0.46 with respect to the acid groups and an average viscosimetric molecular weight of 4,600, containing peroxide bridges (PO = 1.02%) and consisting of a mixture of polymers having different molecular weights were neutralized with 0.1 ml of an ammonia solution at 10% by weight of NH₃ whereafter 0.8 ml of bidistilled water were added. To the system there were added 0.2 ml of a 5 M aqueous solution of a surfactant consisting of the ammonium salt of an acid having a perfluoropolyether structure belonging to class 1 and an average equivalent weight equal to 367. Obtained was a monophase opalescent and room-temperature (25-30°C) stable system, which became limpid at a temperature of 65°C. The weight composition of the system was as follows : - aqueous phase 48.08% - fluorinated surfactant : 17.31% - raw perfluoropolyether : 34.61%. Example 11 To 1.08 g of a raw perfluoropolyether belonging to class 1 having an average equivalent weight of 10,000 with respect to acid groups and an average viscosimetric molecular weight of 4,600, containing peroxide bridges (PO = 1.02%) and consisting of a mixture of polymers with different molecular weights, neutralized with 0.5 ml of an ammonia solution at 10% of NH₃, there was added, under gentle stirring, 1 ml of a solution at a concentration of 360 g/l of a surfactant consisting of the ammonium salt of an acid having a perfluoropolyether structure belonging to class 1 , consisting of a mixture of components with different molecular weights and with an average equivalent weight equal to 446. A microemulsion did form, which macroscopically consisted of a limpid, transparent liquid, which was indefinitely stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 47.44% - fluorinated surfactant : 13.14% - raw perfluoropolyether : 39.42%. Example 12 2 ml of a solution at a concentration of 250 g/l of lithium perfluoro-octansulphonate were added to 0.36 g of a raw perfluoropolyether belonging to class 1, hydrolized by heat-treatment with H₂SO₄, having an average equivalent weight of 7,000 with respect to the acid groups and an average viscosimetric molecular weight of 4,000, containing peroxide bridges (PO = 1.01%) and consisting of a mixture of polymers having different molecular weights, neutralized with 0.1 ml of an ammonia solution at 10% by weight of NH₃. A solution slightly opalescent at room temperature, having birefringence characteristics was obtained. The weight composition of the system was as follows: - aqueous phase : 65.04% - fluorinated surfactant : 20.33% - raw perfluoropolyether : 14.63%. The obtained microemulsion was of the o/w type. Example 13 1.1 ml of t-butanol were added to 0.5 ml of the solubilized composition indicated in example 12. A system composed of a single limpid phase, stable in the temperature range of 25-75°C and optically isotropic was obtained. The weight composition of the system was as follows: - aqueous phase : 47.9 % - alcohol : 26.35% - fluorinated surfactant : 14.97% - raw perfluoropolyether : 10.80%. The resulting microemulsion was of the o/w type. Example 14 0.36 g of a raw perfluoropolyether belonging to class 1, hydrolized by heat-treatment with H₂SO₄, having an average equivalent weight of 7,000 with respect to the acid groups and an average viscosimetric molecular weight of 4,000, containing peroxide bridges (PO = 1.01%) and consisting of a mixture of polymers having different molecular weights, were neutralized with 0.1 ml of an ammonia solution at 10% by weight of NH₃ whereafter 0.5 ml of a 0.1 M solution of KNO₃ were added thereto. To this system there were added 1.5 ml of an aqueous solution of ammonium perfluorooctanoate at a concentration of 360 g/l and 0.2 ml of t-butanol. A system characterized by a single limpid, transparent phase, indefinitely stable at a temperature higher than 40°C, was obtained. The weight composition of the system was as follows: - aqueous phase : 60% - alcohol : 5% - fluorinated surfactant : 21% - raw perfluoropolyether : 14%. The obtained microemulsion was of the o/w type. Example 15 A solution was prepared as is described in example 14. To this solution there were added, under gentle stirring, 0.36 g of a raw perfluoropolyether belonging to class 1, hydrolized by heat-treatment with H₂SO₄, having an average equivalent weight of 7,000 with respect to the acid groups and an average viscosimetric molecular weight equal to 4,000, containing peroxide bridges and consisting of a mixture of polymers having different molecular weights. The resulting system was stable at a temperature lower than 50°C, exhibited birefringence characteristics, and the raw perfluoropolyether therein contained was still solubilized. The weight composition of the system was as follows: - aqueous phase : 53.5% - alcohol : 4.5% - fluorinated surfactant : 18.0% - raw perfluoropolyether : 24.0%. The obtained microemulsion was of the o/w type. Example 16 1.8 g of a raw perfluoropolyether belonging to class 1 , having an average functionality equal to 0.45 in acid groups and an average viscosimetric molecular weight equal to 3,650, consisting of a mixture of polymers having different molecular weights were neutralized with 1 ml of an ammonia solution at 6% by weight of NH₃, whereafter 1 ml of bidistilled water was added thereto. 0.8 ml of isopropanol were added to this system under gentle stirring. The resulting microemulsion macroscopically consisted of a limpid, transparent liquid, indefinitely stable in the temperature range of 25-75°C. The weight composition of the system was as follows: - aqueous phase : 45.1% - alcohol : 14.3% - raw perfluoropolyether : 40.6%. Example 17 18 g of a surfactant consisting of an acid having a perfluoropolyether structure belonging to class 1, consisting of a mixture of components having different molecular weights, and exhibiting an average equivalent weight equal to 690 with respect to the acid groups, were salified with 10 ml of an ammonia solution at 10% by weight of NH₃. Thereto there were added 20 ml of bidistilled water, 6 ml of anhydrous ethanol and 3.6 g of a dialcohol having a perfluoropolyether structure belonging to class 2, having an average molecular weight equal to 2,000 and a functionality equal to 2 with end groups -CH₂OH. The resulting monophase system appeared macroscopically as a limpid, transparent liquid, which was indefinitely stable in the temperature range of 40-50°C. The weight composition of the system was as follows: - aqueous phase : 53.2% - alcohol : 8.5% - perfluorinated phase : 38.0%.

Claims: Microemulsion of the oil-in-water (o/w) or water-in-oil (w/o) type, comprising (i) an aqueous dispersion of a liquid (per)fluoropolyether having an average molecular weight of from 1,500 to 10,000 and end groups (R f , R' f ) which are at least partially of the functionalized (non-perfluoroalkyl) type, said functionalized end groups being represented by the formula: -(B) n T m wherein n = 0 or 1, B is a linking divalent or polyvalent hydrocarbon group, in particular an alkylene, cycloalkylene or arylene group having up to 20 and preferably up to 8 carbon atoms, m ranges from 1 to 3 and preferably is equal to 1, and T is selected from -H, -COOH, -SO₃H, -OH, polyoxyalkylene-OH and ester, amidic, aminic and quaternary ammonium groups; (ii) a perfluorinated surfactant and/or a co-surfactant; and, optionally, (iii) one or more water-soluble electrolytes. Microemulsion according to claim 1, wherein the (per)fluoropolyether comprises fluorooxyalkylene units selected from (CF₂CF₂CF₂O) and (CF₂CF₂CH₂O) and in particular is represented by one of the following formulae: (1) with a random distribution of the perfluorooxyalkylene units; (2) R f O(CF₂CF₂O) n (CF₂O) m R' f with a random distribution of the perfluorooxyalkylene units; (3) (4) (5) R f O(CF₂CF₂O) n R' f (6) R f O(CF₂CF₂CF₂O) n R' f or R f O(CH₂CF₂CF₂O) n R' f wherein the subscripts m, n, p and o have values such that the corresponding (per)fluoropolyether satisfies the molecular weight requirement. Microemulsion according to claim 2, wherein the perfluoropolyethers of formulae (1), (2) and (3) are raw products of the photo-oxidation process and also contain peroxide groups (-OO-) in the chain.

Inventors: LENTI DARIA, VISCA MARIO, LENTI, DARIA, VISCA, MARIO
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1988
Main classification: C08J3
IPC codes: C08J3, C10L1, C08G65, C08L71, B01J13