Fluorochemical sulfonamide surfactants Number:7,417,099 from the United States Patent and Trademark Office (PTO) owispatent

Title: Fluorochemical sulfonamide surfactants

Abstract: Described are fluorochemical surfactants derived from nonafluorobutanesulfonyl fluoride that contain polyalkyleneoxy side chains and may be copolymerized with acrylic acid or methacrylic acid to form polyacrylates or polymethacrylates. The surfactants surprisingly lower the surface tension of water and other liquids in the same or similar low values achieved by premier surfactants such as those derived from perfluorooctane sulfonyl fluoride.

Patent Number: 7,417,099 Issued on 08/26/2008 to Savu,   et al.

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Inventors:	Savu; Patricia M. (Maplewood, MN), Etienne; Sandra A. (St. Paul, MN)
Assignee:	3M Innovative Properties Company (St. Paul, MN)
Appl. No.:	11/052,125
Filed:	February 7, 2005

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	10264591	Oct., 2002	6852781
	09698987	Oct., 2000
	60161842	Oct., 1999

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Current U.S. Class:	526/243
Current International Class:	C08F 114/18 (20060101)
Field of Search:	526/243

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References Cited [Referenced By]

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Other References

Amphoteric Surfactants, Second Edition, edited by Eric G. Lomax, p. 13, Marcel Dekker Inc. (1996). cited by other . Organofluorine Chemicals and their Industrial Applications, edited by R.E. Banks, p. 56, Ellis Harwood Ltd. (1979). cited by other . Industrial Fluoro-Chemicals, J.O. Hendricks, Industrial and Engineering Chemistry, vol. 45, No. 1, p. 103, (1953). cited by other . Wetting of Low-Energy Solids by Aqueous Solutions of Highly Fluorinated Acids and Salts, Marianne K. Bernett and W.A. Zisman, Journal of Physical Chemistry, 63, p. 1912, (1959). cited by other . Long Chain Alkanoic and Alkenoic Acids with Perfluoroalkyl Terminal Segments, N.O. Brace, Journal of Organic Chemistry, 27, p. 4491 (1962). cited by other . Contact Angle, Wettability, and Adhesion, W.A. Zisman, Advances in Chemistry Series, 43, p. 22, American Chemical Society (1964). cited by other . Preparation, Properties, and Industrial Applications of Organofluorine Compounds, edited by R.E. Banks, p. 37, Ellis Horwood Ltd. (1982). cited by other . Fluorinated Surfactants, edited by Erik Kissa, Chapter 4, p. 134; p. 273; and p. 325, Marcel Dekker, Inc. (1996). cited by other . Annual Book of ASTM Standard 2002, E 809-94a. cited by other . U.S. Defensive Publication No. T987,003, Oct. 2, 1979. cited by other.

Primary Examiner: Lipman; Bernard
Attorney, Agent or Firm: Gross; Kathleen B.

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed as a divisional of U.S. application Ser. No. 10/264,591, filed Oct. 4, 2002, now U.S. Pat. No. 6,852,781 which was a divisional of U.S. application Ser. No. 09/698,987, filed Oct. 27, 2000, and which claimed priority U.S. Provisional Application No. 60/161,842, filed Oct. 27, 1999.

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Claims

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We claim:

1. A polymeric. surfactant comprising: at least one unit of the formula ##STR00017## wherein ##STR00018## represents a bond in a polymerizable or polymer chain; R.sub.f is --C.sub.4F.sub.9; R and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; and x is an integer of at least 1; and a polyalkyleneoxy segment.

2. A surfactant according to claim 1, wherein R and R.sub.2 are each independently hydrogen or methyl.

3. A surfactant according to claim 1, wherein n is 2.

4. A surfactant mixture comprising: (a) a compound according to claim 1, and (b) a compound of the formula ##STR00019## wherein R is hydrogen or alkyl of 1-4 carbon atoms; R.sub.a is hydrogen or alkyl of 1 to 4 carbon atoms; and r is an integer of 2 to 20.

5. The mixture of claim 4 wherein component (b) is of the formula ##STR00020##

6. A method of reducing the surface tension of a liquid comprising adding to said liquid a surfactant according to claim 1.

7. A method of reducing the surface tension of a liquid comprising adding a mixture of: (a) a compound according to claim 1; and (b) a compound of the formula ##STR00021## where R is hydrogen or alkyl of 1-4 carbons; R.sub.a is hydrogen or alkyl of 1-4 carbon atoms; and r is an integer from 2 to 20.

8. The method of claim 7, where component (b) is a compound of the formula ##STR00022##

9. A polymeric surfactant of the formula ##STR00023## wherein ##STR00024## represents a bond in a polymerizable or polymer chain; R, R.sub.1 and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R.sub.3 is one straight or branched alkyleneoxy group having 2 to 6 carbon atoms, more than one straight or branched alkyleneoxy groups linked together, each straight or branched alkyleneoxy group having 2 to 6 carbon atoms, or a straight or branched alkylene group having 12 to 20 carbon atoms; n is an integer from 2 to 10; and x, y and z are integers of at least 1.

10. The polymeric surfactant of claim 9, wherein n is 2.

11. The polymeric surfactant of claim 9, wherein R and R.sub.2 are each independently hydrogen or methyl.

12. The polymeric surfactant of claim 9, wherein R is methyl.

13. The polymeric surfactant of claim 1, wherein R is methyl.

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Description

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FIELD OF THE INVENTION

The invention relates to fluorochemical surfactants including those derived from nonafluorobutanesulfonyl fluoride (PBSF) that have been found to be as effective as the known premier surfactants derived from perfluorooctanesulfonyl fluoride (POSF) and can be produced at lower costs.

BACKGROUND OF THE INVENTION

The art of surfactants, particularly surfactants with fluorochemical chains, shows a preference for such surfactants with longer fluorochemical chains, e.g., C.sub.6-C.sub.10 in U.S. Pat. No. 2,803,615 and C.sub.6-C.sub.12 in U.S. Pat. No. 3,787,351. Even in hydrocarbon surfactants, increasing the chain length of the hydrocarbon chain decreases the CMC (critical micelle concentration); the decrease in CMC is roughly one order of magnitude for each --CH.sub.2CH.sub.2-- added to the chain (Amphoteric Surfactants, edited by Eric G. Lomax, Marcel Dekker Inc. (1996), p. 13). The same trend has been noted in surfactants derived from the perfluorocarboxylic acids and sulfonic acids (Organofluorine Chemicals and their Industrial Applications, edited by R. E. Banks, Ellis Horwood Ltd. (1979), p. 56; J. O. Hendrichs, Ind. Eng Chem, 45, 1953, p. 103; M. K. Bernett and W. A. Zisman, J. Phys. Chem., 63, 1959, p. 1912). Data exist that suggest that only after the seven outermost carbon atoms are fully fluorinated do the contact angles of various liquids on the surface approach those of a perfluoro fatty acid monolayer (N. O. Brace, J. Org. Chem., 27, 1962, p. 4491; W. A. Zisman, Advan. Chem. 1964, p. 22). Since models to explain the actions of surfactants often invoke the monolayer of the surfactant on the air/liquid interface, one would expect the same to be true of fluorinated surfactants, and that activity of the surfactant is closely tied to its chain length.

We have found the same trend when the surface tensions of C.sub.4F.sub.9SO.sub.3K and C.sub.8F.sub.17SO.sub.3K were measured in water. The results are shown in FIG. 1. We have also found that the same trend can be observed in a series of homologous fluorinated glycamide salts shown in FIG. 2. In each case the surface tension of the resulting solution of the C.sub.4F.sub.9SO.sub.2N-containing surfactant was significantly higher at the same concentration than the C.sub.8F.sub.17SO.sub.2N-containing surfactant. Based on the above, use of a C.sub.4F.sub.9SO.sub.2N-containing surfactant in an application would be disadvantageous over a C.sub.8F.sub.17SO.sub.2N-containing surfactant because higher levels would be required and the end result would potentially be higher expense and adverse effects on the properties of the composition used in the application.

SUMMARY OF THE INVENTION

We have found that polymeric fluorochemical surfactants with shorter perfluoroalkyl segments, preferably those derived from perfluorobutanesulfonyl fluoride (PBSF), have surface activities that surprisingly rival that of the homologs made from perfluorooctane segments such as perfluorooctanesulfonyl fluoride (POSF). It is particularly advantageous to use PBSF in a surfactant over POSF because of the higher yield of perfluorobutanesulfonyl fluoride (58%) in electrochemical fluorination over perfluorooctanesulfonyl fluoride (31%) (Preparation, Properties, and Industrial Applications of Organofluorine Compounds, edited by R. E. Banks, Ellis Horwood Ltd (1982), p. 37). A significant advantage of PBSF derived surfactants over the more commonly used POSF derived surfactants is that they can be produced at a lower cost per weight because of their higher yields and still maintain their potency as surfactants at the same weight percent. Furthermore, even with less fluorine content, potent surfactant properties are surprisingly achieved.

Many previously known polymeric, fluorochemical surfactants contain perfluorooctyl moieties. These surfactants ultimately degrade to perfluorooctyl-containing compounds. It has been reported that certain perfluorooctyl-containing compounds may tend to bio-accumulate in living organisms; this tendency has been cited as a potential concern regarding some fluorochemical compounds. For example, see U.S. Pat. No. 5,688,884 (Baker et al.). As a result, there is a desire for fluorine-containing compositions which are effective in providing desired surfactant properties, and which eliminate more effectively from the body (including the tendency of the composition and its degradation products).

It is expected that the polymeric, fluorochemical surfactants of the present invention, which contain perfluorobutyl moieties, when exposed to biologic, thermal, oxidative, hydrolytic, and photolytic conditions found in the environment, will break down to various degradation products. For example, compositions comprising perfluorobutylsulfonamido moieties are expected to degrade, at least to some extent, ultimately to perfluorobutylsulfonate salts. It has been surprisingly found that perfluorobutylsulfonate, tested in the form of its potassium salt, eliminates from the body much more effectively than perfluorohexylsulfonate and even more effectively than perfluorooctylsulfonate.

Accordingly, one aspect of the present invention provides a polymeric surfactant comprising at least one unit of Formula I

##STR00001## where R.sub.f is --C.sub.4F.sub.9 or --C.sub.3F.sub.7; R and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; and x is an integer of at least 1. In one preferred embodiment, R.sub.f is --C.sub.4F.sub.9.

Another aspect of the invention provides a polymeric surfactant prepared from the reaction products of the following monomers or oligomers: (a) a compound of the formula

##STR00002## (b) a compound selected from the group consisting of

##STR00003## (c) a compound of the formula

##STR00004## where R, R.sub.1, R' and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; n' is an integer of 1 to 10; p is an integer of 1 to about 128 and q is an integer of 0 to about 55. M is hydrogen, a metal cation, or a protonated tertiary amine.

Another aspect of the invention provides a polymeric surfactant comprising at least one unit of Formula II:

##STR00005## where the nonafluorobutanesulfonyl amido segment is part of a polymeric chain containing a polyalkyleneoxy segment. R, R.sub.1 and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R.sub.3 is at least one or more straight or branched alkylene-oxy groups, linked together when more than one, having 2 to 6 carbon atoms; n is an integer from 2 to 10; and x, y and z are integers of at least 1.

The present invention also includes mixtures thereof in forms of surfactant compositions as well as methods of using the surfactants.

One embodiment of the present invention provides a method of reducing the surface tension of a liquid comprising adding to said liquid a surfactant composition of this invention. Another embodiment of the invention provides a method of increasing the wetting of a coating mixture on a substrate by adding to the coating mixture of surfactant composition of this invention. In one embodiment of the invention, the surface tension of a liquid can be reduced by adding to said liquid a surfactant mixture comprising a compound of Formula I or Formula II and a compound of Formula III

##STR00006## in which R is hydrogen or alkyl of 1-4 carbon atoms; R.sub.a is a hydrogen or an alkyl of 1 to 4 carbon atoms; and r is an integer of 2 to 20. Preferably, R and R.sub.a are methyl and r is an integer from 4 to 10.

A more detailed description of the present invention including particular embodiments is described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic comparison of the surface tensions in water of C.sub.8 and C.sub.4 perfluorosulfonates.

FIG. 2 is a graphic comparison of surface tensions in water of C.sub.8, C.sub.6 and C.sub.4 perfluoroglycamides.

FIG. 3 is a graphic comparison of surface tensions in water of a C.sub.8F.sub.17 copolymeric surfactant and a C.sub.4F.sub.9 copolymeric surfactant.

FIG. 4 is a graphic comparison of surface tensions in water of C.sub.4F.sub.9 copolymer and C.sub.8F.sub.17 copolymer surface-active agents.

FIG. 5 is a graphic comparison of surface tensions in water of C.sub.8F.sub.17, C.sub.6F.sub.13 and C.sub.4F.sub.9 sulfonamido ethyleneoxy surfactants.

FIG. 6 is a graphic comparison of surface tensions in toluene of a C.sub.4F.sub.9 copolymeric surfactant and a C.sub.8F.sub.17 copolymeric surfactant.

FIG. 7 is a graphic comparison of surface tensions in water of polymeric C.sub.4F.sub.9 and C.sub.8F.sub.17 perfluorosulfonamido surfactants combined with C.sub.4F.sub.9 and C.sub.8F.sub.17 perfluoroethoxylates.

FIG. 8 is a graphic comparison of surface tensions in water of a C.sub.4F.sub.9 copolymeric surfactant and a C.sub.8F.sub.17 copolymeric surfactant.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

Compound of the Invention

The present invention provides a polymeric surfactant comprising at least one unit of Formula I

##STR00007## where R.sub.f is --C.sub.4F.sub.9 or --C.sub.3F.sub.7; R and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; and x is an integer of at least 1.

Preferred surfactants of formula I are those where R.sub.f is --C.sub.4F.sub.9. Other preferred surfactants are those in which R and R.sub.2 are each independently hydrogen or methyl and R.sub.f is --C.sub.4F.sub.9. Still other preferred embodiments include the surfactant of Formula I where n is 2.

The invention includes polymers in which there is at least one fluorochemical portion. In one preferred embodiment, the fluorochemical portion is a nonafluorobutanesulfonyl amido segment. The nonafluorobutanesulfonyl amido segments are combined with a reactive portion such as an acrylate or methacrylate group. The polymers may be, for example, polyacrylates, polymethacrylates, polyalkyleneoxy, or mixtures thereof.

In another aspect, the invention provides for short chain fluorochemical surfactants derived from nonafluorobutanesulfonyl amido segments that contain poly(alkyleneoxy) moieties. The invention also includes copolymers which are polyacrylates containing at least one nonafluorobutanesulfonyl amido segment and polyalkyleneoxy moieties. The invention also provides for mixtures of the individual monomers thereof or mixtures of an acrylate or methacrylate derivative of nonafluorobutanesulfonyl amido and corresponding polyalkyleneoxy acrylate or methacrylate copolymers.

The nonafluorobutanesulfonyl amido containing surfactants of the present invention are those in which a plurality of nonafluorobutanesulfonyl amido segments are linked to polyalkyleneoxy moieties through a polymeric chain. The polyalkyleneoxy moieties are particularly useful because they are soluble over a wide range of polarity and, by alteration of the carbon-oxygen ratio, can be tailored for any particular matrix. These copolymeric surfactants are non-ionic or they can be ionic by inclusion of ionic segments. While normally liquid or low melting solids, the coplymeric surfactants can be in the form of a very thick glass in the absence of a solvent. They are soluble in polar synthetic resinous compositions and have about 5 to 30 weight %, preferably 10 to 25 weight %, carbon-bonded fluorine based on the weight of the copolymer.

As polyalkyleneoxy moieties, R.sub.3 is at least one or more straight or branched alkyleneoxy groups having 2 to 6 carbon atoms, preferably 2 to 4 carbon atoms, most preferably 2 or 3 carbon atoms such as ethyleneoxy or propyleneoxy. When ethyleneoxy and propyleneoxy units are linked together, they form polyethyleneoxy or polypropyleneoxy blocks or a mixture of blocks. The oxypropylene units can be branched or linear.

Particularly preferred of these are those containing one polyoxypropylene and having at least one other block of polyoxyethylene attached to the polyoxypropylene block. Additional blocks of polyoxyethylene or polyoxypropylene can be present in a molecule. These materials having an average molecular weight in the range of about 500 to about 15,000 are commonly available as PLURONIC.TM. manufactured by the BASF Corporation and available under a variety of other trademarks from other chemical suppliers. In addition, polymers called PLURONIC.TM. R (reverse Pluronic structure) are also useful in the invention.

Particularly useful polyoxypropylene polyoxyethylene block polymers are those comprising a center block of polyoxypropylene units and blocks of polyoxyethylene units to each side of the center block. These copolymers have the formula shown below: (EO).sub.n--(PO).sub.m--(EO).sub.n wherein m is an integer of about 21 to about 54 and n is an integer of about 7 to about 128. Additional useful block copolymers are block polymers having a center block of polyoxyethylene units and blocks of polyoxypropylene units to each side of the center block. The copolymers have the formula as shown below: (PO).sub.n--(EO).sub.m--(PO).sub.n wherein m is an integer of about 14 to about 164 and n is an integer of about 9 to about 22.

Another preferred polyalkyleneoxy moiety useful in the co-polymers of the present invention containing a nonafluorobutanesulfonamido segment are those derived from polyethylene glycols having a molecular weight of about 200-10,000. Suitable commercially available polyethylene glycols are available from Union Carbide under the trade name CARBOWAX.TM..

Another necessary part of the copolymeric surfactants of the present invention is acrylate and/or methacrylate moieties that form part of the starting monomers as well as the final polyacrylate products. Nonafluorobutanesulfonamido acrylate starting materials or monomers can be copolymerized with monomers containing polyalkyleneoxy moieties to form surface-active agents. Thus, the polyacrylate surfactants of the present invention can be prepared, for example, by free radical initiated copolymerization of a nonafluorobutanesulfonamido radical-containing acrylate with a polyalkyleneoxyacrylate, e.g., monoacrylate or diacrylate or mixtures thereof. Adjusting the concentration and activity of the initiator, the concentration of monomers, the temperature, and the chain-transfer agents can control the molecular weight of the polyacrylate copolymer. The description of the preparation of such polyacrylates is for example described in U.S. Pat. No. 3,787,351, which patent is incorporated herein. The starting nonafluorobutanesulfonamido acrylates described above are also known in the art, e.g., U.S. Pat. No. 2,803,615, which patent is also incorporated herein by reference.

The polyalkyleneoxy acrylates used in the above preparation can be prepared from commercially available hydroxypolyethers or polyoxyalkylene hydroxy compounds such as, for example, the PLURONIC.TM. or CARBOWAX.TM. polymers. Such hydroxy materials are reacted in a known manner with acrylic acid, methacrylic acid, acrylyl chloride or acrylic anhydride. Alternatively, a polyalkyleneoxy diacrylate, prepared in a known manner similar to the monoacrylates, can be copolymerized with the nonafluorobutanesulfonamido acrylate to obtain a polyacrylate copolymer of the present invention.

The above polymeric surfactant may also contain, if desired, a water-solubilizing polar group that may be anionic, nonionic, cationic or amphoteric. Preferred anionic groups include, but are not limited to, sulfonates (e.g., --SO.sub.3M), sulfates (e.g., --OSO.sub.3M), and carboxylates (e.g., --C(.dbd.O)OM). M is hydrogen, a metal cation such as an alkali or alkaline earth metal cation (e.g., sodium, potassium, calcium or magnesium, and the like), or a nitrogen-based cation, such as, for example, ammonium or a protonated tertiary amine (e.g. (HOCH.sub.2CH.sub.2).sub.2N.sup..sym.HCH.sub.3). The sulfonate polar groups are employed as oligomers or polymers that include polyacrylates and polyacrylamides. A particularly useful monomer or oligomer employed in the present invention, if desired to provide water-solubilizing polar groups, is a polyacrylamide sulfonate of the formula

##STR00008## wherein R.sub.2 and R are as defined above; R' is hydrogen, or alkyl of 1-4 carbon atoms, especially methyl; n' is an integer of 1 to 10, and M is hydrogen, a metal cation, or a protonated tertiary amine.

A preferred anionic group is 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) or the potassium salt thereof.

Representative useful cationic water-solubilizing groups include, for example, ammonium or quaternary ammonium salts. Preferred monomers that provide cationic water-solubilizing groups include dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and the like. For example, the surfactant may be made incorporating compounds of the formula A-O--C(.dbd.O)C(R.sub.2).dbd.CH.sub.2 wherein A is an amine-containing group.

The present invention in another general aspect includes a polymeric surfactant prepared from the reaction product of the following monomers or oligomers: (a) a compound of the formula

##STR00009## (b) a compound selected from the group consisting of

##STR00010## (c) a compound of the formula

##STR00011## where R, R.sub.1, R' and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; n' is an integer of 1 to 10; p is an integer of 1 to about 128 and q is an integer of 0 to about 55. M is hydrogen, a metal cation, or a protonated tertiary amine.

The compound containing the nonafluorobutanesulfonamido segment can also be used in a monomeric mixture form or mixture of monomers and polymers or copolymers.

To enhance compatibility with various components found in many adhesive and binder systems, it may be desired to include long chain alkyl compounds in the surfactant. For example, the surfactant may be made incorporating compounds of the formula R.sub.h--O--C(.dbd.O)C(R.sub.2).dbd.CH.sub.2 wherein R.sub.h is an alkyl of 12 to 20 carbon atoms.

The present invention includes a polymeric surfactant of Formula II

##STR00012## where the nonafluorobutanesulfonyl amido segment is part of a polymeric chain containing a polyalkyleneoxy moiety. R, R.sub.1 and R.sub.2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R.sub.3 is at least one straight or branched polyalkylene-oxy group, linked together when more than one, having 2 to 6 carbon atoms, or a straight or branched alkylene group having 12 to 20 carbon atoms; n is an integer from 2 to 10; and x, y and z are integers of at least 1.

Preferred surfactants of Formula II are those where R, R.sub.1, and R.sub.2 are each independently hydrogen or methyl. Other preferred embodiments include the surfactant of Formula I where n is 2.

In one particular aspect of the surfactant of Formula I, the polyalkene oxide group, R.sub.3 is of the formulae A or B: (EO).sub.p--(PO).sub.q--(EO).sub.p (A) or (PO).sub.q--(EO).sub.p--(PO).sub.q (B) wherein p is an integer of 1 to about 128 and q is an integer of 0 to about 54.

A particularly preferred embodiment is employing a CARBOWAX.TM. moiety where R.sub.3 in the surfactant of Formula II is a polyalkylene oxide group of formula B, q is 0 and p is about 17. R and R.sub.1 are methyl.

Alternatively, another preferred embodiment is a copolymer surfactant where the polyalkyleneoxy moiety is derived from a polyalkylene oxide of formula A where q is an integer of about 9 to about 22 and p is an integer of about 14 to about 128. More preferred is a copolymeric surfactant where the ethylene oxide moieties are on the outside of the block copolymer with propylene oxide and p is an integer of about 7 to about 128 and q is an integer of about 21 to about 54. Most preferred is the copolymeric surfactant containing the moiety of formula A where p is about 11 and q is about 21. In this particular embodiment, the copolymeric surfactant is that described in the above Formula H where R is methyl.

In one embodiment of the invention the surfactant is a mixture comprising a compound of Formula I or Formula II and a compound of Formula III

##STR00013## in which R and R.sub.a are independently hydrogen or alkyl of 1-4 carbon atoms and r is an integer of 2 to 20. Preferably, R and Ra.sub.1 are methyl and r is an integer from 4 to 10.

All of the nonafluorobutylsulfonamido-containing structures described above may be made with heptafluoropropylsulfonamido groups by starting with heptafluoropropylsulfonyl fluoride, which can be made by the methods described in Examples 2 and 3 of U.S. Pat. No. 2,732,398 (Brice et al.). Using the methods described in the examples below, the heptafluoropropylsulfonyl fluoride can then be converted to N-methylheptafluoropropylsulfonamide, N-methylheptafluoropropylsulfonamidoethanol, C.sub.3F.sub.7SO.sub.2N(CH.sub.3)(CH.sub.2CH.sub.2O).sub.7.5CH.sub.3, N-methyl-heptafluoropropylsulfonamidoethyl acrylate, N-methyl-heptafluoropropylsulfonamidoethyl methacrylate, and the copolymers corresponding to those described with nonafluorobutylsulfonamido groups.

Methods of Use

The surfactants of the present invention have similar beneficial properties and can be used for the same purposes as the premier surfactants, such as a corresponding perfluorooctanesulfonamido surfactant. Surprisingly, the surfactants of the present invention lower the surface tension of water and other liquids to the same or lower values than achieved by premier surfactants derived from perfluorooctanesulfonyl fluoride. Similarly, the surfactants of the present invention can improve the wetting of a liquid or coating mixture on a substrate to an extent comparable to the premier surfactants.

The surfactants of this invention can be used individually or in combination to produce the desired surface tension reduction or wetting improvement.

One aspect of this invention provides a method of reducing the surface tension of a liquid by adding to the liquid a surface-active agent of the formula

##STR00014##

In another embodiment of the invention, adding a surfactant mixture comprising a compound of Formula I or Formula II and a compound of Formula III reduces the surface tension of a liquid

##STR00015## in which R and R.sub.a are independently hydrogen or alkyl of 1-4 carbon atoms and r is an integer of 2 to 20. Preferably, R and R.sub.a are methyl and r is an integer from 4 to 10.

Fluorochemical surfactants of the present invention have been found to be surprisingly effective in a number of applications. In one application, cellular polymeric membranes are made using fluorochemical surfactants of the present invention. The surfactants provide for and control the formation of a large number of small cells or voids in the membrane, which leads simultaneously to the formation of a cellular membrane with low density and an opaque, uniform appearance. The properties and methods of making cellular pressure-sensitive adhesive (PSA) membranes of this type are described in U.S. Pat. No. 4,415,615 (Esmay, et al), incorporated herein by reference. Cellular PSA membranes or foam tapes can be made not only by forming a cellular polymeric membrane that has PSA properties, but also by applying a layer of PSA to at least one major surface of a cellular polymeric membrane. Preferred fluorochemical surfactants for this application comprise (a) one or more compounds having a perfluorobutanesulfonamide segment and comprising a polyalkyleneoxy segment and (b) one or more polymers comprised of the reaction products of a fluorochemical monomer, a nonionic polar monomer, and optionally an ionic polar monomer. The fluorochemical portion of the fluorochemical monomer is perfluorobutyl and the reactive portion of the fluorochemical monomer is preferably acrylate or methacrylate. The nonionic polar monomer is preferably a poly(ethyleneoxide) acrylate. The optional ionic polar monomer is preferably dimethylaminoethyl methacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, methacrylic acid, acrylic acid, and mixtures thereof.

In another application fluorochemical surfactants of the present invention have been found to be a very effective surface treatment for optical elements such as glass or ceramic beads, thus enabling the beads to float on the surface of organic binder resins used in the manufacture of pavement marking and retroreflective sheeting constructions. Floatation of the beads is an effective means of producing an array of beads all lying in essentially the same plane with each bead protruding from the binder resin, and thereby having an air interface. Preferred fluorochemical surfactants for this application comprise one or more polymers formed from the reaction products of a fluorochemical monomer, a nonionic polar monomer, and an ionic polar monomer. The fluorochemical portion of the fluorochemical monomer is perfluorobutyl and the reactive portion of the fluorochemical monomer is preferably acrylate or methacrylate. The nonionic polar monomer is preferably a poly(ethyleneoxide) acrylate. The ionic polar monomer is preferably dimethylaminoethyl methacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylic acid, and mixtures thereof, with 2-acrylamido-2-methyl-1-propanesulfonic acid being most preferred.

In many retroreflective materials, glass or ceramic beads function as the optical elements. Preferred properties of the optical elements in general are described herein with respect to glass beads. The glass or ceramic beads are fixed in place by means of a cured liquid binder. Because the glass or ceramic beads have a density or specific gravity several times that of the liquid binder, they tend to sink into the liquid binder layer rather than float on the surface. The glass or ceramic beads are coated with a surface treatment that alters the floatation properties of the beads in the liquid binder. "Float", and derivations thereof, refers to the beads assuming a position wherein slightly more than half of each bead is submerged. The liquid binder preferably contacts the embedded beads only up to 5 to 30.degree. above their equators. The floatability of the glass or ceramic beads can be affected to some extent by the particle size, particle size distribution, surface chemistry and chemical make-up of the particular beads as well as the chemical make-up, density, and viscosity of the binder. In general, however, only about 10% or less of the glass beads tend to float in heptane test liquid in the absence of an effective surface treatment.

The diameter of optical elements such as ceramic or glass beads typically ranges from a few microns to approximately 2500 microns and is preferably from about 10 to 1000 microns. Ordinary glass beads typically have a density of about 2.5 and a refractive index of about 1.5. "High index" beads refers to beads having a density of about 3.5 and a refractive index of about 1.9, whereas "super high index" typically refers to beads having a density of about 5 and a refractive index of about 2.6 or higher.

In general, ceramic microsphere optical elements are comprised of metal oxides that are substantially colorless. Suitable metal oxides include Al.sub.2O.sub.3, SiO.sub.2, ThO.sub.2, SnO.sub.2, TiO.sub.2, Y.sub.2O.sub.3 and ZrO.sub.2 with the oxides of zirconium, silicon, and titanium being preferred. The ceramic microspheres can exhibit a range of properties, depending on the kind and amounts of the various metal oxides employed as well as the method of manufacture. Preferred, however, are dense microspheres having substantially no open porosity that have an average hardness greater than sand. Additional information concerning the desired properties for various end-uses and methods of manufacture of microspheres (e.g., sol-gel process) can be found in U.S. Pat. Nos. 3,493,403; 3,709,706; and 4,564,556; incorporated herein by reference.

Glass beads suitable for use as optical elements in the invention are also commercially available from Flex-O-Lite Corporation, Fenton, Mo. and Nippon Electric Glass, Osaka, Japan.

In addition to having the desired particle size and refractive index, the optical elements are typically transparent. The term transparent means that when viewed under an optical microscope (e.g., at 100.times.) the microspheres have the property of transmitting rays of visible light so that bodies beneath the microspheres, such as bodies of the same nature as the microspheres, can be clearly seen through the microspheres when both are immersed in oil of approximately the same refractive index as the microspheres. The outline, periphery or edges of bodies beneath the microspheres are clearly discernible. Although the oil should have a refractive index approximating that of the microspheres, it should not be so close that the microspheres seem to disappear as would be the case of a perfect match.

The surface treatment can be present on the optical elements in an amount sufficient such that at least about 50% of the optical elements float in heptane. Preferably, the treatment of the optical elements with the surfactant (surface-active agent) improves the floatability such that greater than about 80% of the optical elements float in heptane and more preferably about 90-100% of the optical elements float in heptane. The amount of fluorochemical compound employed for coating the optical elements typically ranges from about 10 ppm to about 1000 ppm with respect to the weight of the optical elements. A preferred fluorochemical compound is one that contributes the desired floatation at minimum concentrations. The amount of fluorochemical compound is usually about 600 ppm or less, preferably about 300 ppm or less, more preferably about 150 ppm or less, even more preferably about 100 ppm or less, and most preferably about 50 ppm or less. Typically, the overall coating thickness of the surface treatment of the present invention is greater than about 15 Angstroms, preferably, greater than about 20 Angstroms, and more preferably, greater than about 50 Angstroms. Thicker coatings can be obtained if desired, although it is preferred that the coating thickness be no greater than about 500 Angstroms, more preferably, no greater than about 300 Angstroms, and most preferably, no greater than about 150 Angstroms thick.

The fluorochemical compositions described herein for use as surface treatments for optical elements are typically liquids. The surface treatments are combined with various solvents to form an emulsion, solution, or dispersion. The emulsion(s), solution(s), and dispersion(s) are then further diluted in order to deliver the desired concentration. It is assumed that negligible amounts of the diluted surface treatment are lost and substantially all of the surface treatment present in the emulsion, solution, or dispersion is deposited on the optical elements. Although aqueous emulsions, solutions, and dispersions are preferred, up to about 50% of a co-solvent such as methanol, isopropanol, or methyl perfluorobutyl ether may be added. Preferably, the aqueous emulsions, solutions, and dispersions comprise less than about 30% co-solvent, more preferably less than about 10% co-solvent, and most preferably the aqueous emulsions, solutions, and dispersions are substantially free of co-solvent. The aqueous surface treatment is coated on the optical elements, typically, by combining the optical elements and the aqueous surface treatment and then drying the coated elements. Although aqueous delivery is preferred, the surface treatment could also be applied by other techniques such as vapor deposition.

In addition to the improvement in floatation of the glass or ceramic beads, it is also important that the surface treatment does not adversely affect the adhesion of the glass beads with the cured liquid binder. The adhesion can be evaluated in several ways. The initial adhesion can be determined subjectively by estimating the extent to which the glass or ceramic beads are embedded after curing. The beads are preferably embedded to about 40-70%, and more preferably to about 40-60% of their diameters. Another way of evaluating adhesion is accelerated aging evaluations. A piece of cured glass or ceramic bead-embedded binder is conditioned in boiling water for 24 hours. After conditioning, the beads are preferably embedded to the same extent as prior to conditioning and the individual glass beads are difficult to remove with a dissection probe. Yet, another way to evaluate adhesion is comparative tensile testing. A uniform slurry of binder and untreated beads at a ratio of about 1 to 3 is coated as a film having a thickness of about 0.4 mm. A second slurry of binder and surface treated beads employing the same ratio of ingredients and is coated in a comparable manner. After the coatings are fully cured, the samples are conditioned for 24 hours in water at ambient temperature. Tensile testing is conducted with a 2.54 cm wide sample employing a 5.08 cm gap at a rate of 1.27 cm/minute. The stress required to break the sample containing the surface treated beads is about the same as or preferably greater than the control sample containing untreated beads (greater than or equal to about 90% of the standard deviation of the average value).

In addition to the surface treatment of the invention, the optical elements may comprise one or more additional surface treatments such as adhesion promoters and flow control agents. Various silanes such as .gamma.-aminopropyl triethoxysilane are commonly employed as adhesion promoters, whereas methacrylato chromic chloride, commercially available from Zaclon Inc., Cleveland Ohio, under the trade designation "Volan" is a typical flow control agent.

The surface treated optical elements of the invention can be employed for producing a variety of reflective products or articles such as pavement markings, retroreflective sheeting, and beaded projection screens. Such products share the common feature of comprising a liquid binder layer and embedding a multitude of optical elements into the binder surface followed by solidifying the binder to retain the optical elements in place. In pavement markings, retroreflective sheeting, and beaded projection screens of the invention, at least a portion of the optical elements will comprise the surface treated optical elements of the invention. Typically, the majority of, and preferably substantially all of the optical elements employed in the manufacture of the reflective products will comprise surface treated optical elements of the invention.

Various known binder materials may be employed including one or two-part liquid curable binders, as well as thermoplastic binders wherein the binder attains a liquid state via heating until molten. Common binder materials include polyacrylates, polymethacrylates, polyolefins, polyurethanes, polyepoxides, phenolics, and polyesters. For reflective paints, the binder layer may contain reflective pigment. For reflective sheeting, the binder material itself is typically transparent and the binder layer comprises one or more colorants, e.g., dyes and pigments. Transparent binders can be applied to a reflective base or to a release-coated support. With a release-coated support, the beaded film is stripped away after solidification. The film may then be applied to a reflective base or be given a reflective coating or plating.

There are several types of retroreflective article in which the surface treated optical elements may be used such as exposed lens (e.g., U.S. Pat. Nos. 2,326,634 and 2,354,018), embedded lens (e.g., U.S. Pat. No. 2,407,680), and encapsulated lens (e.g., U.S. Pat. No. 4,025,159) retroreflective sheeting. Retroreflective sheeting can be prepared by known methods including a method comprising the steps of: (i) forming a top coat on a release-coated web (e.g., coating a solution of hydroxy-functional acrylic polyol and aliphatic polyfuntional isocyanate onto a release-coated paper web and then curing by conveying the coating through an oven at about 150.degree. C. for about 10 minutes); (ii) coating the exposed surface of the top coat with a liquid binder (e.g. coating a solution comprising an oil-free synthetic polyester resin and a butylated melamine resin); (iii) drying the binder to form an uncured tacky bead-bond layer; (iv) cascade-coating onto the bead-bond layer a plurality of glass microspheres forming a monolayer of embedded glass microspheres; (v) curing the bead-containing bead-bond layer to a non-tacky state (e.g., by heating to 150.degree. C.); forming a space coat layer over the bead-containing bead-bond layer (e.g., coating a 25% solids solution comprised of a polyvinylbutyral resin and a butylated melamine resin in a solvent and curing at 170.degree. C. for about 10 minutes); (vi) applying a reflective layer over the space coat layer (e.g., via vapor deposition of aluminum metal at a thickness of about 100 nm); and stripping away the release-coated web. An adhesive layer is typically applied to the-reflective layer (e.g., by coating a 0.025 mm thick layer of an aggressive acrylic pressure-sensitive adhesive onto a silicone-treated release liner and pressing the adhesive against the reflective layer).

The surface treated optical elements are also useful in pavement marking materials. The optical elements can be incorporated into coating compositions that generally comprise a film-forming material having a multiplicity of optical elements dispersed therein. The surface treated optical elements may also be used in drop-on applications for such purposes as highway lane striping in which the optical elements are simply dropped onto wet paint or hot thermoplastic and adhered thereto.

One typical pavement-marking sheet is described in U.S. Pat. No. 4,248,932. This sheet material is a prefabricated strip adapted for lying on and securing to pavement for such purposes as lane dividing lines. The pavement-marking sheet comprises a base sheet, such as a soft aluminum foil which is conformable to a roadway surface; a top layer (also called the support film or binder film) adhered to one surface of the base sheet and being very flexible and resistant to rupture; and a monolayer of surface treated optical elements such as transparent microsphere lens elements partially embedded in the top layer in a scattered or randomly separated manner. The pavement marking sheet construction may also include an adhesive (e.g., pressure sensitive, heat or solvent activated, or contact adhesive) on the bottom of the base sheet. The base sheet may be made of an elastomer such as acrylonitrile-butadiene polymer, polyurethane, or neoprene rubber. The top layer in which the surface treated microspheres are embedded is typically a polymer such as vinyls, polyurethanes, epoxies, and polyesters. Alternatively, the surface treated microsphere lenses may be completely embedded in a layer of the pavement-marking sheet.

Processes known in the art may be used to make pavement-marking sheets (see e.g., U.S. Pat. No. 4,248,932). One process comprises the steps of: (i) coating onto a base sheet of soft aluminum (50 micrometers thick) a mixture of resins (e.g., epoxy and acrylonitrile butadiene elastomer mixture), pigment (TiO.sub.2) and solvent (e.g., methylethylketone) to form the support film; (ii) dropping onto the wet surface of the support film ingredients a multiplicity of optical elements surface treated with surfactants of this invention; and curing the support film at 150.degree. C. for about 10 minutes. A layer of adhesive is then usually coated on the bottom of the base sheet.

Pigments or other coloring agents may be included in the top layer in an amount sufficient to color the sheet material for use as a traffic control marking. Titanium dioxide will typically be used for obtaining a white color; whereas, lead chromate will typically be used to provide a yellow color.

A rear projection screen is a sheet-like optical device having a relatively thin viewing layer that is placed at an image surface of an optical projection apparatus. Rear projection screen displays comprising glass microspheres embedded in an opaque matrix are known from U.S. Pat. No. 2,378,252, for example. Generally, the size of the microspheres is less than about 150 microns. For maximum brightness, the microspheres have an index of refraction of less than about 1.8 and preferably from about 1.45 to about 1.75. A plurality of the surface treated glass microspheres are attached to and are in intimate contact with a major surface of a transparent substrate. Alternatively, a diffusion layer can be formed by coating an optically inhomogeneous material as a separate layer onto the transparent substrate prior to application of the opaque binder and microspheres. Rear projection screens are prepared by i) providing a substrate (e.g., polyester, polycarbonate) having an opaque binder disposed thereon (e.g., acrylate loaded with carbon black to make it opaque); and ii) applying the surface treated glass microspheres under conditions effective to produce microspheres in optical contact with the substrate and embedded in the opaque matrix.

A specular reflective means can be provided by vapor depositing a layer of metal (e.g., aluminum) on the surface treated microspheres. Another useful specular reflective means can be a dielectric reflector which comprises one or more layers of a transparent material behind the microspheres where each layer has a refractive index of about 0.3 higher or lower than that of the adjacent layer or beads and each layer has an optical thickness corresponding to an odd numbered multiple of about 1/4 wavelength of light in the visible range. More detail on such dielectric reflectors is found in U.S. Pat. No. 3,700,305.

In yet another application, fluorochemical surfactants of the present invention have been found to be useful as oil well stimulation additives as shown by their ability to form a stable foam with water that is saturated with a hydrocarbon. The low surface energy provided by these surfactants results in faster and more complete stimulation load recovery with less blockage of capillaries by trapped water. Under normal operations at an oil field, water is pumped daily through injector wells and down into the reservoir several thousands of feet below ground in an attempt to pressurize the reservoir and force the hydrocarbons toward the producing wells. On a monthly to yearly basis, a foam is pumped through the injector wells. The foam is formed by mixing the aqueous solution containing the fluorochemical surfactant (at about 0.1 to about 1 weight percent based on the weight of the solution) with a gas such as carbon dioxide or nitrogen. The foam reduces the amount of fluid needed to pressurize the reservoir. Also, the foam increases the level of hydraulic push and is more effective in permeating the crevices of the rock. The fluorochemical surfactant in the foam maintains the foam quality and small bubble size at elevated temperatures and in the presence of dissolved hydrocarbons. Representative useful fluorochemical surfactants for this application are as described above for bead floatation. Preferred surfactants are comprised of both anionic and cationic groups (amphoteric), either within the same surfactant molecule or as a mixture of surfactant molecules, some having anionic groups and some having cationic groups.

In certain other applications the fluorochemical surfactants of the present invention are used as coating additives to provide better wetting of the coating to a substrate surface, or better wetting of a component within the coating formulation, for example, enhancing the wetting characteristics of a thickening agent. When used in water borne coatings, the fluorochemical surfactants are formulated into an aqueous solution or dispersion at a final concentration of about 0.001 to about 0.1 weight percent based on the weight of the solution or dispersion. The formulated product can be used in many coating applications such as floor polishes and finishes, varnish for a variety of substrates, including wood floors, water borne gel applied in the manufacture of photographic film, automotive topcoats, and marine coatings. The fluorochemical surfactants can be used in other protective thin layer coatings as well, by preparing a formulation containing a surfactant, a powder, or a liquid mixture with organic solvents, fillers, and resins, including but not limited to epoxies, urethanes, acrylics, and the like. Typically, the surfactant concentration is about 0.1 to about 0.5 weight percent based on the weight of the formulation. Specific uses for these protective coatings include, for example, corrosion resistance coatings on electronic components for the computer and telecommunications industry, signage, office furniture, and pipes. Application methods of the above coating include dip coating, brushing, spraying, flow coating, and the like. The coatings are typically applied, dried, and cured, leaving the finished product with a solid coating. As an example, the surfactants have been found to be extremely effective in providing smooth clear polyurethane coatings without coating defects on surfaces that are difficult to wet, such as oily surfaces. Preferred fluorochemical surfactants for this application comprise one or more polymers comprised of the reaction products of a fluorochemical monomer, and a nonionic polar monomer. The fluorochemical portion of the fluorochemical monomer is perfluorobut