Fluorinated hydrophilic polymers

Details Fluorinated hydrophilic polymers Fluorinated hydrophilic polymers

2001-01-23

2003-02-18

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S243000, C526S250000, C526S255000, C526S264000, C526S287000, C526S288000, C526S303100, C526S304000, C526S307600, C526S307700, C526S318400, C526S320000

Reexamination Certificate

active

06521730

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of hydrophilic polymers and has more particularly as subject-matter hydrophilic fluoropolymers obtained by radical polymerization in a precipitating medium. These polymers lower the surface tension of aqueous solutions; they are good foaming agents and they are more particularly advantageous as dispersants or thickeners and as additives in multipurpose fire-fighting emulsifiers.
BACKGROUND OF THE INVENTION
Hydrophilic polymers and more particularly those based on acrylamide, on methacrylamide or on their N-substituted derivatives are well known and widely used industrially. Acrylamide, methacrylamide and their derivatives are very often copolymerized with other hydrophilic monomers carrying anionic or cationic ionic or ionizable charges which confer, on the hydrophilic polymer, specific properties suited to each application. These polymers are commonly used in the paper industry, in water treatment or in metallurgy as flocculants for ores; they are also used as thickening agents in numerous formulations, such as textile printing and cosmetic products.
The most widely used methods for preparing these polymers involve aqueous media; such is the case of polymerization in aqueous solution or of micellar polymerization but other methods, such as inverse emulsion polymerization, are also practised. The polymerization is generally initiated by a radical-generating redox couple, such as, for example, the persulphate (S
2
O
8
2−
)/metabisulphite (S
2
O
5
2−
) couple, but also by azo or peroxide radical initiators. Other initiating systems can be used, such as UV rays, X rays, ultrasound or cobalt salts.
The copolymerization of acrylamide, of methacrylamide and of their derivatives in a precipitating medium, in which the monomers are soluble and the polymer precipitates during its formation, is a method which is more rarely used and which is disclosed in particular in Patents FR 1 508 702, GB 1 328 742 and U.S. Pat. No. 3,336,269.
Acrylamide, methacrylamide and their derivatives can also be copolymerized with water-insoluble monomers possessing a hydrocarbonaceous hydrophilic side chain, such as, for example, fatty alcohol acrylates or methacrylates. The copolymers thus formed are associative thickeners, the hydrophobic groups of which, in aqueous solution, tend to form intermolecular associations, thus creating a transitory network. In aqueous solution, the viscosity of these associative polymers depends on the shear rate; the solution generally exhibits a pseudoplastic nature, that is to say that its viscosity decreases with the increase in the shear rate. Such products are disclosed in references [1] to [3], the list of which appears after the examples of the present application.
Acrylamide, methacrylamide and their derivatives can also be copolymerized with monomers possessing a perfluoroalkyl hydrophobic side chain, such as, for example, fluoroalcohol acrylates or methacrylates. The synthesis and the characterization of such hydrophilic fluoropolymers are described by Thieo E. Hogen-Esch and his coworkers and by other authors in references [4] to [12]. These fluorocopolymers were prepared in aqueous medium in the presence of a cosolvent, such as acetone ([4]-[9]), and more rarely in aqueous medium in the absence of cosolvent [12] or under bulk conditions [9], the polymerization reaction having been initiated by a redox couple which is a precursor of radicals by oxidation/reduction ([4]-[9]), by a radical initiator which is a precursor of radicals by thermal decomposition ([9]-[12]) or by triphenylmethylcaesium in anionic polymerization in solution in tetrahydrofuran. U.S. Pat. No. 4,891,306 discloses hydrophilic fluorocopolymers obtained by anionic or cationic polymerization; these products are used in light-sensitive photographic materials.
In all the cases cited above, the hydrophilic fluorocopolymers are synthesized under bulk conditions or in aqueous medium in the presence of surfactants, the purpose of which is to dissolve the hydrophobic fluoromonomers inside the micelles. The surfactants preferably used are fluorosurfactants, the perfluoroalkyl side chain of which is compatible with fluoromonomers, which makes possible the dissolution of these monomers. The hydrophilic fluoropolymers obtained by polymerization in aqueous medium exhibit, as common characteristic, a high molecular weight, which leads to very viscous aqueous solutions, resulting in the use of such products as viscosifying agents. In many cases, the presence of fluorosurfactants interferes with the subsequent use of the polymers, which makes it necessary to resort to precipitation of the polymer from a large excess of solvent, followed by washing the polymer. This precipitating and washing stage, which is additional to the synthesis, has to be carried out with large amounts of solvents, such as, for example, alcohols, which increases the manufacturing cost and produces effluents laden with surfactants. In the case of the polymerization in a precipitating medium, used in the context of the present invention, it is much easier and faster to recover the polymer in the powder form. Although starting from monomers of the same nature as those described above, namely acrylamide or methacrylamide derivatives and monomers comprising a perfluoroalkyl side chain, the hydrophilic fluoropolymers forming the subject-matter of the present invention are distinguished from the above in several respects, the main ones of which are the preparation process proper, the content of fluoromonomers incorporated in the polymer and the nature of the radical-initiating agents. These differences are reflected by very different behaviours from the view point of the applicative properties.
The hydrophilic fluoropolymers according to the invention can, for example, be used as additives in multipurpose fire-fighting emulsifiers, that is to say emulsifiers intended for the extinguishing of hydrocarbon fires and polar liquid fires.
Fire-fighting emulsifiers comprising hydrophilic fluoropolymers have already been disclosed, in particular in Patents FR 2 438 484, U.S. Pat. Nos. 4,563,287 and 4,606,832.
Acrylamide, methacrylamide and their N-substituted derivatives, used in the context of the present invention, and the method for polymerization in a precipitating medium are not mentioned in U.S. Pat. No. 4,563,287, which, for the extinguishing of cooking oil fires, discloses nonfoaming compositions, whereas the emulsifiers comprising a hydrophilic fluoropolymer according to the present invention are foaming compositions.
The extinguishing compositions disclosed in U.S. Pat. No. 4,606,832, also intended for combating cooking oil fires, involved bromofluorohydrocarbons and/or bromochlorofluorohydrocarbons, which is not the case in the present invention, and are not fire-fighting emulsifiers having foaming properties, as in the case of the present invention.
Patent FR 2 438 484, which does not mention acrylamide, methacrylamide or their N-substituted derivatives, indicates that the polymers can be obtained by solution polymerization. In point of fact, solution polymerization, applied to the hydrophilic fluoropolymers according to the invention, does not result in successful products; it is necessary to resort to polymerization in a precipitating medium.
SUMMARY OF INVENTION
A subject-matter of the present invention is therefore hydrophilic fluoropolymers obtained by radical polymerization, in a precipitating medium, of a mixture of monomers composed, by weight, of:
(a) 0 to 49% of at least one nonionic hydrophilic monomer, preferably 25 to 45%, more preferably still 35 to 45%;
(b) 20 to 75% of at least one monomer comprising a perfluoroalkyl radical, preferably 25 to 60%, more preferably still 25 to 50%; and
(c) 5 to 75% of one or more ionic or ionizable hydrophilic monomers, preferably 5 to 35%, more preferably still 5 to 20%.
These polymers have foaming p

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