WO2010038902A1 - Production method of fluoroethercarboxylic acid fluoride and fluoroethercarboxylic acid - Google Patents

Abstract

The present invention is a production method of a fluoroethercarboxylic acid fluoride, comprising the step of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I): CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of -30 to 40 °C in the presence of a catalyst, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

Description

DESCRIPTION

PRODUCTION METHOD OF FLUOROETHERCARBOXYLIC ACID FLUORIDE AND

FLUOROETHERCARBOXYLIC ACID

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U. S. C. §119 to US Provisional Application No.61/101, 745, filed October 1, 2008, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD [0001] The present invention relates to a production method for a fluoroether carboxylic acid fluoride and a fluoroethercarboxylic acid.

BACKGROUND ART [0002]

A fluoroethercarboxylic acid, namely

2,3,3, 3-tetrafluoro-2- [1, 1,2, 3, 3, 3-hexafluoro-2- (trifluorom ethoxy) propoxy] propanoic acid, obtainable from the corresponding fluoroethercarboxylic acid fluoride can be suitably used as a surfactant and can be used in a production of fluoropolymers, in particular. [0003]

It is known in the art that the above intermediate fluoroethercarboxylic acid fluoride can be produced by the methods mentioned below. [0004]

Patent Document 1 discloses that hexafluoropropylene oxide was reacted with carbonyl fluoride in diethylene glycol dimethyl ether at 50 ⁰C using cesium fluoride as a catalyst to give a mixture of oligomers of the formula CF₃O(CF(CF₃)CF₂O)_nCF(CF₃)COF in which n = 1 to 6, the fluoroethercarboxylic acid fluoride in which n = 1 was recovered by distillation of the mixture and, further, the corresponding carboxylic acid was obtained by hydrolysis thereof. However, those components in which n = not smaller than 2 account for the most part of such mixture. [0005]

Patent Document 2 discloses that the same reaction as described in Patent Document 1 was carried out at 75 ⁰C to give the above-mentioned fluoroethercarboxylic acid fluoride in which n = 0, which was further reacted with an alkali to give the corresponding perfluoro (methyl vinyl ether). However, there is no description of the acquisition of the above-mentioned fluoroethercarboxylic acid fluoride in which n = 1 or of the corresponding carboxylic acid. [0006]

Patent Document 3 discloses that hexafluoropropylene oxide was reacted with carbonyl fluoride in diethylene glycol dimethyl ether at -20 ⁰C in the presence of potassium iodide, followed by reaction with methanol, to give oligomers of the

^' formula CF₃O(CF(CF₃)CF₂O)_nCF(CF₃)COOMe in which n = 1 to 5.

However, there is no description of the yield of the oligomer component in which n = 1. That the oligomers in which n = 1 to 5 were obtained suggests that the oligomer component in which n = 1 was not selectively obtained. [0007]

In Patent Documents 4 and 5, it is described that the reaction between hexafluoropropylene oxide and carbonyl fluoride in an aprotic solvent in the presence of a lower tetraalkylurea or alkyleneurea compound gives perfluoromethoxypropionic acid fluoride. In this case, too, it is described that high-molecular-weight components are obtained in small amounts whereas there is no description to the effect that the above-mentioned fluoroethercarboxylic acid fluoride in which n = 1 was obtained and, of course, there is no description of the yield thereof.

[0008]

Patent Documents 6 and 7 describe that the reaction of hexafluoropropylene oxide with a perfluoroalkanoic acid fluoride gives a perfluoroalkoxypropionic acid fluoride.

[0009]

Patent Documents 8 to 12 describe production methods of hexafluoropropylene oxide homooligomers.

[0010] [Patent Document 1] United States Patent No. 3,250,808

[Patent Document 2] United States Patent No. 3,114,778

[Patent Document 3] Japanese Kokai (Laid-open) Publication

S63-77835

[Patent Document 4] Japanese Kokai Publication H02-4733 [Patent Document 5] Japanese Kokai Publication H04-159246

[Patent Document 6] Japanese Kokai Publication S52-156810

[Patent Document 7] United States Patent No. 3,271,341

[Patent Document 8] Japanese Kokai Publication H02-237955

[Patent Document 9] Japanese Kokai Publication S55-51032 [Patent Document 10] Japanese Kokai Publication H01-157933

[Patent Document 11] Japanese Kokai Publication S57-64641

[Patent Document 12] Japanese Kokai Publication H02-172944

DISCLOSURE OF INVENTION PROBLEMS WHICH THE INVENTION IS TO SOLVE [0011]

Meanwhile, a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) is useful as an intermediate for the preparation of a fluoroethercarboxylic acid to be used as a surfactant in the production of a fluoropolymer. The above-mentioned fluoroethercarboxylic acid fluoride can be produced as one of a plurality of products obtainable by reacting hexafluoropropylene oxide with an acid fluoride. [0012]

However, when the reaction of hexafluoropropylene oxide with an acid fluoride is carried out according to the conventional art methods, compounds other than the fluoroethercarboxylic acid of the above formula (I) are formed due to such side reactions as mentioned below. [0013] a) Addition reaction of three or more molecules of hexafluoropropylene oxide [HFPO] : COF₂ + k (HFPO) → CF₃O(CF(CF₃)CF₂O)_IC-_ICF(CF₃)COF (In the formula, k represents an integer of 3 or higher.) [0014] b) Oligomerization of hexafluoropropylene oxide: l(HFPO) → CF₃CF₂CF₂O (CF (CF₃) CF₂O) ₁-₂CF(CF₃) COF (In the formula, 1 represents an integer of 2 or higher.) [0015]

In view of the above-discussed state of the art, it is an object of the present invention to provide a method of producing the fluoroethercarboxylic acid fluoride of the above formula (I) selectively and in good yields. [0016]

The present invention is a production method of a fluoroethercarboxylic acid fluoride, which comprises the step of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent. [0017]

The present invention is a production method of a fluoroethercarboxylic acid, which comprises the steps of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) :

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst and obtaining a fluoroethercarboxylic acid represented by the general formula (II):

CF₃O (CF(CF₃) CF₂O) CF (CF₃) COOX (II) wherein X represents hydrogen atom, ammonium group and an alkali metal atom, from the fluoroethercarboxylic acid fluoride, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent. [0018]

The present invention is a production method of a fluoroethercarboxylic acid fluoride, which comprises the step of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with a fluoroethercarboxylic acid fluoride represented by the formula

(i) : CF₃OCF(CF₃)COF (i) in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, non-cyclic tetraalkylureas, cyclic alkylureas, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent. [0019]

The present invention is a production method of a fluoroethercarboxylic acid, which comprises the steps of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with a fluoroethercarboxylic acid fluoride represented by the formula

(i) : CF₃OCF(CF₃)COF (i) in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst and obtaining a fluoroethercarboxylic acid represented by the general formula (II) : CF₃O (CF (CF₃) CF₂O) CF (CF₃) COOX (II) wherein X represents hydrogen atom, ammonium group and an alkali metal atom, from the fluoroethercarboxylic acid fluoride, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, non-cyclic tetraalkylureas, cyclic alkylureas, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

MEANS FOR SOLVING THE PROBLEMS

[0020] In the following, the present invention is described in detail.

[0021]

In an aspect, a production method according to the invention comprises the step of reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of

-30 to 40 ⁰C in the presence of a catalyst to selectively give the fluoroethercarboxylic acid fluoride represented by the formula (I) :

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I). [0022]

In another aspect, the production method according to the invention comprises the step of reacting hexafluoropropylene oxide with a fluoroethercarboxylic acid fluoride represented by the formula (i) : CF₃OCF(CF₃)COF (i) in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst to selectively give the fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I). [0023]

The fluoroethercarboxylic acid fluoride of the above formula (I) is useful as an intermediate for the production of fluoroethercarboxylic acids represented by the general formula

(II): CF₃O(CF(CF₃)CF₂O)CF(CF₃)COOX (II) wherein X represents hydrogen atom, ammonium group or an alkali metal atom. [0024]

The production method according to the invention makes it possible to obtain the fluoroethercarboxylic acid fluoride of the above formula (I) by using a specific catalyst and a specific solvent within a specific temperature range. [0025]

The catalyst used for the reaction of hexafluoropropylene oxide with carbonyl fluoride comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts. In view of selectively obtaining the fluoroethercarboxylic acid fluoride represented by the formula (I), the catalyst is preferably the metal fluoride and more preferably at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride is more preferred, among others. [0026] When hexafluoropropylene oxide is reacted with carbonyl fluoride, using the non-cyclic tetraalkylurea or cyclic alkylurea alone as the catalyst fails to obtain the fluoroethercarboxylic acid fluoride represented by the formula (I) selectively. However, it is preferred that the metal fluoride be used as the catalyst and further at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas be used therewith, since the fluoroethercarboxylic acid fluoride represented by the formula (I) can be selectively obtained in lower usage of the metal fluoride. It is more preferred that using both at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride and at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas. [0027]

The catalyst used for the reaction of hexafluoropropylene oxide with the fluoroethercarboxylic acid fluoride represented by the formula (i) comprises at least one species selected from the group consisting of metal fluorides, non-cyclic tetraalkylureas, cyclic alkylureas, tertiary amines, tertiary diamines and tetraalkylammonium salts. In view of selectively obtaining the fluoroethercarboxylic acid fluoride represented by the formula (I) , the catalyst is preferably the metal fluoride and more preferably at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride is more preferred, among others. Further, it is preferred that both the metal fluoride and at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas be used, and more preferred that both at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride and at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas be used as the catalyst. [0028]

As the above metal fluorides, there may be mentioned fluorides of alkali metals (group 1) , alkaline earth metals (group 2), group 11 metals and group 12 metals, among others. Preferred alkali metal (group 1) fluorides are cesium fluoride, potassium fluoride, sodium fluoride and lithium fluoride, among others. Calcium fluoride is preferred among the alkaline earth metal (group 2) fluorides, and silver fluoride is preferred among the group 11 metal fluorides. Preferably selected as the above-mentioned metal fluorides are alkali metal (group 1) fluorides. At least one species selected from the group consisting of cesium fluoride and potassium fluoride is more preferably selected.

[0029] As the non-cyclic tetraalkylureas, there may be mentioned tetramethylurea, tetrabutylurea and the like.

Tetramethylurea is preferably selected.

[0030]

As the cyclic alkylureas, there may be mentioned 1, 3-dimetyl-2-imidazolidinone,

1, 3-dimethyl-3, 4, 5, 6-tetrahydro-2-pyrimidinone and the like.

[0031]

As the tertiary amines, there may be mentioned trimethylamine, triethylamine, tripropylamine, tributylamine, N,N-dimethylaniline and pyridine, among others.

[0032]

As the tertiary diamines, there may be mentioned tertiary tetraalkyl-substituted aliphatic diamine compounds in which the alkanediyl chain contains not more than 10 carbon atoms and each alkyl group contains not more than 6 carbon atoms, and heterocyclic diamines; as examples, there may be mentioned

N, N, N' ,N' -tetramethylmethylenediamine,

N, N, N' ,N' -tetraethylmethylenediamine,

N, N, N' ,N' -tetramethylethylenediamine, N, N, N' ,N' -tetraethylethylenediamine,

N, N, N' , N' -tetrapropylethylenediamine,

N, N, N' ,N' -tetramethylpropylenediamine,

N, N, N' ,N' -tetramethylisopropylenediamine,

N, N, N' , N' -tetramethylhexylidenediamine, bis (3-methylpiperidino) methane and N, N' -dimethylpiperazine. [0033]

Preferably selected as the tetraalkylammonium salts from a ready availability viewpoint, among others, are those represented by the general formula: NR₄X wherein the four R groups are the same or different and each represents a straight chain or branched chain hydrocarbon group containing 1 to 4 carbon atoms and X represents fluorine, chorine, bromine or iodine atom. [0034]

Preferably selected as the solvent mentioned above are aprotic polar solvents, and at least one species selected from the group consisting of nitrile solvents, nitro solvents, sulfoxide solvents, sulfone solvents, N,N-dialkyl-substituted amide solvents and ether solvents is more preferably selected. [0035]

As the ether solvents, there may be mentioned glymes, diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, anisole and crown ethers, among others. Among them, at least one species selected from the group consisting of glymes and crown ethers. [0036]

The glymes mentioned above are hydrocarbon ethers represented by the general formula RO (CH₂CH₂O) _qR (in which R represents -C_pH_2p+i (p representing an integer of 1 to 5) and q represents an integer of 1 to 10) . [0037]

As the glymes, there may be mentioned dimethoxyethane, diethoxyethane, monoethylene glyocl dimethyl ether, diethylene glycol dimethyl ether (diglyme) , triethylene glycol dimethyl ether (triglyme) , tetraethylene glycol dimethyl ether (tetraglyme) , diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and the like. Among them, at least one species selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether is preferably employed. [0038]

As the nitrile solvents, there may be mentioned acetonitrile, propionitrile, butyronitrile, benzonitrile and adiponitrile, among others. [0039]

As the nitro solvents, there may be mentioned nitromethane, nitrobenzene and so forth. [0040] As the sulfoxide solvents, there may be mentioned dimethyl sulfoxide and the like. [0041]

As the sulfone solvents, there may be mentioned sulfolane and the like. [0042]

As the N,N-dialkyl-substituted amide solvents, there may be mentioned N,N-dimethylformamide and the like. [0043]

The fluoroethercarboxylic acid fluoride represented by the above formula (i) can be prepared by such a known method as described in Japanese Kokai Publication H02-4733, for instance. [0044]

In carrying out the production method according to the present invention, a reaction temperature is -30 to 40 ⁰C, preferably -20 to 30 ⁰C, more preferably -15 to 20 ⁰C. While an optimum temperature range may vary depending on the catalyst system employed, excessively high reaction temperatures may promote side reactions such as a hexafluoropropylene oxide oligomerization reaction. [0045]

Preferably, the catalyst is used in an amount of 100 to 0.1 mole percent, more preferably 100 to 1 mole percent, relative to carbonyl fluoride fed to a reaction vessel, or 30 to 0.01 mole percent, more preferably 20 to 0.1 mole percent, still more preferably 10 to 0.5 mole percent, relative to the fluoroethercarboxylic acid fluoride fed to a reaction vessel. The use of the catalyst in an excessively large amount is economically disadvantageous and, when the catalyst amount is excessively small, the hexafluoropropylene oxide oligomerization reaction and other side reactions may be promoted. When two or more different catalysts are used simultaneously, the above amount of usage of the catalyst is total amount thereof. [0046]

The solvent is used preferably in a proportion of 100 to 0.1 parts by mass, more preferably 50 to 1 parts by mass, per part by mass of carbonyl fluoride, or 10 to 0.01 parts by mass, more preferably 1 to 0.1 parts by mass, per part by mass of the fluoroethercarboxylic acid fluoride. The use of the solvent in an excessively large amount is economically disadvantageous and, when the solvent amount is excessively small, the hexafluoropropylene oxide oligomerization reaction and other side reactions may be promoted. [0047]

The solvent, catalyst and the like can be reused. When reused, they may be additionally added to compensate for the loss. [0048] In carrying out the production method according to the invention, it is preferred, from the viewpoint of selectivity for the product fluoroethercarboxylic acid fluoride, that at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride be used as the catalyst and diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether as the solvent. In this preferred mode of practice, the reaction temperature is preferably -20 to 5 ⁰C, more preferably -15 to 0 ⁰C. When the reaction temperature is excessively high, side reactions such as the hexafluoropropylene oxide oligomerization reaction may be promoted, resulting decreases in selectivity and, when the reaction temperature is excessively low, the rate of reaction may fall. [0049] When carbonyl fluoride is one of the starting materials in carrying out the production method according to the invention, hexafluoropropylene oxide is preferably used in the amount of 100 to 500 mole percent, more preferably 100 to 300 mole percent, relative to carbonyl fluoride. When the fluoroethercarboxylic acid fluoride of formula (i) is used in lieu of carbonyl fluoride, the starting material hexafluoropropylene oxide is preferably used in the amount of 50 to 500 mole percent, more preferably 50 to 200 mole percent, relative to the fluoroethercarboxylic acid fluoride. The reaction for obtaining the desired fluoroethercarboxylic acid fluoride is preferably carried out, for example, for 1 to 48 hours, although the reaction time may vary according to the reaction conditions. [0050]

The reaction between hexafluoropropylene oxide and carbonyl fluoride may sometimes cause the formation of the fluoroethercarboxylic acid fluoride represented by the formula

(i) :

CF₃OCF(CF₃)COF (i) , in addition to the fluoroethercarboxylic acid fluoride represented by the formula (I) . In this case, it is also possible to recover the fluoroethercarboxylic acid fluoride of formula (i) and react hexafluoropropylene oxide with the recovered fluoroethercarboxylic acid fluoride to selectively give the fluoroethercarboxylic acid fluoride represented by the formula (I) :

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) .

[0051]

Since such recovery and recycling as mentioned above is possible, the industrial disadvantage of the side reaction-due formation of the fluoroethercarboxylic acid fluoride of formula (i) is slight. However, such side reactions as an addition reaction of three or more molecules of hexafluoropropylene oxide to carbonyl fluoride and the oligomerization of hexafluoropropylene oxide should preferably be inhibited as far as possible. It is a technological significance of the present invention that such side reactions in particular can be inhibited. [0052]

According to the production method of the invention, the fluoroethercarboxylic acid fluoride of formula (I) can be obtained in a yield of not lower than 40 mole percent, preferably not lower than 50 mole percent, with a selectivity of not lower than 40 mole percent, preferably not lower than 50 mole percent. [0053] The selectivity mentioned above is calculated as the proportion (mole percent) of the fluoroethercarboxylic acid fluoride of formula (I) relative to the sum of the fluoroethercarboxylic acid fluorides represented by the general formula: CF₃O(CF(CF₃)CF₂O)_nCF(CF₃)COF wherein n represents 0, 1, 2 or 3, and the fluoroethercarboxylic acid fluorides represented by the general formula: CF₃CF₂CF₂O (CF (CF₃) CF₂O) _nCF (CF₃) COF wherein m represents 0, 1 or 2, as obtained by carrying out the reaction. [0054]

The proportions of the respective fluoroethercarboxylic acid fluorides are the values determined by gas chromatographic analysis using a Shimadzu model GC-14A gas chromatograph with an SE-30 column (3.0 m) mounted thereon. [0055]

The production method according to the invention may comprise the step of recovering the fluoroethercarboxylic acid fluoride following the step of selectively obtaining the fluoroethercarboxylic acid fluoride. When the reaction product occurs as two separate phases, the recovery may comprise a procedure of separating the upper phase and lower phase from each other and recovering either of the phases. [0056] The production method according to the invention may also comprise the step of distilling the fluoroethercarboxylic acid recovered. The distillation may be either simple distillation or rectification. [0057] The present invention also relates to a fluoroethercarboxylic acid production method which comprises the step of converting the fluoroethercarboxylic acid fluoride obtained by the production method mentioned above to a fluoroethercarboxylic acid represented by the general formula (II):

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COOX (II) . [0058]

The symbol X represents hydrogen atom, ammonium group (NH₄) or an alkali metal atom. As the alkali metal atom, there may be mentioned Li, Na and K, among others. Thus, the fluoroethercarboxylic acid obtained may be in the form of an acid or in the form of an ammonium salt or an alkali metal salt. [0059]

The production method of a fluoroethercarboxylic acid according to the invention preferably comprises the steps of selectively obtaining the fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I), recovering the fluoroethercarboxylic acid fluoride obtained, contacting the fluoroethercarboxylic acid fluoride recovered with water or an acid, optionally neutralizing the product obtained by the water or acid treatment with an alkali or ammonia, and recovering the fluoroethercarboxylic acid represented by the general formula (II): CF₃O (CF (CF₃) CF₂O) CF (CF₃) COOX (II) wherein X represents hydrogen atom, ammonium group or an alkali metal atom. [0060] The acid mentioned above is preferably hydrochloric acid, sulfuric acid or nitric acid. [0061]

The alkali mentioned above is preferably an alkali or alkaline earth metal, or a hydroxide thereof. [0062]

The process of production method of the invention can be carried out as either a batch, a semi-batch, or a continuous (CSTR) process. The fluoroethercarboxylic acid fluoride represented by the formula (I) can be selectively obtained by either a batch, a semi-batch, or a continuous (CSTR) process. For example, the semi-batch process, wherein hexafluoropropylene is added into the reaction vessel properly according to the progress of the reaction, may be employed. Further, it is also a preferred process wherein the raw materials are added into the reaction vessel to react by the semi-batch process, followed by the product fluoroethercarboxylic acid fluoride is recovered, and then the raw materials are added into the reaction vessel again. This is also a preferred aspect of the invention. [0063]

The fluoroethercarboxylic acid obtained by the production method according to the invention can be suitably used as a surfactant. Any surfactant composition containing at least one fluoroethercarboxylic acid species represented by the general formula (II) can be used as a surfactant, and the surfactant may contain two or more fluoroethercarboxylic acid species of general formula (II) .

[0064]

The surfactant comprising the fluoroethercarboxylic acid mentioned above can show moderate surfactant activity in various fields of use. The surfactant can be used in the production of a fluoropolymer, among others. [0065]

From a water solubility viewpoint, the above-mentioned surfactant is preferably used in the form of a salt, and the ammonium salt is preferred from the viewpoint that it can be readily removed by heating treatment, hence hardly remains in product resins. [0066] The above surfactant is also preferably used in the carboxylic acid form. In this case, the surfactant activity in water is increased as compared with a salt form; for example, at the same molar concentration level, the carboxylic acid lowers the surface tension to a larger extent. Therefore, when used in a polymerization process, the carboxylic acid provides, among others, the following advantages: more stable and smaller polymer particles are obtained, a polymer colloid obtained shows high stability, the occurrence of aggregates during polymerization is less frequent and a polymerization can be carried out until high polymer concentration. [0067]

The above fluoroethercarboxylic acid can be suitably used in a fluoropolymer production method comprising the step of carrying out a polymerization of a fluoromonomer in an aqueous medium. [0068]

The above-mentioned production method of a fluoropolymer makes it possible to produce a fluoropolymer efficiently by using at least one of the fluoroethercarboxylic acids mentioned above. In carrying out the production method of a fluoropolymer, two or more of the above-mentioned fluoroethercarboxylic acids may be used simultaneously as a surfactant; alternatively, some surface active compound other than the above fluoroethercarboxylic acids may be used in combination in cases where that compound is volatile or allowed to remain in a final fluoropolymer moldings or the like. The surface-active compound is not particularly restricted but may be any of those known in the art. In carrying out the above-mentioned production method of a fluoropolymer, use can be made of one or more additives to stabilize each compound in addition to the above-mentioned fluoroethercarboxylic acid and the surface-active compound used optionally. As the additives, there may be mentioned, chain transfer agents, radical scavengers, buffering agents, emulsion stabilizers, dispersion stabilizers and so forth. [0069]

In producing a fluoropolymer mentioned above, a polymerization is carried out by charging a polymerization vessel with an aqueous medium, at least one of the fluoroethercarboxylic acid, and a monomer, if necessary together with one or more additives, stirring the contents in the reaction vessel, maintaining the reaction vessel at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, a monomer, a polymerization initiator, a chain transfer agent and/or at least one of the fluoroethercarboxylic acid mentioned above may be additionally fed to the reaction vessel in accordance with the intended purpose.

In the above polymerization, the polymerization temperature is generally 5 to 120 ⁰C, and the reaction pressure is generally 0.05 to 10 MPa. The polymerization temperature and polymerization pressure are to be properly selected according to the monomer species used, a desired fluoropolymer molecular weight and the rate of reaction. [0070]

In carrying out the above-mentioned production method of a fluoropolymer, a pH at the start of polymerization is preferably adjusted, for example to 6 or lower, preferably 5 or lower, more preferably 4 or lower, still more preferably 3 or lower, whereby a more stable polymer colloid can be obtained. [0071]

The above-mentioned fluoroethercarboxylic acid or acids are added preferably in a total amount of 0.0001 to 10% by mass relative to 100% by mass of the aqueous medium. Amore preferred lower limit to that amount is 0.001% by mass, and amore preferred upper limit thereto is 1% by mass. At addition levels lower than 0.0001% by mass, the dispersability may become insufficient and, at addition levels exceeding 10% by mass, the effect is no longer proportional to the amount added and the rate of polymerization may rather drop and/or the reaction may be terminated. The level of addition of the fluoroethercarboxylic acid mentioned above is properly determined according to the monomer species used and a desired fluoropolymer molecular weight, among others. [0072]

The polymerization initiator is not particularly restricted but may be any of those capable of radical generation within the polymerization temperature range mentioned above. This, the oil-soluble and/or water-soluble polymerization initiators known in the art can be used. Further, the polymerization can also be initiated by using a reducing agent, for instance, in combination to form a redox system. The concentration of the polymerization initiator is to be properly selected according to the monomer species, a desired fluoropolymer molecular weight and the rate of reaction. [0073]

The aqueous medium so referred to herein is a reaction medium for carrying out the polymerization therein and means a water-containing liquid. The aqueous medium is not particularly restricted provided that it contains water; thus, it may comprise water and, for example, a non-fluorinated organic solvent, such as an alcohol, ether or ketone, and/or a fluorinated organic solvent having a boiling point of not higher than 40 C. For example, such a fluorinated organic solvent as C318 can be used in the case of suspension polymerization.

Further, in the above polymerization, the rate of polymerization and the molecular weight can be adjusted by adding one or more of the chain transfer agents and radical scavengers known in the art in accordance with an intended purpose. [0074] The above fluoropolymer production method may also comprise the step of obtaining an aqueous emulsion (seed dispersion) by emulsion polymerization of an monomer in the presence of the above-mentioned fluoroethercarboxylic acid in the aqueous medium and the step of subjecting an monomer to emulsion polymerization (seed polymerization) in the presence of the aqueous emulsion (seed dispersion) . [0075]

The fluoropolymer is a product of polymerization of a fluoromonomer and, according to an intended purpose, a non-fluorinated monomer may also be copolymerized. [0076]

As the fluoromonomers, there may be mentioned, among others, fluoroolefins, preferably fluoroolefins containing 2 to 10 carbon atoms; fluorinated cyclic monomers; and fluorinated alkyl vinyl ethers represented by the formula

CY₂=CYOR or CY₂=CYOR²OR³ (in which Y is H or F, R and R³ are a partially or fully fluorinated alkyl group containing 1 to 8 carbon atoms and R² is a partially or fully fluorinated alkylene group containing 1 to 8 carbon atoms) . [0077]

The fluoroolefins preferably contain 2 to 6 carbon atoms. As the fluoroolefins containing 2 to 6 carbon atoms, there may be mentioned, for example, tetrafluoroethylene [TFE] , hexafluoropropylene [HFP] , chlorotrifluoroethylene [CTFE] , vinyl fluoride, vinylidene fluoride [VDF] , trifluoroethylene, hexafluoroisobutylene and perfluorobutylethylene. As preferred examples of the fluorinated cyclic monomers, there may be mentioned perfluoro-2_f 2-dimethyl-1, 3-dioxole [PDD] and perfluoro-2-methylene-4-methyl-l, 3-dioxolane [PMD] . The group R and R³ in the above-mentioned fluorinated alkyl vinyl ethers preferably contains 1 to 4 carbon atoms and, more preferably, one in which all the hydrogen atoms have been replaced by fluorine atoms. The group R² preferably contains 2 to 4 carbon atoms and, more preferably, is one in which all the hydrogen atoms have been replaced by fluorine atoms. [0078]

As the non-fluorinated monomers mentioned above, there may be mentioned hydrocarbon monomers reactive with the fluorinated monomers mentioned above. The hydrocarbon monomers include, among others, alkenes such as ethylene, propylene, butylene and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether and cyclohexyl vinyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl versatate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinyl p-tert-butylbenzoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxyisobutyrate and vinyl hydroxycyclohexanecarboxylate; alkyl allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether and cyclohexyl allyl ether; and alkyl allyl esters such as allyl acetate, allyl propionate, allyl butyrate, allyl isobutyrate and allyl cyclohexanecarboxylate . [0079] The non-fluorinated monomers further include functional group-containing hydrocarbon monomers. As the functional group-containing hydrocarbon monomers, there may be mentioned, for example, hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether and hydroxycyclohexyl vinyl ether; carboxyl group-containing, non-fluorinated monomers such as itaconic acid, succinic acid, succinic anhydride, fumaric acid, fumaric anhydride, crotonic acid, maleic acid, maleic anhydride andbutenoic acid; glycidyl group-containing, non-fluorinated monomers such as glycidyl vinyl ether and glycidyl allyl ether; amino group-containing, non-fluorinated monomers such as aminoalkyl vinyl ethers and aminoalkyl allyl ethers; amide group-containing, non-fluorinated monomers such as (meth) acrylamide and methylolacrylamide. [0080]

As the fluoropolymer suitably producible by the production method of the fluoropolymer mentioned above, there may be mentioned TFE polymers in which the monomer accounting for the highest monomer mole fraction in the polymer

(hereinafter "most abundant monomer") is TFE, VDF polymers in which the most abundant monomer is VDF, and CTFE polymers in which the most abundant monomer is CTFE. [0081] The TFE polymers may suitably be TFE homopolymers, or copolymers derived from (1) TFE, (2) a fluorinated monomer other than TFE, which contain 2 to 8 carbon atoms, in particular HFP and/or CTFE, and (3) another monomer or other monomers. As the other monomers mentioned above under (3) , there may be mentioned, for example, fluoro(alkyl vinyl ether) species having an alkyl group containing 1 to 5 carbon atoms, in particular 1 to 3 carbon atoms; fluorodioxole; perfluoroalkylethylenes; ω-hydroperfluoroolefins, etc.

The TFE polymers may also be copolymers of TFE and one or more non-fluorinated monomers. The non-fluorinated monomers are, for example, alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers. The TFE polymer may further be copolymers of TFE, one or more fluorinated monomers containing 2 to 8 carbon atoms and one or more non-fluorinated monomers . [0082]

Suitable examples of the VDF polymers are, among others,

VDF homopolymers [PVDF] , and copolymers composed of (1) VDF and

(2) one or more fluoroolefins other than VDF, which contain 2 to 8 carbon atoms, in particular TFE, HFP and/or CTFE, and (3) perfluoro (alkyl vinyl ether) species having an alkyl group containing 1 to 5 carbon atoms, in particular 1 to 3 carbon atoms . [0083]

The CTFE polymers may suitably be CTFE homopolymers, or copolymers composed of (1) CTFE, (2) one or more fluoroolefins other than CTFE, which contain 2 to 8 carbon atoms, in particular TFE or HFP, and (3) one or more perfluoro (alkyl vinyl ether) species having an alkyl group containing 1 to 5 carbon atoms, in particular 1 to 3 carbon atoms. The CTFE polymers may further be copolymers of CTFE and one or more non-fluorinated monomers and, as the non-fluorinated monomers, there may be mentioned alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers, among others . [0084]

The fluoropolymers produced by the production method of the fluoropolymer mentioned above may be glass-like, plastic or elastomeric. These are noncrystalline or partially crystalline and can be subjected to compression baking processing, melt processing or non-melt processing.

In accordance with the production method of the fluoropolymer mentioned above, there can suitably be produced, for example, (A) tetrafluoroethylene polymers [TFE polymers] as non-melt processible resins, (B) ethylene/TFE copolymers [ETFE], TFE/HFP copolymers [FEP] and TFE/perfluoro (alkyl vinyl ether) copolymers [PFA, MFA, etc.] as melt-processible resins, and (C) such elastomeric copolymers as TFE/propylene copolymers,

TFE/propylene/third monomer copolymers (the third monomer being VDF, HFP, CTFE, perfluoro (alkyl vinyl ether) and/or the like), TFE/perfluoro (alkyl vinyl ether) copolymers;

HFP/ethylene copolymers, HFP/ethylene/TFE copolymers; PVDF;

VDF/HFP copolymers, HFP/ethylene copolymers, VDF/TFE/HFP copolymers and like thermoplastic elastomers; and fluorine-containing segmented polymers described in Japanese Patent Publication S61-49327.

The perfluoro (alkyl vinyl ether) referred to above is represented by the general formula:

Rf³ (OCFQCF₂) ki (OCR⁴Q²CF₂CF₂) _M (OCF₂) _k30CF=CF₂ wherein Rf³ represents a perfluoroalkyl group containing 1 to 6 carbon atoms, kl, k2 and k3 are the same or different and each represents an integer of 0 to 5, Q, Q² and R⁴ are the same or different and each represents F or CF₃.

[0085]

The fluoropolymers mentioned above may have a core-shell structure. As the fluoropolymers having a core-shell structure, there may be mentioned modified PTFE polymers comprising particles each of which consists of a high-molecular-weight PTFE core and a lower-molecular-weight

PTFE shell or a modified PTFE shell. As such a modified PTFE polymer, there may be mentioned a PTFE polymer described in

Japanese Kohyo (Laid-open under PCT) Publication 2005-527652.

[0086]

The above-mentioned non-melt processible resins (A) , melt-processible resins (B) and elastomeric polymers (C), which are suitably producible by the production method of the fluoropolymer mentioned above, are preferably produced in the following manner.

[0087]

(A) Non-melt processible resins In carrying out the production method of the fluoropolymer mentioned above, the polymerization of TFE is generally carried out at a polymerization temperature of 10 to 100 ⁰C and a polymerization pressure of 0.05 to 5 MPa.

In the above polymerization, a pressure-resistant reaction vessel equipped with a stirrer is charged with pure water and the fluoroethercarboxylic acid mentioned above and, after deoxygenation, further charged with TFE, the temperature is raised to a predetermined level, and a polymerization initiator is added to initiate the reaction. Since otherwise the pressure lowers with the progress of the reaction, an additional quantity of TFE is fed to the reaction vessel continuously or intermittently so as to maintain the initial pressure. After completion of feeding of a predetermined amount of TFE, the feeding is stopped, the TFE remaining in the reaction vessel is purged, and the temperature is returned to room temperature. The reaction is thus finished. [0088]

In the TFE polymer production mentioned above, one or more of the various modifier monomers known in the art may be used concomitantly. In the present specification, the term

"tetrafluoroethylene polymer [TFE polymer]" conceptually includes not only TFE homopolymers but also those copolymers of TFE and a modifier monomer (s) which are non-melt-processible (hereinafter referred to as "modified PTFEs") . As the modifier monomers, there may be mentioned, among others, perhaloolefins such as HFP and CTFE; fluoro (alkyl vinyl ether) species having an alkyl group containing 1 to 5, in particular 1 to 3, carbon atoms; fluorinated cyclic monomers such as fluorodioxole; perhaloalkylethylenes; and ω-hydroperhaloolefins. The modifier monomer feeding may be carried out initially all at once, or continuously, or intermittently in portions, according to the intended purpose and the feeding of TFE. The modifier monomer content in the modified PTFEs is generally within the range of 0.001 to 2 mole percent. [0089]

In producing the TFE polymer, the above-mentioned fluoroethercarboxylic acid can be used within the range of usage in the production method of the fluoropolymer mentioned above. Generally, they are used at an addition level of 0.0001 to 2% by mass relative to the aqueous medium. The fluoroethercarboxylic acid concentration is not particularly restricted provided that it is within the above range but the addition is generally carried out at the time of start of the polymerization at a level not higher than the critical micelle concentration (CMC) . When the addition level is excessively high, acicular particles with a large aspect ratio are formed, hence the aqueous dispersion becomes gel-like and the stability is impaired. [0090]

In producing the TFE polymer, persulfate salts (e.g. ammonium persulfate) or organic peroxides such as disuccinoyl peroxide and diglutaroyl peroxide may be used as the polymerization initiator, either singly or in the form of a mixture of these. These may also be used in combination with a reducing agent such as sodium sulfite to give redox systems. Further, during polymerization, the radical concentration in the system can be adjusted by adding a radical scavenger such as hydroquinone or catechol or a peroxide-decomposing agent such as ammonium sulfite. [0091]

In producing the TFE polymer, use can be made of any of the known chain transfer agents, for example saturated hydrocarbons such as methane, ethane, propane and butane, halogenated hydrocarbons such as chloromethane, dichloromethane and difluoromethane, alcohols such as methanol and ethanol, and hydrogen. Those which are gaseous at ordinary temperature and ordinary pressure are preferred. The chain transfer agent is generally used in an amount of 1 to 1000 ppm, preferably 1 to 500 ppm, relative to the total feed Of TFE. [0092]

In producing the TFE polymer, use can further be made, as a dispersion stabilizer for the reaction system, of 2 to 10 parts by mass, per 100 parts by mass of the aqueous medium, of a saturated hydrocarbon which contains not less than 12 carbon atoms, is substantially inert to the reaction and occurs as a liquid under the reaction conditions mentioned above. Furthermore, ammonium carbonate, ammonium phosphate or the like may be added as a buffering agent for adjusting the pH during reaction. [0093]

At the time of completion of the polymerization for producing the TFE polymer, an aqueous dispersion having a solid matter concentration of 30 to 70% by mass can be obtained; the average particle diameter is 50 to 500 nm. The aqueous dispersion contains the fluoroethercarboxylic acid and a fluoropolymer. The use of the fluoroethercarboxylic acid makes it possible for the aqueous dispersion to contain TFE polymer particles having a very small particle diameter, namely 0.3 μm or smaller. The TFE polymer at the time of completion of the polymerization has a number average molecular weight of 1,000 to 10,000,000. [0094] The above-mentioned aqueous TFE polymer dispersion may be formed into a fine powder by coagulation, washing and drying. The fine powder can be used in various fields of application. In subjecting the aqueous TFE polymer dispersion to coagulation, the aqueous dispersion obtained by emulsion polymerization, for example a polymer latex, is generally diluted to a polymer concentration of 10 to 20% by mass using water and, after pH adjustment to a neutral or alkaline level under certain circumstances, stirred, in a vessel equipped with a stirrer, more vigorously than the stirring during reaction. The coagulation may also be carried out by stirring while adding, as a coagulating agent, a water-soluble organic compound such as methanol or acetone, an inorganic salt such as potassium nitrate or ammonium carbonate or an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid or the like. The coagulation may also be carried out continuously using an in-line mixer or the like. [0095]

When one or more of pigments for coloration and/or one or more of various fillers for improvements in mechanical properties are added before or during the coagulation mentioned above, it is possible to obtain a pigment- and/or filler-containing TFE polymer fine powder containing the pigment (s) and/or filler (s) uniformly mixed therein. [0096] The drying of the wet powder obtained by coagulation of the aqueous TFE polymer dispersion is generally effected using, such techniques as vacuum, high-frequency or hot air while maintaining the wet powder in a condition such that it flows little, preferably it stands still. Friction among powder particles at elevated temperatures, in particular, generally exerts unfavorable influences on the TFE polymer in fine powder form. This is because this kind of the particles comprising TFE polymer have a property such that they readily fibrillate upon exposure to even a weak shearing force and lose their original stable particle structure.

The above drying is carried out at a drying temperature of 10 to 250 ⁰C, preferably 100 to 200 ⁰C. [0097]

The TFE polymer fine powder thus obtained is preferably used for molding and, as proper uses thereof, there may be mentioned, among others, tubes for use in hydraulic or fuel systems in airplanes or automobiles, and, further, flexible hoses for transporting liquid chemicals, steam or the like, and electric wire coatings or coverings. [0098] The aqueous TFE polymer dispersion obtained by the above-mentioned polymerization, when supplemented with a nonionic surfactant, is stabilized and, after further concentration, is preferably used in various fields of application in the form of a composition supplemented with an organic or inorganic filler (s) according to the intended purpose. The above composition, when applied to metal or ceramic substrates, can give coated surfaces having nonstickiness and a low coefficient of friction and excellent in gloss, wear resistance, weather resistance and heat resistance. Thus, it is suited for use in coating rolls and cooking utensils and impregnating processing of glass cloths. [0099]

The above-mentioned aqueous TFE polymer dispersion or the above-mentioned TFE polymer fine powder is also preferably used as a processing aid. In a case of use thereof as a processing aid, the aqueous dispersion or fine powder mentioned above is admixed with a host polymer, for instance, whereby the host polymer is improved in melt strength on the occasion of melt processing thereof and/or the resulting polymer composition obtained may show improvements in mechanical strength, electrical characteristics, flame retardancy, anti-dripping performance and sliding property.

The above-mentioned aqueous TFE polymer dispersion or TFE polymer fine powder is also preferably used as a binder for cells or batteries. [0100]

The aqueous TFE polymer dispersion or TFE polymer fine powder mentioned above is also preferably used as the processing aid in the form of a composite material together with a resin other than the TFE polymer. The aqueous TFE polymer dispersion or TFE polymer fine powder is suited for use as a raw material for the production of those PTFEs which are described in Japanese Kokai Publications Hll-49912 and 2003-24693, United States Patent No. 5,804,654 and Japanese Kokai Publications Hll-29679 and 2003-2980. The processing aid comprising the above-mentioned aqueous dispersion or fine powder is not inferior at all to the processing aids described in the respective publications cited above. [0101]

The aqueous TFE polymer dispersion mentioned above is also preferably processed by admixing the same with an aqueous dispersion of a melt-processible fluoropolymer, followed by coagulation, to give a co-coagulated powder. This co-coagulated powder is suited for use as a processing aid. [0102]

As the melt-processible fluoropolymer, there may be mentioned, for example, FEP, PFA, ETFE and EFEP resins. Among them, FEP resins are preferred. [0103]

The fluorine-free resin to which the above co-coagulated powder is to be added may be in the form of a powder or pellets or an emulsion. The addition is preferably carried out under shearing force application by such a known method as extrusion kneading or roll kneading from the viewpoint of sufficient mixing up of the respective resins. [0104]

The aqueous TFE polymer dispersion mentioned above is also preferably used as a dust-control treatment agent. This dust-control treatment agent can be used in the method of inhibiting a dust-emitting substance from emitting dust by admixing the aqueous dispersion with the dust-emitting substance and subjecting the resulting mixture to compression-shearing action at a temperature of 20 to 200 ⁰C to thereby fibrillate the TFE polymer, for example in carrying out the method described in Japanese Patent No. 2827152 or Japanese Patent No. 2538783. The above-mentioned aqueous TFE polymer dispersion can be suitably used in a dust-control treatment composition, for example the one described in WO 2007/004250 and can also be suitably used in carrying out the dust control treatment method described in WO 2007/000812. [0105]

The dust-control treatment agent mentioned above is suitably used in dust control treatment in the fields of building and construction, soil stabilizers, solidifying agents, fertilizers, landfill of incineration ash and hazardous substances, explosion protection, cosmetics and so forth. [0106]

The aqueous TFE polymer dispersion mentioned above is also suitably used as a raw material for obtaining a TFE polymer fiber by a dispersion spinning method. The dispersion spinning method is a method of obtaining TFE polymer fibers by admixing the aqueous TFE polymer dispersion with an aqueous dispersion of a matrix polymer, subjecting the resulting mixture to extrusion processing to form an intermediate fibrous structure and baking the intermediate fibrous structure to thereby cause decomposition of the matrix polymer and sintering of TFE polymer particles . [0107] It is also possible to produce high-molecular-weight PTFE using the fluoroethercarboxylic acid mentioned above. The high-molecular-weight PTFE powder obtained by emulsion polymerization is also useful as a raw material for producing a porous PTFE article (membrane) . For example, a porous PTFE article (membrane) can be obtained by subjecting the high-molecular-weight PTFE powder to paste extrusion, followed by rolling, and stretching the rolled intermediate product in a non-baked or half-baked condition in at least one direction (preferably stretching it by rolling in the direction of rolling, followed by stretching on a tenter in the width direction) . Stretching makes the PTFE easy to fibrillate and give a porous PTFE article (membrane) consisting of knots and fibers. [0108]

This porous PTFE article (membrane) is useful as a filter for various purposes and can be suitably used as a filter for liquid chemicals and as an air filter medium, in particular. [0109]

It is also possible to produce low-molecular-weight PTFE using the fluoroethercarboxylic acid mentioned above. The low-molecular-weight PTFE may be produced by polymerization or by reducing the molecular weight of high-molecular-weight PTFE obtained by polymerization by an appropriate method known in the art (e.g. thermal degradation, degradation by radiation irradiation) . [0110]

Low-molecular-weight PTFE species having a molecular weight of 600,000 or below (also called PTFE micropowders) are excellent in chemical stability and very low in surface energy and, in addition, hardly fibrillate and, therefore, are suited for use as an additive for achieving improvements in lubricant property and/or in coat surface texture in manufacturing plastic products, inks, cosmetics, coatings, greases, office automation equipment members, toners and so forth (cf. e.g. Japanese Kokai Publication H10-147617) . [0111]

The low-molecular-weight PTFE may also be obtained by dispersing a polymerization initiator and the above-mentioned fluoroethercarboxylic acid as an emulsifier in an aqueous medium in the further presence of a chain transfer agent and polymerizing TFE or TFE and a monomer (s) copolymerizable therewith in the resulting medium. [0112]

In cases where the low-molecular-weight PTFE obtained by emulsion polymerization is to be used in the form of a powder, the aqueous dispersion mentioned above, when subjected to coagulation, can give powder particles. [0113]

Unsintered tapes (raw tapes) can also be obtained from the fine PTFE powder obtained by using the fluoroethercarboxylic acid mentioned above. [0114]

A regenerated fluoroethercarboxylic acid may be produced by a method comprising the step of recovering one or more fluoroethercarboxylic acids represented by the general formula (II) from a wastewater formed by the above-mentioned coagulation or washing and/or from the off-gas formed in the drying step, and the step of purifying the same. Methods for the above-mentioned recovery and purification are not particularly restricted but may be conventional ones known in the art. [0115]

(B) Melt-processible resin

(1) In the production method of the fluoropolymer mentioned above, the polymerization for producing the FEP is preferably carried out at a polymerization temperature of 60 to 100 ⁰C and a polymerization pressure of 0.7 to 4.5 MPa.

The monomer composition (on the % by mass basis) of the FEP is preferably TFE:HFP = (60 to 95) : (5 to 40) , more preferably (85 to 90) : (10 to 15) . The FEP may be one modified with a perfluoro (alkyl vinyl ether) as a third component used in a proportion within the range of 0.5 to 2% by mass relative to the sum of the monomers.

In the above-mentioned FEP production by polymerization, the fluoroethercarboxylic acid mentioned above can be used in the same usage range as in the fluoropolymer production method mentioned above; generally, the fluoroethercarboxylic acid is added in an amount of 0.0001 to 2% by mass relative to 100% by mass of the aqueous medium.

In the above-mentioned FEP production by polymerization, such a chain transfer agent as cyclohexane, methanol, ethanol, carbon tetrachloride, chloroform, methylene chloride or methyl chloride is preferably used, and such a pH buffering agent as ammonium carbonate or disodium hydrogenphosphate is preferably used. [0116] (2) In the production method for the fluoropolymer mentioned above, the polymerization for producing the

TFE/perfluoro (alkyl vinyl ether) copolymer, such as PFA and MFA copolymers, is preferably carried out generally at a polymerization temperature of 60 to 100 ⁰C and a polymerization pressure of 0.7 to 2.5 MPaG.

Preferred as the monomer composition (in mole percent) for the TFE/perfluoro (alkyl vinyl ether) copolymer is TFE: (perfluoro alkyl vinyl ether) = (95 to 99.7): (0.3 to 5), more preferably (97 to 99) : (1 to 3) . Preferably used as the perfluoro (alkyl vinyl ether) s are those represented by the formula: CF₂=CFORf⁴ (in which Rf⁴ is a perfluoroalkyl group containing 1 to 6 carbon atoms) .

In the above-mentioned TFE/perfluoro (alkyl vinyl ether) copolymer production by polymerization, the fluoroethercarboxylic acid mentioned above can be used in the same usage range as in the fluoropolymer production method mentioned above; generally, the fluoroethercarboxylic acid is added preferably in an amount of 0.0001 to 10% by mass relative to 100% by mass of the aqueous medium.

In the above-mentioned TFE/perfluoro (alkyl vinyl ether) copolymer production by polymerization, such a chain transfer agent as cyclohexane, methanol, ethanol, carbon tetrachloride, chloroform, methylene chloride, methyl chloride, methane or ethane is preferably used, and such a pH buffering agent as ammonium carbonate or disodium hydrogenphosphate is preferably used. [0117]

(3) In the production method of the fluoropolymer mentioned above, the polymerization for producing the ETFE copolymer is preferably carried out at a polymerization temperature of 20 to 100 ⁰C and a polymerization pressure of 0.5 to 0.8 MPaG.

Preferred as the monomer composition (in mole percent) of the ETFE is TFE: ethylene = (50 to 99) : (50 to 1) . The ETFE may be those modified with a third monomer in a proportion within ^

the range of 0 to 20% by mass relative to the sum of the monomers . The ratio is preferably TFE: ethylene: third monomer = (63 to 94) : (27 to 2) : (4 to 10) . Preferred as the third monomer are perfluoro (butylethlene) , 2,3,3,4,4,5,5-heptafluoro-2-pentene (CH₂=CFCF₂CF₂CF₂H) and 2-trifluoromethyl-3, 3, 3-trifluoropropene ( (CF₃) ₂C=CH₂) .

In the ETFE production by polymerization, the fluoroethercarboxylic acid mentioned above can be used in the same usage range as in the fluoropolymer production method mentioned above; generally, the fluoroethercarboxylic acid is added in an amount of 0.0001 to 2% by mass relative to 100% by mass of the aqueous medium.

In the ETFE production by polymerization, such a chain transfer agent as cyclohexane, methanol, ethanol, carbon tetrachloride, chloroform, methylene chloride or methyl chloride is preferably used. [0118]

(4) By utilizing the fluoropolymer production method mentioned above, it is also possible to produce an electrolyte polymer precursor. The electrolyte polymer precursor production by the polymerization according to the fluoropolymer production method mentioned above is preferably carried out at a polymerization temperature of 20 to 100 ⁰C and a polymerization pressure of 0.3 to 2.0 MPaG. The electrolyte polymer precursor is a precursor which comprises such a vinyl ether monomer as specified below and is capable of being converted to an ion-exchanging polymer via a hydrolysis treatment step. [0119] As the vinyl ether monomer to be used for producing the electrolyte polymer precursor, there may be mentioned fluoromonomers represented by the general formula (IV) : CF₂=CF-O-

(CFY²) _X-A (IV) wherein Y¹ represents fluorine or chlorine atom or a perfluoroalkyl group, y represents an integer of 0 to 3 and, when y is 2 or 3, the y atoms of Y¹ may be the same or different; Y² represents fluorine or chlorine atom, x represents an integer of 1 to 5 and, when x is 2 to 5, the x atoms of Y² may be the same or different; and A represents -SO₂X¹ (X¹ representing a halogen atom) and/or -COZ¹ (Z¹ representing an alkoxy group containing 1 to 4 carbon atoms) . A preferred monomer composition (mole percent) for producing the polymer electrolyte precursor is as follows: TFE: vinyl ether = (50 to 93) : (50 to 7) . [0120]

The above-mentioned electrolyte polymer precursor may be the one modified with a third monomer used in an amount within the range of 0 to 20% by mass of all the monomers.

As the third monomer, there may be mentioned CTFE, vinylidene fluoride, perfluoro (alkyl vinyl ether) species, and divinylbenzene and other polyfunctional monomers. [0121]

The thus-obtained electrolyte polymer precursor is molded into a membrane form, for instance, and then subjected to hydrolysis with an alkali solution and to mineral acid treatment for use as a polymer electrolyte membrane in fuel cells, among others. [0122]

The melt-processible resin obtained by the method mentioned above is also preferably used as a raw material for obtaining melt-processible resin fibers by an expansion spinning. The expansion spinning is a method of obtaining melt-processible resin fibers by melt-spinning of a melt-processible resin, followed by cooling for solidification, to obtain undrawn yarns and then causing the undrawn yarns to run through a heated cylindrical body for drawing thereof.

The above-mentioned aqueous melt-processible resin dispersion or melt-processible resin is also preferably used as a binder for electric cells or batteries. [0123] ^

(C) Elastomeric polymer

In carrying out the polymerization for producing the elastomeric polymer according to the method for producing the fluoropolymer mentioned above, a pressure-resistant reaction vessel equipped with a stirrer is charged with pure water and the fluoroethercarboxylic acid of the invention and, after deoxygenation, further charged with the monomers, the temperature is raised to a predetermined level, and a polymerization initiator is added to initiate the reaction. Since otherwise the pressure lowers with the progress of the reaction, additional quantities of the monomers are fed to the reaction vessel continuously or intermittently so as to maintain the initial pressure. After completion of feeding of predetermined amounts of the monomers, the feeding is stopped, the monomers remaining in the reaction vessel are purged away, and the temperature is returned to room temperature. The reaction is thus finished. In the case of emulsion polymerization, the polymer latex formed is preferably taken out of the reaction vessel continuously. In particular when a thermoplastic elastomer is to be produced, it is also possible to employ the method of accelerating the eventual rate of polymerization as compared with the conventional polymerizations by synthesizing fine fluoropolymer particles once at high concentration and, after dilution, further carrying out the polymerization, as disclosed in International Publication WO 00/01741. [0124]

In producing the elastomeric polymer, the reaction conditions are to be properly selected from the viewpoint of desired physical properties of the polymer and of a polymerization rate control. Generally, the polymerization is carried out at a polymerization temperature of -20 to 200 ⁰C, preferably 5 to 150 ⁰C, and a polymerization pressure of 0.5 to 10 MPaG, preferably 1 to 7 MPaG. Preferably, the pH of the polymerization medium is maintained generally at 2.5 to 9 with a pH adjusting agent, which is to be described later herein, in the conventional manner, for instance.

[0125]

As the monomer to be used in producing the elastomeric polymers, there may be mentioned vinylidene fluoride as well as fluorine-containing, ethylenically unsaturated monomers containing at least the same number of fluorine atoms as the number of carbon atoms and capable of copolymerizing with vinylidene fluoride. As the fluorine-containing ethylenically unsaturated monomers, there may be mentioned, among others, trifluoropropene, pentafluoropropene, hexafluorobutene and octafluorobutene. Among them, hexafluoropropene is particularly suited for use in view of the characteristics of the elastomers obtainable when it blocks the polymer crystal growth. As the fluorine-containing, ethylenically unsaturated monomers, there may further be mentioned trifluoroethylene, TFE, CTFE, etc., and fluorine-containing monomers having one or more chlorine and/or bromine substituents may also be used. Perfluoro (alkyl vinyl ether) species, for example perfluoro (methyl vinyl ether), can also be used. TFE and HFP are preferred for the production of the elastomeric polymer.

The elastomeric polymer preferably has a monomer composition (in % by mass) of vinylidene fluoride: HFP: TFE = (20-70) : (30-48) : (0-32) . The elastomeric polymer the composition of which is within this range shows good elastomer characteristics, chemical resistance and thermal stability. [0126] In the above-mentioned elastomeric polymer production by polymerization, the fluoroethercarboxylic acid mentioned above can be used in the same usage range as in the fluoropolymer production method mentioned above; generally, the fluoroethercarboxylic acid is added in an amount of 0.0001 to 2% by mass relative to 100% by mass of the aqueous medium. [0127]

In the polymerization of the elastomeric polymer, any of inorganic radical polymerization initiators known in the art can be used as the polymerization initiator. Those water-soluble inorganic peroxides known in the art, for example sodium, potassium and ammonium persulfate, perphosphate, perborate, percarbonate and permanganate, are particularly useful as the inorganic radical polymerization initiator. The radical polymerization initiator can be further activated by a reducing agent such as sodium, potassium or ammonium sulfite, bisulfite, metabisulfite, hyposulfite, thiosulfate, phosphite or hypophosphite, or by a readily oxidizable metal compound such as a ferrous salt, cuprous salt or silver salt. Ammonium persulfate is a suitable inorganic radical polymerization initiator, and a combined use of ammonium persulfate and sodium bisulfite in a redox system is more preferred.

The level of addition of the polymerization initiator is to be properly selected according to a desired molecular weight of the fluoropolymer and the rate of the polymerization reaction; generally, it is set at 0.0001 to 10% by mass, preferably 0.01 to 5% by mass, relative to 100% by mass of the total monomer amount.

[0128]

In the polymerization of the above elastomeric polymer, any of chain transfer agents known in the art can be used. In the case of PVDF polymerization, hydrocarbons, esters, ethers, alcohols, ketones, chlorine compounds, carbonates or the like can be used and, in the case of the thermoplastic elastomer, hydrocarbons, esters, ethers, alcohols, chlorine compounds, iodine compounds or the like can be used. Among them, acetone and isopropyl alcohol are preferred in the case of PVDF polymerization and, in the case of thermoplastic elastomer polymerization, isopentane, diethyl malonate and ethyl acetate are preferred from the viewpoint that the rate of reaction is hardly lowered thereby, and 1(CF₂J₄I, 1(CF₂J₆If ICH₂I and like ^

diiodide compounds are preferred from the viewpoint that the polymer termini can be iodinated and the polymer can be used as a reactive one.

The chain transfer agent is used generally in an amount of 0.5 x 10^"3 to 5 x 10^~3 mole percent, preferably 1.0 x 10^"3 to 3.5 x 10^~3 mole percent. [0129]

In the polymerization of the elastomeric polymer, the polymerization of PVDF can be preferably carried out using a paraffin wax or the like as an emulsion stabilizer, and the polymerization of the thermoplastic elastomer can be preferably carried out using a phosphate salt, sodium hydroxide, potassium hydroxide or the like as a pH adjusting agent. [0130] At the time when the polymerization is complete, the elastomeric polymer obtained by the fluoropolymer production method mentioned above has an average particle diameter of 0.03 to 1 μm, preferably 0.05 to 0.5 μm and a number average molecular weight of 1,000 to 2,000,000; the solid concentration is 10 to 40% by mass. [0131]

The elastomeric polymer obtained by the production method for the fluoropolymer mentioned above can be converted, according to need, to a dispersion suited for rubber molding processing by adding a dispersion stabilizer such as a hydrocarbon surfactant, and concentrating, for instance. The dispersion is treated by pH adjustment, coagulation, heating, etc. The respective treatments are carried out in the following manner. [0132]

The pH adjustment consisting in adjusting a pH to 2 or below by adding a mineral acid such as nitric acid, sulfuric acid, hydrochloric acid or phosphoric acid and/or a carboxylic acid containing not more than 5 carbon atoms and having a pK = 4.2 or below, for instance. The coagulation is carried out by adding an alkaline earth metal salt. As the alkaline earth metal salt, there may be mentioned calcium or magnesium nitrate, chlorate and acetate. Either of the pH adjustment and the coagulation may be carried out first. Preferably, however, the pH adjustment is carried out first.

After both procedures, the elastomer is washed with an equal volume of water to remove the buffer solution, salt and other impurities occurring in slight amounts within the elastomer, followed by drying. The drying is generally carried out in a drying oven at elevated temperatures of about 70 to 200 ⁰C under circulating hot air. [0133]

The concentration of the fluoropolymer mentioned above in the aqueous dispersion obtained by carrying out the polymerization mentioned above is generally 10 to 50% by mass. A preferred lower limit to the fluoropolymer concentration in the above-mentioned aqueous dispersion is 10% by mass, a more preferred lower limit thereto is 15% by mass, a preferred upper limit thereto is 40% by mass, a more preferred upper limit thereto is 35% by mass and a still more preferred upper limit thereto is 30% by mass. [0134]

The aqueous dispersion obtained by carrying out the polymerization mentioned above may be concentrated or treated for dispersion stabilization to give a dispersion or may be subjected to coagulation or flocculation, followed by recovery and drying, to give a powder or a solid in some other form. [0135] The fluoroethercarboxylic acid mentioned above can also be suitably used as a dispersant for dispersing a fluoropolymer obtained by polymerization in an aqueous medium. [0136]

The aqueous dispersion mentioned above comprises fluoropolymer particles, the fluoroethercarboxylic acid mentioned above and an aqueous medium. The aqueous dispersion is the one obtained by dispersing the fluoropolymer particles in the aqueous medium in the presence of the fluoroethercarboxylic acid. [0137]

Preferably, the fluoroethercarboxylic acid is contained in the aqueous dispersion mentioned above at a concentration of 0.0001 to 15% by mass . At concentration levels below 0.0001% by mass, the dispersion stability may be poor in certain instances and, at levels exceeding 15% by mass, the dispersing effect is impractically no longer proportional to the addition level. A more preferred lower limit to the concentration of the fluoroethercarboxylic acid is 0.001% by mass, a more preferred upper limit thereto is 10% by mass and a still more preferred upper limit thereto is 2% by mass. [0138]

The aqueous dispersion mentioned above may be any of an aqueous dispersion as obtained by carrying out the polymerization mentioned above, a dispersion obtained by subjecting this aqueous dispersion to concentration or dispersion stabilization treatment, and a dispersion prepared by dispersing a fluoropolymer powder in an aqueous medium in the presence of the fluoroethercarboxylic acid mentioned above. [0139] As regards the method of producing the aqueous dispersion mentioned above, it is also possible to produce a purified aqueous dispersion by a step (A) of contacting the above-mentioned aqueous dispersion obtained by polymerization with an anion exchange resin in the presence of a nonionic surfactant and a step (B) of concentrating the aqueous dispersion obtained in the step (A) to a solid matter concentration of 30 to 70% by mass relative to 100% by mass of the aqueous dispersion. [0140] The nonionic surfactant is not particularly restricted ^

but any one known in the art can be used. The anion exchange resin mentioned above is not particularly restricted but any one known in the art can be used. As for the method of contacting with the anion exchange resin, any method known in the art can be used. [0141]

The method of concentration may be any one known in the art, for example the technique of phase separation, electrical concentration or ultrafiltration. In the above concentration step, the fluoropolymer concentration can be increased to 30 to 70% by mass according to the intended use. Upon concentration, the stability of the dispersion may be reduced in certain cases; in such cases, a dispersion stabilizer may further be added. The above-mentioned fluoroethercarboxylic acid or any of other various surfactants may be added as the dispersion stabilizer. The various dispersion stabilizers include, but are not limited to, nonionic surfactants such as polyoxyalkyl ethers, in particular polyoxyethylene alkylphenyl ethers (e.g. Triton X-100 (trade name) manufactured by Rohm and Haas), polyoxyethylene isotridecyl ethers (e.g. Noigen TDS80C (trade name) manufactured by Daiichi Kogyo Seiyaku, Leocol TD90D (trade name) manufactured by Lion Corporation, Genapol X080 (trade name) manufactured by Clariant) and polyoxyethylene ethers, among others. [0142]

The total amount of the dispersion stabilizer (s) is at a level corresponding to a concentration of 0.5 to 20% by mass based on the solid matter in the above-mentioned dispersion. At levels lower than 0.5% by mass, the dispersion stability may be poor in certain instances and, at levels exceeding 20% by mass, the dispersing effect is impractically no longer proportional to the addition level. A more preferred lower limit to the level of addition of the dispersion stabilizer (s) is 2% by mass, and a more preferred upper limit thereto is 12% by mass. [ 0143]

The fluoroethercarboxylic acid mentioned above may be removed by the concentration procedure mentioned above. The fluoroethercarboxylic acid is high in solubility in water and, therefore, a removal efficiency is higher as compared with the case of the conventional fluorinated surfactants. [0144]

The aqueous dispersion obtained by carrying out the polymerization mentioned above may be subjected, without concentration, to dispersion stabilization treatment to prepare an aqueous dispersion prolonged in pot life according to application requirements. As a dispersion stabilizer to be used, there may be mentioned the same ones as those enumerated hereinabove. [0145]

The uses of the aqueous dispersions are not particularly restricted but, when it is applied as the aqueous dispersion as it is, the following uses may be mentioned among others: coating of a substrate which comprises applying it to a substrate and drying the coatings, if necessary followed by baking; impregnation of nonwoven fabrics, resin moldings and other porous supports which comprises impregnating the supports with the dispersion, followed by drying, if necessary further followed by baking; and cast film formation which comprises applying the dispersion onto a substrate such as glass substrates, drying the coated substrate and, if necessary after immersion in water, peeling off the coatings from the substrate to give a thin film or membrane. In these applications, the dispersion is used as an aqueous dispersion type coating composition, an electrode binder, or a water repellent composition for electrodes, for instance. [0146]

The aqueous dispersion mentioned above can be used as an aqueous coating composition after incorporation of one or more known formulation ingredients selected from among pigments, thickening agents, dispersing agents, antifoaming agents, antifreezing agents, film-forming auxiliaries and the like and further optionally compounding of another polymeric compound. [0147] A regenerated fluoroethercarboxylic acid may be produced by a method comprising the step of recovering the one or more fluoroethercarboxylic acids represented by the general formula

(II) from a wastewater formed by the above-mentioned coagulation or washing and/or from the off-gas formed in the drying step, and the step of purifying the same. Methods for the above-mentioned recovery and purification are not particularly restricted but may be^' conventional ones known in the art. [0148] The methods of recovering and purifying the fluoroethercarboxylic acid from a wastewater generated in the coagulation step, a wastewater generated in the washing step and/or the off-gas generated in the drying step are not particularly restricted but those methods known in the art can be employed. Thus, for example, mention may be made of the methods described in United States Patent Application Publications 2007/15937, 2007/25902 and 2007/27251 and, more specifically, the following methods may be mentioned. [0149] As a method of recovering the fluoroethercarboxylic acid from the wastewater mentioned above, there may be mentioned a method comprising contacting the wastewater with such adsorbent particles as ion exchange resin, active carbon, silica gel, clay or zeolite particles for adsorption of the fluoroethercarboxylic acid thereon, followed by separation of the wastewater from the adsorbent particles. By incinerating the adsorbent particles with the fluoroethercarboxylic acid adsorbed thereon, it becomes possible to prevent the fluoroethercarboxylic acid from being released into the environment. [ 0150 ]

It is also possible to recover the fluoroethercarboxylic acid from the ion exchange resin particles with the fluoroethercarboxylic acid adsorbed thereon by desorption or elution therefrom in the conventional manner. For example, when the ion exchange resin particles are anion exchange resin particles, the fluoroethercarboxylic acid or the salt thereof can be eluted by contacting a mineral acid with the anion exchange resin. Then, a water-soluble organic solvent is added to an eluate obtained, whereupon the mixture generally separates into two phases; the fluoroethercarboxylic acid can be recovered by recovering the fluoroethercarboxylic acid-containing lower phase, followed by neutralization. As the water-soluble organic solvent, there may be mentioned such polar solvents as alcohols, ketones and ethers. [0151]

As another method of fluoroethercarboxylic acid recovery from ion exchange resin particles, there may be mentioned a method using an ammonium salt and a water-soluble organic solvent and a method using an alcohol, if desired together with an acid. The latter method forms an ester derivative of the fluoroethercarboxylic acid, which can be separated with ease from the alcohol by distillation. [0152] In cases where the wastewater mentioned above contains a fluoropolymer particle and/or some other solid matter, the solid fraction is preferably removed prior to contacting the wastewater with adsorbent particles. As a method of removing the fluoropolymer particles and/or other solid matter, there may be mentioned a method comprising adding an aluminum salt or the like to cause the solid fraction to precipitate, followed by separation of the precipitate from the wastewater, and an electric coagulation method, for instance. Mechanical methods for removal may also be employed; for example, crossflow filtration, depth filtration method and precoat filtration method may be mentioned. [0153]

As a method of recovering the fluoroethercarboxylic acid mentioned above from the above-mentioned off-gas, there may be mentioned a method comprising contacting the off-gas with deionized water, an aqueous alkali solution or an organic solvent such as a glycol ether solvent, for instance, using a scrubber to obtain a scrubber solution containing the fluoroethercarboxylic acid. The use of a high-concentration aqueous alkali solution as the aqueous alkali solution makes it possible to recover the scrubber solution in a state in which the fluoroethercarboxylic acid presents as a separate phase, thus making it easy to recover and reutilize the fluoroethercarboxylic acid. As the alkali compound, there may be mentioned alkali metal hydroxides and quaternary ammonium salts, among others. [0154]

The fluoroethercarboxylic acid-containing scrubber solution may also be concentrated using a reverse osmosis membrane or the like. While the concentrated scrubber solution generally contains fluoride ion, it is also possible to facilitate the reuse of the fluoroethercarboxylic acid by adding alumina to the scrubber solution after concentration for removing the fluoride ion. The fluoroethercarboxylic acid may also be recovered by contacting the scrubber solution with the adsorbent particles for adsorption of the fluoroethercarboxylic acid, followed by the recovering method mentioned above. [0155] The fluoroethercarboxylic acid recovered by any of the methods mentioned above can be reused in the production of fluoropolymers .

EFFECTS OF THE INVENTION [0156] According to the production method of the invention, the fluoroethercarboxylic acid fluoride and the corresponding fluoroethercarboxylic acid can be obtained in high yields with high selectivity.

BEST MODES FOR CARRYING OUT THE INVENTION [0157]

The numerical data reported for each example were obtained by the following measurement method. [0158]

Gas chromatographic analysis

Sampling was made through a sampling tube mounted on the reaction vessel after standing following discontinuation of stirring, and about 5 g of the lower layer, namely the layer comprising the acid fluoride, resulting from phase separation into two layers within the reaction vessel was taken out. This was sufficiently admixed with 10 ml of ice-cooled methanol for conversion to the methyl ester, and the mixture was further admixed with about 0.5 ml of pure water, whereupon the resulting mixture separated into two layers. The lower layer thereof was used as the analytical sample. In each of the following examples, the acid fluoride composition of the product formed was determined by gas chromatographic analysis in terms of the corresponding methyl ester composition. [0159]

The gas chromatographic analysis was carried out using a Shimadzu model GC-14A gas chromatograph equipped with an SE-30 column (3.0 m) ; a TCD (thermal conductivity detector) was used as the detector and about 0.1 μl of the analytical sample was introduced into the chromatograph. The sum of the areas of the thus-detected peaks for all the compounds shown in Table 1 was taken as 100, and the peak area proportion (GC %) of each compound was calculated. Separately, various mixtures prepared by mixing together these compounds in purified form in various ratios were subjected to the same gas chromatographic analysis, and a correlation between area proportion and mole proportion was determined for each compound. The proportion (GC %) of each compound was corrected by calculation based on that correlation to give the corrected proportion (mole percent) of each compound. [0160]

In the following examples, the compounds represented by the general formula: CF₃O (CF (CF₃) CF₂O) _nCF (CF₃) COF are referred to as PMPF, and the compounds represented by the general formula:

CF₃CF₂CF₂O (CF (CF₃) CF₂O) _mCF (CF₃) COF are referred to as PF. [0161] Example 1

A 6-L autoclave equipped with a pressure gage, a valve, a safety valve and a sampling tube and further provided with a j acket produced by Taiatsu Techno Corporation was charged with 1000 mL of tetraglyme and 75 g of CsF and then the autoclave was tightly closed. The autoclave inside was purged several times with nitrogen and then the pressure was reduced. The jacket was connected to a refrigerator (Yamato Scientific model BB3440) and cooled until arrival of the inside temperature at -11 ⁰C. Then, 2100 g of CF₃OCF(CF₃)COF (n=0 PMPF) was fed into the autoclave. After cooling again to the inside temperature of -10 ⁰C, HFPO was introduced into the autoclave to start the reaction. HFPO was continuously introduced into the autoclave while the rate flow thereof was adjusted so that the reaction temperature might be maintained at -10⁰C; in the end, the amount of HFPO fed amounted to a total of 1510 g. Thereafter the temperature was raised to room temperature with stirring. After overnight standing, the contents were drawn out through a bottom drain valve. The contents had separated into two layers. The upper layer and lower layer were separated from each other using a separatory funnel. The upper layer weighed 1320 g, and the lower layer weighed 3290 g. As a result of gas chromatographic analysis of the reaction product, the desired compound CF₃OCF(CF₃)CF₂OCF(CF₃)COF (n=l PMPF) was detected as a main component in the lower layer, and the composition of the product was as shown in Table 1. [0162]

Further, the lower layer, namely the layer comprising the acid fluoride, was rectified, whereby 1810 g of n=l PMPF could be isolated. The boiling point was 82 ⁰C, and the yield was 50 mole percent. [0163]

Then, 1000 g of the n=l PMPF isolated was hydrolyzed by adding 1000 g of pure water. Thereafter, the organic layer (lower layer) was recovered by layer separation using a separatory funnel made of a PFA resin. The solution recovered was washed in sequence with pure water, 5% (by weight) aqueous H₂SO₄, 10% (by weight) aqueous H₂SO₄ and a concentrated sulfuric acid. This was further subjected to simple distillation to give 991 g of CF₃OCF(CF₃)CF₂OCF(CF₃)COOH (n=l PMPA). [0164]

Then, 500 g of n=l PMPA was added dropwise with stirring over 1 hour to an aqueous solution prepared by mixing together 76 g of 28% (by weight) aqueous ammonia and 600 g of pure water. After completion of the dropping, the resulting mixture was stirred for 30 minutes and then adjusted to pH 7 by addition of 28% (by weight) aqueous ammonia. The whole mixture was lyophilized to give 521 g of CF₃OCF(CF₃)CF₂OCF(CF₃)COONH₄ (n=l PMPA(N) ) . [0165] Example 2

The procedure of Example 1 was followed in the same manner except that the reaction temperature was -7 ⁰C. [0166] Example 3 The procedure of Example 1 was followed in the same manner O -L

except that the reaction temperature was -5 °C.

[0167]

Example 4

The procedure of Example 1 was followed in the same manner except that the reaction temperature was -2 ⁰C and that the same amount of triglyme was used instead of tetraglyme as the solvent . [0168] Example 5 A 200-mL autoclave equipped with a pressure gage, a valve, a safety valve and an insertion tube and further provided with a j acket produced by Taiatsu Techno Corporation was charged with 70.5 g of triglyme and 4.9 g of CsF and then the autoclave was tightly closed. The autoclave inside was purged several times with nitrogen and then the autoclave was filled with nitrogen until arrival of the inside pressure at atmospheric pressure. The jacket was connected to the refrigerator and cooled until arrival of the inside temperature at -10 ⁰C. Then, the valve was opened so that the autoclave constituted an open system, a mixed gas composed of carbonyl fluoride [COF₂] and HFPO in a mole ratio of COF₂/HFPO = 2.09 (COF₂: 83.5 cc/minute, HFPO: 40.0 cc/minute) was then introduced into the autoclave through the insertion tube, and the reaction was allowed to proceed for 120 minutes. The unreacted gas was released into the air. During the reaction, the inside temperature was maintained at -10 ⁰C by means of the refrigerator. Thereafter, the temperature was raised to room temperature with stirring, and the contents were drawn out through a bottom drain valve. The contents had separated into two layers. The upper layer and lower layer were separated from each other using a separatory funnel. The lower product layer was analyzed by gas chromatography, whereupon the desired compound CF₃OCF(CF₃)CF₂OCF(CF₃)COF (n=l PMPF) was detected as the main component; the composition of the product was as shown in Table 1. The corresponding acid was obtained by carrying out the same treatment as in Example 1. [0169] Example 6

The procedure of Example 5 was followed in the same manner except that, after several repetitions of purging of the autoclave inside with nitrogen, the autoclave was evacuated and, while the valve was closed, the reaction was carried out by introducing a mixed gas composed of COF₂ and HFPO (mole ratio: COF₂/HFPO = 2.09) so that the inside pressure might be maintained at a constant level of 0.04 MPa. [0170] Example 7

A 200-mL autoclave equipped with a pressure gage, a valve, a safety valve and an sampling tube produced by Taiatsu Techno Corporation was charged with 70 g of triglyme and 0.3 g of splay-dried KF and then the autoclave was tightly closed. The autoclave inside was purged several times with nitrogen and then the autoclave was depressurized. The autoclave was cooled in a dry ice-acetone bath until arrival of the inside temperature at -15⁰C. Then, 4.8 g of COF₂ was fed into the autoclave. After cooling again to the inside temperature of -15 ⁰C, HFPO was introduced into the autoclave to start the reaction. HFPO was continuously introduced into the autoclave while the rate flow thereof was adjusted to 13 cc/min and the reaction temperature was maintained at -15 to -10 ⁰C; in the end, the amount of HFPO fed amounted to a total of 24.1 g. The mole ratio of COF₂/HFPO was 2.0. Thereafter, the contents were stirred for 30 minutes, followed by standing for 30 minutes . The contents had separated into two layers. The lower layer (product layer) was sampled by the sampling tube. As a result of gas chromatographic analysis of the reaction product of the lower layer, the desired compound CF₃OCF(CF₃)CF₂OCF(CF₃)COF (n=l PMPF) was detected as a main component, and the composition of the product was as shown in Table 1. [0171] Example 8

The procedure of Example 7 was followed in the same manner except that the amount of splay-dried KF was 0.5 g. [0172] Example 9

The procedure of Example 7 was followed in the same manner except that the same amount of tetraglyme was used instead of triglyme as the solvent. [0173] Example 10

A 200-mL autoclave equipped with a pressure gage, a valve, a safety valve and an sampling tube produced by Taiatsu Techno Corporation was charged with 70 g of triglyme, 4.5 g of tetramethylurea and 0.5 g of splay-dried KF and then the autoclave was tightly closed. The autoclave inside was purged several times with nitrogen and then the autoclave was depressurized. The autoclave was cooled in a dry ice-acetone bath until arrival of the inside temperature at -15 ⁰C. Then, 4.8 g of COF₂ was fed into the autoclave. After cooling again to the inside temperature of -15 ⁰C, HFPO was introduced into the autoclave to start the reaction. HFPO was continuously introduced into the autoclave while the rate flow thereof was adjusted to 13 cc/min and the reaction temperature was maintained at -15 to -10 ⁰C; in the end, the amount of HFPO fed amounted to a total of 24.1 g. The mole ratio of COF₂/HFPO was 2.0. Thereafter, the contents were stirred for 30 minutes, followed by standing for 30 minutes . The contents had separated into two layers. The lower layer (product layer) was sampled by the sampling tube. As a result of gas chromatographic analysis of the reaction product of the lower layer, the desired compound CF₃OCF(CF₃)CF₂OCF(CF₃)COF (n=l PMPF) was detected as a main component, and the composition of the product was as shown in Table 1. [0174] Example 11 The procedure of Example 10 was followed in the same manner except that the same amount of CsF was used instead of splay-dried KF as the catalyst. [0175] Example 12

A 500-mL autoclave equipped with a pressure gage, a valve, a safety valve and an sampling tube and further provided with a jacket produced by Taiatsu Techno Corporation was charged with 100 g of tetraglyme and 7 g of CsF and then the autoclave was tightly closed. The autoclave inside was purged several times with nitrogen and then the autoclave was depressurized. The jacket was connected to a refrigerator (Yamato Scientific model BB3440) and cooled until arrival of the inside temperature at -3 ⁰C. Then, 200 g of CF₃OCF(CF₃)COF (n=0 PMPF) was fed into the autoclave. After cooling again to the inside temperature of -3 ⁰C, HFPO was introduced into the autoclave to start the reaction. HFPO was continuously introduced into the autoclave while the rate flow thereof was adjusted to 50 cc/min and the reaction temperature was maintained at -3 ⁰C; in the end, the amount of HFPO fed amounted to a total of 143 g. The mole ratio of n=0 PMPF/HFPO was 1.0. Thereafter the temperature was raised to room temperature with stirring, then the contents were continued to stir for 30 minutes, followed by standing for 30 minutes. The contents had separated into two layers. The lower layer (product layer) was sampled by the sampling tube. As a result of gas chromatographic analysis of the reaction product of the lower layer, the desired compound CF₃OCF(CF₃)CF₂OCF(CF₃)COF (n=l PMPF) was detected as a main component, and the composition of the product was as shown in Table 1. [0176] Example 13

After the reaction was finished in Example 12, only the lower layer (product layer) was drawn out through a bottom drain valve and the upper layer (tetraglyme layer containing CsF) was left alone in the system. Then 200 g of n=0 PMPF was fed thereinto, followed by the reaction temperature was maintained at -3 ⁰C and then 143 g of HFPO was fed thereinto in the same manner as described Example 12. After the reaction was finished, a procedure, wherein the lower layer (product layer) was drawn out and then n=0 PMPF and HFPO were fed into the system while the upper layer was remaining therein, was repeated 10 times. As a result of the 10th reaction, the composition of the lower layer was as shown in Table 1

[0177]

[Table 1]

INDUSTRIAL APPLICABILITY [0178]

The production method according to the invention is useful as a method of obtaining a surfactant useful in the production of a fluoropolymer, in particular.

Claims

1. A production method of a fluoroethercarboxylic acid fluoride, which comprises the step of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula

(D :

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

2. The production method of fluoroethercarboxylic acid fluoride according to Claim 1, wherein the catalyst is a metal fluoride.

3. The production method of fluoroethercarboxylic acid fluoride according to Claim 1 or 2, wherein the catalyst is at least one metal fluoride selected from the group consisting of cesium fluoride and potassium -fluoride.

4. The production method of fluoroethercarboxylic acid fluoride according to Claim 1, 2 or 3, wherein the catalyst is a metal fluoride, and, in addition, at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas is used therewith.

5. A production method of fluoroethercarboxylic acids, which comprises the steps of: selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with carbonyl fluoride in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst; obtaining a fluoroethercarboxylic acid represented by the general formula (II):

CF₃O (CF (CF₃) CF₂O) CF (CF₃) COOX (II) wherein X represents hydrogen atom, ammonium group and an alkali metal atom, from the fluoroethercarboxylic acid fluoride, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

6. The production method of fluoroethercarboxylic acids according to Claim 5, wherein the catalyst is a metal fluoride.

7. The production method of fluoroethercarboxylic acids according to Claim 5 or 6, wherein the catalyst is at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride.

8. The production method of fluoroethercarboxylic acids according to Claim 5 ,6 or 7, wherein the catalyst is a metal fluoride, and, in addition, at least one species selected from the group consisting of non-cyclic tetraalkylureas and cyclic alkylureas is used therewith.

9. A production method of a fluoroethercarboxylic acid fluoride, which comprises the step of selectively producing a fluoroethercarboxylic acid fluoride represented by the formula

(D :

CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with a fluoroethercarboxylic acid fluoride represented by the formula (i) : CF₃OCF(CF₃)COF (i) in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, non-cyclic tetraalkylureas, cyclic alkylureas, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

10. The production method of fluoroethercarboxylic acid fluoride according to Claim 9, wherein the catalyst is a metal fluoride.

11. The production method of fluoroethercarboxylic acid fluoride according to Claim 9 or 10, wherein the catalyst comprises at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride.

12. A production method of fluoroethercarboxylic acids, which comprises the steps of: selectively producing a fluoroethercarboxylic acid fluoride represented by the formula (I) : CF₃O(CF(CF₃)CF₂O)CF(CF₃)COF (I) by reacting hexafluoropropylene oxide with a fluoroethercarboxylic acid fluoride represented by the formula

(i):

CF₃OCF(CF₃)COF (i) in a solvent at a temperature of -30 to 40 ⁰C in the presence of a catalyst; obtaining a fluoroethercarboxylic acid represented by the general formula (II):

CF₃O (CF (CF₃) CF₂O) CF (CF₃) COOX (II) wherein X represents hydrogen atom, ammonium group and an alkali metal atom, from the fluoroethercarboxylic acid fluoride, wherein the catalyst comprises at least one species selected from the group consisting of metal fluorides, non-cyclic tetraalkylureas, cyclic alkylureas, tertiary amines, tertiary diamines and tetraalkylammonium salts, and the solvent is an aprotic polar solvent.

13. The production method of fluoroethercarboxylic acids according to Claim 12, wherein the catalyst is a metal fluoride.

14. The production method of fluoroethercarboxylic acids according to Claim 12 or 13, wherein the catalyst comprises at least one metal fluoride selected from the group consisting of cesium fluoride and potassium fluoride.

15. The production method of fluoroethercarboxylic acid fluoride according to Claim 1, 2, 3, 4, 9, 10 or 11, wherein the aprotic polar solvent comprises at least one species selected from the group consisting of diethylene glycol dimethyl ether> triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

16. The production method of fluoroethercarboxylic acids according to Claim 5, 6, 7, 8, 12, 13 or 14, wherein the aprotic polar solvent comprises at least one species selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.