Azide group-containing fluoropolymers and method for preparing the same

Abstract

An azide group-containing fluoropolymer of formula (1) having a perfluoropolyether group of specific molecular structure as the backbone and terminated with an azide group via methylene group is provided.
N.sub.3CH.sub.2Rf.sup.1CH.sub.2N.sub.3(1)

Claims

1. An azide group-containing fluoropolymer having the following general formula (1):
N.sub.3CH.sub.2Rf.sup.1CH.sub.2N.sub.3(1) wherein Rf.sup.1 is a divalent perfluoropolyether group having the following general formula (2): ##STR00009## wherein a and b are each independently an integer in the range: a1, b1, 2a+b150.

2. A method for preparing the azide group-containing fluoropolymer of claim 1, comprising the steps of: reacting a fluoropolymer capped with a hydroxymethyl group at both ends of the molecular chain, having the following general formula (6):
HOCH.sub.2Rf.sup.1CH.sub.2OH(6) wherein Rf.sup.1 is as defined above with a halogenated sulfonyl compound, to form a fluoropolymer capped with a sulfonyl ester group at both ends of the molecular chain, and reacting the fluoropolymer capped with a sulfonyl ester group at both ends of the molecular chain with sodium azide in a mixture of a non-fluorinated organic solvent and a partially or fully fluorinated organic solvent.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram showing .sup.1H-NMR spectrum of the fluoropolymer of formula (10) in Example 1.

(2) FIG. 2 is a diagram showing .sup.1H-NMR spectrum of the fluoropolymer of formula (11) in Example 1.

(3) FIG. 3 is a diagram showing .sup.1H-NMR spectrum of the product in Comparative Example 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

(4) One embodiment of the invention is an azide group-containing fluoropolymer having the following general formula (1).
N.sub.3CH.sub.2Rf.sup.1CH.sub.2N.sub.3(1)

(5) In formula (1), the backbone: Rf.sup.1 is a divalent perfluoropolyether group having any one of the following general formulae (2) to (5).

(6) ##STR00002##
Herein a and b are each independently an integer in the range: a1, b1, 2a+b150, and c is an integer of 1 to 150. Preferably Rf.sup.1 is a divalent perfluoropolyether group having formula (2) or (3).

(7) In formulae (2) to (5), a, b and c are each independently an integer, a is a1, preferably 1a75, b is b1, preferably 1b75, and 2a+b150, preferably 6a+b100, and c is an integer of 1 to 150, preferably 5 to 100. As long as a+b is at least 2 and up to 150 and c is at least 1 and up to 150, desirably the operation following the reaction is easy.

(8) Referring to the azide group-containing fluoropolymer having formula (1) wherein Rf.sup.1 is a divalent perfluoropolyether group having formula (2) or (3) as a typical polymer, examples of the azide group-containing fluoropolymer having formula (1) are shown below, but not limited thereto.

(9) ##STR00003##

(10) In formula (7), a1 and b1 are each independently an integer, a11, b11 and 2a1+b1150, preferably 6a1+b1120, more preferably 35a1+b1100. In formula (8), a2 and b2 are each independently an integer, a21, b21 and 2a2+b2150, preferably 6a2+b2100.

(11) Another embodiment is a method for preparing the azide group-containing fluoropolymer represented by the general formula (1), comprising the steps of reacting a fluoropolymer capped with a hydroxymethyl group at both ends of the molecular chain, represented by the following general formula (6):
HOCH.sub.2Rf.sup.1CH.sub.2OH(6)
wherein Rf.sup.1 is as defined above, at its hydroxyl groups, with a halogenated sulfonyl compound, to form a fluoropolymer capped with a sulfonyl ester group at both ends of the molecular chain, and reacting the sulfonyl ester-capped fluoropolymer at its sulfonyl ester groups with sodium azide in a mixture of a non-fluorinated organic solvent and a partially or fully fluorinated organic solvent.

(12) Reference is now made to the azide group-containing fluoropolymer having formula (1) wherein Rf.sup.1 is a divalent perfluoropolyether group having formula (2) as a typical example. The preparation of this fluoropolymer through the following first and second steps is described.

(13) 1st Step

(14) In the first step, a fluoropolymer capped with a hydroxymethyl group at both ends of the molecular chain, for example, a fluoropolymer as shown below is reacted with a halogenated sulfonyl compound, for example, perfluoro-1-butanesulfonyl fluoride in the presence of a base (e.g., triethylamine) to convert the hydroxy group to a sulfonyl ester group to form a fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via a methylene group, for example, a polymer having hexafluoropropylene oxide (HFPO) structure as the backbone as shown below.

(15) ##STR00004##
Herein a, b, and a+b are as defined above.

(16) The method starts with a fluoropolymer capped with a hydroxymethyl group at both ends of the molecular chain. When a fluoropolymer capped with a hydroxymethyl group at both ends of the molecular chain and having a skeleton of formula (3), (4) or (5) as the backbone is used instead of the fluoropolymer having hexafluoropropylene oxide (HFPO) to structure as the backbone, represented by formula (2), there is obtained a sulfonyl ester polymer having the corresponding backbone structure.

(17) In the reaction, the halogenated sulfonyl compound is preferably used in an amount of at least 1.0 equivalent, more preferably at least 1.0 equivalent and up to 5.0 equivalents per equivalent of hydroxyl group on the fluoropolymer capped with hydroxymethyl at both ends of the molecular chain. Suitable halogenated sulfonyl compounds include perfluoro-1-butanesulfonyl fluoride, p-toluenesulfonyl chloride, methanesulfonyl chloride, and p-nitrobenzenesulfonyl chloride.

(18) The base such as triethylamine is added to the reaction system for the purpose of neutralizing the hydrogen halide which is formed during reaction of terminal hydroxyl groups on the fluoropolymer with the halogenated sulfonyl compound. The base is preferably used in an amount of at least 1.1 equivalents and up to 1.5 equivalents per equivalent of hydroxyl group on the fluoropolymer capped with hydroxymethyl at both ends of the molecular chain. Suitable bases include triethylamine, diisopropylethylamine, and pyridine.

(19) The reaction is preferably performed in a nitrogen blanket. The reaction temperature may be of the order of 20 to 50 C., especially 20 to 40 C. Since the reaction is exothermic immediately after the start, the reaction system may be cooled for about 10 minutes from the start if the temperature elevates to a high level. Stirring is continued for 1 hour to 3 days, especially 3 hours to 24 hours from the start of reaction, after which the reaction is complete. After the completion of reaction, the triethylamine-hydrogen fluoride salt resulting from reaction is dissolved in water. The fluorinated organic solvent layer is collected and concentrated under reduced pressure, obtaining a fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via methylene.

(20) 2nd Step

(21) In the second step, the fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via methylene, for example, a polymer having hexafluoropropylene oxide (HFPO) structure as the backbone, as shown below, is reacted at its sulfonyl ester groups with sodium azide in a mixture of a partially or fully fluorinated organic solvent and a non-fluorinated organic solvent, obtaining the desired azide group-containing fluoropolymer having an azide group at both ends of the molecular chain via methylene, represented by formula (1), for example, an azide group-containing fluoropolymer having hexafluoropropylene oxide (HFPO) structure as the backbone, as shown below.

(22) ##STR00005##

(23) Herein a, b and a+b are as defined above.

(24) In the reaction, the sodium azide is preferably used in an amount of at least 1.0 equivalent, more preferably at least 1.1 equivalents and up to 3.0 equivalents per equivalent of sulfonyl ester group on the fluoropolymer having a sulfonyl ester group. If the equivalent amount of the sodium azide is below the range, the reaction may not take place to an acceptable extent. If the equivalent amount of the sodium azide is above the range, an excess of the sodium azide is left in the system after the completion of reaction, with the risk of explosion during separatory operation.

(25) Suitable non-fluorinated organic solvents include dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and acetonitrile. The non-fluorinated organic solvent is preferably used in an amount of at least 0.5 time, more preferably at least 1.5 times and up to 2.5 times the weight of the fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via methylene. If the amount of the non-fluorinated organic solvent is below the range, the reaction rate may become lower and side reaction may take place.

(26) As used herein, the term partially fluorinated should be understood to mean that only some of the hydrogen atoms on the backbone are replaced by fluorine. The term fully fluorinated should be understood to mean that all hydrogen atoms on the backbone are replaced by fluorine atoms. Sometimes, the partially or fully fluorinated organic solvent is simply referred to as fluorinated organic solvent.

(27) Examples of the fluorinated organic solvent include hexafluoro-m-xylene (HFMX), H Galden ZV130 (Solvay), AC-6000 (AGC Inc.), and other solvents in which the fluoropolymer having a sulfonyl ester group is dissolved. The fluorinated organic solvent is preferably used in an amount of at least 0.5 time, more preferably at least 1.5 times and up to 2.5 times the weight of the fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via methylene. If the amount of the fluorinated organic solvent is below the range, the reaction rate may become lower and side reactions may take place.

(28) The fluorinated organic solvent and the non-fluorinated organic solvent are preferably used in a weight ratio of from 0.5:1 to 3:1, more preferably from 1:1 to 2:1, most preferably 1:1. If the ratio of the fluorinated organic solvent is too low, the rate of azide-forming reaction may become lower and side reactions may take place. If the ratio of the fluorinated organic solvent is too high, the rate of azide-forming reaction may become lower and side reactions may take place.

(29) The reaction may be performed by adding a fluorinated organic solvent, a non-fluorinated organic solvent, and sodium azide to the fluoropolymer having a sulfonyl ester group at both ends of the molecular chain via methylene, and heating the mixture at a temperature of 60 to 120 C., especially 80 to 115 C. for 12 hours to 3 days, especially 1 to 2.8 days. After the completion of reaction, water and a fluorinated organic solvent such as hexafluoro-m-xylene (HFMX) are added to the reaction mixture, from which a water layer is removed by separatory operation. Another organic solvent such as acetone is added to the solvent layer for precipitation. The precipitate is collected, concentrated under reduced pressure, and treated with activated carbon, obtaining the desired compound, fluoropolymer having an azide group at both ends of the molecular chain via methylene, represented by formula (1).

EXAMPLE

(30) Examples are given below by way of illustration and not by way of limitation. The number of repetition of perfluorooxyalkylene units (or degree of polymerization) is a number average degree of polymerization as analyzed by gel permeation chromatography (GPC) using a fluorinated solvent as eluent.

Example 1

(31) A 3-L flask was charged with 1,045 g of a fluoropolymer of HFPO (35-mer) skeleton backbone and having hydroxymethyl at both ends of the molecular chain, represented by the formula (9) (hydroxy group concentration=0.3010.sup.3 mol/g).

(32) ##STR00006##
To the flask under nitrogen blanket, 389 g of perfluoro-1-butanesulfonyl fluoride and 46 g of triethylamine were added whereupon stirring was started. At this point, the internal temperature elevated to 30 C. at maximum. After stirring for about 20 hours, HFMX and water were added whereupon the HFMX layer was collected by separatory operation. Acetone was added to the layer for precipitation. The precipitate was collected and concentrated in vacuum (267 Pa, 100 C.) for 1 hour. As a result, 1,128 g of a fluoropolymer having the formula (10) was obtained as a colorless transparent mass.

(33) ##STR00007##

(34) The fluoropolymer of formula (10), 1.0105 g, was mixed with 0.0535 g of toluene and 4.0084 g of hexafluoro-m-xylene (HFMX). The resulting solution was analyzed by .sup.1H-NMR spectroscopy. On calculation, the fluoropolymer of formula (10) had a OSO.sub.2C.sub.4F.sub.9 value of 0.27810.sup.3 mol/g. FIG. 1 shows the .sup.1H-NMR spectrum. .sup.1H-NMR 4.69 (m, CH.sub.2)

(35) A 10-L flask was charged with 1,128 g of the fluoropolymer having formula (10) and 1,692 g of DMSO, which were purged with nitrogen for 10 minutes. Under the nitrogen blanket, the flask was further charged with 1,692 g of HFMX and 60 g of sodium azide, and heated at an internal temperature of 110 C., whereupon stirring was started. After 66.5 hours of stirring, water was added to quench the reaction, and HFMX was added. By separatory operation, the HFMX layer was recovered. Acetone was added to the HFMX layer for precipitation. The precipitate was collected, filtered and concentrated in vacuum (267 Pa, 100 C.) for about 1 hour. To the concentrate, 1,018 g of PF5060 (3M) and 51 g of activated carbon (Shirasagi AS, Osaka Gas Chemicals Co., Ltd.) were added. The mixture was stirred at room temperature for 1 hour. After removal of the activated carbon by filtration, the filtrate was concentrated in vacuum (267 Pa, 100 C.) for about 1 hour. There was obtained 960 g of an azide group-containing fluoropolymer having the formula (11) as a colorless transparent mass.

(36) ##STR00008##

(37) The azide group-containing fluoropolymer having formula (11), 1.0083 g, was mixed with 0.0508 g of toluene and 4.0031 g of hexafluoro-m-xylene (HFMX). The resulting solution was analyzed by .sup.1H-NMR spectroscopy. On calculation, the fluoropolymer of formula (11) had an azide value of 0.27410.sup.3 mol/g. FIG. 2 shows the .sup.1H-NMR spectrum. .sup.1H-NMR 3.56 (m, CH.sub.2)

Comparative Example 1

(38) A 100-mL flask was charged with 20 g of a fluoropolymer of HFPO (35-mer) skeleton backbone and having hydroxymethyl at both ends of the molecular chain, to represented by the above formula (9) (hydroxy group concentration=0.3010.sup.3 mol/g). To the flask under nitrogen blanket, 7.6 g of perfluoro-1-butanesulfonyl fluoride and 0.85 g of triethylamine were added whereupon stirring was started. After stirring for about 3 days, HFMX and water were added whereupon the HFMX layer was collected by separatory operation. Acetone was added to the layer for precipitation. The precipitate was collected and concentrated in vacuum (267 Pa, 100 C.) for 1 hour. There was obtained 17 g of a fluoropolymer having the above formula (10) as a colorless transparent mass.

(39) On calculation by the same method as above, the fluoropolymer had a OSO.sub.2C.sub.4F.sub.9 value of 0.28110.sup.3 mol/g.

(40) A 100-mL flask was purged with nitrogen and charged with 10 g of the fluoropolymer having formula (10) and 30 g of DMSO, which were allowed to stand for 10 minutes. Under the nitrogen blanket, the flask was further charged with 0.55 g of sodium azide and heated at an internal temperature of 110 C., whereupon stirring was started. After 45.5 hours of stirring, water was added to quench the reaction, and HFMX was added. By separatory operation, the HFMX layer was recovered. Acetone was added to the HFMX layer for precipitation. The precipitate was collected and concentrated in vacuum (267 Pa, 100 C.) for about 1 hour. There was obtained a complex mixture of compounds, but not the azide group-containing fluoropolymer having the above formula (11). FIG. 3 shows the .sup.1H-NMR spectrum of the mixture.

INDUSTRIAL APPLICABILITY

(41) The azide group-containing fluoropolymer of the invention is useful in crosslinking using 1,3-dipolar cycloaddition, for example, Huisgen cycloaddition reaction between an azide and an alkyne, and especially useful as a base polymer for fluorinated elastomers. The resulting elastomers find use as parts requiring chemical resistance and oil resistance in various fields including automobiles, chemical plants, automatic business machines (e.g., copiers and ink jet printers), semiconductor manufacture lines, analytical and scientific instruments, medical instruments, aircraft, and fuel cells. Exemplary parts include rubber moldings such as diaphragms, valves, sealing parts (e.g., O-rings, oil seals, packings, to gaskets, joints and face seals), gel materials, adhesives, (sensor) potting materials, tent coating materials, sealants, molded parts, extruded parts, coatings, copier roll materials, electrical moisture-proof coatings, laminate rubber fabrics, protective materials for automobile pressure sensors, and materials for the protection and vibration-damping of automobile-mounted electronic parts. There is a possibility that the azide-containing fluoropolymer finds use in a variety of other applications after functionality modification.

(42) Japanese Patent Application No. 2017-232578 is incorporated herein by reference.

(43) Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.