DE1901872A1 - Stabilization of fluorocarbon polymers - Google Patents

Description

Stabilization of fluorocarbon polymers

The invention relates to a process to improve the stability of high molecular weight fluorocarbon polymers.

They USA patent specification 3 035 083 discloses a process for converting such reactive end groups, such as vinyl and monomeric and dimeric carboxylate groups in high molecular weight fluorocarbon polymers, for example tetrafluoroethylene / hexafluoropropylene _r copolymer, e.g. Äusseteen the fluorocarbon polymer against relatively strong and prolonged heating in the presence of moisture. They hardness of this treatment leads to difficulties in processing.

In another Stabiliaierunga publication, the USA patent 3 242 218, is decarboxylation and fluo ~

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ication of Fluorokohlenetoff-.oolyätherpolymerisaten with elemental fluorine described. In this process, the polyether polymer has a low molecular weight and is only treated in the liquid phase, i.e. either as a liquid or in solution in an inert solvent. which is in the> 8-position to the carboxyl end group of the polymer and which is known to have a stabilizing effect on free radicals. In the carboxylation reaction, the end group of the intermediate stage is the free radical -0-.CF ₂ *. It has hitherto been assumed that the stability »which the ether oxygen atom imparts to this intermediate free radical group» is responsible for the ability of the unstable end group (formed from the precursor end group COF) to be decarboxylated Group -CF ₂ * remains, which unites with -P to form the stable end group -CF.

It has now been found that the stability of high molecular weight fluorocarbon polymers can be improved by exposing the fluorocarbon polyaerene in a solid form and under permanently mild conditions and during relatively short periods of time to a source of fluorine radicals under bonds resulting from this Source which release fluorine radicals. In the process according to the invention, the fluorine radicals react with the unstable end groups of the main polymer chain in order to convert them into a more stable form. However, this implementation is not limited to the

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Terminal groups are limited because it may be assumed that unstable groups in the form of unsaturated bonds are present in the interior, that is to say within the main polymer chain, and that the fluorine radicals react with saturation of these unstable inner groups. The unstable end groups which are converted according to the invention include the carboxylate and vinyl end groups, as described in USA Patent 3,085,083, and other end groups which can be converted into a more stable form, for example -CF ₂ H and Aaid are. These end groups are visible in the ultra-red spectrum of the polymer, provided that the molecular weight of the polymer is such, that is not too high, so that the number of end groups present is sufficiently high to be detectable. Insofar as the molecular weight is so high, the presence of unstable end groups is suggested by analogy with the chemistry which leads to the formation of unstable end groups in fluorocarbon polymers of lower molecular weight, for which ultrared analysis can be used. The conversion of the end groups visible in the ultra-red is indicated by the reduction or the disappearance of the absorption unit, depending on the degree of completeness of the conversion, which results from the specific end groups which are originally present.

The end groups "which are formed by the reaction according to the invention with fluorine radicals" are non-reactive end groups "which are assumed" to be saturated fluorocarbon groups, in particular —CF groups. Proof of this is the absence of absorption

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Peaks (which correspond to the new end groups) identified as from other than -CF ^ groups would be recognizable, im Ultra-red spectrum of the fluorocarbon polymer after treatment in the process according to the invention.

The improvement in the stability of the fluorocarbon polymers after treatment by means of this process is shown when comparing the behavior of treated and not treated polymers in suitable practical or laboratory tests, as they are subsequently described in more detail and determination of the improvement that is achieved in the treated polymer. That same improvement one finds in polymers, which have molecular weights that are too high, um.die chemical changes to make the end groups visible by means of ultrared analysis, but since the improvement is achieved in this way, can assume that the chemical changes have occurred.

In considering the detailed description of the reactants according to the invention, the source of fluorine radicals can be any compound which supplies these radicals under the conditions used, mainly on heating. Such compounds are known to the person skilled in the art and include, for example, elemental fluorine, CoF ₅ , AgF ₂ , UF ₆ , OF ₂ , N ₂ F ₂ , 0F, OF and the interhalogen fluorides, for example JF ₅ and ClF ₃ .

The fluorocarbon polymers stabilized according to the invention are high molecular weight polymers which normally

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are solid and capable of handling objects such as foils, that are tough and flexible to be pressed. Accordingly, the polymers contemplated here are of much higher quality Molecular weight, as the molecular weights of the fats and / or waxes. The number average molecular weight of the fluorocarbon polymers is usually at least 10,000 and generally greater than 25,000. Furthermore, the fluorocarbon polymers have a carbon atom in the Main polymer chain in $ position to the unstable bond group. In general, the main polymer chain of these fluorocarbon polymers, with the exception of the end groups, consists of carbon atoms. Any substituents on the main polymer chain including side chain ^ »which branch off from this, are of such a nature that they do not break down the polymer chain when exposed to fluorine radicals according to the invention cause. These substituents are preferably inert towards fluorine radicals, so that the reaction with the fluorine radicals is essentially limited to the end groups. In order to meet these conditions, these are substituents typically be such that the fluorocarbon polymer either perfluorinated or highly fluorinated with substituents other than fluorine, e.g. Cl and CF ~ in no greater frequency than every other Carbon atom of the polymer main chain are present.

To representative fluorocarbon polymers which are according to the invention are stabilized belong to those of Chlortriflüoi'äfchylen or tetrafluoroethylene-derived polymers and the copolymers of one of these monomers with one or several other copolymerizable monomers. Usually

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the main monomer will be tetrafluoroethylene and, on the other hand, copolymerizable monomers can be monomers such as the perfluorinated monomers such as hexafluoropropylene according to US Pat. Perfluoro (propyl or ethyl vinyl ether) according to US Pat. No. 3,132,123 and perfluoro (2-methylene-4-methyl-1,3-dioxolane) according to US Pat. No. 3,303,107 also include the highly fluorinated monomers That is, monomers in which a single hydrogen substituent remains, which does not change the fluorocarbon character of the polymer, such as the 2-hydroperfluoroalkenes with 3 to 10 carbon atoms, eg 2-hydropentafluoropropene, JX. -Hydroperfluoroalkenes with 3 to 10 carbon atoms and the JTL hydroperfluoroalkyl perfluorovinyl ethers, the alkyl group of which has 1 to 3 5 carbon atoms. In general, sufficient comonomer is present to make jiBC Poly te met luoräthylensehmelss processable; however, lesser or greater amounts, but usually between 1 and 40% by weight, based on the weight of the copolymer, may be present. Palle of the copolymer with hexafluoropropylene are 5 to 35 $> of units which are derived from this Oomonomeren preferred. For the other monomers, 1 to 20 percent by weight are preferred.

Further fluorocarbon polymers, which according to the invention can be stabilized are the fluorocarbon polymers, which groups have branching off from the polymer chain. These branching groups can be used in the present process reactive or non-reactive with fluorine radicals Be groups. In one embodiment of the

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In the invention, the branching groups are either ionic groups such as -SOjH or precursor groups which can be converted to -SO ₃ H. Such precursor groups are discussed below. It is preferred, although not essential, that the branched precursor groups are non-reactive in the present process. The last-mentioned ionic groups preferably result in an ion exchange capacity of at least 0.3 equivalent per gram of the polymer. The preferred ionic group is -SO ₃ H. A class of such polymers with pendant precursor groups are the copolymers of an ethylenically unsaturated, sulfonyl fluoride-containing monomer and one or more of the fluorocarbon polymer-forming monomers described above. Examples of these copolymers are disclosed in U.S. Patents 3,041,317, 3 2B2 875 and U.S. Patent Application Serial Ho. 639 515 of May 18, 1967, which also describes the production and use of such polymers as ion exchange membranes in electrochemical cells, the helsst fuel cells and secondary electrochemical cells is described. Examples of monomeric units in ion exchange membranes derived from the sulfonyl fluoride-containing monomers include

• I

QFo CF _n

FO SO ₃ H and F (S (OCP ₂ CFY) _n OCP ₂ CR _f SO ₃ H

where Y is P or CF ₃ »R _{f is} fluorine or perfluoroalkyl having 1 to 10 carbon atoms, and η is an integer from 1 to 3 inclusive. The copolymer preferably has 0.5 to

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50 mole SS of the sulfonic acid-containing units and an equivalent weight (Average weight of the repeating unit) from 260 to 20,000, but more preferably from 800 to 2000. The preferred comonomer is tetrafluoroethylene. if the sulfonic acid adheres directly to the main polymer chain, a third monomer unit, a perfluoro (alkyl vinyl ether), is preferably present in the polymer. It is to be noted that copolymerization is not the only method after which a polymer chain with pendant ionic Groups or precursors thereof can be made. Such groups can be attached to an existing fluorocarbon polymer chain by grafting or chemical substitution. to be introduced.

Even if ion exchange membranes of this special class of fluorocarbon polymers have a high stability against temperatures up to about 250 ° C, as well as against acidic conditions at these temperatures, it was found that after long-term use in the hydrogen / oxygen fuel cell in the water outflow from the Fuel cell HP occurs. It is believed that there is a highly reactive species, the hydroxyl radical, which degrades the membrane and yields HP. The treatment of this class of fluorocarbon polymers by the process according to the invention improves the stability of the polymers and appears to eliminate the difficulty which arises with this form of application.

With a detailed consideration of the process conditions the method according to the invention can be carried out

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by bringing the fluorine radical-forming compound and the fluorocarbon polymer into intimate contact with one another brings the increased temperature, which is necessary for the formation of the fluorine radicals from the compound. The temperature, at which the process is carried out * therefore depends on the temperature at which this formation occurs for the specific the fluorination compound used occurs and the reaction rate, which is desired close to decomposition. Generally the temperature will be between 20 ° and 300 ° G lie.· ·

The fluorocarbon polymers treated according to the invention are in a solid (not molten) state during the treatment. The solid state can be in the crushed or pre-molded form or in the pressed form; however, the thicker the cross-section _y, the longer the time required for treatment. Oxygen is excluded from the reaction system.

When the fluorine-radical generating compound is gaseous, such as F ₉ or UFG, can be the intimate contact with the FIU or ~ Low carbon off - "Polymer en by holding said polymer in an atmosphere of fluorine-free radical-forming compound during such time. obtained that the fluorine radicals penetrate the solid polymer and result in the desired end group conversion. An inert ßäa, for example N ₂ », can be present to dilute the Fg.

In the event that compounds that form fluorine radicals occur in the The reaction conditions are in the solid state, e.g. CoF- *

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and AgF ₂ *, intimate contact with the fluorocarbon polymer is achieved by dissolving or dispersing the fluorinating agent in an organic liquid which is inert to fluorine radicals and which wets the surface of the polymer and brings this liquid into contact with the polymer. Some swelling of the polymer can occur, but the liquid should not be one which dissolves the fluorocarbon polymer. In general, the inert liquid will be one of the well known perfluorocarbon liquids such as oils derived from hexafluoropropylene epoxide, cyclic dimer of hexafluoropropylene, and perfluorinated kerosene; the choice of liquid used will depend on the particular polymer being treated.

The fluorination can be carried out batchwise or continuously. For example, the fluorocarbon polymer « can be guided in one direction and the fluorine radical-forming compound in contact with it can flow in countercurrent to flow.

In the case of fluorocarbon polymers, such as polytetrafluoroethylene and its copolymers with hexafluoropropylene, the color of the polymer treated according to the present process is improved, that is to say in comparison to not treated polymers white fiber.

In the case of fluorocarbon polymers, which pending have ionic groups, if these are derived from a copolymerization, the ionic groups are usually

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Chemical tea In the form of a precursor group which is stable against the fluorination * according to the irradiation. If the pendant ionic group is a hydroxy acid, the fore-buffer group will generally have the formula -SO ₂ H, where N is the locus · F * amide or groups of the formula -OMe where Me is an alkali metal or quaternary ammonium. If N is the group F or amide, the pending group is converted to -SO ₅ H by first reacting with a strong base such as sodium hydroxide, forming the corresponding salts and then forming the salts with a strong inorganic acid such as Oxygenated acid, which gives the hydroxy acid forti (-80JS), which is desired for the Xonenaue polymer. When H is the -OHe group (defined above), the pendant su -SO ₅ H group is converted by deposition of a strong inorganic acid. This conversion process is described in detail in the USA-Bateatschrift 3,282,875. If the appendage groups are in the acidic fluoro form (-'SO ₂ F), the fluorocarbon polymer can easily be inherited from the shell; However, the Hyöroxyacid form is not so easy to process from a Schmelse eu. For this reason it is generally desirable to fluorinate (according to the invention) fluorocarbon polymers in which the pendent groups are in the 3Eurefluoridfora (-SO ₂ F), then the polymer obtained with the fluorinated end groups and the pendent -SOgF -Process groups from the melt in your desired form and finally convert the latter product into the hydroxy acid form (-SOxH).

The duration of implementation will depend on such factors as the special country groups and their TJm

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degree of conversion and depend on the special reaction conditions and the most applied reaction. Preferably the conversion is quantitative. However, there are forms of application in which the degree of stabilization achieved through quantitative conversion is not required. Accordingly, the process can result in a conversion of at least 40 $> of the unstable end groups to stable end groups, but preferably a conversion of at least 75 #. In the event that the molecular weight of the fluorocarbon polymer is such that the unstable end groups are somewhat visible in the infrared spectrum, the degree of conversion can be determined by counting the end groups using standard methods of infrared analysis on (treated and untreated) samples of the fluorocarbon polymer particles determine which are pressed for 5 minutes at a temperature of 350 ° C to form a film about 0.25 mm thick, with the exception of the pendant ionic groups having fluorocarbon polymers, in which a pressing temperature of 240 ° C is used «, Im In the event that the molecular weight of the fluorocarbon polymer is so high that the ultra-red analysis cannot be used, the degree of conversion can be determined by comparing the amount of gas evolved from treated and untreated samples by subjecting the samples to an elevated temperature close to decomposition, , in which the gas development from the untreated The first sample appears to be the largest. An example of this test by gas evolution is given in Example 30.

The "peroxide test" mentioned in the following examples is carried out in the following way: A sample from 0.5 to

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1.5 g of the fluorocarbon polymer to be tested is dried in a vacuum oven at 100 ° C. for 1 hour, weighed and placed in a test tube 25 × 200 mm. 50 ml of 30% HgO ₂ , which in dissolved form contains 0.0025 g of FeSO, 7H ₂ O, are added to the reagent glass. Over a period of 1 hour, the test tube is heated to 85 ° C and held at this temperature for 20 hours, followed by cooling to room temperature, decanting the liquid contents of the test tube and rinsing the

Inside the reagent gas and the polymer ^ Xnhal & JS twice with 20 ocm portions of distilled water takes place · bas polymer « is removed from the test tube, between -ftlfcrUvpApie-r » dries and under the same conditions in the hit «© gstrook« net, like the drying in the beginning of the investigation «Then the dried sample weighed, the weight loss being a wet for the end groups, which are defined by the litasetgiarig of the Polyae » with the solution of Perejsid / fel & an (IZ) ~ Ion are «This procedure could be repeated to obtain the average weight loss per cycle.

The fluorocarbon polymers treated according to the invention can be used in the same way as untreated polymers, with the exception that, in cases in which stability is a problem, the application of the invention treated polymers is preferred.

The process of the present invention is illustrated by the following examples, in which parts and percentages are based on weight, unless otherwise stated.

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Examples 1 to 11

In these examples, the fluorocarbon polymer is a copolymer of tetrafluoroethylene with the monomer FS0 ₂ CP ₂ Ci * ₂ 0CF (CP ₃ ) CP ₂ OGP = CP ₂ , which essentially follows the process of Example 3 of US Pat. No. 3,282,875 It polymerizes, with the exception that the initiator is perfluoropropionyl peroxide, the polymerization temperature is 45 ° C and the solvent is "Preon" 113. Ea three different molecular weights, as indicated by the Sehmelsfluas behavior, you aieseai Ccpolymefiaat produced Daa Polymers A has a melt flow rate of 542.5 »the polymer © B has a melt flow rate ν ca 146» 4 ime! the polymer ϋ has "βί, Ώο '. Melt flow of 113 * 0. The melt flow is determined " in Sr & i outflow in 10 iliüutaa üal 250 ° 0 using a 5 003 g punch (9 _f 42 mm diameter) »which daa mixed polymers pushes through an access opening with a 2.093 mbi burglar marker and 8.00 mm length. This method of Schiaelzflussiaessung is used in the remaining examples below, with some changes! as indicated

Da3 Pluorierungs-'Verfahrsn proceeds as follows s samples of the polymers A _t B and C are placed in lined Hiekel Schüttelrohre (Kaaaität 320 cc), which was then evacuated and nitrogen dröiiiial old werdea rinsed Dami "evacuated in fourth Kai v / ground and roit O _s 35 atü l'lir.orgas pressed on and under autogenous? Pressure 2 hours srhitst wsrd'jn> Then the pipe cools down ?? down to room temperature, and vent the fluorine gas. The accuracy of this experiment and the results are detailed in Table I below. ¹ : shares. In Examples 1 to 5 and 9 to 11 there is a shaking

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tube sugefuhrte polymers in the form of irregularly shaped granules, which are about 0.4 mm to 6.35 mm in diameter The polymer soling in Examples 6 to 8 la is in the form of a 0.127 mm thick film.

The results of the fluorination treatment can be seen through Comparison of the group number by means of ultrared spectral analysis, which are found on samples of the same, non-fluorinated polymers (Example x 1, 6 and 9), with the end group number of the fluorinated samples. In all cases the number is of the unstable band groups. The indication "K.f." in Table I means "none detected". the Orensen of the adjustability in the applied ultrared apparatus are assumed as follows * 5 end groups carboxy- ' lat-Honosjsr or -Diner and 10 vinyl groups (10 carbon atoms each in polymer). The improvement in the stability of the fluorinated polymers can be recognized by the strong Durable reduction in weight loss per cycle in peroxide tea compared to the non-fluorinated controls. The weight loss results are based on 5 to 6 Cycles Jt example.

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example

1 2 3 4th 5

9 10 11th

Poly- Besohikmerea kung des
Shaker tube (g)

A. A. A. A. A.

Wk 6th B. σ \ I. 7th B. a B.

C. C.

50 50 50 25th

50 29

50 25th

Table I.

Equivalent fluorination addition groups per 10 C-weight conditions atoms

Carboxylate Monomer Dimer CP * CP,

1210 1230 1230 1210 1195

1335 1360 1275

1265 1300

1225

no

100 ° C - 2 hours 150 ° C - 2 hours 190 ° C - 2 hours

-50 100 150 *

100 '

5;

100 150 ⁽

190 * 190 ⁽

C CC

2 hours + 2 hours + 2 hours

no

C - 2 hours

C - 2 hours + C - 2 hours + C - 2 hours

no

0 - 2 hours

C - 2 hours

23

565

K.P ..

K.P.-

K.P.

K.P.

520 K.P.

16 550 K.P. 6th

255

109

K.P.

K.P.

Peroxide teat

Sewicbtöverluet (mg each Cycle)

17th
2.0 1.3 2.5 1.7

16
3.3

6.0 21 1.5 1.5

KP means "none detectable ¹ *

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Example 12

A 320 ml stainless steel shaking tube is charged Steel with 60 g of polymer A from Example 1 and 30 al cyclic! Perfluorocarbon ether solvent "ΪΟ-75% which contains 30 g of CoP- dispersed therein, heats the contents 3 hours at 200 ° C and removed the cobalt residue from the polymer by washing with 10 # HCl in ethanol. The washed polymer has an equivalent weight of 1,500. The end groups for the polymer prior to fluorination are given in Table I (Example 1). After fluorination according to in the present example no end groups can be found in the ultrared spectrum of the polymer «

A pile of the fluorinated polymer is pressed and hydrolyzed to convert the pendant ~ SO ₂ F groups to -SO ^ H groups. The hydrolysis process consists in immersing the polie in a 10 # NaOH solution at 80 + 10 ° C for 24 hours. The polie is then rinsed with water and bathed in three successive solutions of 10% HgS0 «at room temperature (3 hours per bath). The polie is then washed with distilled water until the pH of the wash water exceeds 4.5 after standing for 1 hour. The polie is air-dried and then subjected to the peroxide-Ieet (7 cycles). The actual · Qtawiohtsverluitj «cycle is 1 mg in the term of 17% per cycle for di · non-fluorinated · lontrollprob ·.

Examples 13-18

5s samples of T * tr «fluorKtQyl« a / fcM »fl & or $ foiyI ·» Cal »

0QM9IMI) «

it * · F

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Wa 16 £ hexafluoropropylene) is poured into a series of shaking tubes in the form of a fine powder, followed by alternating three evacuation and flushing with H ₂ . Then the tubes are evacuated again and pressurized with fluorine to 0 _f 35 atmospheres at room temperature, which is followed by placing the tubes in a shaking device "shaking and heating to the desired reaction" temperature for a period of about 1 hour. Elements of the polymer charge, temperature and time of fluorination and the results are given in Table II.

Conversion results reported in Table II the end groups are obtained by end group counting using the ultra-red spectrum of each of the polymer samples. The volatility index is a measure of the gas development from the polymer at a given temperature, which reflects the stability of the polymer. From Table II is to recognize »that the volatility index is highest in example 13, which is not fluorinated, and that he -mit with decreasing end group conversion, well progressively decreases. The improvement in the color of the polymer follows the same Direction, the non-fluorinated polymer being gray-white and the polymer with 100 pounds of converted terminal groups being the whitest. The improvement in extrudability also follows the gltioh · »ftnians, where <ias non-fluorinated polymers as Foam is characterized (the blfecae originate from the unstable endtmi with an independent transformation of the bundles

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Example 19

Example 16 is repeated sufficiently often to collect about 600 g of fluorinated polymer which has passed through extruded a 2.54 cm extruder and cut into press cubes which are then divided into 3 samples. The melt viscosity stability of the extruded cubes remains unchanged from the initial determination immediately, after extrusion, after 8 layers and after 17 days. These Melt viscosity uniformity over time indicates the shelf life of the plating treatment obtained polymers. ^

Bei piele, 20 to 26

In this experiment, a series of solid layers is of 20 g of copolymer powder of Examples produced 12 to 18, each heated to the desired temperature by by flowing Ng through the bed, followed by mixtures of P ₂ ^{and N} 2 ^durcn fllessen ^daa bed be left. Furthermore, each bed is heated to 240 to 250 ° C by means of a heating mantle. The temperatures of the Pg / ^ "*" ⁶⁰³ "* mixture, the duration of the test and the results of these tests are given in Table 3. The percent conversion of the end groups in each of these tests is 100%.

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33

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COVO OKN O

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fl ^ «k * t * fc« k · »*

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C- VO O ιη ON τ- VO KN KN VlT VlT in P ^ C ^ CM νβ VO ON ^^ Λ ^^ \ ^ fi KN KN ιη \ Γ \ \ Ο C * ·

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CVl CM CVt CM CVI W CVJ

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Example 27

A copolymer of tetrafluoroethylene / perfluoro (propyl vinyl ether) / trifluorovinyl sulfonyl fluoride is prepared in the following way: 165 g of irifluorovinylsulfonyl fluoride and 24 g of perfluoro (propyl vinyl ether) are added to a 250 ml flask containing about 20 g of MgO and the mixture obtained is added to Vacuum distilled in a 300 micron thick-walled polymer vessel to which 1 com perfluoropropionyl hydroxide in "Freon" 113 (3 × 10 "* molar) is added. The air is removed by cooling the contents and evacuating the vessel, followed by heating It follows the evacuated vessel to room temperature and then small amounts of fetvafluoroethylene are added while the temperature of the vessel is increased to 45 ° C. The tetrafluoroethylene pressure is increased to 2.8 atmospheres and held at this pressure for 5 hours Lower the pressure to 1.9 atmospheres, then cool the vessel to -78 ° C and pump off the unreacted tetrafluoroethylene · The vessel is on rough Heated m temperature and the volatile contents are distilled off, leaving 179 g 'residue, which is washed with about 200 ml of "ireon" 113, filtered and dried for 2 hours at 150 ° C under vacuum to obtain 15.0 g of Oopolymeres eu, which As can be seen from the ultrared spectrum, the copolymer contains units of each of the monomers present. The copolymer has 6.2 % trifluorovinyl sulfonyl fluoride, an equivalent weight of about 1700 and 153 terminal groups on the carboxylate dimer and 475 vinyl terminal groups per 10 carbon atoms.

The copolymer is fluorinated according to the method of example 3, with the exception that the polymeric acid is used

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7.7 g of 50 g. After fluorination, the equivalent weight appears unchanged and Iu No end groups were found in the ultrarotapektnm of the copolymer.

Example 28

It converts dae / ^ polymer de "Examples 9 to the sodium carboxylate form, inter alia, Bulfonylfluorid by heating 50 g thereof susaaaen" it 15 g IaOAo-H ₂ O and 200 al of glacial acetic acid at reflux conditions, in a flask under stirring Geesthacht. The oopolyerizate obtained is filtered, washed with about 500 ml of distilled water, dried overnight and then at 125 ° C. in a vacuum oven. The copolymer has an equivalent weight of 1265 and 182 bsw. I3I carboxylate end groups monomeric, diaer and 99 yinyl end groups, all 10 carbon atoms each.

The copolymer is then made according to the method of Example 3 3 fluorinated bit the Auenahae that the polymer coating is 25 g. After fluorination, no end groups are found in the infrared spectrum of the copolymer.

Example 29

A copolymer of tetrafluoroethylene / perfluoro (propyl vinyl ether) is prepared by adding 4200 ml of HgO, 6 g of ammonium persulfate, 15 g of ammonium carbonate, 220 g of paraffin and 10 g of ammonium perfluorooctanate to a polymerization vessel, then adding methane to 1.76 pressure, followed by pressure with tetrafluoroethylene up to zn 19.3 atm at 70 ° 0 for 92 minutes, followed by movement of the

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fäsaes is accompanied with 125 rpm. The washed copolymer obtained from the polymer! Sationsgefäß contains 1.7 ^, perfluoro (propyl vinyl ether) and possesses a Sohmelzviscosität of 33.5 χ 10 ⁴ poise at 380 ° C. In the ultra-red spectrum of the copolymer, amide end groups are the only detectable ^ Bnd groups and it is estimated that there are about 140 carbon atoms per 10. f _{i (}

If the fluorination procedure of Example 3 is followed with the exception that a charge of 100 g, an oil temperature of 250 ° C. and a P ₂ pressure of 2.53 atmospheres are used , only 21 end groups are determined by means of ultrarottal analysis,

Ba is ρ IeI 30

A commercially available, granular polytetrafluoroethylene polymer (average particle size 20 microns) is fluorinated in a shaker tube at 250 ° C. for half an hour using a mixture of β Hol- £ F «in H ₉ . The fluorinated polymer is pressed onto a disk at 210.9 kg / cm * p ^ eseexuotk, sintered at 420 ° C. for 2 hours and cooled to 270 ° C. at a rate of 1.07 ° C./minute. The internal specific weight according to the measurement by ultra-red analysis of the polymer in the disk is 2.2253 g / cn ⁵ . The internal specific gravity of the control polymer after the identical treatment with the exception of the fluorination is 2.2333. The lower specific weight of the fluorinated polymer, which has a higher molecular weight, indicates its improved stability compared to the control polymer.

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Han heats 1.46 g each of the granular, fluorinated tetrafluoroethylene polymer and the same amount of the same polymer but not fluorinated (control) for half an hour under a vacuum of 10 am Hg at 410 ° C. to determine how much gas develops, which is indicated by an increase in the pressure of the system. The control polymer gives off about 2 1/2 times the amount of gas compared to the fluorinated polymer and thus shows the greater stability of the fluorinated polymer, as well as a conversion of about 60 % of the unstable groups.

Example 31

If the procedure of Example 29 is followed except that no ammonium buffer is used, a copolymer of tetrafluoroethylene / perfluoro (propyl vinyl ether) with a melt viscosity of 122 χ 10 " ⁴ poise at 360 ° 0.2.2 results # Units derived from vinyl monomer and 117 carboxylate end groups per 10 carbon atoms.

The copolymer is prepared according to the method of Example 3. fluorinated except that the polymer charge is 25 g. The copolymer obtained has 13 carboxylate end groups.

- 25 -

009808/1630

Claims (4)

Claims A method for stabilizing high molecular weight fluorocarbon polymers by chemically modifying at least some of the unstable end groups of the polymer! - aatketten, characterized in that one uses high molecular weight fluorocarbon polymers, namely polytetrafluoroethylene, tetrafluoroethylene / ^ exafluoropropylene copolymer or tetrafluoropropylene copolymer / Perfluoro (alkyl vinyl ether) copolymer in solid form is brought into intimate contact with a source of fluorine radicals under conditions in which this source forms fluorine radicals, with at least 40 $> of the unstable end groups of the polymer being converted to stable end groups , the polymer optionally having groups with the formula -SO ₂ H pendant from the main polymer chain, in which H is the radicals-Ϊ, amide or -GHe, and Me is alkali metal or quaternary ammonium. 2. The method according to claim 1, characterized in that the fluorocarbon polymer is in the form of an ion exchange membrane, the polymer at the Polymer main chain has pendant -S C ^ F groups and the polymer is first treated with the source of fluorine radicals under conditions in which this source Forms fluorine radicals and then converts the -SO ^ F groups to -SG>, H groups, 3. Fluorocarbon polymers, characterized in that they are stabilized naoh the method of claim 1. - 26 - 009808/1630 AD-4360 Q * 4. Ion exchange membranes, thereby known that ■ The near «procedure dee claims 2 are stabilized. - 27 - 003808/1630