DE1901872B2 - PROCESS FOR STABILIZING HIGH MOLECULAR PERFLUOROUS POLYMERS - Google Patents

Description

JF, and C1F _V

The fluorocarbon polymers stabilized according to the invention are high molecular weight polymers, which are usually firm and able to

sit, which is in ^ -position to the carboxyl end group of the polymer is located and is known to have a stabilizing effect on free radicals Effectiveness exercises.

The invention relates to a method for stabilizing high molecular weight perfluoropolymers, which with the exception of the end groups only carbon atoms in the polymer chain and optionally

Furthermore, US Pat. No. 3,242,218
the decarboxylation and fluorination of fluorocarbon polyether polymers with elemental 15
Fluorine described. The polyether polymer has
has a low molecular weight and is only used in the
liquid phase treated, ie either as a liquid or in solution in an inert solvent.
Furthermore, these polyether polymers are objects, such as foils, which are tough and flexible, characterized in that they are pressed with an ether oxygen. The number average molecular weight of the fluorocarbon polymers is usually at least 10,000 and is generally greater than 25,000. The fluorocarbon polymers also have a carbon atom in the main polymer chain in the / 9-position to the unstable end group. In general, the main polymer chain of these fluorocarbon polymers, with the exception of the end groups, consists of carbon atoms.

Ether oxygen atoms contained in side chains, through 30 Any substituents on the polymer main chemical modification of the unstable end groups, chain including side chains are of such a nature that in which the polymers are intimately contained in solid form, they break down the polymer chain when in contact with fluorine radicals. proper exposure to the fluorine radicals

Cause reacting in the method according to the invention. These substituents are inert to the fluorine radicals with the unstable end groups 35 radicals, so that the reaction with the fluorine polymer main chain to convert them into a more stable radicals essentially to the end groups. One of the unstable end groups is restricted. These conditions correspond to which fluorinated fluorocarbon polymers are converted according to the invention. _y
hear the carboxy and vinyl end groups as they belong to representative perfluorocarbon polymers,

in U.S. Patent 3,085,083, 40 which are stabilized according to the invention belong and other end groups which make the tetrafluoroethylene derived polymers more stable

and the copolymers of this monomer with one or more other copolymerizable perfluorinated ones Monomers. Usually the main monomer will be tetrafluoroethylene and for other perfluorinated monomers, such as hexafluoropropylene, perfluoroalkenes with 4 to 10 carbon atoms, Perfluoro (alkyl vinyl ether), such as perfluoro (propyl or ethyl vinyl ether) and perfluoro (2-methylene

carbon groups, in particular - CF ₃ groups, 5 ° 4-methyl-1,3-dioxolane). The comonomer is usually present between 1 and 40 percent by weight based on the improvement in the stability of the fluorocarbons on the weight of the copolymer. In the substance polymers after treatment by means of this case of the copolymer with hexafluoropropylene, a comparison of the behavior shows that 5 to 35% of the units which are derived from this comono from treated and untreated polymers are preferred,
sowed in suitable practical or laboratory tests, such as those further perfluorocarbon polymers, which are subsequently described in more detail and which can be stabilized according to the invention, are the ascertainment of the improvement which is achieved in the treated fluorocarbon polymers which are achieved by the polydelt polymer. Have groups branching off this same merging chain. This improvement is found in polymers which have 60 branching groups compared to fluorine-radi molecular weights which are too high to be calcium reactive or non-reactive, the chemical changes of the end groups with close; but since the branching groups are either ionic groups, improvement is achieved in this way, one can like - SO ₃ H or precursor groups, which to assume that the chemical changes can be converted into _{65 - SO 3 H.} It is preferred when stepped. Nor is it essential that the branched precursors are unreactive when going into the detailed description of the groups. The last-mentioned reactants according to the invention can give the ionic groups, preferably an ionic

gpp,

Shape, e.g. B. - CF ₂ H, are convertible. These end groups are visible in the ultrared spectrum of the polymer, provided that the molecular weight of the polymer is not too high.

The end groups formed by the inventive reaction with fluorine radicals are unreactive end groups believed to be saturated fluorine

exchange capacity of at least 0.3 milliequivalents per gram of the polymer. The preferred ionic group is - SO ₃ H. Examples of monomeric units in ion exchange membranes derived from the sulfonyl fluoride-containing monomers include

IO

CF ₂
FC - SO ₃ H

20th

'CF ₂

FC - (OCF ₂ CFY) _n OCF ₂ CR ₇ SO ₃ H

where Y is F or CF ₃ , Rj is fluorine or perfluoroalkyl having 1 to 10 carbon atoms and η is an integer from 1 to 3, inclusive. Preferably the copolymer has from 0.5 to 50 mole percent 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.

Albeit ion exchange membranes of this special class of perfluorocarbon polymers a high stability against temperatures up to about 250 ° C as well as against acidic conditions at these Have temperatures, it has been found that after long-term use in the hydrogen-oxygen fuel cell Fluorine oxygen occurs in the water outflow from the fuel cell. The treatment this class of perfluorocarbon polymers improved by the process according to the invention also the stability of the polymers in this application.

With a detailed consideration of the process conditions, the inventive Processes are carried out by adding the fluorine radical generating compound and the fluorocarbon polymer bring them into intimate contact with each other at the elevated temperature required for formation the fluorine radical from the compound is required. ' The temperature at which the procedure is carried out therefore depends on the temperature at which this formation is used for the particular Fluorination compound enters and of the reaction rate, which is close to the decomposition is desired. In general the temperature will be between 20 and 300 ° C.

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

When the fluorine radical generating compound is gaseous, e.g. B. F ₂ or UF ₆ , the intimate contact with the fluorocarbon polymer can be obtained by holding the polymer in an atmosphere of the fluorine radical-forming compound for a time such that the fluorine radicals penetrate the solid polymer and the desired end group conversion result. To dilute the F ₂ , an inert gas, e.g. B. N ₂ , be present.

In the event that compounds which form fluorine radicals are present in the solid state under the reaction conditions, e.g. B. CoF ₃ and AgF ₂ , an 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 this liquid in contact with the Polymer brings. In general, the inert liquid will be one of the well known perfluorocarbon liquids, e.g. B. from hexafluoropropylene epoxide derived oils, 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, this can Perfluorocarbon polymers are guided in one direction and are in contact with it Compound that forms fluorine radicals can flow in countercurrent.

In the case of perfluorocarbon polymers, such as polytetrafluoroethylene and copolymers of Tetrafluoroethylene with hexafluoropropylene, the polymer is compared to the untreated Polymers whiter.

In the case of perfluorocarbon polymers having pendant ionic groups, when derived from copolymerization, the ionic groups are usually in the form of a precursor group which is stable to fluorination according to the invention. When the pendant ionic group is a hydroxy acid, the precursor group will generally have the formula - SO ₂ M, where M is the group F, amide 'or groups of the formula - OMe, where: Me is an alkali metal or quaternary ammonium! is. If M is the group F or amide, the! pendant group is converted to - SO ₃ H by first reacting with a strong base such as sodium hydroxide to form the corresponding salt and then reacting this salt with a strong inorganic acid such as hydrochloric acid, which has the hydroxy acid form ( - SO ₃ H) results, which is desired for the ion exchange polymer. When M is the group - OMe (defined above), the pendant group is converted to --SO ₃ H by reaction with a strong inorganic acid. When the pendant acid groups are in the acid fluoride (—SO ₂ F) form, the fluorocarbon polymer is readily melt processible; however, the hydroxy acid form is not so easy to process from a melt. For this reason it is generally

It is desirable to fluorinate perfluorocarbon polymers (according to the invention) in which the pendant groups are in the acid fluoride form (—SO ₂ F), then the resulting polymer with ¹ the fluorinated end groups and the pendant — SO ₂ F groups from the melt to process the desired form and finally to convert the latter product into the hydroxy acid form (- SO ₃ H).

The duration of the reaction will depend on such factors as the particular end groups being converted and their degree of conversion, and on the particular reaction conditions and reaction system employed. In general, the conversion is quantitative. However, there are application forms in which the degree of stabilization which is achieved by quantitative conversion is not required. Thus, 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 perfluorocarbon polymer is such that the unstable end groups are reasonably visible in the infrared spectrum, one can determine the degree of conversion by end group counting according to standard methods of ultrared 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 fluorocarbon polymers having pendant ionic groups, in which a pressing temperature of 240 ° C. is used. In the event that the molecular weight of the perfluorocarbon 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 keeping the samples at an elevated temperature close to decomposition subject, in which the gas evolution from the untreated sample appears to be greatest. The "peroxide test" mentioned in the following examples is carried out in the following way: A sample of 0.5 to 1.5 g of the perfluorocarbon polymer to be tested is ^{dried in a vacuum oven at 100 °} C. for 1 hour, weighed and then placed in a Test tube 25 χ 200 mm brought. 50 ml of 30% H ₂ O ₂ , which in dissolved form contains 0.0025 g of FeSO _{4 .7H 2} O, are added to the test tube. During a period of 1 hour, the test tube is heated to 85 ° C and kept at this temperature for 20 hours, after which it is cooled to room temperature, the liquid contents of the test tube are decanted and the inside of the test tube and the polymer contents are rinsed twice with 20 ecm portions of distilled water . The polymer is removed from the test tube, dried between filter paper and heat dried under the same conditions as the drying at the beginning of the test. The dried sample is then weighed, the weight loss being a measure of the end groups which have been attacked by the reaction of the polymer with the solution of peroxide / iron (II) ion. This procedure can be repeated to obtain the average weight loss per cycle.

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

Examples 1 to 11

In these examples the fluorocarbon polymer is a copolymer of tetrafluoroethylene with the monomer

FSO ₂ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCf = CF ₂

which has been copolymerized essentially according to the method of Example 8 of U.S. Patent 3,282,875 with the exception that the initiator is perfluoropropionyl peroxide, the polymerization temperature is 45 ° C and the solvent 1,2-trichloro-1,2 , 2-trifluoroethane is. Three products with different molecular weights are made. Polymer A has a melt flow of 342.5, Polymer B has a melt flow of 146.4, and Polymer C has a melt flow of 113.0. The melt flow is determined in grams of outflow in 10 minutes at 250 ^° C. using a 5000 g punch (9.42 mm diameter) which presses the mixed polymer through an outlet opening 2.095 mm in diameter and 8.00 mm in length. This method of melt flow measurement is used in the remaining examples below, with individual changes being made as indicated.

The fluorination process is as follows: Pro- ' ben the polymers A, B and C are placed in shaking tubes lined with nickel (capacity 320 ecm), which is then evacuated and purged three times with nitrogen, then evacuated a fourth time and with 0.35 atmospheres of fluorine gas are injected and heated under autogenous pressure for 2 hours. Then you cool Bring the tubes down to room temperature and vent the fluorine gas. The details of these experiments and the The results are compiled in Table I below. In Examples 1 to 5 and 9 to 11 the polymer was in the form of irregularly shaped granules with about 0.4 to 6.35 mm Diameter, used in Examples 6 to 8 in the form of a 0.127 mm thick film.

The results of the fluorination treatment can be seen by comparing the number of end groups by means of ultrared spectral analysis, which are determined on samples of the same, non-fluorinated polymers (Examples 1, 6 and 9); with the end group number of the fluorinated samples. In all cases the number of unstable end groups is greatly reduced. The indication "KF" in Table I means "none found". The limits of detectability with the ultrared apparatus used are assumed as follows: 5 end groups of carboxylate monomer or dimer and 10 vinyl end groups (each 10 ⁶ carbon atoms in the polymer). The improvement in the stability of the fluorinated polymers can be seen from the strong average reduction in weight loss per cycle in the peroxide test compared to the non-fluorinated controls. Weight loss results are based on 3 to 6 cycles per example.

Table I.

Poly
meres Loading of the
Shaking tube equivalent to
weight Fluorination conditions End groups per 10 ⁶ carbon atoms Monomer Carboxylates CF = CF ₂ Peroxide test
Weight loss at
game (G) ι 625 Dimer 255 (mg per cycle) A. _ 1210 no - 565 - 17th 1 A. 50 1230 100 ⁰ C - 2 hours - K. F. - ■ 2.0 2 A. 50 1230 150 ⁰ C - 2 hours - K. F. - 1.3 3 A. 50 1210 190 ° C - 2 hours - K.F. - 2.5 4th A. 25th 1195 -50 ° C - 2 hours + K. F. 1.7 5 100 ⁰ C - 2 hours + 150 ⁰ C - 2 hours 662 109! B. - 1335 no '. - 520 - ^: 16 6th B. 50 1360 100 ° C - 2 hours K.F. 3.3 7th B. 29 1275 , 50 ⁰ C - 2 hours + 8th 100 ° C - 2 hours + 37 K.F. 150 ° C - 2 hours 565 18th 171 6.0 C. - 1265 no - 550 - 21 9 C. 50 1300 190 ⁰ C - 2 hours 23 K. F. K.F. 1.5 10 C. 25th 1225 190 ° C - 2 hours 6th 1.5 11th

K.F. means »none detectable«.

example

A 320 ml shaking tube made of stainless steel is charged with 60 g of polymer A from Example 1 and 80 ml of perfluoro (2-butyl-tetrahydrofuran), which _{contains 30 g of CoF 3} dispersed therein, and the contents are heated at 200 ° C. for 3 hours and removes the cobalt residue from the polymer by washing with 10% HCl in ethanol. The washed polymer has an equivalent weight of 1500. The end group number for the polymer prior to fluorination is given in Table I (Example 1). After the fluorination according to the present example, no end groups can be found in the ultra-red spectrum of the polymer.

A sheet of the fluorinated polymer is pressed and hydrolyzed to convert the pendant - SO ₂ F groups to - SO ₃ H groups. The hydrolysis process is that the film strength 24 hours at 80 ± 1O ⁰ C in a 10% NaOH solution appeared. The film is then rinsed with water and _{bathed in three successive solutions of 10% H 2} SO ₄ at room temperature (3 hours per bath). The film is then washed with distilled water until the pH of the wash water exceeds 4.5 after standing for 1 hour.

The film is air-dried and then subjected to the peroxide test (7 cycles). Of the actual weight loss per cycle is 1 mg compared to 17 mg per cycle for the non-fluorinated Control sample.

Examples 13 to

Samples of tetrafluoroethylene / hexafluoropropylene (about 16% hexafluoropropylene) in the form of a fine powder are poured into a series of shaker tubes, followed by alternating evacuation and purging with N ₂ three times. The tubes are then evacuated again and pressurized with fluorine to 0.35 atmospheres at room temperature, followed by placing the tubes in a shaker, shaking and heating to the desired reaction temperature over a period of about 1 hour. "Details of the polymer charge, temperature and time of fluorination and the results are given in Table II.

The end group conversion results reported in Table II are obtained by end group counting obtained using the infrared spectrum of each of the polymer samples. The volatility index is a measure of the gas evolution from the polymer at a given temperature, which is the stability of the polymer reproduces. From Table II it can be seen that the volatility index is highest in Example 13 which is not fluorinated is said to progress well with increasing end group conversion decreases. The improvement in the color of the polymer is in the same direction, but not fluorinated polymers is off-white and the polymer with 100% converted end groups is the whitest is. The improvement in extrudability also follows the same trend, with the non-fluorinated polymer extruded as foam (the bubbles originate from the unstable end groups) and as the conversion of the end groups increases, the amount of Blisters diminished.

109 515/380

Table II

10

Polymer
feed temperature F ₂ -
pressure Trial time End groups
conversion Melt viscosity 15 minutes. χ 1 (T ⁴ Volatility
index at
game (G) Γ C) (atü) (Hours.) (%) (Poise at 360 ^c 5.5 C) _ no _ 5 min. 8.5 30 min. 95 to 100 13th 100 150 1.05 2 30th 4.7 7.8 5.6 68 14th 100 200 1.4 3 75 7.3 5.2 9.0 53 15th 100 250 1.4 2 100 7.5 7.5 7.8 28 16 150 225 1.4 2 75 5.1 9.4 5.0 34 17th 150 225 1.4 2 100 6.9 7.2 - 18th 9.3 7.2

Example 16 is repeated enough times to collect about 600 g of fluorinated polymer which is extruded through a 2.54 cm extruder and cut into press cubes, which are then cut into three Samples are divided. The melt viscosity stability of the extruded cubes remains unchanged from the initial determination immediately after extrusion, after 8 days and after 17 days. These Melt viscosity uniformity over time indicates the shelf life of the agent the polymer obtained by the fluorination treatment.

Examples 19 to

In this experiment a series of solid layers of 20 g each of the copolymer powder of Examples 13-18 are prepared, each heated to the desired temperature by flowing N ₂ through the bed, whereupon mixtures of F ₂ and N ₂ flow through the bed be left. Further, each bed is heated by a mantle heater to 240 to 250 ⁰ C. The temperatures of the F ₂ / N ₂ gas mixture, the duration of the test and the results of these tests are given in Table III. The percent conversion of the end groups in each of these runs is 100%.

Table III

temperature Viol percent F ₂ in N ₂ Time Melt viscosity χ 10 * 5 min. 10 min. 15 minutes. Volatility index example (° C) (Min.) (Poise at 360 ⁰ C) 3.2 3.7 3.6 200 to 250 20th 16 3.6 3.6 3.5 40 19th 195 to 210 20th 5 5.6 6.0 6.2 45 20th 183 4th 37 6.9 6.5 6.4 37 21 192 to 197 4th 15th 5.6 5.9 5.6 48 22nd 204 to 213 : 4 5 6.9 7.1 6.9 50 23 212 to 215 4th 18th 7.6. 7.6 7.6 39 24 _; 200 to 205 8th 20th 39 25th

Example 26

A copolymer of tetrafluoroethylene / perfluoro (pf opylvinylether) / trifluorovinylsulfonyl fluoride is prepared in the following way: 163 g of trifluorovinylsulfonyl fluoride and 24 g of perfluoro (propyl vinyl ether) are added to a 250 ml flask containing about 20 g of MgO, and the resulting mixture is vacuum iri a 300 cc sive polymerization vessel with dicken'Wänden distilled, the ECM 1 perfluoropropionyl peroxide is added (molar 3 x 10 ~ ⁴⁾ in 1,1,2-trichloro-1,2,2-trifluoroethane. The air is removed by cooling the contents and evacuating the vessel, followed by warming the evacuated vessel to room temperature and then adding small amounts of tetrafluoroethylene while the temperature of the vessel is increased to 45 ° C. The tetrafluoroethylene pressure is increased to 2.8 atmospheres and maintained at this pressure for 5 hours, the pressure is then allowed to drop to 1.9 atmospheres, the vessel is then cooled to -78 ° C. and the unreacted tetrafluoroethylene is pumped off. The vessel is warmed to room temperature and the volatile contents are distilled off, leaving 179 g of residue, which is washed with about 200 ml of 1,1,2-trichloro-1,2,2-trifluoroethane, filtered and heated at 150 ° C. for 2 hours Vacuum dried to obtain 15.0 g of the copolymer which, as seen from the ultra-red spectrum of the copolymer, contains units of each of the monomers present. The copolymer has 6.2% trifluorovinylsulfonyl fluoride, an equivalent weight of about 1700 and 153 end groups in the form of carboxy dimers and 475 vinyl end groups per 10 ⁶ carbon atoms.

The copolymer is fluorinated according to the procedure of Example 3, except that the polymer feed 7.7 g instead of 50 g. After the elution, the equivalent appears

unchanged in weight, and no end groups are found in the ultra-red spectrum of the copolymer.

Example 27

The copolymer of Example 9 is converted to the sodium carboxylate-sulfonyl fluoride form by heating 50 g of it together with 15 g of NaOAc.H ₂ O and 200 ml of glacial acetic acid to reflux conditions in a flask with stirring overnight. The copolymer 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 or 131 carboxyl end groups, monomeric or dimeric, and 99 vinyl end groups, all of which are 10 ⁶ carbon atoms.

Then the copolymer is fluorinated according to the procedure of Example 3 with the exception that the polymer charge is 25 g. After fluorination, des Copolymer no end groups found.

Example 28

A copolymer of tetrafluoroethylene / perfluoro (propyl vinyl ether) is prepared by adding 4200 ml of H ₂ O, 6 g of ammonium persulfate, 15 g of ammonium carbonate, 220 g of paraffin and 10 g of ammonium perfluorooctanate to a polymerization vessel, and then adding methane to the vessel to 1.76 atm imprints, followed by pressing with tetrafluoroethylene up to 19.3 atm follows at 7O ⁰ C for 92 minutes, which is accompanied by a movement of the vessel with 125 rpm. The recovered from the polymerization vessel, washed copolymer contains 1.7% perfluoro (propylvinyläther) and has a melt viscosity of 33.5 x 10 ⁴ poise at 38O ⁰ C. In the infrared spectrum of the copolymer are amide end groups, the only detectable end groups, and it is estimated that about 140 of these are present for every 10 ⁶ carbon atoms.

If one follows the fluorination of Example 3 except that a Beschikkung of 100 g, a temperature of 25O ⁰ C and an F ₂ pressure be applied atm of 2.53, 21 end groups are determined by means of Ultrarotanalyse.

B e i s ρ i e 1 29

A commercial granular polytetrafluoroethylene polymer (average particle size 20 microns) is fluorinated in a shaker tube at 25O ⁰ C for half an hour, using a mixture of 8 Molprozerit F ₂ in N _2. The fluorinated polymer is pressed at 210.9 kg / cm ² compression pressure to a slice, sintered for 2 hours at 420 ⁰ C and cooled at a rate of l, 07 ° C / minute to 270 ° C. The internal specific gravity as measured by ultra-red analysis of the polymer in the disc is 2.2258 g / cm ³ . The internal specific gravity of the control polymer after the identical treatment with the exception of the fluorination is 2.2333. The lower specific gravity of the fluorinated polymer, which indicates a higher molecular weight, indicates its improved stability compared to the control polymer.

The mixture is heated depending 1.46 g of the granular, fluorinated tetrafluoroethylene polymers and the same amount of the same polymer but not fluorinated (control) for half an hour under a vacuum of 10 ^"5 mm Hg at 410 ⁰ C to determine how much gas The control polymer emits about 2Y ₂ times the amount of gas compared to the fluorinated polymer and thus shows the greater stability of the fluorinated polymer and a conversion of about 60% of the unstable groups.

B e i s ρ i e 1 30

If the procedure of Example 29 is followed with the exception that no ammonium buffer is used, a copolymer of tetrafluoroethylene / perfluoro (propyl vinyl ether) results with a melt viscosity of 122 · 10 ^ ⁴ poise at 360 ⁰ C, 2.2% of Units derived from vinyl monomers and 117 carboxyl end groups per 10 ⁶ carbon atoms.

The copolymer is fluorinated according to the procedure of Example 3 with the exception that the Polymer charge is 25 g. The copolymer obtained has 13 carboxyl end groups.

Claims (2)

Patent claims: 1. Process for stabilizing high molecular weight perfluoropolymers, except of the end groups only carbon atoms in the polymer chain and optionally ether oxygen atoms contained in side chains, through chemical modification of the unstable end groups, characterized in that the polymers are in intimate contact in solid form with fluorine radicals. 2. The method according to claim 1, characterized in that the high molecular weight perfluoropolymer used in the form of an ion exchange membrane.