HYBRID ELASTOMERIC MATERIAL

Abstract

An elastomeric material is disclosed, which is suitable, in particular, as a sealing material between the fuel cells of a fuel cell stack and the stacks as such, wherein the hybrid elastomeric material includes a hybrid elastomer with a proportion of a siloxane polymeric material and a proportion of a polyolefin elastomeric material, wherein the two materials are crosslinked with one another by addition. Further aspects relate to polyelectrolyte fuel cells, which include sealing elements made of the hybrid elastomeric material, as well as the use of the hybrid elastomeric material in a screen printing process.

Claims

1. A hybrid elastomeric material, in particular for use as a sealing material in fuel cells, wherein the hybrid elastomeric material comprises a hybrid elastomer with a proportion of a siloxane polymeric material and a proportion of a polyolefin elastomeric material, wherein the two materials are crosslinked with one another by addition.

2. The hybrid elastomeric material in accordance with claim 1, wherein the siloxane polymeric material has one or more polysiloxanes with pendant groups and/or terminal groups, which are selected from H, C.sub.1-C.sub.30 alkyl groups, C.sub.2-C.sub.30 alkenyl groups, and aryl groups.

3. The hybrid elastomeric material in accordance with claim 2, wherein the siloxane polymeric material comprises one or more modified dimethyl siloxanes, wherein the methyl groups are partially substituted by hydrogen with the formation of SiH groups and vinyl groups.

4. The hybrid elastomeric material in accordance with claim 1, wherein the siloxane polymeric material comprises a siloxane polymer of formula (I) ##STR00007## wherein the radicals R independent of one another mean H, CH.sub.3, vinyl, phenyl, (CH.sub.2).sub.xCH.sub.3, and/or C.sub.3H.sub.6O(C.sub.2H.sub.4O).sub.y(C.sub.3H.sub.5O).sub.zR′; wherein m=1 to about 100, n=0 to 1000, x=1 to 30, y=0 to 20, z=0 to 30, and wherein the sum of m+n≥3 and R′ mean H, CH.sub.3, or (CH.sub.2).sub.xCH.sub.3; and comprises a siloxane of formula ##STR00008## (II) wherein the radicals R.sup.1 independent of one another each mean CH.sub.3, vinyl, and phenyl and n.sup.1 has a value in the range of 0 to 3000.

5. The hybrid elastomeric material in accordance with claim 1, wherein the hybrid elastomeric material is cross-linked by addition using a siloxane crosslinker.

6. The hybrid elastomeric material in accordance with claim 5, wherein the siloxane crosslinker is selected from crosslinkers of formula (III) ##STR00009## wherein the radicals R.sup.2 independent of one another represent H and CH.sub.3 and wherein the value for m.sup.2 is in the range of 1 to about 100 and the value for n.sup.2 is in the range of 0 to about 500; wherein preferably three or more SiH groups per siloxane molecule are present.

7. The hybrid elastomeric material in accordance with claim 3, wherein the ratio of the proportions of SiH groups to vinyl groups in the siloxane polymer of formula (I) and in the siloxanes of formulas (II) and (III) considered in the totality is in the range of about 1:0.5 to about 1:4.5, in particular in the range of about 1:1.5 to about 1:2.5.

8. The hybrid elastomeric material in accordance with claim 1, wherein the polyolefin elastomeric material is selected from 1,2-polybutadiene, 1,4-polybutadiene, block copolymers of 1,2-polybutadiene and 1,4-polybutadiene, hydrated polybutadiene, acrylonitrile rubber, hydrated acrylonitrile rubber, epoxidized liquid polybutadiene, (poly)norbornenes with terminal and/or pendant vinyl groups, silane compounds with terminal vinyl groups, vinyl functional alkoxysilanes and styrene-butadiene rubber.

9. The hybrid elastomeric material in accordance with claim 1, wherein the polyolefin elastomeric material has functional groups as shielding groups, which are selected from linear and branched C.sub.2-C.sub.5 alkyl and alkenyl groups.

10. The hybrid elastomeric material in accordance with claim 9, wherein the polyolefin elastomeric material has a proportion of shielding groups of about 40% by weight to about 92% by weight, wherein the shielding groups are selected, in particular, from vinyl, alkyl, 2,3-butylene, and mixtures thereof.

11. The hybrid elastomeric material in accordance with claim 1, wherein the proportion of siloxanes in the polymer portion of the hybrid elastomeric material is about 70% by weight to about 99% by weight, wherein, in particular, the sum of the proportions of the siloxane polymer of formula (I) and the siloxane of formula (II) is about 50% by weight to about 90% by weight, preferably about 60% by weight to about 70% by weight.

12. The hybrid elastomeric material in accordance with claim 1, wherein the proportion of the polyolefin elastomeric material in the polymer portion of the hybrid elastomeric material is about 1% by weight to about 50% by weight, in particular about 1% by weight to about 30% by weight.

13. The hybrid elastomeric material in accordance with claim 1, wherein the hybrid elastomeric material comprises one or more fillers, wherein the proportion of the fillers in the hybrid elastomeric material is about 5% by weight to about 50% by weight, in particular about 15% by weight to about 30% by weight.

14. The hybrid elastomeric material in accordance with claim 13, wherein the filler or fillers is/are selected from silica-based, silicone resin-based, and titanate-based fillers.

15. The hybrid elastomeric material in accordance with claim 1, wherein the siloxane polymeric material that can be crosslinked by addition and the polyolefin elastomeric material are catalytically crosslinked by addition.

16. A method for producing a hybrid elastomeric material in accordance with claim 1, comprising the steps providing a reaction mixture comprising a proportion of a siloxane polymeric material and a proportion of a polyolefin elastomeric material; and crosslinking the two materials by addition.

17. The method in accordance with claim 16, wherein the reaction mixture is produced from a component A and a component B, wherein the component A comprises a proportion of a first polysiloxane material, a proportion of a polyolefin elastomeric material, and a catalyst for the crosslinking by addition, and wherein the component B comprises a proportion of the first polysiloxane material and a proportion of a second siloxane material that is different from the first polysiloxane material, wherein the first polysiloxane material comprises a vinyl polysiloxane with terminal vinyl groups and the second siloxane material comprises a siloxane with pendant and/or terminal SiH groups.

18. The method in accordance with claim 16, wherein the reaction mixture comprises a filler, in particular in the form of a hydrophobized and/or hydrophilic mineral filler.

19. The method in accordance with claim 18, wherein the filler is provided in a masterbatch and the masterbatch is added to the reaction mixture, preferably as part of the component A and/or the component B.

20. The method in accordance with claim 17, wherein the component B comprises a proportion of a retarder.

21. A polymer electrolyte fuel cell stack with a plurality of fuel cells, wherein the stack comprises sealing elements, which are produced using a hybrid elastomeric material in accordance with claim 1.

22. A use of a hybrid elastomeric material in accordance with claim 1 in a screen printing process, in particular for applying the hybrid elastomer as a sealant to a substrate.

23. The use in accordance with claim 22, wherein the hybrid elastomeric material is applied to the substrate in a layer thickness of about 10 μm to about 500 μm, in particular about 10 μm to about 100 μm.

24. The use in accordance with claim 22, wherein the hybrid elastomeric material comprises a filler forming a closed-cell pore structure, the content of which is, in particular, about 0.5% by weight to about 4% by weight relative to the total weight of the hybrid elastomeric material.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0185] FIG. 1 shows the progression of a static long-term sealing force of conventional elastomeric materials and hybrid elastomeric materials in accordance with the invention after oxidative hot air degradation under the influence of the proportion of polyolefin protecting groups;

[0186] FIGS. 2A to 2C show depolymerization effects on conventional elastomeric materials and hybrid elastomeric materials in accordance with the invention after storage in sulfonic acid on the basis of electron microscope images;

[0187] FIGS. 3A to 3C show depolymerization effects on conventional elastomeric materials and hybrid elastomeric materials in accordance with the invention after storage in an FKM ionomer dispersion on the basis electron microscope images;

[0188] FIG. 4 shows schematically the influence of the 1,2-polybutadiene content of polymeric materials on the hydrogen permeation coefficient P; and

[0189] FIG. 5A to 5D show electron microscope images of a conventional elastomeric material and different hybrid elastomeric materials in accordance with the invention and after storage in an FKM ionomer dispersion.

DETAILED DESCRIPTION OF THE FIGURES

[0190] General Experimental Procedure for Determining the Properties of Conventional Elastomers and Hybrid Elastomeric Materials in Accordance with the Invention

[0191] In order to test the application-specific properties of the elastomers obtainable from Examples 1 to 9, plates crosslinked using the respective components A and B are made as test pieces, as described in the following.

[0192] For this purpose, the two respective components A and B are brought together in a ratio of 1:1 in a vacuum speedmixer (U. Hauschild) under vacuum (about 100 mbar) at room temperature during a mixing time of about 2 minutes and then poured into the molds for the production of plates (2 mm thickness) and are vulcanized (1 h/150° C.).

[0193] The chemical crosslinking reaction during the production of the hybrid elastomeric materials in accordance with the invention begins directly after mixing components A and B, and the exposure to temperatures (20° C. to 200° C.). Both components A and B are each set to a similar viscosity level for better mixability.

[0194] Test pieces corresponding to the respective norms are produced from these plates for determining: [0195] DIN 53505−Shore A hardness [0196] DIN 53504S2−Tensile testing−tear resistance and elongation at break [0197] DIN ISO 34-1, Method B, Test (a)+(b) tear resistance [0198] ISO 188, DIN ISO 1817 Chemical resistance [0199] Rheological properties (curemeter test), 150° C. to 180° C., 3 min. [0200] ISO 815−Compression set test

[0201] The results are summarized in the following Tables 5 to 12 and depicted in part in FIGS. 1 to 5.

Influence of the Polyolefin Proportion on the Kinetics of the Crosslinking Reaction and on the Mechanical Properties of the Hybrid Elastomeric Materials in Accordance with the Invention

[0202] Commencing from Example 1 (BF109), the influence of different concentrations of 1,2-polybutadiene in the total formulation on the kinetics of the chemical crosslinking reaction and the obtained initial mechanical values was tested. Furthermore, the viscoelastic behavior of the obtained test pieces in the compression set test is described. The material of Test Piece 4 corresponds to Example 1 (BF109). The materials of Test Pieces 1 and 2 correspond to Examples 8 and 7, respectively. The materials of Test Pieces 3 and 5 correspond to Examples 6 and 5, respectively.

[0203] The t10 value specified in Table 5 corresponds to the time in which a relative crosslinking conversion of 10% takes place at 180° C., the t90 value represents the time in which a relative crosslinking conversion of 90% is achieved. The same applies to the t50 and t80 values. The values are determined by means of so-called crosslink isotherms. They are measured on a curemeter by the torque over the measuring time indicating the increase in the internal crosslink density in the elastomeric material. A lower heated chamber half oscillates about a deflection angle, an upper heated rigid chamber half detecting the torque required therefor. Device manufacturer: GÖTTFERT Werkstoff-Prufmaschinen GmbH, MonTech Werkstoffprüfmaschinen GmbH.

[0204] The minimum describes the uncrosslinked state, while the maximum corresponds to the completely crosslinked state. The different between minimum and maximum represents the relative crosslink density.

[0205] Unlike in a pure LSR material, a reaction retarder is not absolutely necessary in the hybrid material systems in accordance with the invention, and therefore is often 0 ppm, such that the reaction kinetics can be increased.

[0206] The stress moduli obtained from the tensile testing according to DIN 53504 S2 describe the static stiffness of the crosslinked hybrid elastomeric material in accordance with the invention and correspond to the E-modulus.

[0207] The characterization of the different test pieces and the data obtained in the tests are summarized in Table 5.

TABLE-US-00027 TABLE 5 Constituents Test Piece 1 2 3 4 5 ALPA 130201 [% by weight] 100 100 100 100 100 1,2-polybutadiene [% by weight] 20 10 5 2 1 Crosslinker [% by weight] 9 9 9 9 9 Pt(0) catalyst (ppm] 28 28 28 28 28 Crosslinking characteristics at 180° C. Minimum [Nm] 0.00 0.00 0.01 0.04 0.09 Maximum [Nm] 0.91 1.36 1.86 2.33 2.17 t10 [min] 0.15 0.11 0.09 0.07 0.05 t50 [min] 0.37 0.30 0.25 0.16 0.11 t80 [min] 1.18 1.09 1.00 0.37 0.22 t90 [min] 1.53 1.45 1.35 1.09 0.40 Initial values at 23° C. (chemically crosslinked) Hardness Shore A 43.0 49.8 55.4 57.8 50.0 (DIN53505) Tensile testing (DIN53504 S2) Stress modulus [MPa] 0.60 0.70 0.90 0.90 0.70 M25% Stress modulus [MPa] 1.11 1.41 1.79 1.95 1.26 M50% Stress modulus [MPa] 2.20 2.90 3.60 3.90 2.50 M100% Stress modulus [MPa] 3.56 4.63 5.62 6.13 4.70 M200% Tear resistance [MPa] 4.40 5.60 6.60 7.00 6.80 Elongation at break [%] 289 286 264 277 316 Compression set testing (ISO 815) Compression set [%] 38.5 30 32 28 34 24 h/150° C./hot air/demolded in the cold state

[0208] Hybrid elastomers become increasingly slowly reactive with increasing degree of grafting, e.g. with 1,2-polybutadiene, as can be seen in the comparison of the crosslinking characteristics of the different test pieces in Table 5.

[0209] High catalyst and crosslinker concentrations can compensate to a certain degree for such kinetic losses that occur with increasing degree of grafting on 1,2-polybutadiene.

Technical Properties of Hybrid Elastomeric Materials in Accordance with the Invention

[0210] Too low or too high concentrations of shielding groups in the hybrid elastomers in accordance with the invention are qualitatively not beneficial, as already mentioned. Grafted shielding groups should hinder fission and back reactions in aqueous media.

[0211] An increasing degree of grafting on 1,2-polybutadiene units, i.e. greater than about 2% by weight at molecular weights of 3000 g/mol leads to an increasingly significant drop in the tear resistance compared to the pure standard LSR materials that can be crosslinked by addition (backbone), as can be seen in FIG. 7 at equal concentration of the crosslinking chemicals.

[0212] Moreover, the static long-term sealing force behavior is significantly deteriorated with an increasing proportion of 1,2-polybutadiene, specifically after aerobic and anaerobic hot air degradation. This effect restricts the use of the hybrid elastomers in accordance with the invention to temperatures under 120° C.

[0213] FIG. 1 shows the long-term sealing force behavior of different conventional elastomeric materials and hybrid elastomeric materials in accordance with the invention after oxidative hot air degradation at 120° C., the decrease in static sealing force in % being graphed against the storage time in hours. Serving as a comparison to the hybrid elastomeric materials in accordance with the invention based on the formulations of Example 1 (BF109) (2% by weight 1,2-PB B-3000), Example 7 (10% by weight 1,2-PB B-3000), and Example 8 (20% by weight 1,2-PB B-3000) are, for one, an LSR standard material from Example 4 (ALPA 130201;) without organic protecting groups and, on the other hand, the Keltan 2650 polyolefin material referred to by ENB-EPDM (ARLANXEO Netherlands B.V.). The sealing force testing took place according to DIN EN ISO 1183-1, Procedure A.

[0214] FIG. 1 shows the influence of an increasing proportion of polyolefin groups in the hybrid elastomeric material in accordance with the invention on the progression of the static sealing force in the long-term test after oxidative hot air degradation at 120° C. using test pieces of Examples 1, 7, and 8 in accordance with the invention, as well as conventional LSR and EPDM materials, Example 4 (LSR standard ALPA 130201) or Keltan 2650 (ARLANXEO Netherlands B.V.).

[0215] Too high a residual portion of reactive SiH groups or vinyl groups not consumed in the crosslinking by addition that are still present in the hybrid elastomer in accordance with the invention negatively affects the chemical aging behavior and the chemical long-term stability. This has an effect on the siloxane network due to an increased number of fission or back reactions.

[0216] The chemical resistance of the modified hybrid elastomers against so-called pitting is of decisive importance, meaning the aging resistance against polymer degradation and fission reactions due to aggressive acids and with increasing acid concentrations.

[0217] An important example is sulfonic acid, which in PEM-FC fuel cells can be created on the membrane by fission reactions of sulfonic groups and then is present in aqueously diluted form. Due to its particular properties, sulfonic acid is used as an equilibration catalyst in the synthesis of LSR polymers and causes ring opening reactions there.

[0218] Alkyl benzene sulfonic acid is a suitable testing medium with which the damage pattern of the polymer pitting or so-called silicification on the standard LSR material can be recreated very authentically, even if these structures do not typically occur in the fuel cell.

[0219] The contact of the standard LSR material with the smallest concentrations of aqueously diluted alkyl benzene sulfonic acid leads to pronounced polymer degradation in the shortest contact times of 72 h and 144 h, as can be seed in Table 5 for storage temperatures of 75° C.

[0220] The electron microscope images in FIGS. 2A to 2C illustrate on the basis of the damage patterns the differences in chemical resistance between a standard LSR material and the hybrid elastomeric materials in accordance with the invention of Examples 1 and 2 (BF109 and BF131) in accordance with the invention in addition to the test results summarized in Table 6.

TABLE-US-00028 TABLE 6 Storage in alkyl benzene sulfonic acid (acid group concentration 0.091 mol/l) at 75° C. Reference Example 4 (LSR standard ALPA 130201) Example 1 BF109 Example 2 BF131 Test parameter/test piece Base Base Base Storage temperature [° C.] 75 75 75 75 75 75 Storage duration [h] 72 144 72 144 72 144 pH value 2 2 2 2 2 2 Hardness [Shore A] 41.3 39.3 35.3 58.8 55.8 54.8 53.0 53.8 54.6 Change in hardness [Shore −2.0 −6.0 −3.0 −4.0 +0.8 +1.6 A] Tear resistance [MPa] 4.90 2.20 1.32 6.50 4.40 3.59 5.90 3.39 2.25 Change in the tear −55.1 −73.1 −32.3 −54.8 −42.5 −61.9 resistance [%] Elongation at break [%] 296 162.5 79.6 194 263 185.2 135.4 Change in the elongation at −35.6 −62.3 +1.4 −23.8 −29.6 −48.5 break [%] Volume change [%] +0.25 +3.5 +0.8 +1.2 +0.4 +2.4 Electron microscope image FIG. FIG. FIG. 2A 2B 2C

TABLE-US-00029 TABLE 7 Storage in aqueously diluted FKM ionomer dispersion 3M980EW (acid group concentration: 0.091 mol/l) Reference Example 4 (LSR standard ALPA 130201 Example 1 BF109 Example 2 BF131 Test parameter/test piece Base Base Base Storage temperature [° C.] 75 75 75 75 75 75 Storage duration [h] 72 336 72 336 72 336 pH value 2 2 2 2 2 2 Hardness [Shore A] 41.3 42.4 44.0 58.8 58.4 58.5 53.0 53.5 54.1 Change in hardness [Shore A] +1.1 +2.7 −0.4 −0.3 +0.5 +1.1 Tear resistance [MPa] 4.90 2.01 0.93 6.50 6.00 5.70 5.90 4.00 3.60 Change in the tear resistance −59.0 −81.1 −7.7 −12.3 − 32.2 −39.0 [%] Elongation at break [%] 296 154.2 95.6 194 182 191 263 190 145 Change in the elongation at −47.9 −67.7 −6.2 −1.5 −27.8 −44.9 break [%] Volume change [%] +1.9 +3.7 +0.12 ±0 +1.3 +2.5 Weight change [%] +1.1 +2.8 +0.15 ±0 +0.7 +2.0 Electron microscope image FIG. FIG. FIG. 3A 3B 3C
The base values specified in the Table correspond to the values measured on the not yet stored test pieces.

[0221] A further test with FKM ionomer dispersions, which represents the starting product for the coating of a fuel cell membrane, was performed on test pieces of Examples 1 and 2 as well as with the LSR reference material. The results are summarized in Table 7 and visualized in the electron microscope images of FIGS. 3A to 3C.

[0222] The coatings produced from the dispersions are necessary for proton transport in the electrochemical processes in a fuel cell. The FKM ionomer dispersions are composed of polytetrafluoroethylene and perfluorosulfonyvinylether, the latter forming PFSA (PerFluoroSulfonic Acid) in an aqueous medium. These are available from various manufacturers such as, e.g., Dow Chemicals, Du Pont, and Solvay.

[0223] The test pieces were stored in the product 3M980EW (manufacturer: 3M) with an acid group concentration of 0.091 mol/l, also at 75° C., 72 h and 336 h. The advantage of the hybrid elastomers in accordance with the invention compared to a standard LSR material becomes particularly clear in this real test medium with regard to the chemical resistance, because it produces the unfavorable, i.e. chemically aggressive conditions due to its high concentration of PFSA. While pure LSR (reference ALPA 130201, Example 4) severely degrades under these conditions (cf. FIG. 3A), the hybrid elastomeric materials in accordance with the invention, especially according to Example 1 (BF109), show an excellent media resistance (Table 7 and FIGS. 2A and 2B).

[0224] The hybrid elastomeric material in accordance with the invention according to Example 1 (BF109), followed by Example 2 (BF131), shows significantly better chemical resistance in the test media (Table 6 and Table 7) than conventional LSR materials. This is the main advantage of the hybrid elastomers in accordance with the invention.

[0225] The effect of the degree of grafting of organic shielding groups on the gas permeation resistance P is finally depicted schematically in FIG. 4.

[0226] For standard LSR, typically a so-called P-value for hydrogen permeation in the dimension [cm.sup.3(NTP).Math.mm/(m.sup.2.Math.h bar] of 810 P is obtained at 20° C. and 0% relative humidity, while EPDM materials (ethylene-propylene-diene-rubber; here as an equivalent for 100% by weight 1,2-polybutadiene) typically have P-values of 56 P. Compared to the standard LSR, the hybrid elastomers in accordance with the invention have significantly reduced P values, as is illustrated schematically in FIG. 4 as a function of the 1,2-polybutadiene content.

[0227] The test results of the hybrid elastomeric material obtained in Example 9 after storage at 75° C. for 1000 h in an aqueous FKM ionomer dispersion with an acid group proportion of c=0.091 mol/1 (pH=1.5 to 2; available as 3M980EW from 3M) are summarized in Table 8 in comparison with further corresponding test values of the materials of Examples 1 and 8 as well as a material from the prior art (ShinEtsu X34-4269). Electron microscope images of these materials after storage are shown in FIGS. 5A to 5D.

TABLE-US-00030 TABLE 8 ShinEtsu Example 1 Example 8 Example 9 Test parameter/test piece X34-4269 BF 109 BF 290 BF 307 Hardness [Shore A] 39.39 44.1 48.1 36.0 Hardness change [Shore A] −0.7 −0.1 +2.7 −1.2 Elongation at break [%] 117 390 290 155 Change in the elongation at break [%] −54.5 +14.3 −3.7 −8.7 Tear resistance [MPa] 1.17 5.8 4.1 2.5 Change in the tear resistance [%] −74.0 +1.8 −8.5 −11.5 Volume change [%] −1.6 −0.43 −0.11 +0.21 Weight change [%] after redrying −13.7 −0.67 −0.41 −0.30 for 24h at 100° C. Electron microscope image FIG. 5A FIG. 5B FIG. 5C FIG. 5D

[0228] The compression set determined in the case of the materials of Example 9 (BF307) was 23.5% after hot air degradation (24 h/150° C./demolded in the cold state). The degree of compression was 25%.

[0229] The hybrid elastomeric materials according to Example 9 in accordance with the invention show a significantly improved chemical resistance against an aqueously diluted FKM ionomer dispersion compared to the conventional ShinEtsu X34-4269 material (available from SHIN-ETSU SILICONES EUROPE B.V.) and also compared to the hybrid elastomer BF 109 obtained in accordance with the invention in Example 1.

[0230] Furthermore, a significantly improved extraction resistance can be observed in the hybrid elastomeric material obtained in Example 9 (cf. Table 12 below).

[0231] Further test results for hybrid elastomeric materials in accordance with the invention from Examples 1, 1A, 1B, 1C, and 1D are summarized in the following Table 9.

TABLE-US-00031 TABLE 9 Test parameter/test piece Example 1A Example 1B Example 1C Example 1D Example 1 Hardness [Shore A] 55.6 53.8 57.6 57.0 53.7 Density [g/cm.sup.3] 1.103 0.864 1.066 1.090 1.127 Stress modulus M25% [MPa] 1.00 1.00 0.90 1.00 0.90 Stress modulus M50% [MPa] 1.77 1.72 1.73 1.92 1.63 Stress modulus M100% [MPa] 3.20 2.40 3.10 3.10 3.00 Stress modulus M200% [MPa] 4.92 3.22 — — 4.78 Tear resistance [MPa] 5.30 3.70 4.40 4.40 6.58 Elongation at break [%] 229 253 189 179 291 Compression set *.sup.) [%] 73 82 52 — 14 *.sup.) The compression set values in Table 9 were measured on test pieces after demolding in the cold state, which were previously exposed to hot air of 150° C. for 24 h at a degree of compression of 25%.

[0232] In the following Table 10, mechanical parameters of the hybrid elastomeric materials in accordance with the invention that can be achieved in accordance with the invention are compared with the values of a conventional LSR material, which is available under the trade name ShinEtsu X34-4269 from SHIN-ETSU SILICONES EUROPE B.V. Significant differences emerge, in particular, in the chemical resistance against aqueous FKM ionomer dispersions (here: 3M725EW) with an acid group content of c=0.091 Mol/l. The storage time was therefore shortened for the reference material from 1000 h to 336 h.

TABLE-US-00032 TABLE 10 ShinEtsu Parameter/test piece Example 1E Example 1F Example 8A X34-4269 Storage temperature [° C.] 75 75 75 75 Storage duration [h] 1000 1000 1000 336 Acid concentration [mol/1] 0.091 0.091 0.091 0.091 Hardness change [ Shore A] +6.5 +0.2 +0.1 +2.7 Tear resistance [Mpa] after storage 5.60 5.80 3.50 0.80 Change in tear resistance [%] +1.4 +1.8 +2.9 −85.2 Elongation at break [%] 277 390 138 92 Change in elongation at break [%] −13.9 +14.3 +/−0 −68.4 Volume change [%] −0.3 −0.4 +3.5 +4.4 Weight change [%] −0.1 −0.2 +3.6 +4.1

[0233] Test results for hybrid elastomeric materials in accordance with the invention from Examples 1 (BF 109), 8 (BF 290), and 9 (BF 307) are summarized in the following Table 11.

TABLE-US-00033 TABLE 11 Example 1 Example 8 Example 9 Test parameter/test piece BF109 BF290 BF307 Hardness [Shore A] 44.0 45.4 37.2 Stress modulus M25% [MPa] 0.90 1.00 0.90 Stress modulus M50% [MPa] 1.63 1.62 1.22 Stress modulus M100% [MPa] 3.00 3.00 1.90 Stress modulus M200% [MPa] 4.78 — — Tear resistance [MPa] 6.58 4.50 2.90 Elongation at break [%] 291 160 170 Compression set [%] *.sup.) 14 20 27 *.sup.) The compression set values in Table 11 were measured on test pieces after demolding in the cold state, which were exposed to hot air of 150° C. for 24 h at a degree of compression of 25%.

[0234] In addition, a better gas permeation resistance can be observed at higher polybutadiene contents, in particular at polybutadiene contents of 30% to 40% by weight in the total formulation.

[0235] A further important property of elastomeric sealing materials, in particular of hybrid elastomers in accordance with the invention, is their extraction resistance, which counteracts so-called pitting or so-called silicification. Weight loss of the sealing materials is often associated with the washing away of particles, which can block or clog the electrochemically active proton exchange membranes in fuel cells. This leads to irreversible performance losses in fuel cells.

[0236] The property of extraction resistance can be easily tested using the weight loss after storage in the FKM ionomer dispersion specified above. The weight losses of five different hybrid elastomers in accordance with the invention at different storage times are summarized in the following Table 12. The weight losses in % by weight were determined after the previously stored test pieces were redried for 25 h at 80° C. For comparison, two test pieces of conventional materials, namely LSR ShinEtsu X34-4269 (available from SHIN ETSU SILICONES EUROPE B.V.) and addition-crosslinking liquid fluorosilicone DOW Silastic FL30-9201 (available from Dow Chemicals Company) were added to the Table.

TABLE-US-00034 TABLE 12 Test piece/storage time 500 h 1000 h 1500 h 2400 h Example 1E (BF 109B) −0.50 −0.67 −1.12 −1.27 Example 8 (BF290) −0.38 −0.41 −0.40 −0.52 Example 9 (BF 307) −0.02 −0.30 — — ShinEtsu X34-4269 −12.00 13.70 18.70 25.01 DOW Silastic FL30-9201 −2.32 −2.36 −2.41 −2.55

[0237] The data in Table 12 show that the extraction resistance is improved with increasing polybutadiene proportions and tends towards zero at a proportion of hydrated polybutadiene of 30% by weight. By contrast, the extraction values for the two conventional test pieces are significantly higher.

[0238] The extraction values specified in Table 12 can also be applied to the pure water resistance and the resistance to aqueous coolants.