Foamable silicone composition and its use

Abstract

A foamable silicone composition is disclosed, which comprises: (a) at least one organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule; (b) at least one organopolysiloxane containing at least two hydrogen atoms bonded to silicon atoms per molecule; (c) (c1) an organopolysiloxane containing at least one hydroxyl group bonded to silicon atoms per molecule and (c2) a porogen agent that generates gaseous hydrogen in the presence of component (b), which comprises water; and (d) a hydrosilylation catalyst, with the proviso that the ratio of the number of moles of hydroxyl groups provided by component (c2) to the number of moles of hydroxyl groups provided by component (c1) is within the range of 1:5 to 20:1. This composition has a low viscosity and a relatively high pot life, and the foam cured therefrom has a low density, uniform porosity, and a fine cell structure.

Description

[Technical Field]

[0001] The present disclosure relates to foamable silicone compositions and uses thereof. [Background technology]

[0002] Among new energy vehicle accidents, fires or explosions caused by lithium-ion batteries have become a major safety concern. One way to reduce or eliminate such accidents is to use liquid silicone rubber as a potting material for batteries to improve heat conduction or heat dissipation to protect against fires or explosions. However, liquid silicone rubbers typically have a relatively high specific gravity. Using them as a potting material increases the weight of the battery pack and reduces the specific energy per unit volume, ultimately affecting the energy density.

[0003] Liquid foamable silicone rubbers are advantageous for reducing the weight of battery packs, but there are few literatures reporting their application in battery potting. US 4,760,098B discloses a viscous liquid composition comprising part A and part B, where part A consists essentially of a vinyl-terminated siloxane, a reactive diluent (hydroxyl-terminated siloxane), water, and a catalyst, and part B consists essentially of a hydrogen siloxane and a filler. The viscosity of part A is about 30,000 to about 65,000 cps at 32-34°C, and the addition of part B does not significantly affect the viscosity of the foamable mixture. Such a viscous liquid composition is not suitable for battery potting. CN106589954A discloses a low-viscosity, flame-retardant, and room-temperature-curable silicone composition, which comprises the following: α,ω-dihydroxypolydimethylsiloxane having a viscosity of 300 to 5,000 mPa·s as a primary polymer; hydrogen-containing silicone oil and hydroxyl-terminated silicone oil having a viscosity of 60 to 150 mPa·s as a porogen agent; and a viscosity of 0.58 to 0.68 g / cm 3 The resulting foam can be used for potting protection in new energy battery modules. A planetary mixer is required to obtain the desired properties. However, it is still difficult to obtain a foam with uniform porosity, and the cost of producing such foam is high.

[0004] US 4,189,545 A discloses in Example 4 another silicone rubber foam composition containing a vinyl polydimethylsiloxane having a viscosity of 380 cps as the primary polymer, a hydrogen-containing silicone oil, and water as a porogen agent. Such a composition has a short pot life of 45 seconds, and water is not compatible with the siloxane.

[0005] Potting materials for batteries are generally required to have low viscosity due to the need for fluidity and a relatively long pot life to facilitate potting operations. However, preparing silicone foams with low density and uniform porosity from foamable compositions with relatively low viscosity and long pot life has always been a challenge in the art. A low viscosity usually means that bubbles formed from the reaction between Si-H and hydroxyl groups easily escape from the foamable composition. A relatively long pot life usually means that the reaction between Si-H groups and alkenyl groups begins too slowly to form a network to capture the bubbles generated by the foaming reaction. As a result, foams with higher density are obtained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Chinese Patent Application Publication No. 106589954 [Patent Document 2] U.S. Patent No. 4,189,545 Summary of the Invention

[0007] In view of the existing problems, the present disclosure provides a foamable silicone composition by using a given ratio of water and silanol as a porogen agent, which successfully resolves the conflict between the relatively low viscosity and long pot life of the foamable composition and the relatively low density of the resulting foam.

[0008] A first aspect of the present disclosure is a foamable silicone composition comprising: (a) at least one organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule; (b) at least one organopolysiloxane containing at least two hydrogen atoms bonded to silicon atoms per molecule; (c) a porogen agent that generates gaseous hydrogen in the presence of component (b), including: (c1) an organopolysiloxane containing at least one hydroxyl group bonded to a silicon atom per molecule; and (c2) Water, and (d) Hydrosilylation catalyst wherein the ratio of the number of moles of hydroxyl groups provided by component (c2) to the number of moles of hydroxyl groups provided by component (c1) is in the range of 1:5 to 20:1.

[0009] <Component (a)> Organopolysiloxane (a) as a base polymer is well known. Suitable alkenyl groups bonded to silicon atoms contain 2 to 6 carbon atoms, such as vinyl, allyl, propenyl, butenyl, and hexenyl, preferably vinyl, allyl, and propenyl, and more preferably vinyl. The remaining organic groups bonded to silicon atoms in organopolysiloxane (a) are each independently selected from monovalent organic groups free of aliphatic unsaturation having 1 to 20, preferably 1 to 10, carbon atoms, such as alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, and octyl); aryl (e.g., phenyl, tolyl, xylyl, mesityl, ethylphenyl, benzyl, and naphthyl); and halogenated or organic group-functionalized derivatives of the above groups, such as 3,3,3-trifluoropropyl, o-, p-, and m-chlorophenyl, aminopropyl, 3-isocyanatopropyl, and cyanoethyl, preferably methyl and phenyl, more preferably methyl.

[0010] The organopolysiloxane (a) is typically linear. Some exemplary polyorganosiloxanes (a) can be described by the following formula: R 1 R 2 2SiO(R 2 2SiO) m (R 1 R 2 SiO) n SiR 2 2nd Round 1 (In the formula, R 1 is, independently in each occurrence, an alkenyl group having 2 to 6 carbon atoms, as exemplified above; R 2 is independently in each occurrence a monovalent organic radical, particularly a monovalent hydrocarbon radical free of aliphatic unsaturation having 1 to 20, preferably 1 to 10, carbon atoms, as exemplified above; m is a positive number, n is zero or a positive number, and m+n is the viscosity at 25°C of the organopolysiloxane (a) of 10 to 5,000 mPa·s, for example, 50 to 2,000 mPa·s. Adhesive It's like having a degree.

[0011] The organopolysiloxane (a) of the present disclosure may be a single alkenyl-containing organopolysiloxane, or a mixture of different alkenyl-containing organopolysiloxanes differing in molecular structure (e.g., type and number of substituents) or viscosity. For a mixture of organopolysiloxanes, m+n represents an average value, and the viscosity range satisfied by m+n is for the viscosity of the mixture.

[0012] Generally, foamable silicone compositions used as potting materials are required to have lower viscosities, and correspondingly, the viscosity of the alkenyl-containing organopolysiloxane is usually low. In an embodiment of the present specification, component (a) is (a1) a viscosity at 25°C of Adhesive(a2) a first organopolysiloxane having a viscosity of 10 to 1,000 mPa·s, for example, 100 to 500 mPa·s, and containing at least two alkenyl groups bonded to silicon atoms per molecule; and Adhesive and a second organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule, and having a viscosity of 1,000 to 50,000 mPa·s, for example, 5,000 to 20,000 mPa·s. According to the above embodiment, component (a) preferably contains 80 wt % or more of component (a1), based on the total weight of component (a).

[0013] Component (a) is a component containing R 1 SiO 3 / 2 and R 2 SiO 3 / 2 trifunctional units such as, and / or SiO 4 / 2 and R 1 and R 2 is as defined above. In an embodiment herein, component (a) is R 1 R 2 2SiO 1 / 2 Units and SiO 4 / 2 and an organopolysiloxane consisting essentially of R units. 1 and R 2 is as defined above. As used herein, "essentially" means that the polyorganosiloxane comprises at least 80 mol %, such as at least 90 mol %, or even at least 95 mol % of the above-listed units.

[0014] In the present disclosure, component (a) is suitably used in an amount of 20% to 80% by weight, for example, 30% to 70% by weight, based on the total weight of the composition.

[0015] <Component (b)> The organopolysiloxane (b) can be linear, cyclic, branched, or resinous. The linear or cyclic polyorganosiloxane (b) is typically R2 3SiO 1 / 2 , H.R. 2 SiO 2 / 2 , H.R. 2 2SiO 1 / 2 and R 2 2SiO 2 / 2 R 2 is as defined above. The branched or resinous polyorganosiloxane (b) is HSiO 3 / 2 and R 2 SiO 3 / 2 trifunctional units such as, and / or SiO 4 / 2 and R 2 is as defined above.

[0016] The organopolysiloxane (b) used as a crosslinking agent is well known in the art and typically has at least three hydrogen atoms bonded to silicon atoms. The organopolysiloxane used as a crosslinking agent preferably has a hydrogen content of 1.2 to 1.7% by weight to achieve a good balance between two competing reactions, namely, the curing reaction between the Si-H groups and the alkenyl groups and the foaming reaction between the Si-H groups and the hydroxyl groups.

[0017] Component (b) of the present disclosure may further comprise an organopolysiloxane as a chain extender containing two hydrogen atoms bonded to silicon atoms per molecule at each end of the chain, typically represented by the formula HR 2 2SiO(R 2 2SiO) w SiR 2 2H (in the formula, R 2 is as defined above, and w is a positive number. The organopolysiloxane as a chain extender preferably has a viscosity at 25°C of 10 to 2,000 mPa·s, particularly 50 to 2,000 mPa·s. The viscosityThe chain extender may be a single hydrogen-terminated organopolysiloxane or a mixture of different hydrogen-terminated organopolysiloxanes. For mixtures, the viscosity ranges above refer to the total viscosity of the mixture. It should be understood that organopolysiloxane (b) as a crosslinker is different from organopolysiloxane (b) as a chain extender.

[0018] In an embodiment of the present specification, component (b) comprises the following: (b1) an organopolysiloxane containing at least three hydrogen atoms bonded to silicon atoms per molecule, and (b2) an organopolysiloxane containing two hydrogen atoms bonded to silicon atoms per molecule at both ends of the chain. According to the above embodiment, component (b1) preferably has a hydrogen content of 1.2% to 1.7% by weight, and component (b2) has a viscosity at 25°C of 100°C. Adhesive It is preferable that the component (b2) contains 80% by weight or more of an organopolysiloxane having a viscosity of 10 mPa·s to 2,000 mPa·s, for example, 50 to 2,000 mPa·s, and particularly 500 to 2,000 mPa·s, and containing two hydrogen atoms bonded to silicon atoms at both ends of the chain per molecule.

[0019] In the present disclosure, the ratio of the number of moles of Si—H groups provided by component (b) to the number of moles of silicon-bonded alkenyl groups provided by component (a) is preferably 2:1 to 15:1, for example, 2:1 to 12:1, in particular 2:1 to 8:1.

[0020] Component (b) is suitably used in an amount of 20% to 70% by weight, for example 30% to 60% by weight, based on the total weight of the composition.

[0021] <Ingredient (c)> Component (c) is used as a porogen that reacts with the Si-H groups from component (b) to produce gaseous hydrogen to influence the foaming behavior, but does not contribute to crosslinking. The ratio of the number of moles of hydroxyl groups provided by component (c2) to the number of moles of hydroxyl groups provided by component (c1) is preferably in the range of 1:2 to 10:1, for example, 1:1 to 8:1, in particular 2:1 to 6:1.

[0022] Some exemplary polyorganosiloxanes (c1) can be described by the following formula: R 3 R 2 2SiO(R 2 2SiO) p (R 3 R 2 SiO) q SiR 2 2nd Round 3 (In the formula, R 2 is as defined above, R 3 represents, independently in each occurrence, a hydroxyl group or R 2 and at least one R 3 is a hydroxyl group, and preferably both R 3 is a hydroxyl group, p is a positive number, q is zero or a positive number, and p+q is the viscosity at 25°C of the organopolysiloxane (c1) of 10 to 1,000 mPa·s, for example, 50 to 500 mPa·s. Adhesive It's like having a degree.

[0023] Organopolysiloxanes (c1) of the following formula are particularly preferred: HO(Me2SiO) p (HOMeSiO) q OH, where p and q are as defined above.

[0024] Water (c2) is preferably introduced in the form of an aqueous emulsion, such as an aqueous silicone emulsion including an oil-in-water silicone emulsion or a water-in-oil silicone inverse emulsion, to facilitate dispersion of water in the composition. The aqueous silicone emulsion comprises a polysiloxane oil phase, an aqueous phase, and an emulsifier. The emulsifier may be a nonionic emulsifier, an anionic surfactant, a cationic surfactant, or a zwitterionic surfactant, preferably a nonionic surfactant. The aqueous silicone emulsion can be obtained by an emulsification process well known to those skilled in the art. The viscosity of the aqueous silicone emulsion is not particularly limited. In a preferred embodiment of the present specification, component (c2) has a viscosity of 1,000 to 30,000 mPa·s at 25°C. The viscosity It is an aqueous emulsion of polysiloxane having a high viscosity.

[0025] Component (c) may further contain a certain amount of alkanol, which can be an organic alcohol containing at least one hydroxyl group, but is not an alcohol that acts as a hydrosilylation inhibitor, such as an alkynol, and includes monohydric alcohols having 1 to 12 carbon atoms, such as ethanol, n-propanol, isopropanol, n-butanol, n-hexanol, n-octanol, cyclopentanol, cyclohexanol, cycloheptanol, and polyols having 2 to 12 carbon atoms, such as ethylene glycol, propylene glycol, glycerin, butylene glycol, pentanol glycol, and heptanediol. In a preferred embodiment of the present specification, component (c) does not contain an alkanol.

[0026] In the present disclosure, component (c) is suitably used in an amount of 15 wt% or less based on the total weight of the composition. Component (c1) is preferably used in an amount of 1 wt% to 15 wt%, for example, 2 wt% to 10 wt%, and component (c2) is preferably used in an amount of 0.01 wt% to 1 wt%, for example, 0.05 wt% to 0.5 wt%, based on the total weight of the composition.

[0027] The ratio of the number of moles of Si—H groups provided by component (b) to the number of moles of hydroxyl groups provided by component (c) is preferably 1:2 to 15:1, for example 2:1 to 12:1, in particular 2:1 to 8:1.

[0028] <Ingredient (d)> Component (d) can be any of the various hydrosilylation catalysts used in the prior art for addition curing silicone compositions, preferably platinum-based catalysts, such as chloroplatinic acid, chloroplatinic acid salts, platinum olefin complexes, and platinum alkenylsiloxane complexes.The platinum-based catalyst can be used in an amount that depends on the desired cure rate and economic considerations, and is usually the minimum level required to ensure an effective hydrosilylation reaction.Generally, the weight amount of platinum metal in the foamable silicone composition is 0.1 to 1,000 ppm, for example 1 to 200 ppm.

[0029] <Ingredient (e)> The foamable silicone composition may further contain an inhibitor (e) to control the pot life and curing rate of the composition. The inhibitor can be any of various inhibitors used in the art, such as alkynols such as 1-ethynyl-1-cyclohexanol and 2-methyl-3-butyn-2-ol, polymethylvinylcyclosiloxanes such as 1,3,5,7-tetravinyltetramethyltetracyclosiloxane, and alkyl maleates. The amount of the inhibitor can be selected according to its chemical structure and the desired curing rate. Generally, the weight amount of the inhibitor in the composition is 1 to 50,000 ppm, for example, 10 to 10,000 ppm.

[0030] <Other optical components> The siloxane composition may contain appropriate amounts of other components, such as filler (f), diluent (g), and color paste (h), as long as the effects of the present invention are not impaired.

[0031] Examples of fillers (f) include, but are not limited to, calcium carbonate, silica, fine silica powder, diatomaceous earth, organic montmorillonite, and titanium dioxide. Silica is particularly preferred. Examples of silica include fumed silica, precipitated silica, and mixtures thereof. The specific surface area of ​​the silica, as measured by the BET method, is preferably at least 50 m. 2 / g, preferably 100 to 400m 2 / g, e.g., 150-350m 2 / g range. Silica can be hydrophilic or hydrophobic.

[0032] Examples of diluents (g) are: Adhesive Dimethyl silicone oil with a viscosity of 10 to 5,000 mPa·s at 25°C Adhesive MDT silicone oil with a kinematic viscosity of 15 to 300 mPa·s and a kinematic viscosity of 10 to 100 mmHg at 25°C 2 / sec mineral oil. Generally, the addition of a diluent can reduce the viscosity of the composition and change its rheological properties. Nevertheless, considering the potential bleeding problem, the foamable silicone composition of the present disclosure preferably does not contain a diluent.

[0033] In a preferred embodiment, the foamable silicone composition comprises: (a) 20 to 80% by weight of at least one organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule; (b1) 1 to 8% by weight of an organopolysiloxane containing at least three hydrogen atoms bonded to silicon atoms per molecule; (b2) 20 to 70% by weight of an organopolysiloxane containing two hydrogen atoms bonded to silicon atoms per molecule at both ends of the chain; (c1) 1 to 15% by weight of an organopolysiloxane containing at least one hydroxyl group bonded to a silicon atom per molecule; (c2) 0.01 to 1% by weight of water, and (d) Hydrosilylation catalyst.

[0034] Preferably, the foamable silicone composition of the present disclosure is stored as two or more separate packages in which components (b) and (c) are not stored in the same package and components (a), (b), and (d) are not stored in the same package.

[0035] The foamable silicone composition of the present disclosure preferably has a viscosity of 200 to 10,000 mPa·s, for example 500 to 5,000 mPa·s, at room temperature (23±2°C). ·s , particularly 500 to 2,000 mPa·s. Here, viscosity refers to the mixed viscosity of the composition before curing. If the composition is stored in two or more separate packages, viscosity also refers to the viscosity of each package. Generally, the higher the viscosity of the composition, the lower the density of the resulting foam. It is technically difficult to form a low-density foam from a low-viscosity composition.

[0036] A second aspect of the present disclosure provides a foam cured from the foamable silicone composition of the first aspect of the present disclosure.

[0037] This is obtained by crosslinking or curing the composition described in the first aspect of the present disclosure, or by mixing separate packages as described above, followed by crosslinking or curing.

[0038] Generally, crosslinking or curing is carried out at a temperature of 15 to 180°C for 10 minutes to 72 hours. Lower curing temperatures and shorter curing times are desirable. Considering that the curing and foaming reactions occur simultaneously and are both highly temperature-sensitive, curing at a temperature of 20 to 80°C for 15 to 60 minutes, e.g., curing at room temperature for 60 minutes, is preferred. In this specification, "room temperature" refers to (23±2)°C unless otherwise specified.

[0039] The foam of the present disclosure has a density of 0.3 to 0.6 g / cm 3and a closed cell ratio of more than 90%. The density of the foam is measured according to GB / T standard 6343-2009 Cellular plastics and rubbers - Determination of apparent density. The closed cell ratio is measured according to GB / T standard 10799-2008 Rigid cellular plastics - Determination of the volume percentage of open cells and of closed cells.

[0040] A third aspect of the present disclosure provides the use of the foamable silicone composition of the first aspect of the present disclosure as a potting material, particularly for batteries.

[0041] The foamable silicone composition of the present disclosure has low viscosity, good fluidity, and a relatively long pot life, facilitating potting operations. The resulting foam has excellent high and low temperature resistance, weather resistance, and electrical insulation, effectively protecting the battery during operation and helping to dissipate battery heat over time. In addition, the presence of air bubbles can further insulate the battery, improving its safety and service life. The foam of the present disclosure also has a relatively low density, which effectively solves the problem of the reduction in energy density of battery packs caused by conventional injectable silicone rubbers, which have a high specific gravity.

[0042] In this specification, "viscosity" is measured according to conventional methods in the art, unless otherwise specified. [Example]

[0043] The present invention will be further illustrated by the following examples, but is not limited in scope. Any experimental methods in the following examples that do not specify conditions are selected according to conventional methods and conditions, or product specifications.

[0044] <Viscosity measurement> The viscosities of components A and B were measured by a Brookfield viscometer using a No. 2 spindle at room temperature (23±2)° C. and a speed of 10 rpm.

[0045] <Pot life measurement> Pot life refers to the time window during which the mixture of Components A and B can be used once Components A and B are mixed. The phrase "usable" means that the mixture of Components A and B is a free-flowing slurry and has not begun to solidify. The pot life of the present disclosure was measured at (23±2)°C and 50±10% relative humidity.

[0046] <Measurement of foam density> This was done according to GB / T standard 6343-2009.

[0047] <Porous state> The cross section of the foam was visually inspected for pore uniformity across the entire cross section. If the presence of localized excessively large pores or the absence of localized pores was observed in the cross section, the pore uniformity was rated as "non-uniform." If the cross section showed pores uniformly distributed across the cross section without excessively large pores, the pore uniformity was rated as "uniform."

[0048] <Bubble size> The central part of the cross section of the foam was observed under an electron microscope. If 90% or more of the cells were observed to have a maximum diameter of 1 mm or less, the cell size was rated as "fine cell," otherwise it was rated as "coarse cell."

[0049] Details of the raw materials used in the examples and comparative examples are as follows.

[0050] a1: Approximately 20,000 mPa·s at 25°C The viscosity Dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 psi and a vinyl content of 0.042 mmol / g, supplied by Wacker Chemicals.

[0051] a2: Approximately 500 mPa·s at 25°C The viscosity Dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 psi and a vinyl content of 0.17 mmol / g, supplied by Wacker Chemicals.

[0052] a3: Approximately 200 mPa·s at 25°C The viscosity Dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 psi and a vinyl content of 0.26 mmol / g, supplied by Wacker Chemicals.

[0053] a4: Multiple vinyls, 20,000 to 23,000 mPa·s at 25°C The viscosity Polydimethylsiloxane having a viscosity of 1000 psi and a vinyl content of 0.24 mmol / g, supplied by Wacker Chemicals.

[0054] b1: Contains multiple hydrogen atoms, approximately 20 mPa·s at 25°C The viscosity Polydimethylsiloxane having a viscosity of 1000 psi and a hydrogen content of 16.3 mmol / g, supplied by Wacker Chemicals.

[0055] b2: Approximately 1,000 mPa·s at 25°C The viscosity Dimethylhydrosiloxy-terminated polydimethylsiloxane having a viscosity of 1000 MPa and a hydrogen content of 0.12 mmol / g, supplied by Wacker Chemicals.

[0056] c1: Dimethylhydroxylsiloxy terminated polydimethylsiloxane supplied by Wacker Chemicals with a hydroxyl content of 1.2 wt.%.

[0057] c2: 5,000 to 10,000 mPa·s at 25°C The viscosity A water-based emulsion of polydimethylsiloxane having a viscosity of 1000 psi and a hydroxyl content of 59.9% by weight, supplied by Wacker Chemicals.

[0058] d: Platinum-based catalyst, WACKER® CATALYST EP, supplied by Wacker Chemicals.

[0059] e: Inhibitor WACKER® INHIBITOR PT88 supplied by Wacker Chemicals.

[0060] f: Vinyl MQ resin with a molar ratio of 0.7:1 mpM to Q units and a vinyl content of 0.78 mmol / g, supplied by Wacker Chemicals.

[0061] g: Approximately 100 mPa·s at 25°C The viscosity Trimethylsiloxy-terminated polydimethylsiloxane supplied by Wacker Chemicals.

[0062] h: Color paste ELASTOSIL® COLOR PASTE FL BLACK RAL 9005F supplied by Wacker Chemicals.

[0063] [Examples 1 to 3 and Comparative Examples 1 to 2] The components of Components A and B were thoroughly mixed according to the formula in Table 1. Components A and B were then mixed together, and the resulting mixture was cured at room temperature for 60 minutes to obtain a silicone foam.

[0064] Table 2 shows the pot life, foam density, porosity, and cell size of the compositions obtained in each Example and Comparative Example. The foams of Examples 1 to 3 have low density, uniform porosity, and a fine cell structure due to the use of water and hydroxy-terminated polydimethylsiloxane as porogen agents. The foam of Comparative Example 1 has a higher density due to the use of only hydroxy-terminated polydimethylsiloxane as a porogen agent. The foam of Comparative Example 2 has a higher density, non-uniform porosity, and a coarse cell structure due to the use of only water as a pore-forming agent.

[0065]

Table 1

[0066]

Table 2

Claims

1. 1. A foamable silicone composition comprising: (a) at least one organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule; (b) at least one organopolysiloxane containing at least two hydrogen atoms bonded to silicon atoms per molecule, including: (b1) an organopolysiloxane containing at least three hydrogen atoms bonded to silicon atoms per molecule; and (b2) an organopolysiloxane containing two silicon-bonded hydrogen atoms per molecule at both ends of the chain; (c) a porogen agent that generates gaseous hydrogen in the presence of component (b), the porogen agent comprising: (c1) an organopolysiloxane containing at least one hydroxyl group bonded to a silicon atom per molecule; and (c2) water, and (d) a hydrosilylation catalyst; wherein the ratio of the number of moles of hydroxyl groups provided by component (c2) to the number of moles of hydroxyl groups provided by component (c1) is in the range of 1:5 to 20:1; The foamable silicone composition has a viscosity of 500 to 5,000 mPa·s at (23±2)° C. before curing.

2. 2. The composition of claim 1, wherein the ratio of the number of moles of hydroxyl groups provided by component (c2) to the number of moles of hydroxyl groups provided by component (c1) is in the range of 1:2 to 10:

1.

3. 3. The composition of claim 1, wherein component (c) is used in an amount of 15% by weight or less, based on the total weight of the composition.

4. The composition of any one of claims 1 to 3, wherein the ratio of the number of moles of Si-H groups provided by component (b) to the number of moles of silicon-bonded alkenyl groups provided by component (a) is from 2:1 to 15:

1.

5. The composition of any one of claims 1 to 4, wherein the ratio of the number of moles of Si-H groups provided by component (b) to the number of moles of hydroxyl groups provided by component (c) is from 1:2 to 15:

1.

6. The composition according to any one of claims 1 to 5, wherein component (c1) has a viscosity of 10 to 1,000 mPa·s at 25°C.

7. The composition according to any one of claims 1 to 6, wherein component (a) comprises 80% by weight or more, based on the total weight of component (a), of an organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule and having a viscosity of 10 to 1,000 mPa s at 25°C.

8. 2. The composition of claim 1, wherein component (b1) has a hydrogen content of 1.2 to 1.7 wt. %.

9. The composition according to claim 1 or 8, wherein component (b2) comprises 80 wt. % or more, based on the total weight of component (b2), of an organopolysiloxane containing two silicon-bonded hydrogen atoms per molecule at both chain ends and having a viscosity of 10 to 2,000 mPa s at 25°C.

10. 10. The composition of any one of claims 1 to 9, comprising: (a) 20 to 80 weight percent of at least one organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms per molecule; (b1) 1 to 8% by weight of an organopolysiloxane containing at least three hydrogen atoms bonded to silicon atoms per molecule; (b2) 20 to 70% by weight of an organopolysiloxane containing, per molecule, two silicon-bonded hydrogen atoms at both chain ends; (c1) 1 to 15% by weight of an organopolysiloxane containing at least one hydroxyl group bonded to a silicon atom per molecule; (c2) 0.01 to 1% by weight of water, and (d) a hydrosilylation catalyst.

11. A cured foam from the composition of any one of claims 1 to 10.

12. Use of the composition according to any one of claims 1 to 10 as a potting material.

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