Silicone compositions crosslinkable into adhesive gels

1. A silicone composition comprising:

(A) at least one polyorganosiloxane POS (I) having:

a) endgroup siloxyl units of type M=(R) 2 (H)SiO 1/2 in which the R radicals, which may be identical or different, are each an optionally substituted linear or branched C 1 -C 6 alkyl radical and/or a substituted or unsubstituted aryl radical, and

b) identical or different siloxyl units of type D=(R 1 ) p (H) q SiO 2/2 in which the R 1 radicals have the same definition as R and p=1 or 2, g=0 or 1 and p+g=2;

with the proviso that the polyorganosiloxane POS (I) comprises at least two SiH radicals per molecule;

(B) at least one polyorganosiloxane POS (II) having:

a) endgroup siloxyl units of type M=(X) s (R 2 ) t SiO 1/2 in which the R 2 radicals have the same definition as R, the X radicals are alkenyl radicals having from 2 to 6 carbon atoms, s=0 or 1, 1=2 or 3 and s+t=3; and

b) identical or different siloxyl units of type D=(X) u (R 3 ) v SiO 2/2 in which the R 3 radicals have the same definition as R, the X radicals are alkenyl radicals having from 2 to 6 carbon atoms, u=0 or 1, v=1 or 2 and u+v=2,

with the proviso that the polyorganosiloxane POS (II) comprises at least two X radicals per molecule;

(C) at least one monofunctional polyorganosiloxane POS (III) which is essentially linear, having less than 2 mol % of siloxyl unit T=RSiO 3/2 , and which comprises, per molecule, one alkenyl radical (X) having from 2 to 6 carbon atoms directly bonded to a silicon atom, the said POS (III) having:

a) identical or different endgroup siloxyl units of type M=(X) w (R 4 ) x SiO 1/2 in which the R 4 radicals have the same definition as R, w=0, x=3; and

b) at least one siloxyl unit D=(X) y (R 5 ) z SiO 2/2 in which the R 5 radicals have the same definition as R, y=1, z=1,

(D) an effective amount of at least one hydrosilylation reaction catalyst; and

(E) at least one nonfunctionalized polyorganosiloxane POS (IV) having:

a) endgroup siloxyl units of type M=(R 6 ) 3 SiO 1/2 in which the R 6 radicals have the same definition as R, and

b) identical or different siloxyl units of type D=(R 7 ) 2 SiO 2/2 in which the R 7 radicals have the same definition as R;

with the proviso that the amount of the constituents (A), (B), (C) and (E) is such that the molar ratio r of the hydrogen atoms bonded to silicon to the alkenyl radicals (X) bonded to silicon is 1:1;

wherein the composition is crosslinkable into a gel by hydrosilylation and said composition, upon crosslinking, has a viscous modulus, (G″) and an elastic modulus (G′) greater than a comparable composition lacking component (C), POS (III).

2. The silicone composition as defined by claim 1 , in which the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 radicals are methyl radicals.

3. The silicone composition as defined by claim 1 , in which the hydrosilylation reaction catalyst is based on platinum.

4. The silicone composition as defined by claim 1 , in which:

the POS (I) is substantially linear and has a dynamic viscosity of less than or equal to 10,000 mPa·s;

the POS (II) is substantially linear and has a dynamic viscosity of less than or equal to 200,000 mPa·s;

the POS (III) has a dynamic viscosity of less than or equal to 150,000 mPa·s; and/or

the POS (IV) is present and is substantially linear and has a dynamic viscosity of less than or equal to 50,000 mPa·s.

5. A system having at least two components (A1) and (B1) comprising the constituents (A), (B), (C) and (D) and optionally the constituent (E) of the silicone composition as defined by claim 1 , with the condition that the hydrosilylation reaction catalyst (D) is separate from the constituent (B).

6. A crosslinked gel obtained by crosslinking the silicone composition as defined by claim 1 .

7. A crosslinked gel obtained by crosslinking the system as defined by claim 5 .

8. An adhesive, coating, leaktight mastic, encapsulated electronic device, implant, prosthesis, impact-cushioning element, cement or dressing comprising the crosslinked gel as defined by claim 6 .

9. An adhesive, coating, leaktight mastic, encapsulated electronic device, implant, prosthesis, impact-cushioning element, cement or dressing comprising the crosslinked gel as defined by claim 7 .

10. The silicone composition as defined by claim 1 , wherein POS (II) and POS (III), the radicals X are vinyl radicals.

11. The silicone composition as defined by claim 1 , said POS (III) having less than 1.5 mol % of siloxyl unit T=RS10 3/2 .

12. The silicone composition as defined by claim 1 , said POS (III) having less than 1 mol % of siloxyl unit T=RSiO 3/2 .

13. The silicone composition as defined by claim 4 , said POS (I) having a dynamic viscosity of less than or equal to 6,000 mPa·s, said POS (II) having a dynamic viscosity of less than or equal to 170,000 mPa·s, said POS (III) having a dynamic viscosity ranging from 20 to 100,000 mPa·s and/or said POS (IV) having a dynamic viscosity ranging from 20 to 40,000 mPa·s.

14. The silicone composition as defined by claim 12 , said POS (I) having a dynamic viscosity ranging from 5 to 5,000 mPa·s and said POS (II) having a dynamic viscosity ranging from 20 to 165,000 mPa·s.

15. A crosslinked adhesive gel obtained by crosslinking the silicone composition as defined by claim 1 .

16. A crosslinked adhesive gel obtained by crosslinking the system as defined by claim 5 .

17. A silicone composition consisting of:

(A) at least one polyorganosiloxane POS (I) having:

a) endgroup siloxyl units of type M=(R) 2 (H)SiO 1/2 in which the R radicals, which may be identical or different, are each an optionally substituted linear or branched C 1 -C 6 alkyl radical and/or a substituted or unsubstituted aryl radical, and

b) identical or different siloxyl units of type D=(R 1 ) p (H) g SiO 2/2 in which the R 1 radicals have the same definition as R and p=1 or 2, g=0 or 1 and g+g=2;

with the proviso that the polyorganosiloxane POS (I) comprises at least two SiH radicals per molecule;

(B) at least one polyorganosiloxane POS (II) having:

a) endgroup siloxyl units of type M=(X) s (R 2 ) t SiO 1/2 in which the R 2 radicals have the same definition as R, the X radicals are alkenyl radicals having from 2 to 6 carbon atoms, s=0 or 1, t=2 or 3 and s+t=3; and

b) identical or different siloxyl units of type D=(X) u (R 3 ) v SiO 2/2 in which the R 3 radicals have the same definition as R, the X radicals are alkenyl radicals having from 2 to 6 carbon atoms, u=0 or 1, v=1 or 2 and u+v=2,

with the proviso that the polyorganosiloxane POS (II) comprises at least two X radicals per molecule;

(C) at least one monofunctional polyorganosiloxane POS (III) which is essentially linear, having less than 2 mol % of siloxyl unit T=RSiO 3/2 , and which comprises, per molecule, one alkenyl radical (X) having from 2 to 6 carbon atoms directly bonded to a silicon atom, the said POS (III) having:

a) identical or different endgroup siloxyl units of type M=(X) w (R 4 ) x SiO 1/2 in which the R 4 radicals have the same definition as R, w=0, x=3; and

b) at least one siloxyl unit D=(X) y (R 5 ) z SiO 2/2 in which the R 5 radicals have the same definition as R, y=1, z=1,

(D) an effective amount of at least one hydrosilylation reaction catalyst; and

(E) at least one nonfunctionalized polyorganosiloxane POS (IV) having:

a) endgroup siloxyl units of type M=(R 6 ) 3 SiO 1/2 in which the R 6 radicals have the same definition as R, and

b) identical or different siloxyl units of type D=(R 7 ) 2 SiO 2/2 in which the R 7 radicals have the same definition as R;

with the proviso that the amount of the constituents (A), (B), (C) and (E) is such that the molar ratio r of the hydrogen atoms bonded to silicon to the alkenyl radicals (X) bonded to silicon ranges is 1:1;

wherein the composition is crosslinkable into a gel by hydrosilylation and said composition, upon crosslinking, has a viscous modulus, (G″) and an elastic modulus (G′) greater than a comparable composition lacking component (C), POS (III).