Sealant composition

1. A one-part condensation curable low modulus room temperature vulcanisable (RTV) silicone composition comprising:

(a) an organopolysiloxane polymer having at least two hydroxyl or hydrolysable groups per molecule and of the general formula

X 3-n R n Si—(Z) d —(O) q —(R 1 y SiO (4-y)/2 ) z —(SiR 1 2 —Z) d —Si—R n X 3-n   (1)

in which each X is independently a hydroxyl group or a hydrolysable group, each R is an alkyl, alkenyl or aryl group, each R 1 is an X group, alkyl group, alkenyl group or aryl group and Z is a divalent organic group; d is 0 or 1, q is 0 or 1 and (d+q)=1; n is 0, 1, 2 or 3, y is 0, 1 or 2, or optionally y is 2, and z is an integer such that organopolysiloxane polymer (a) has a viscosity of from 30,000 to 80,000 mPa·s at 25° C., or optionally from 40,000 to 75,000 mPa·s at 25° C., in an amount of from 35 to 60% by weight of the composition;

(b) a hydrophobically treated calcium carbonate reinforcing filler having a surface area of from 2.5 to 12 m 2 /g and an average particle size of >0.1 μm, in an amount of from 30 to 60% by weight of the composition;

(c) one or more difunctional silane chain extenders having two hydroxyl or hydrolysable groups per molecule, in an amount of from 0.2 to 5% by weight of the composition;

(d) a titanate and/or zirconate catalyst, in an amount of from 0.2 to 1.0% by weight of the composition; and

(e) an aminosilane adhesion promoter having two hydroxyl or hydrolysable groups per molecule, in an amount of from 0.1 to 3.75% by weight of the composition; and optionally, further comprising:

(f) one or more silane cross-linkers having at least three hydroxyl and/or hydrolysable groups per molecule, in an amount of from 0 to 3% by weight of the composition.

2. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , wherein organopolysiloxane polymer (a) is of the general formula

X 3-n R n Si—(Z)—(R 1 y SiO (4-y)/2 ) z —(SiR 1 2 —Z)—SiR n X 3-n

wherein n is 0 or 1, each of R, Z, R 1 , y, and z is as defined above, and each X is an alkoxy group.

3. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , wherein the reinforcing filler (b) comprises a hydrophobically treated precipitated calcium carbonate having a surface area of from 5.0 to 12 m 2 /g and an average particle size of >0.1 μm.

4. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , wherein the reinforcing filler (b) comprises a hydrophobically treated precipitated calcium carbonate wherein at least 75% of the particles are within a particle size distribution of 0.075 to 0.4 μm.

5. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , wherein the aminosilane adhesion promoter (e) is of the general formula

R 4 (R′O) 2 Si—Z 1 —N(H)—(CH 2 ) m NH 2

in which R 4 is an alkyl group containing from 1 to 10 carbon atoms; each R′ is the same or different and is H or R 4 , Z 1 is a linear or branched alkylene group having from 2 to 10 carbon atoms, and m is from 2 to 10.

6. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , wherein the aminosilane adhesion promoter (e) is N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane.

7. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , which is gunnable and/or self-levelling.

8. The one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , capable of being applied as a paste to a joint between two adjacent substrate surfaces where it can be worked, prior to curing, to provide a smooth surfaced mass which will remain in its allotted position until it has cured into an elastomeric body adherent to the adjacent substrate surfaces.

9. A silicone elastomer which is the reaction product of the one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 .

10. The silicone elastomer in accordance with claim 9 , which upon cure provides a sealant with a low modulus of ≤0.45 MPa at 100% elongation.

11. The silicone elastomer in accordance with claim 9 , which is non-staining.

12. A method of making the one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , the method comprising mixing all of the ingredients together.

13. A sealant suitable for use in the facade, insulated glass, window construction, automotive, solar and construction fields, wherein the sealant comprises or is formed from the one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 .

14. A sealant comprising or formed from the one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 .

15. A method for filling a space between two substrates so as to create a seal therebetween, the method comprising:

a) providing the one-part room temperature vulcanisable (RTV) silicone composition in accordance with claim 1 , and either b) or c);

b) applying the silicone composition to a first substrate, and bringing a second substrate in contact with the silicone composition that has been applied to the first substrate, or

c) filling a space formed by the arrangement of a first substrate and a second substrate with the silicone composition and curing the silicone composition.

16. The method for filling a space between two substrates in accordance with claim 15 , wherein the space is filled by introducing the silicone composition by way of extrusion or through a sealant gun.