Moisture curable compositions

1. A two part moisture curing composition, said composition comprising: a part A); and a part B);

wherein part A) comprises

a polymer mixture of polymer (i) and polymer (ii), where polymer (i) is a siloxane polymer having at least two terminal hydroxyl or hydrolysable groups and a viscosity≥25,000 m·Pas at 25° C., and where polymer (ii) is a siloxane polymer having at least two terminal hydroxyl or hydrolysable groups and a viscosity of between 1,000 and 20,000 m·Pas at 25° C.; wherein part A) further comprises a reinforcing filler and a low-density filler;

wherein the total filler content is between 30 and 45% in volume of the total composition;

wherein part B) comprises a moisture curing agent formulation comprising;

a tin based catalyst, and

one or more crosslinkers having three or more hydroxyl and/or hydrolysable groups for curing part A); and

wherein part A) and/or the composition of part A)+part B) after mixing has a thermal conductivity≤0.20 W/m·K according to ISO 8301.

2. The two part moisture curing composition in accordance with claim 1 , wherein polymer (i) is present in the composition in an amount of from 10 to 70% by weight based on the total weight of part A).

3. The two part moisture curing composition in accordance with claim 1 , wherein polymer (ii) is present in the composition in an amount of from 10 to 70% by weight based on the total weight of part A).

4. The two part moisture curing composition in accordance with claim 1 , wherein the reinforcing filler is selected from the group consisting of fumed silicas, precipitated silicas and/or precipitated or ground calcium carbonates, and is present in the composition in an amount of from 15 and 35% by weight of the total composition.

5. The two part moisture curing composition in accordance with claim 4 , wherein the reinforcing filler comprises precipitated calcium carbonate.

6. The two part moisture curing composition in accordance with claim 1 , wherein the low-density filler comprises mineral hollow microspheres having a particle density of between 0.15 to 0.5 g/cm 3 , and is present in the composition in an amount of from 3 to 35% by weight of the total composition.

7. The two part moisture curing composition in accordance with claim 6 , wherein the low-density filler comprises hollow glass beads.

8. The two part moisture curing composition in accordance with claim 1 , wherein the viscosity of the polymer mixture is between 20,000 and 40,000 mPa·s at 25° C.

9. The two part moisture curing composition in accordance with claim 1 , further comprising polymer (iii), a siloxane polymer having terminal hydroxyl or hydrolysable groups and a viscosity of between 10 and 500 mPa·s at 25° C.

10. The two part moisture curing composition in accordance with claim 9 , wherein polymer (iii) is present in an amount of from 0.5 to 10% by weight based on the total weight of part A).

11. The two part moisture curing composition in accordance with claim 1 , wherein part A) comprises:

10 to 70 weight % of polymer (i);

10 to 70 weight % of polymer (ii);

up to 10 weight % of polymer (iii), a siloxane polymer having terminal hydroxyl or hydrolysable groups and a viscosity of between 10 and 500 mPa·s at 25° C.;

15 to 35 weight % of the reinforcing filler; and

3 to 35 weight % of the low-density filler, optionally hollow mineral microspheres; and

optionally, one or more additives;

with the total being 100 weight % of the part A) composition.

12. The two part moisture curing composition in accordance with claim 1 , wherein the ratio of part A):part B) in the composition is between 15:1 and 1:1.

13. A one part moisture curing composition, said composition comprising a mixture of part A) and part B) in accordance with claim 1 .

14. The one part moisture curing composition in accordance with claim 13 , comprising:

30 to 70 weight % of the polymer mixture (II) containing reactive hydroxyl or hydrolysable groups bonded to silicon, which groups are reactive in the presence of moisture;

0.5 to 10 weight % of a crosslinker comprising at least three groups reactive with the silicon-bonded hydroxyl or hydrolysable groups of the polymer mixture;

15 to 35 weight % of the reinforcing filler;

3 to 35 weight % of the low-density filler, optionally hollow mineral microspheres;

with the total filler content being ≤45% by volume of the composition; and

tin based catalyst; and

optionally, one or more additives;

with the total composition being 100 weight %.

15. The two part moisture curing composition in accordance with claim 14 , wherein the polymer mixture (II) further comprises polymer (iii), a siloxane polymer having terminal hydroxyl or hydrolysable groups and a viscosity of between 10 and 500 mPa·s at 25° C.

16. A coating, sealing, caulking, mold making, or encapsulating material, said material comprising or formed from the two part moisture curing composition in accordance with claim 1 .

17. An insulating glass sealant, a sealant in refrigerators or freezers, a sealant in an oven and/or a low thermally conductive coating on a substrate and/or a structural coating on a substrate comprising or formed from the two part moisture curing composition in accordance with claim 1 .

18. An insulating glass unit and/or a building façade element and/or a structural glazing unit and/or a gas filled insulation construction panel which in each case is sealed with a secondary sealant cured from a silicone sealant composition, wherein the sealant composition comprises or is formed from the two part moisture curing composition in accordance with claim 1 .

19. A process of making an insulating glass unit, said process comprising:

procuring two glass panes;

providing a spacer between the two glass panes;

adhering the spacer to each pane of glass using a primary sealant;

introducing into a cavity defined by the two glass panes and the spacer an inert or heavy gas; and

applying a layer of a sealant composition as a secondary sealant around the periphery of the insulating glass unit in contact with external surfaces of the spacer;

wherein the sealant composition comprises or is formed from the two part moisture curing composition in accordance with claim 1 .