Additive for a silicone encapsulant

1. An additive for a silicone encapsulant, said additive having the structure:

wherein subscript a is 3 or 4,

wherein R 1 and R 2 are each —O—Si(R 4 )(R 5 )(R 6 ) and each of R 4 , R 5 , and R 6 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkenyl groups, C 2 -C 2 C 10 alkenyl groups, and C 6 -C 10 aryl groups, and

wherein R 3 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups.

2. The additive of claim 1 wherein at least 20 mol percent of a total of the groups R 3 -R 6 are methyl groups.

3. The additive of claim 1 wherein at least 20 mol percent of a total of the groups R 3 -R 6 are phenyl groups.

4. The additive of claim 1 wherein each R 3 , R 4 , and R 6 is a methyl group.

5. The additive of claim 1 wherein each R 3 , R 4 , and R 6 is a phenyl group.

6. The additive of claim 1 that is further defined as having the structure:

wherein Me is methyl.

7. The additive of claim 1 that is further defined as having the structure:

wherein Me is methyl.

8. The additive of claim 1 that is further defined as having the structure:

wherein Me is methyl and Ph is phenyl.

9. The additive of any preceding claim that is further defined as:

a reaction product of a reaction of a cerium alkoxide and a hydroxyl functional organosiloxane; or

a reaction product of a reaction of cerium ammonium nitrate and a hydroxyl functional organosiloxane; or

a reaction product of a reaction of cerium metal and a hydroxyl functional organosiloxane; or

an exchange reaction product of a reaction of a trifunctional silyloxy cerium (III) or (IV) compound and a hydroxyl functional organosiloxane.

10. The additive of claim 9 wherein the hydroxyl functional organosiloxane has the formula M 1 D R,OH M 2 , wherein R is chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups.

11. The additive of claim 1 having a density of from 0.95 to 1.2 g/cm 3 .

12. The additive of claim 1 that is free of an alkaline metal salt and/or alkaline earth metal salt.

13. The additive of claim 1 that comprises 3 to 25 weight percent of cerium based on a total weight of said additive.

14. A cerium silyloxide cluster comprising 2 to 10 units of the additive of claim 1 .

15. A silicone encapsulant comprising said additive of claims 1 and a silicone.

16. A silicone encapsulant comprising:

A. an additive having the structure:

wherein subscript a is 3 or 4,

wherein R 1 and R 2 are each —O—Si(R 4 )(R 5 )(R 6 ) and each of R 4 , R 5 , and R 6 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups, and

wherein R 3 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups; and

B. a polyorganosiloxane.

17. A device comprising an optoelectronic component and said encapsulant of claim 16 .

18. A method of making an additive having the structure:

wherein subscript a is 3 or 4,

wherein R 1 and R 2 are each —O—Si(R 4 )(R 5 )(R 6 ) and each of R 4 , R 5 , and R 6 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups, and

wherein R 3 is independently chosen from C 1 -C 10 hydrocarbyl groups, C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups, and C 6 -C 10 aryl groups,

wherein the method comprises the step of reacting cerium metal or a cerium (III) or (IV) compound with a hydroxyl functional organosiloxane.