Uses of UV-curable polythioether sealants for sealing fasteners and for smoothing surfaces

1. A seal cap comprising:

a preformed, at least partially cured, first sealant composition forming a shell; and

an at least partially uncured, second sealant composition filling the shell, wherein the first sealant composition and the second sealant composition comprise:

(i) a thiol-terminated polythioether;

(ii) a divinyl ether; and

(iii) a filler, wherein the filler is selected such that the first sealant composition and the second sealant composition are visually clear.

2. The seal cap of claim 1 , wherein the first sealant composition is at least partially transmissive to ultraviolet radiation and the second sealant composition is curable by ultraviolet radiation.

3. The seal cap of claim 1 , wherein the first sealant composition is fully cured.

4. The seal cap of claim 1 , wherein the first sealant composition is curable by ultraviolet radiation.

5. The seal cap of claim 1 , wherein the second sealant composition is fully uncured.

6. The seal cap of claim 1 , wherein the second sealant composition is curable by ultraviolet radiation.

7. The seal cap of claim 1 , wherein the first sealant composition and the second sealant composition comprise the same composition.

8. The seal cap of claim 1 , wherein the first sealant composition and the second sealant composition comprise different compositions.

9. The seal cap of claim 1 , wherein the thiol-terminated polythioether comprises a structure having the formula:

—R 1 —[—S—(CH 2 ) 2 —O—[—R 2 —O—] m —(CH 2 ) 2 —S—R 1 —] n —;

wherein

(1) each R 1 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, —[(—CH 2 —) p —X—] q —(—CH 2 —) r — or —[(—CH 2 —) p —X—] q —(—CH 2 —) r — in which at least one —CH 2 — unit is substituted with a —CH(CH 3 )— group, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(2) each R 2 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, or —[(—CH 2 —) p —X—] q —(—CH 2 —) r —, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(3) m is a rational number from 0 to 10; and

(4) n is an integer having a value ranging from 1 to 60.

10. The seal cap of claim 1 , wherein the thiol-terminated polythioether comprises a thiol-terminated polythioether having the structure of the formula:

HS—R 1 —[—S—(CH 2 ) 2 —O—[—R 2 —O—] m —(CH 2 —) 2 —S—R 1 —] n —SH

wherein

(1) each R 1 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, —[(—CH 2 —) p —X—] q —(—CH 2 —) r — or —[(—CH 2 —) p —X—] q —(—CH 2 —) r — in which at least one —CH 2 — unit is substituted with a —CH(CH 3 )— group, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(2) each R 2 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, or —[(—CH 2 —) p —X—] q —(—CH 2 —) r —, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(3) m is a rational number from 0 to 10; and

(4) n is an integer having a value ranging from 1 to 60.

11. The seal cap of claim 1 , wherein the thiol-terminated polythioether comprises a thiol-terminated polythioether having the structure of the formula: B-(A-[R 3 ] y —SH) z wherein:

(1) A denotes a structure having the formula:

—R 1 —[—S—(CH 2 ) 2 —O—[—R 2 —O—] m —(CH 2 ) 2 —S—R 1 —] n —

 wherein

(I) each R 1 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, —[(—CH 2 —) p —X—] q —(—CH 2 —) r — or —[(—CH 2 —) p —X—] q —(—CH 2 —) r — in which at least one —CH 2 — unit is substituted with a —CH(CH 3 )— group, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(II) each R 2 independently denotes a C 2-10 linear alkanediyl group, a C 2-6 branched alkanediyl group, a C 6-8 cycloalkanediyl group, a C 6-10 alkanecycloalkanediyl group, or —[(—CH 2 —) p —X—] q —(—CH 2 —) r —, wherein:

(i) each X is independently selected from O, S, and —NR 6 —, wherein R 6 is hydrogen or methyl;

(ii) p is an integer having a value ranging from 2 to 6;

(iii) q is an integer having a value ranging from 0 to 5; and

(iv) r is an integer having a value ranging from 2 to 10;

(III) m is a rational number from 0 to 10; and

(IV) n is an integer having a value ranging from 1 to 60;

(2) y is 0 or 1;

(3) R 3 denotes a single bond when y=0 and —S—(CH 2 ) 2 —[—O—R 2 —] m —O— when y=1;

(4) z is an integer from 3 to 6; and

(5) B denotes a z-valent residue of a polyfunctionalizing agent.

12. The seal cap of claim 1 , wherein the second sealant composition further comprises an ethylenically unsaturated silane.

13. The seal cap of claim 1 , wherein the second sealant composition further comprises a photoinitiator.

14. The seal cap of claim 1 , wherein the second sealant composition comprises an essentially stoichiometric equivalent amount of thiol groups to alkenyl groups.

15. The seal cap of claim 1 , wherein the filler transmits ultraviolet (UV) radiation.

16. The seal cap of claim 1 , wherein the filler is selected in part by an index of refraction of the filler.

17. The seal cap of claim 1 , wherein the filler comprises fumed silica.

18. The seal cap of claim 1 , wherein the filler has a specific gravity from 0.1 to 0.7.

19. The seal cap of claim 1 , wherein the filler internally scatters reflected ultraviolet (UV) radiation.

20. A method of sealing a fastener comprising:

applying the seal cap of claim 1 to the fastener; and

exposing the seal cap to ultraviolet radiation to fully cure the second sealant to seal the fastener.

21. A fastener comprising the seal cap of claim 1 .

22. A method of smoothing a surface defect comprising:

applying a sealant composition to the surface defect;

smoothing the sealant composition to fill the surface defect;

exposing the smoothed sealant composition to ultraviolet radiation to cure the smoothed sealant composition,

wherein the sealant composition is UV-curable and comprises:

(i) a thiol-terminated polythioether; and

(ii) an alkenyl-terminated compound comprising a divinyl ether.

23. The method of claim 22 , wherein the surface defect comprises a surface depression.

24. The method of claim 22 , wherein the surface defect comprises a gap between two adjacent panels.