Lightweight particles and compositions containing them

1. A particle comprising an exterior surface having a coating thereon, wherein the coating comprises a reaction product of reactants comprising:

(a) an aminoplast resin; and

(b) a polythiol, wherein the polythiol has the structure:

HS—R 1 —SH

wherein

R 1 is selected from a C 2-6 n-alkylene group; a C 3-6 branched alkylene group having one or more pendent groups; a C 6-8 cycloalkylene; C 6-10 alkylcycloalkylene group; heteroatomic substituted analogs of any of the foregoing, —[(—CHR 3 —) s —O—] q —(—CHR 3 —) r —, and —[(—CHR 3 —) s —S—] q —(—CHR 3 —) r —;

each R 3 is hydrogen;

s is an integer having a value ranging from 2 to 6;

q is an integer having a value ranging from 1 to 5; and

r is an integer having a value ranging from 2 to 10.

2. The particle of claim 1 , wherein:

R 1 is —[(—CHR 3 —) s —O—] q —(—CHR 3 —) r -or-[(—CHR 3 —) s —S—] q —(—CHR 3 —) r —, and

q is an integer having a value ranging from 1 to 3.

3. The particle of claim 2 , wherein q is 2.

4. The particle of claim 3 , wherein s is 2 and r is 2.

5. A method of using the particle of claim 1 , comprising dispersing the particle in a composition comprising a thiol-functional binder.

6. The method of claim 5 , wherein the binder comprises a thiol-functional sulfur-containing polymer.

7. The method of claim 5 , wherein the composition, after the dispersing step, has a specific gravity of less than 1.0 g/cm 3 .

8. The particle of claim 1 , wherein the coating is substantially continuous from 70 percent to 100 percent of the exterior surface.

9. The particle of claim 1 , wherein the polythiol comprises a polythioether.

10. The particle of claim 1 , wherein the particle comprises a thermally expandable capsule.

11. The particle of claim 10 , wherein the thermally expandable capsule comprises a thermally expandable thermoplastic capsule.

12. The particle of claim 1 , wherein the particle comprises a polystyrene foam, a polyacrylate microsphere, a polyolefin microsphere, a silica microsphere, an alumina/silica microsphere, an aluminum silicate microsphere, a calcium carbonate-coated polyvinylidene copolymer microsphere, or a thermally expandable capsule.

13. A composition comprising:

a plurality of particles of claim 1 ; and

a sulfur-containing polymer.

14. The composition of claim 13 , wherein the sulfur-containing polymer comprises a thiol-functional polythioether.

15. The composition of claim 13 , comprising a curing agent.

16. The composition of claim 15 , wherein the curing agent comprises an epoxide.

17. The composition of claim 13 , formulated as a sealant having a specific gravity less than 1.0 g/cm.

18. A cured sealant, comprising the composition of claim 13 .

19. The cured sealant of claim 18 , characterized by a specific gravity less than 1.0 g/cm 3 .

20. The cured sealant of claim 18 , wherein the cured sealant exhibits:

a percent volume swell of not greater than 40% after immersion for one week at 140° F. (60° C.) and ambient pressure in Jet Reference Fuel Type 1;

an elongation of at least 80% when measured as described in AMS 3269a; and

a tensile strength of at least 2000 mega-Pascals when measured according to AS 5127/1a7.7.

21. The particle of claim 1 , wherein the coating is characterized by a thickness less than 25 μm.

22. The particle of claim 1 , wherein the coating is characterized by a thickness less than 500 nm.

23. The particle of claim 1 , wherein the aminoplast resin comprises a highly alkylated low imino aminoplast resins characterized by a degree of polymerization less than 3.75.

24. The particle of claim 1 , wherein the polythiol comprises a polythiol selected from 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,2-propoanedithiol, 1,3-butanedithol, 2,3-butanedithiol, 1,3-pentanedithiol, 1,3-dithiol-3-methylbutane, dipentenedimercaptan, ethylcyclohexyldithiol, dimercaptodiethylsulfide, dimercaptodioxaoctane, 1,5-dimercapto-3-oxapentane, and a combination of any of the foregoing.

25. The particle of claim 1 , wherein the polythiol comprises a polythiol selected from HS—CH 2 CH(—CH 3 )—S—CH 2 CH 2 —SH, HS—CH(—CH 3 )CH 2 —S—CH 2 CH 2 —SH, HS—CH 2 CH(—CH 3 )—S—CH(—CH 3 )CH 2 —SH, HS—CH(—CH 3 )CH 2—S—CH 2 CH(—CH 3 )—SH, and a combination of any of the foregoing.

26. A particle comprising an exterior surface having a coating thereon, wherein the coating comprises:

(a) a first film comprising an aminoplast resin reacted with the exterior surface; and

(b) a second film comprising a polythiol reacted with the first film, wherein the polythiol has the structure:

HS—R 1 —SH

wherein

R 1 is selected from a C 2-6 n-alkylene group; a C 3-6 branched alkylene group having one or more pendent groups; a C 6-8 cycloalkylene; C 6-10 alkylcycloalkylene group; heteroatomic substituted analogs of any of the foregoing, —[(—CHR 3 —) s —O—] q —(—CHR 3 —) r —, and —[(—CHR 3 —) s —S—] q —(—CHR 3 —) r —;

each R 3 is hydrogen;

s is an integer having a value ranging from 2 to 6;

q is an integer having a value ranging from 1 to 5; and

r is an integer having a value ranging from 2 to 10.

27. A particle comprising an exterior surface having a coating thereon, wherein the coating comprises:

(a) the reaction product of an aminoplast resin and the exterior surface; and

(b) the reaction product of a polythiol with (a), wherein the polythiol has the structure:

HS—R 1 —SH

wherein

R 1 is selected from a C 2-6 n-alkylene group; a C 3-6 branched alkylene group having one or more pendent groups; a C 6-8 cycloalkylene; C 6-10 alkylcycloalkylene group; heteroatomic substituted analogs of any of the foregoing, —[(—CHR 3 —) s —O—] q —(—CHR 3 —) r —, and —[(—CHR 3 —) s —S—] q —(—CHR 3 —) r —;

each R 3 is hydrogen;

s is an integer having a value ranging from 2 to 6;

q is an integer having a value ranging from 1 to 5; and

r is an integer having a value ranging from 2 to 10.