Lightweight particles and compositions containing them

Abstract

Disclosed are particles that have an exterior surface coated with a thin polymeric coating, such as a coating that includes a sulfur-containing polymer. Also disclosed are compositions, such as fuel-resistant sealant and coating compositions, which include such particles. Aerospace vehicles having an aperture at least partially scaled with a sealant deposited from such a sealant composition are also disclosed.

We claim: 
     
         1 . A particle comprising an exterior surface having a coating thereon, wherein the coating comprises:
 a reaction product of reactants comprising:
 (1) an aminoplast resin; and 
 (2) a compound comprising a hydroxyl group and a group reactive with the aminoplast resin; and 
   unreacted hydroxyl groups.   
     
     
         2 . The particle of  claim 1 , wherein the particle comprises a thermally expandable capsule. 
     
     
         3 . The particle of  claim 2 , wherein the thermally expandable capsule comprises a thermally expandable thermoplastic capsule. 
     
     
         4 . 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. 
     
     
         5 . The particle of  claim 1 , wherein the group reactive with the aminoplast resin is selected from a thiol group, a hydroxyl group, and a combination thereof. 
     
     
         6 . The particle of  claim 1 , wherein the coating is substantially continuous from 70 percent to 100 percent of the exterior surface. 
     
     
         7 . The particle of  claim 1 , wherein the aminoplast resin is coupled to the exterior surface of the particle prior to reaction with the compound comprising a hydroxyl group and a group reactive with the aminoplast resin. 
     
     
         8 . A composition comprising:
 a plurality of particles of  claim 1 ; and   a sulfur-containing polymer.   
     
     
         9 . The composition of  claim 8 , wherein the sulfur-containing polymer is selected from a polythioether, a polysulfide, a sulfur-containing polyformal, and a combination of any of the foregoing. 
     
     
         10 . The composition of  claim 8 , comprising a curing agent reactive with the unreacted hydroxyl groups and the sulfur-containing polymer. 
     
     
         11 . The composition of  claim 8 , formulated as a sealant having a specific gravity less than 1.0 g/cm. 
     
     
         12 . A cured sealant comprising the composition of  claim 11 . 
     
     
         13 . The cured sealant of  claim 12 , formulated as a sealant having a specific gravity less than 1.0 g/cm 3 . 
     
     
         14 . The cured sealant of  claim 12 , 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.   
     
     
         15 . A method of using the particle of  claim 1 , comprising dispersing the particle in a composition comprising a sulfur-containing polymer.