Vapor deposition of a thin polymer film on solid propellant rocket grain surface

Abstract

A thin film of ignition inhibitor is applied uniformly to a rocket propelt grain which may be large and have a complex shape. The film is applied by condensation and polymerization of a vaporized monomer to which the grain is subjected. The monomer is prepared by thermally cracking the dimer of paraxylylene or a halogenated paraxylylene derivative.

What is claimed is: 
     
       1. A method of applying a polymer coating to a surface of a solid propellant rocket grain, the method comprising: fabricating the grain without the coating;   generating a vaporized monomer that is inert with respect to the grain and that is polymerizable by vapor deposition polymerization; and   subjecting the grain to the vaporized monomer, so that the monomer condenses and polymerizes on the surface of the grain to form the coating.   
     
     
       2. The method of claim 1 wherein the coating is an ignition inhibitor and the coating is selected from polymers of paraxylylene and halogenated paraxylenes. 
     
     
       3. The method of claim 1 wherein the monomer is selected from paraxylyene or a halogenated paraxylyene and wherein the method further comprises generating the monomer by thermally cracking a diner corresponding to the selected paraxylyene or halogenated paraxylyene. 
     
     
       4. The method of claim 1 wherein the grain is stationary while subjecting the grain to the vaporized monomer. 
     
     
       5. The method of claim 1 wherein the method further comprises fabricating the grain so that said surface is an interior surface of the grain. 
     
     
       6. The method of claim 1 wherein the method further comprises fabricating the grain within a casing and subsequently subjecting the grain to the vaporized monomer. 
     
     
       7. A method of applying a ignition inhibiting coating to an interior surface of a solid propellant rocket grain, the method comprising: fabricating the grain with said interior surface and without said coating;   generating a vaporized monomer by thermally cracking a dimer selected from a dimer of paraxylyene or a halogenated paraxylyene; and   subjecting the grain to the vaporized monomer, the grain being stationary while being subjected to the vaporized monomer, so that the monomer condenses and polymerizes on said interior surface of the grain to form the coating as a homopolymer of the selected paraxylylene or halogenated paraxylenes.