Method for coating an article with a ladder siloxane polymer and coated

Abstract

The invention provides a method for coating an article with a siloxane-based coating composition that results in a coating with high thermal mechanical stability, the method also allowing commercially acceptable speeds to be employed while inhibiting beading of the coating prior to cure. In one embodiment, an article is coated with a composition containing a first methylsilsequioxane oligomer having an initial viscosity of about 2000 cp or less, a second methylsilsequioxane oligomer having an initial viscosity of about 40,000 to about 90,000 cp, a viscosity-lowering additive of a lower aliphatic ketone, and a catalyst. In another embodiment, the invention provides a method for coating an article with a modified methylsilsequioxane coating suitable for higher temperature applications than an all-methyl coating. This embodiment involves coating an article with a composition comprising an oligomer characterized by A:B:C, where A represents the number of methyl pendant groups in the oligomer and is about 13 to about 67, B represents dimethyl pendant groups and is about 0 to about 33, and C represents phenyl pendant groups and is about 10 to about 80, a lower aliphatic ketone viscosity-lowering additive, and a catalyst of a moderately strong protic acid. In a third embodiment, it is possible to attain an even higher temperature coating. The method involves a step of applying a coating containing modified methylsilsequioxane oligomer that was prepared by mixing methyltriethoxysilane monomer with dimethyldiethoxysilane monomer that has already been partially hydrolyzed and oligomerized.