Pneumatic tire with built-in sealant containing pre-hydrophobated silica

The present invention relates to a pneumatic tire with a built-in depolymerized butyl rubber based sealant layer. The built-in sealant layer is of a composition comprised of a partially depolymerized butyl rubber or alternatively comprised of a polymer composite of partially depolymerized butyl rubber, together with partially depolymerized cis 1,4-polyisoprene rubber and/or partially depolymerized liquid polyisoprene polymer, which contains a pre-hydrophobated silica. The sealant layer may also contain a colorant of a non-black color which produces a built-in sealant layer of a color which contrasts with a black. Thus the sealant layer may be black in color or may be a color which contrasts with a black color. The butyl rubber-based sealant precursor is built into the tire as a layer to form a tire assembly including such sealant precursor layer wherein the butyl rubber or butyl rubber-based composite portion of the sealant precursor layer is at least partially depolymerized during a subsequent curing of the tire at an elevated temperature in a suitable mold to form the tire having the resultant built-in sealant layer. The sealant precursor composition may additionally contain conventional clay, exfoliated intercalated clay platelets, calcium carbonate and/or corn cob granule fillers.