This invention relates to a pneumatic tire having a built-in
sealant layer and its preparation. The
sealant layer precursor is a layer of a
butyl rubber based composition which contains an organoperoxide. The
butyl rubber of said precursor is a
copolymer of
isobutylene and
isoprene containing from about 0.5 to about 5, alternately less than 1, mole percent
isoprene. The precursor composition contains
carbon black and / or
coal dust and may contain a dispersion of liquid
conjugated diene polymer (e.g. liquid cis 1,4-polyisoprene
polymer), short fibers and / or hollow glass microspheres. A layer of the
sealant precursor is built into the tire between a
sulfur vulcanized halobutyl rubber innerliner and
conjugated diene-based rubber of the tire carcass. The
butyl rubber of the sealant precursor is partially depolymerized by the organoperoxide during the elevated temperature
vulcanization of the tire to form the built-in sealant layer. In one aspect of the invention, said uncured butyl rubber sealant precursor layer composition has a storage modulus G'(80° C.) in a range of about 100 to about 400 kPa and said partially depolymerized butyl rubber sealant layer composition has a storage modulus G' (80° C.) in range of about 5 to about 50 kPa.