A core-shell particle for use as filler in rubber compositions. In one
embodiment, the particle comprises a crosslinked core having repeat
aromatic vinyl units. During an emulsion polymerization, a crosslinked
shell comprising of conjugated diene units is grafted onto the core
through residual vinyl units. The polymeric shell provides for better
interaction and dispersion of the styrene core in an otherwise immiscible
polymer matrix, particularly diene-based polymers. In another embodiment,
the core has repeat units of (i) about 0% to about 25% by weight of a
conjugated diene unit, (ii) about 70% to about 85% by weight of an
aromatic vinyl unit, and (iii) about 15% to about 30% by weight of a
crosslinking monomer unit.
