Abstract: The present invention is directed to peroxide curable rubber compositions, processes for their preparation, and modified fillers therefor. The compositions contain one or more polymers having repeating units derived from one or more isoolefin monomers (e.g. isobutene) and repeating units derived from one or more multiolefin monomers (e.g. isoprene). The compositions also contain modified fillers comprising a particulate composite of a particulate filler (e.g. carbon black) and a multiolefin crosslinking agent (e.g. divinylbenzene). Such rubber compositions find application particularly in condenser caps, biomedical devices, pharmaceutical devices (e.g. stoppers in medicine-containing vials, plungers in syringes, etc.), and seals for fuel cells.

Abstract: The present invention provides a process for preparing a filled halobutyl elastomer, which includes mixing a halobutyl elastomer with at least one mineral filler and at least one dry liquid modifier and optionally curing the filled elastomer with sulfur or other curative systems. Filled halobutyl elastomers prepared according to the present invention possess improved levels of filler dispersion which results in a reduction in the hardness of the compound and an increased tensile strength.