The maximum tensile strength of carbon black reinforced hydrogenated nitrile rubber (HNBR) vulcanizates that can be achieved is about 30MPa. A newly developed composite of HNBR/Zinc Dimethacrylate (ZDMA) has a tensile strength of 55Mpa when vulcanized with a peroxide.During this curing process, in situ polymerization of the ZDMA takes place, forming a micro-network structure that was observed by an electronmicroscopic examination of the reaction.The network micro structure consisted of a continuous phase 20nm wide band formed by the agglomeration of primary particles of 2nm diameter created during the polymerization. This micro structure formation, which is smaller than the structure of carbon black, is postulated to be the reason for the very high tensile strength that is achieved with HNBR/ZDMA.