Poly(ethylene-co-syndiotactic propylene) functionalized with group(s), that enable crosslinking, e.g., vinyl or anhydride group(s), in admixture with crosslinking agent and filler is subjected to crosslinking reaction to provide filled copolymer. The presence of propylene in syndiotactic sequences provides lower entanglement molecular weight compared to other propylene placement and therefore allows more filler to be present than for other propylene placement. Crosslinking provides filled materials with good elastomeric properties.