A peroxide-curable ethylene copolymer composition having (A) a crosslinkable ethylene/alpha-olefin copolymer, (B) an effective amount of triallyl phosphate (TAP), (C) an organic peroxide, and, optionally, (D) a supplemental polymer; wherein the (A) crosslinkable ethylene/alpha-olefin copolymer is made by copolymerizing ethylene and an olefin-functional comonomer in the presence of a molecular catalyst useful therefor. Also provided are a cured product made from the composition, methods of making and using same, and articles containing same.