A composition comprises (A) an ethylene/alpha-olefin/diene interpolymer; (B) a peroxide comprising at least one peroxide bond; and (C) a bis-TEMPO compound having the Structure (I), wherein R1-4 are each independently H or a C1-C6 alkyl group; X is S, O, N, P, Se, a carbonyl group, a carboxyl group, an amide group, an azo group, an imino group, a carbamate group, a peroxy group, a phosphono group, a phosphate group, a sulfonyl group, a sulfinyl group, a sulfonate ester group, a sulfonate ester group, or combinations thereof; Y is a substitute or unsubstituted aliphatic alkyl group or aromatic alkyl group, a heterocyclic group, a siloxane group, an ethylene glycol group, an imide group, or combinations thereof; and n is greater than 1. The ratio of the molar amount of nitroxide groups of component (C) to the molar amount of the peroxide bonds of component (B) is from 0.100:1.000 to 2.000:1.000.