Described are methods and composition for inhibiting polymerization of a monomer (e.g., styrene) composition using an aminated quinone antipolymerant, such as an aminated benzoquinone or aminated naphthoquinone antipolymerant having one or more secondary or tertiary amine group(s). The aminated quinone antipolymerant can be used with little or no nitroxyl group containing antipolymerant yet still provide excellent antipolymerant activity in a monomer-containing composition.