Abstract: Described are compositions and methods for inhibiting and retarding polymerization of a monomer composition, which use a naphthoquinone and a hydroxylamine. When present in a monomer-containing composition, the combination of the naphthoquinone and hydroxylamine provides an unexpected beneficial antipolymerant effect inhibiting unwanted formation of fouling polymer. The antipolymerant combination can be added to a hydrocarbon composition, such as a petroleum, that can include a polymerizable components, such as styrene, where the hydrocarbon composition is purified or processed, such as in the case of distillation.

Abstract: Inhibitor compositions for abating undesirable polymerization during processing of hydrocarbon stream laden with reactive vinylic monomers are provided. The polymerization inhibitor compositions include at least a first inhibitor compound having a stable nitroxide radical and a second inhibitor including phenylenediamine. Methods of inhibiting the polymerization of monomers using the compositions of the disclosure are also provided. The methods of inhibiting polymerization of monomers include a step of adding a composition of the disclosure to the monomer. In some instances, the monomer is an ethylenically unsaturated monomer. Such ethylenically unsaturated monomers include, but are not limited to, vinyl acetate, acrylonitrile, acrylates, methacrylates, 1,3-butadiene, styrene, isoprene, (meth)acrylic acid, and combinations thereof. Methods of preparing the polymerization inhibitors and compositions of the disclosure are also provided.