Materials for making apparatus and a method of inhibiting polymerization during manufacture, purification, handling and storage of subject ethylenically unsaturated monomers are disclosed. In particular, copper or metals containing copper, in the presence of oxygen, have inhibit undesired polymerization resulting in polymer fouling in apparatus used during the manufacture, purification, handling and storage of the monomers, such as acrylic acid, methacrylic acid, acrylic acid esters and methacrylic acid esters. The copper or copper alloys as described herein, in the presence of an oxygen-containing gas, exhibit self-inhibiting surface characteristics when used to make at least a portion of the apparatus to inhibit polymerization of the monomers in contact with the portion of the apparatus including such copper-containing metal.