Compositions and method of inhibiting polymerization of vinyl-aryl monomers

An inhibitor composition comprising a mixture of a vinyl-aryl monomer and a polymerization-inhibiting effective amount of a substituted amidine of formula (I):

• or a prototropic tautomer thereof,
• Wherein:
• Z is 1,3-(C3 or C7)hydrocarbylene or 1,3-(C2-C6)heterohydrocarbylene such that ring (r) is a six-membered ring;
• benzo-fused substituted six-membered ring wherein Z comprises a 3-atom linker portion having 2 contiguous ring carbon atoms that are fused to the benzo;
• or 5-membered or 6-membered heteroarylene-fused substituted six-membered ring wherein Z comprises a 3-atom linker portion having 2 contiguous ring carbon atoms that are fused to the 5-membered or 6-membered heteroarylene, wherein when Z is unsubstituted, ring (r) is non-aromatic and when Z is substituted, ring (r) is non-aromatic or aromatic;
• And (a), (b), or (c):
• (a) X is NR2a, C(H)R2b, or O;
• and
• Each of R1, R2a, and R2b independently is a hydrogen atom, (C1-C20)hydrocarbyl, or (C1-C20)heterohydrocarbyl;
• (b) X is NR2a;
• and
• R1 and R2a are taken together to form ZA, wherein ZA independently is as defined for Z;
• or
• (c) X is C(H)R2b;
• and
• R1 and R2b independently are taken together to form ZA, wherein ZA independently is as defined for Z;
• Wherein each heterohydrocarbylene, and heterohydrocarbyl independently comprises carbon atoms, hydrogen atoms, and 1 or 2 heteroatoms wherein each heteroatom independently is O, S, S(O), S(O)2, or N(RN);
• Wherein each RN independently is a hydrogen atom or unsubstituted (C1-C10)alkyl;
• Wherein each benzo, heteroarylene, hydrocarbylene, heterohydrocarbylene, hydrocarbyl, and heterohydrocarbyl independently is unsubstituted or substituted with from 1 to 3 substituents RS;
• and
• Wherein each RS independently is bonded to a carbon atom and is unsubstituted (C1-C10)alkyl, unsubstituted (C3-C10)cyclo alkyl, unsubstituted (C1-C10)alkyl-O—, —OH, oxo (i.e., ═O), or fluorine atom.