Aromatic sulfonic acids, amines, and nitrophenols in combination with nitroxyl radical-containing compounds or C-nitrosanilines as polymerization inhibitors

1. A method for inhibiting and retarding the premature polymerization and the polymer growth of vinyl aromatic monomers comprising adding to said monomers an effective amount of an inhibitor and retarder blend comprising:

(A) from about 50 ppm to about 500 ppm by weight, based on the weight of the monomers, of at least one aromatic sulfonic acid;

(B) at least one amine;

(C) at least one nitrophenol; and

(D) at least one member of the group consisting of nitroxy radical-containing compounds and nitrosoanilines.

2. The method of claim 1 wherein the aromatic sulfonic acid is a compound of the structure:

wherein R represents an alkylphenyl or an alkylnaphthyl group each having at least one straight or branched chain alkyl group having 1-32 carbon atoms.

3. The method of claim 1 wherein the amine is selected from the group consisting of N-methyl-2-pyrrolidinone, α-naphthylamine, thiodiarylamines, p-phenylenediamine, o-phenylenediamine, 2,4-diamino diphenylamine, cyclohexyl naphthyl amine, polybutyl amines, methyl aniline, diphenyl-p-phenylene diamine, phenyl-β-naphthylamine, isopropoxydiphenylamine, aldol-α-naphthyl amine, symmetrical di-β-naphthyl-p-phenylenediamine, trimethyl dihydroquinoline, ditolylamines, phenyl-α-naphthylamine, phenyl-β-naphthylamine, diaminophenol, 4-cyclohexylaminophenol, p-aminophenol, o-aminophenol, and 5-amino-2-hydroxytoluene.

4. The method of claim 1 wherein the nitrophenol is selected from the group consisting of 2,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, 2,4-dinitro-1-naphthol, 2,4,6-trinitrophenol (picric acid), 2,4-dinitro-6-methylphenol, 2,4-dinitrophenol, 2,4-dinitro-6-sec-butylphenol, 4-cyano-2-nitrophenol, 3-iodo-4-cyano-5-nitrophenol, m-nitro-p-cresol, and 2,6-dinitro-p-cresol.

5. The method of claim 1 wherein (D) is a nitrosoaniline having the structure:

wherein either

(i) R 31 , and R 32 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, nitroso, and sulfonyl, or

(ii) R 31 and R 32 can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic; and

wherein either

(i) R 33 through R 37 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, acyloxy, NR 38 (R 39 ), nitro, nitroso, halogen, and sulfonyl, provided that at least one of R 33 through R 37 must be a nitroso group, or

(ii) any two adjacent R's can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic, provided that at least one of R 33 through R 37 must be a nitroso group; and

R 38 and R 39 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, and nitroso.

6. The method of claim 1 wherein (D) is a stable hindered nitroxyl compound having the structural formula:

wherein R 4 and R 7 are independently selected from the group consisting of hydrogen, alkyl, and heteroatom-substituted alkyl and R 5 and R 6 are independently selected from the group consisting of alkyl and heteroatom-substituted alkyl; and X 1 and X 2 (1) are independently selected from the group consisting of halogen, cyano, —COOR 10 , —S—COR 10 , —OCOR 10 , (wherein R 10 is alkyl or aryl), amido, —S—C 6 H 5 , carbonyl, alkenyl, or alkyl of 1 to 15 carbon atoms, or (2) taken together, form a ring structure with the nitrogen.