Means for controlling the exothermic reaction of styrenic monomers with sulfonic acids

1. A method for inhibiting the premature polymerization of styrenic monomers comprising adding to said monomers a combination of:

(A) from about 0.5 percent by weight to about 3 percent by weight of at least one sulfonic acid compound selected from the group consisting of toluenesulfonic acid, xylenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, pentadecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid; and

(B ) about 0.25 to about 0.5 molar equivalents per molar equivalent of said sulfonic acid compound of at least one amine selected from the group consisting of pyridine, 2,6-dimethyl-4-aminopyridine, 2,6-lutidine, N-(1,4-dimethylpentyl)aniline, and methyl aniline; and,

(C) at least one inhibitor selected from the group consisting of a nitrophenol, a nitroxyl compound, and a nitrosoaniline

whereby an uncontrolled exothermic reaction of styrenic monomer will be prevented.

2. The method of claim 1 wherein said inhibitor (C) is 2,4-dinitro-6-sec-butylphenol.

3. The method of claim 1 wherein said inhibitor (C) is a nitrosoaniline of the structure:

wherein R 21 and R 22 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, nitroso, and sulfonyl, or R 21 and R 22 can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic;

R 23 through R 27 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, acyloxy, NR 28 (R 29 ), nitro, nitroso, halogen, and sulfonyl, or any two adjacent R's can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic, provided that at least one of R 23 through R 27 must be a nitroso group; and

R 28 and R 29 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, and nitroso.