Method for stabilizing vinyl aromatic monomers using selected polymerization inhibitors and polymers prepared

Abstract

Disclosed is the observation that 7-aryl-quinone methides and 4-tert-butylcatechol, when used in combination in a vinyl aromatic monomer to inhibit polymerization, do not inhibit polymerization to the same extent as each would if used separately. Stated another way, a phenomenon has been observed that when these two compounds are used together, they can, to a large extent, render each other unable to inhibit polymerization in a vinyl aromatic monomer. Also disclosed are methods of preventing adverse results of this interaction when undesired and a method of using this interaction to prepare a reactive vinyl aromatic monomer having a concentration of 4-tert-butylcatechol that would otherwise inhibit polymerization. The invention is disclosed to be useful with the production and storage of any vinyl aromatic monomer and is disclosed to be particularly useful with the production and storage of styrene monomer.

1 . A method for reworking a vinyl aromatic monomer and 4-tert-butylcatechol admixture in a process for preparing a vinyl aromatic monomer using a 7-aryl-quinone methide as a polymerization inhibitor comprising removing substantially all of the 4-tert-butylcatechol from the vinyl aromatic monomer and 4-tert-butylcatechol admixture prior to the vinyl aromatic monomer and 4-tert-butylcatechol admixture coming into contact with the vinyl aromatic monomer stabilized using a 7-aryl-quinone methide.  
   
   
       2 . The method of  claim 1 , wherein the vinyl aromatic monomer is styrene and the 7-aryl-quinone methide is 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone.  
   
   
       3 . The method of  claim 2 , wherein removing substantially all of the 4-tert-butylcatechol is performed by a process selected from the group consisting of distillation, washing with an aqueous base, and filtering through aluminia.  
   
   
       4 . The method of  claim 3 , wherein the vinyl aromatic monomer has a 4-tert-butylcatechol concentration of less than 1 ppm.  
   
   
       5 . A method for the in-situ deactivation of a selected polymerization inhibitor in a vinyl aromatic monomer comprising admixing: 
 (A) an admixture of a vinyl aromatic monomer and a polymerization inhibitor selected from the group consisting of 4-tert-butylcatechol and a 7-aryl-quinone methide, and    (B) a compound selected from the group consisting of 4-tert-butylcatechol and a 7-aryl-quinone methide, wherein the polymerization inhibitor of (A) is not the same as the compound of (B), and the ratio of the polymerization inhibitor of(A) and the compound of (B) is such that polymerization of the vinyl aromatic monomer is substantially not inhibited.    
   
   
       6 . The method of  claim 5 , wherein the vinyl aromatic monomer is styrene and the 7-aryl-quinone methide is 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone.  
   
   
       7 . The method of  claim 5 , wherein the ratio of 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone to 4-tert-butylcatechol is from about 3:1 to about 40:1.  
   
   
       8 . The method of  claim 7 , wherein the ratio of 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone to 4-tert-butylcatechol is from about 4:1 to 25:1.  
   
   
       9 . The method of  claim 7 , wherein the ratio of 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone to 4-tert-butylcatechol is from about 5:1 to 6:1.  
   
   
       10 . A method for preparing vinyl aromatic monomers comprising heating a vinyl aromatic monomer in the presence of a 7-aryl-quinone methide polymerization inhibitor and a 4-tert-butylcatechol polymerization inhibitor and further comprising also using at least one other polymerization inhibitor wherein the at least one other polymerization inhibitor is present in an amount effective to prevent polymerization of the vinyl aromatic monomer and is not a hydroxylamine.  
   
   
       11 . The method of  claim 10  wherein the vinyl aromatic monomer is styrene and the 7-aryl-quinone methide is 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone.  
   
   
       12 . The method of  claim 11 , wherein the at least one other polymerization inhibitor is selected from the group consisting of phenothiazine, 2,6-dinitro-p-cresol, 2-sec-butyl-4,6-dinitrophenol, hydroquinone, hydroquinone monomethyl ether; N,N′-di-2-naphthyl-p-phenylenediamine, N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine, and N,N′-diphneyl-p-phenylenediamine.  
   
   
       13 . A vinyl aromatic polymer prepared from a formulation including an unstabilized vinyl aromatic monomer, 4-tert-butylcatechol, and a 7-aryl-quinone methide.  
   
   
       14 . The vinyl aromatic polymer of  claim 13 , wherein the vinyl aromatic polymer is polystyrene and the 7-aryl-quinone methide is 2,6-di-tert-butyl-4-benzylidene-cyclo-2,5-dienone.