Methods and compositions for inhibiting vinyl aromatic monomer polymerization

Abstract

Methods and compositions are provided for inhibiting the polymerization of a vinyl aromatic monomer, such as styrene monomer, during elevated temperature processing thereof or during storage or shipment of polymer containing product. The compositions comprise a combination of a quinone methide derivative A) and a phenol compound B). The methods comprise adding from about 1-10,000 ppm of the combination to the monomer containing medium, per one million parts of the monomer.

1 . A method for inhibiting the polymerization of vinyl aromatic monomer comprising adding to said monomer an effective polymerization inhibiting amount of a compound comprising (A) a quinone methide derivative having the formula 
       
         
           
           
               
               
           
         
       
       wherein:
 R 1  and R 2  are independently H, C 4  to C 18  alkyl; C 5  to C 12  cycloaklyl; or C 7  to C 15  phenylalkyl, and 
 R 3  is aryl, or aryl substituted with C 1  to C 6  alkyl, alkoxy, hydroxy, nitro, amino, carboxy, or mixtures thereof; and 
 (B) a phenol compound having the formula 
 
       
         
           
           
               
               
           
         
       
       wherein R 4  and R 5  may be the same or different and are chosen from C 1 -C 20  alkyl, C 1 -C 30  alkaryl and substituted C 1 -C 30  alkaryl; R 6  is selected from C 1 -C 20  alkyl, thiophenol, substituted thiophenol, C 1 -C 40  alkanoic acid ester, C 1 -C 30  alkaryl, substituted C 1 -C 30  alkaryl, C 1 -C 6  alkylamino, C 1 -C 6  alkoxy, amine, polynuclear aryl and substituted polynuclear aryl. 
     
     
         2 . The method as recited in  claim 1  wherein the weight ratio of A to B is about 90:10 to about 10:90. 
     
     
         3 . The method as recited in  claim 2  wherein said quinone methide derivative A) is 2,6-di-tert-butyl-4-benzylidene-cyclohexa-2,5-dienone. 
     
     
         4 . The method as recited in  claim 3  wherein said phenol compound B) is 2,6-di-tert-butyl phenol. 
     
     
         5 . The method as recited in  claim 4  wherein from about 1,-10,000 ppm of A and B collectively is brought into contact with said vinyl aromatic monomer, based on 1 million parts of said vinyl aromatic monomer. 
     
     
         6 . The method as recited in  claim 5  wherein said vinyl aromatic monomer comprises styrene monomer. 
     
     
         7 . The method as recited in  claim 5  wherein the weight ratio of A:B is about 70:30. 
     
     
         8 . The method as recited in  claim 7  further comprising the step of heating said styrene monomer. 
     
     
         9 . The method as recited in  claim 7  further comprising the step of distilling said styrene monomer to remove impurities therefrom. 
     
     
         10 . Vinyl aromatic monomer anti-polymerization composition comprising a liquid carrier and dissolved or dispersed therein A) a quinone methide derivative having the formula 
       
         
           
           
               
               
           
         
       
       wherein:.
 R 1  and R 2  are independently H, C 4  to C 18  alkyl; C 5  to C 12  cycloaklyl; or C 7  to C 15  phenylalkyl, and 
 R 3  is aryl, or aryl substituted with C 1  to C 6  alkyl, alkoxy, hydroxy, nitro, amino, carboxy, or mixtures thereof; and 
 
       (B) a phenol compound having the formula 
       
         
           
           
               
               
           
         
       
       wherein R 4  and R 5  may be the same or different and are chosen from C 1 -C 20  alkyl, C 1 -C 30  alkaryl and substituted C 1 -C 30  alkaryl; R 6  is selected from C 1 -C 20  alkyl, thiophenol, substituted thiophenol, C 1 -C 40  alkanoic acid ester, C 1 -C 30  alkaryl, substituted C 1 -C 30  alkaryl, C 1 -C 6  alkylamino, C 1 -C 6  alkoxy, amine, polynuclear aryl and substituted polynuclear aryl. 
     
     
         11 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 10  wherein A) and B) are present in a weight ratio of about 90:10 to about 10:90. 
     
     
         12 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 11  wherein said quinone methide derivative A) is 2,6-di-tert-butyl-4- benzylidene-cyclohexa-2,5-dienone. 
     
     
         13 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 12  wherein said phenol compound B) is 2,6-di-tert-butyl phenol. 
     
     
         14 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 12  wherein said liquid carrier comprises a non-polar organic solvent and wherein A) and B) are both dissolved in said solvent. 
     
     
         15 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 14  wherein said non-polar organic solvent comprises heavy aromatic naphtha or xylene. 
     
     
         16 . Vinyl aromatic monomer anti-polymerization composition as recited in  claim 10  further comprising styrene monomer.