Scorch-retardant composition

Abstract

The present invention relates to the prevention of scorching before crosslinking of a thermoplastic and/or elastomeric composition with peroxides or azo compounds. This is achieved by using a family of specific nitroxides as additive.

What is claimed is:  
     
         1 . A scorch-retardant crosslinking composition comprising a nitroxide (N) containing at least one unsaturation and a free-radical initiator comprising an organic peroxides, an azo compound, or mixtures thereof.  
     
     
         2 . The composition of  claim 1 , wherein the nitroxide (N) is represented by formulae (I) to (III):  
       
         
           
           
               
               
           
         
         in which at least one of the substituents R′ 1 , R′ 2 , R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9  and R 10  contains at least one unsaturation which is reactive towards free-radical addition; the remaining substituents, which may be identical or different, represent a hydrogen atom, a halogen atom, a linear, branched or cyclic, saturated hydrocarbon-based group, a substituted or unsubstituted aromatic group, a cyano group —CN, an amide group —CONRR a , an ester group —COOR, an alkoxy group —OR, a phosphonate group —PO(OR)(OR a ), a hydroxyl group —OH or an acid group; R and R a , which may be identical or different, may represent a hydrogen atom, a linear, branched or cyclic alkyl group containing a number of carbons ranging from 1 to 20, or an optionally substituted phenyl group.  
       
     
     
         3 . The composition of  claim 2 , wherein said halogen atom is fluorine, chlorine, bromine or iodine  
     
     
         4 . The composition of  claim 2 , wherein said saturated hydrocarbon-based group is an alkyl radical.  
     
     
         5 . The composition of  claim 2 , wherein said acid group is —COOH or —PO(OH) 2  or SO 3 H.  
     
     
         6 . The composition of  claim 2 , wherein the substituents containing at least one unsaturation each represent a linear, branched or cyclic unsaturated hydrocarbon-based group or an acrylate, methacrylate, acrylamide or methacrylamide group.  
     
     
         7 . The composition of  claim 1 , wherein the nitroxide (N) is represented by formula (IV):  
       
         
           
           
               
               
           
         
         in which X represents a divalent group —OC(O)—, —NR b C(O)— or —P(O)(OR b )O— with R b  having the same meaning as R and n is an integer ranging from 2 to 20.  
       
     
     
         8 . The composition of  claim 7 , wherein n ranges from 2 to 10.  
     
     
         9 . The composition of  claim 7 , wherein the nitroxide (N) is: 
 2,2,6,6-tetramethyl-4-piperidyloxy acrylate,    2,2,6,6-tetramethyl-4-piperidyloxy methacrylate,    2,2,6,6-tetramethyl-4-piperidyloxyacrylamide, or    2,2,6,6-tetramethyl-4-piperidyloxymethacrylamide.    
     
     
         10 . The composition of  claim 1 , wherein the free-radical initiator is dicumyl peroxide or α,α′-di[(t-butylperoxy)isopropyl]benzene.  
     
     
         11 . The composition of  claim 1 , further comprising a thermoplastic polymer and/or an elastomeric polymer.  
     
     
         12 . The composition of  claim 11 , wherein the polymer is a low density polyethylene, a high density polyethylene, a chlorinated polyethylene, an ethylene-propylene-butadiene terpolymer, an ethylene-vinyl acetate copolymer, an ethylene-propylene copolymer, a silicone rubber, a chlorosulphonated polyethylene, a fluoroelastomer, an ethylene-methyl (meth)acrylate copolymer or an ethylene-glycidyl methacrylate copolymer.  
     
     
         13 . The composition of  claim 1 , wherein the weight ratio of the free-radical initiator to the nitroxide (N) is between 1 and 50.  
     
     
         14 . The composition of  claim 13 , wherein the weight ratio is between 2 and 10.  
     
     
         15 . The composition of  claim 11 , wherein the free-radical initiator represents between 0.2% and 5% by weight of the amount of polymer.  
     
     
         16 . The composition of  claim 15 , wherein the free radical initiator represents between 0.5% and 3% by weight of the amount of polymer.  
     
     
         17 . A process for crosslinking a crosslinkable composition comprising a thermoplastic polymer and/or an elastomeric polymer which may be crosslinked with a peroxide or an azo compound, comprising the step of mixing said polymer with a free-radical initiator comprising an organic peroxide, an azo compound, or mixtures thereof, in the presence of a nitroxide (N) containing at least one unsaturation and a free-radical initiator comprising an organic peroxides, an azo compound, or mixtures thereof.  
     
     
         18 . The process of  claim 17 , comprising converting the crosslinkable composition into molded or extruded articles during or after crosslinking.  
     
     
         19 . Molded or extruded articles obtained according to the process of  claim 18 .  
     
     
         20 . The composition of  claim 2 , wherein R and R a  may represent a cyclic alkyl group containing a number of carbons ranging from 1 to 20, or a substituted phenyl group.