Methylene bis(alkylsulfides) as antioxidant synergists in rubber

A process for the preparation of a stable rubbery diene polymeric compositions, said process comprising:

• mixing a rubbery diene polymer with an antioxidant sufficient amount of
• (1) a methylene bis(alkylsulfide) represented by the structural formula:
• ##STR6## wherein R.sup.1 and R.sup.2 are the same or different radical selected from the group consisting of hydrogen and methyl radicals:
• when R.sup.1 is a hydrogen radical, R is an alkyl radical of 5 to 11 carbon atoms;
• when R.sup.1 is a methyl radical, R is a radical of 4 to 10 carbon atoms;
• when R.sup.2 is a hydrogen radical, R.sup.3 is an alkyl radical of 5 to 11 carbon atoms;
• and when R.sup.2 is a methyl radical, R.sup.3 is an alkyl radical of 4 to 10 carbon atoms;
• and
• (2) an antidegradant selected from phenolic antioxidants and amine antioxidants;
• wherein the ratio of antioxidant to methylene bis(alkylsulfide) can range from 4:1 to 1:4 by weight.