Rubber compositions having improved adhesion after thermal aging

A method for improving the retention of adhesion after thermal aging of a rubber composition to a metal surface comprising compounding a highly unsaturated rubber with a magnesium compound capable of donating electrons, and a carboxylated cobalt oxy metal complex comprising at least one metal atom selected from Groups IIIA, IIIB, IVA, IVB, VA and VB of the Periodic Table, at least one cobalt atom, said metal and cobalt atoms being linked through oxygen atoms, at least one acyloxy radical attached to a cobalt atom, and any residual valences of said complex being satisfied by acyloxy, aryloxy or alkoxy radicals, said magnesium compound and said cobalt complex being used in small amounts which are sufficient for obtaining a high level of adhesion between the rubber and the metal surface and improving the retention of such adhesion after thermal aging,

• and contacting the rubber composition with the metal surface.

A composition comprising a magnesium compound capable of donating electrons and a carboxylated cobalt oxy metal complex comprising at least one metal atom selected from Groups IIIA, IIIB, IVA, IVB, VA and VB of the Periodic Table, at least one cobalt atom, said metal and cobalt atoms being linked through oxygen atoms, at least on acyloxy radical attached to a cobalt atom, and any residual valences of said complex being satisfied by acyloxy, aryloxy or alkoxy radicals, said magnesium compound and said cobalt complex being used in small amounts which are sufficient for obtaining a high level of adhesion between a highly unsaturated rubber and a metal surface and improving the retention of such adhesion after the thermal aging when the composition is used in the rubber.