PYRIMIDINE DERIVATIVES AS HARDNESS STABILIZERS

The invention comprises a vulcanizable composition comprising a sulfur vulcanizable rubber, a sulfur vulcanizing agent, an accelerating agent selected from the group consisting of non-thiazole sulfenamide accelerators and a hardness stabilization agent comprising a pyrimidine derivative of formula (I), where X=H, R1 through R4, NR3R4, OR5, SR5, SO2R6, M, (SO3)zM (M=metal ion), and n and z can be the same or different and 1, 2 or 3, depending on whether the respective valence of X and M is 1, 2 or 3, R1 through R4 are the same or different and selected from the group consisting of the substituents H, halogen, OH, NH2, alkyl, cycloalkyl, aryl, alkylaryl, aralkyl, with each of such substituents optionally having additional functional groups selected form the group consisting of NH2, OH, substituted amino, substituted hydroxyl, halogen, and carbonyl containing group, R3 and R4 may be in the same constituent together with N to form a heterocyclic group, R5 is the same as any of R1 through R4, or a radical derived from a carbon based heterocyclic group containing at least one of S or N, or both S and N, R6 is selected from the same as any of R1 through R4, OH, OM, O R5, NH2 NR3R4 the respective amount of accelerating agent and hardness stabilization agent being effective to not substantially inhibit vulcanization and to stabilize the hardness properties of said rubber upon vulcanization, the amount of accelerating agent in said composition being greater than about 0.6 phr when said rubber is SBR and at least about 0.5 phr when said rubber is natural rubber, and the amount of hardness stabilization agent being at least about 0.5 phr. The invention also comprises a method of improving the hardness stabilization of a composition comprising a sulfur vulcanizable rubber by adding the above accelerators and pyrimidine derivative to the composition. La invencion comprende una composicion vulcanizable que comprende un hule vulcanizable con azufre, un agente vulcanizador de azufre, un agente acelerador seleccionado del grupo que consiste de aceleradores de sulfenamida que no contienen tiazol y un agente de estabilizacion de dureza que comprende un derivado de pirimidina de la formula (I):(ver formula I) en donde X=H1 R1 a R4, NR3R4, OR5, SR5, SO2R6, M, (SO3)zM (M=ion metalico), y n y z pueden ser los mismos o diferentes y 1, 2 o 3, dependiendo de si la valencia respectiva de X y M es 1, 2 o 3, R1, a R4 son los mismos o diferentes y se seleccionan del grupo que consiste d