STABILIZATION OF RAW DIENIC SYNTHETIC RUBBER POLYMERS

Abstract

Abstract The mechanism of rubber polymer autoxidation is briefly reviewed with an emphasis and an appreciation for what these uninhibited free radical reactions can do to polymer properties and quality. Significant differences between hydrocarbon and rubber oxidation are discussed. Differences in polymer substructure are described which affect the mode of oxidation as well as the choice of stabilizer to protect these materials. An explanation of color formation and color prevention for 2,6-dialkyl-4-methylphenols is provided which also includes a discussion of how their oxidized transformation products interact with the rubber polymer. Additional factors that affect polymer quality include proxidative effects of the stabilizer, oxygen diffusion, and the formation of gel. Studies which varied the steric bulk of the alkyl groups in the 2,6 position were conducted to optimize the antioxidant activity of this system in its function in the hydrogen atom donor—hydrogen atom acceptor mechanism of stabilization. A description of the preparation and activity impact of the secondary antioxidant synergist Wingstay® SN-1 is included. Finally, the discovery of highly active 2,6-di(alkylthiomethyl) substituted phenols is described which led to the discovery of Wingstay® K and its contained synergist methylene-bis(dodecylsulfide). This material is a highly persistent auto synergistic stabilizer which is outstanding for the protection of emulsion-styrene butadiene rubber when used 50/50 with Wingstay® 29. When used by itself in polybutadiene rubber polymers, it is highly effective against the effects of oxidation and also for the prevention of gel formation and Mooney viscosity changes.