Metal deactivator for cobalt catalyzed polymers

Various benefits can be attained by utilizing trans-1,4-polybutadiene in tire rubber compounds. For instance, the green strength of tire rubber compounds can be improved by including trans-1,4-polybutadiene therein. The inclusion of trans-1,4-polybutadiene in tire rubber compounds is also beneficial because it is strain crystallizable. However, due to its high melting point, it is normally necessary to heat trans-1,4-polybutadiene in order for it to be processed using conventional mixing equipment. This heating step is typically carried out by storing the trans-1,4-polybutadiene in a "hothouse" for a few days prior to its usage. During this storage period, the polymer typically undergoes undesirable oxidative crosslinking which is caused by residual cobalt catalyst and leads to gelation. In fact, the gelation can render the trans-1,4-polybutadiene unprocessable. This invention is based upon the unexpected finding that certain substituted benzoic acids, such as salicylic acid, thiosalicylic acid and acetylsalicylic acid, will act as metal deactivators in polymers. By utilizing the technique of this invention, residual cobalt and/or other metals, such as nickel, that act as prooxidants in polymers, such as trans-1,4-polybutadiene, can be deactivated. This invention more specifically discloses a stabilized trans-1,4-polybutadiene composition which is comprised of trans-1,4-polybutadiene and a substituted benzoic acid selected from the group consisting of salicylic acid, thiosalicylic acid and acetylsalicylic acid.