Patent attributes
Rubbery polymers made by anionic polymerization can be coupled with tin halides or silicon halides to improve the characteristics of the rubber for use in some applications, such as fire treads. In cases where the rubbery polymer was synthesized utilizing a polar modifier it is difficult to attain a high level of coupling. This invention is based upon the unexpected finding that coupling efficiency can be significantly improved by conducting the coupling reaction in the presence of a lithium salt of a saturated aliphatic alcohol, such as lithium t-amylate. This invention discloses a process for coupling a living rubbery polymer that comprises reacting the living rubbery polymer with coupling agent selected from the group consisting of tin halides and silicon halides in the presence of a lithium salt of a saturated aliphatic alcohol. The lithium salt of the saturated aliphatic alcohol can be added immediately prior to the coupling reaction or it can be present throughout the polymerization and coupling process. Lithium t-amylate reacts with water to form t-amyl alcohol during steam stripping. Since t-amyl alcohol forms an azeotrope with hexane, it co-distills with hexane and can contaminate recycle feed streams. This problem of recycle stream contamination can be solved by using metal salts of cyclic alcohols that do not co-distill with hexane or form compounds during steam stripping which co-distill with hexane. Thus, the use of metal salts of cyclic alcohols is preferred for this reason and because they are considered to be environmentally safe.
