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 tire 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.