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.