Stereospecificity of the polymerization of
tert-butylacetylene by Mo-based catalysts was
investigated. The polymer obtained by the
MoOCl4−n-Bu4Sn system just
after complete monomer
consumption had an all-cis structure. However, the
stereoregularity decreased when the polymerization
was allowed to stand further. These findings indicate that, though
the propagation reaction proceeds
stereospecifically, the geometric isomerization of polymer lowers
stereoregularity. This isomerization
was catalyzed by several acids as well as by polymerization catalysts
and, hence, is an acid-catalyzed
reaction. Highly stereoregular polymer could be obtained by
accelerating polymerization (by use of
cocatalysts) and/or by decelerating isomerization (by use of
cocatalysts, poor solvents of the polymer, or
the less acidic Mo(CO)6-based catalyst and by
polymerization at low temperatures).
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