Metalation ended polydiene

It follows from the existence of conformational scissors (Fig. 4) that in the polymerization of symmetric or quasisymmetric dienes in hydrocarbon media on an active center with a slightly polar carbon-metal bond the primary acts of monomer attachment lead to the cis-conformation of the end unit. This conclusion is in good agreement with the modern concepts of the formation mechanism of the cis-structure of anionic polydienes [70]. According to these concepts this is followed by either the attachment of the next monomer molecule or by the cis-trans isomerization of the end unit. The microstructure is fixed at the moment of the attachment of a new monomer unit to the active center, the configuration (cis- or trans-) of the end unit being retained in the polymer chain ... 

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