Enantioelective stereoelective and enantioselective stereoselective polymerization

Enantioelective polymerization [94-98] is a process where, from a mixture of two enantiomeric forms of a monomer, macromolecules are produced 

In polymerizations of cyclic monomers, the product is isotactic. This is not necessarily so when optically active alkenes are polymerized. 

By enantioselective polymerization polymer chains, each containing only one configurational kind of monomeric unit, are produced from a mixture of stereoisomeric monomer molecules. The number of kinds of polymer chain generated therefore equals the number of various stereoisomers in the monomer mixture. In the course of propagation, the enantiomeric composition of the polymer and unreacted monomer remains identical to the intial composition. When optically active monosubstituted cyclic monomers are polymerized, stereoregular polymers are formed with both isotactic polyR and polyS chains 

It is important that the ring is opened at the / bond. Attack at the a position leads to irregularities and to asymmetric C inversion. 

As initiators usually serve Ziegler-Natta catalysts or Zn, Cd, Mg or A1 compounds [for example of the type Et2Zn + optically active (-)-3,3-dimethyl-l,2-butanediol]. The polymerizations are mostly heterogeneous. 

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