Synthesis of Cis,syndiotactic A-alt-B Copolymers from Two Enantiomerically Pure Trans-2,3-Disubstituted-5,6-Norbornenes.

Cis,syndiotacticA-alt-B copolymers, where A and B are two enantiomerically pure trans-2,3-disubstituted-5,6-norbornenes with "opposite" chiralities, can be prepared with stereogenic-at-metal initiators of the type M(NR)(CHR')(OR")(pyrrolide). Formation of a high percentage of alternating AB copolymer linkages relies on an inversion of chirality at the metal with each propagating step and a relatively fast formation of an AB sequence as a consequence of a preferred diastereomeric relationship between the chirality at the metal and the chirality of the monomer. This approach to formation of an alternating AB copolymer contrasts dramatically with the principle of forming AB copolymers from achiral monomers and catalysts.