Correlation Between Catalyst Nature and Polymer Selectivity in Romp of Cycloolefins with WCI₆-Based Catalytic Systems

Summary

Ring-opening metathesis polymerisation (ROMP) of a series of cycloolefins (cyclopentene, cyclooctene, cyclododecene, dicyclopentadiene) in the presence of different WCl₆-based catalysts exhibited a wide range of polymer stereoselectivity depending mainly on the nature of the catalytic system employed. It is of interest that in the reaction of cyclopentene catalysts derived from WCl₆ and organoaluminium compounds lead preferentially to trans-polypentenamer while catalysts obtained from WCl₆ and organotin compounds form mainly cis-polypentenamer. The role of organometallic cocatalyst showed to be crucial in determining the polypentenamer stereoselectivity. The polymer stereoconfiguration is also substantially influenced by the presence of electron donor or acceptor compounds added to the catalytic system and in some cases by other reaction parameters such as temperature, solvent and mode of catalyst preparation. In the reactions of cyclooctene, cyclododecene and dicyclopentadiene the polymer stereoconfiguration depends in addition to the catalyst nature on the type of monomer employed. The trans and cis stereoconfiguration of the polyalkenamers obtained from higher cycloolefins, however, is not so strongly dependent of the catalyst type. With this class of cycloolefins it is obvious that the structure of the monomer plays a significant role in determining the reaction stereoselectivity.

The way in which the catalytic system and particularly the cocatalysts influence the polymer stereostructure, the effect of electron acceptor and donor compounds on polymer microstructure and the role of the cycloolefin are rationalised in terms of metallacarbene-metallacyclobutane mechanism generally accepted for ring-opening metathesis reaction of cycloolefins.