NEW PROSPECTS IN HOMOGENEOUS RING-OPENING POLYMERIZATION OF HETEROCYCLIC MONOMERS.

Since the early days of ring-opening polymerization of oxirane and related monomers, many initiators have been described for this type of chain reaction, belonging respectively to acid-base, ionic, and coordination catalysis. In particular, it has been shown that the highly active coordination type initiators are the only ones able to promote the ring-opening polymerization of methyloxirane (propylene oxide, PO) to high molecular weight, and eventually stereoregular polyethers. In the reported experiments a new family of ring-opening polymerization catalysts, namely bimetallic mu -oxoalkoxides, were prepared and used in the study of mechanisms of ring-opening polymerization. It is concluded that the good control and knowledge of these oxoalkoxides structures have led to a better understanding of the key factors governing the ring-opening polymerization processes; the results emphasize dramatically the determinant influence of the association phenomena in the catalytic species. They have also promoted the discovery of new phenomena (like the topochemical controls of the chains formation), and of new synthesis methods (for the block copolymers), which could most probably be extended to more classical catalysts. These species constitute a very promising tool for many problems in polymer and general chemistry.