Anionic ring opening polymerization of oxygenated heterocycles with supported zirconium and rare earths alkoxides as initiators in protic conditions.Towards a catalytic heterogeneous process

The polymerization of epsilon-caprolactone and 2,2-dimethyltrimethylene car bonate (DTC) initiated by various Lewis acid metal alkoxides (Zr and rare e arths) in the presence of alcohol molecules has been investigated. Adding a lcohol induces a fast transfer reaction which allows to synthesise function alized oligomers. The polymerization can be described according to a Living process with fast transfer reaction, so that the molecular weight is easil y controlled. In the case of lactones, rare earths alkoxides allow to get higher activiti es so that functionalized oligomers can be obtained within less than 5 minu tes. Some transesterification are noticed if the polymer chains are left in contact with the active centers after polymerization. These active centers have been grafted onto porous supports. These solids act as actual chemica l ligands able to modify drastically the kinetic behaviour, particularly wi th regard to the controlled polymerization of ethylene and propylene oxides . Supported Y and Nd alkoxides are the best active centers for the polymeri zation of DTC. Finally, the heterogeneous character has been used to develop a new continu ous polymerization process by using a plug flow reactor filled with grafted silica. The conversion as well as the degree of polymerization depend eith er on the height of the bed or on the flow rate.