KINETIC-STUDY OF THE HETEROGENEOUS ANIONIC COORDINATED POLYMERIZATIONOF ETHYLENE-OXIDE

New heterogeneous catalytic systems for anionic ring opening polymeriz ation of oxygenated heterocycles are obtained by grafting alkylalumini um moieties on porous silica. Adding alcohol in excess causes the form ation of aluminium alkoxides and allows a rapid exchange reaction betw een the grafted active centers and the free alcohols remaining in the solution, so that more polymer molecules than the number of metal atom s used are produced. An interesting feature is the facility to obtain functionalized oligomers because these exchange reactions lead to poly mer chains end-capped by moieties derived from the alcohol molecules. The kinetic behaviour was investigated for different monomer, alcohol and aluminium concentrations. An activation is observed for a well-def ined alcohol concentration range which is interpreted in terms of the enhancement of the nucleophilic reactivity of the oxygen atom of the a lkoxide due to the coordination of the free alcohol onto the active ce nters and the share of the acidic vacancy of the aluminium atom.