A POSSIBLE ROUTE TO THE CONTROLLED SYNTHESIS OF POLYMETHYLOXIRANE OLIGOMERS USING BIMETALLIC MU-OXOALKOXIDES

Soluble mu-oxo-bimetallic trinuclear alkoxides are known to be very ef fective catalysts for the ring-opening polymerization of oxiranes. In the particular case of methyloxirane, oligomers are formed in addition to high molecular weight polyethers. An alkoxide-alcohol exchange rea ction has proved to be an efficient way to form oligomers preferential ly, when the monomer-alcohol molar ratio is small. Upon increasing thi s ratio, formation of high MW chains occurs increasingly. The use of T i instead of Al in Al, Zn mu-oxo-n-butoxide in the presence for phenox yethanol as a co-initiator inhibits formation of exceedingly long poly ether chains and the chain length is basically controlled by the monom er to all potential initiating species molar ratio until MW of ca. 600 0. Substitution of phenoxyethanol by polypropylene glycol has led to o ligomers of a monomodal MW distribution and a MW of 13,000. This study has highlighted that conditions unfavorable to coordination of the po lyether chains onto the catalyst improve the control of the oligomer f ormation. (C) 1995 John Wiley and Sons, Inc.