Mechanism of cyclics formation in the cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols

Cationic copolymerization of ethylene oxide (EO) with tetrahydrofuran (THF) in the presence of diols leads to the formation of hydroxytelechelic copol ymers. The process combines the features of an activated monomer mechanism (secondary oxonium ions as active species) with those of an active chain en d mechanism (tertiary oxonium ions as active species). Due to the participa tion of tertiary oxonium ions, backbiting leads to the formation of cyclic oligomers. The effect of reaction conditions on the content of the cyclic f raction was studied, the individual cyclic oligomers were identified, and t he results are interpreted in terms of a reaction mechanism.