Abstract
AbstractThe formation of cyclic oligomers in the cationic polymerization of 3,3‐dimethyloxetane (1) was investigated. By means of gas chromatography coupled with mass spectroscopy, cyclic oligomers from tetramer up to nonamer (2a–f) were detected in decreasing concentration. The oligomer/polymer ratio at complete monomer consumption changes with the initiating system used. This ratio is not influenced by the initiator concentration but it increases with decreasing monomer concentration. It is proposed that the cyclic oligomers are formed by reaction of the monomer with macrocyclic oxonium ions of type 5 which in turn are formed by an intramolecular (temporary) termination reaction. The high preference to form cyclic tetramer is discussed in terms of the preferred polymer backbone conformation. In the polymerization of oxetane, cyclic tetramer is the most important oligomer, but, contrarily with previous reports, higher oligomers were also found to be present.
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