Superacids and Their Derivatives. V. Kinetics and Mechanism of the Cationic Polymerization of 3,3-Bis(chloromethyl)oxacyclobutane Initiated by Ethyl Trifluoromethanesulfonate. Evidence for Ester Type Propagating Species

Kinetic analysis of the cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane (BCMO) initiated by ethyl trifluoromethanesulfonate (EtOSO2CF3) was carried out by direct determination of the instantaneous concentrations of monomer, initiator, and propagating species by means of 1H and 19F NMR spectroscopy. It was established that the polymerization of BCMO proceeds via an ester type propagating species (4). The propagating species of the first (P1*) and subsequent propagations (Pn*, n≥2) were directly observed. The rate constants of initiation (ki) and propagations of the first (kp1), second (kp2) and subsequent steps (kpn, n≥3) were determined. Activation parameters as well as the solvent effect supported the proposed mechanism, in which the rate-determining step is a dipole-dipole reaction between monomer and propagating ester species to form the intermediate cyclic oxonium ions (7, 8, and 10) as unstable transient species.