Cationic polymerization of exo‐2‐methyl‐7‐oxabicyclo [2, 2, 1] heptane. II. Catalysis by PF5

The polymerization of exo‐2‐methyl‐7‐oxabicyclo[2, 2, 1] heptane by PF 5 in ethylene dichloride solution was investigated. The reaction was followed in vacuum dilatometers fitted with platinum wire electrodes, which allowed us to measure the variations of conductivity during the polymerization. The ultraviolet and visible spectra of the polymerizing solution have also been determined by a high vacuum technique. The conversion‐time curves showed an acceleration period which was gradually reduced by addition of water. The Rmax first increased with water concentration, reached a maximum at a α = [H2O] /[PF5] = 0.17, then decreased, and became zero at α = 1. The polymerizations gave limited yields at room temperature, which was not due to an equilibrium. At temperatures below O°C, 100% yields were obtained and experiments with a second addition of monomer showed that no termination was present but only transfer, as the second quantity of monomer was completely converted without increase of the molecular weight. The reaction mechanism is discussed.