Elementary reactions in the cationic polymerization of oxepane. Comparison with the polymerization of tetrahydromfuran

In the polymerization of oxepane (OXP), initiated with derivatives of trifluoromethanesulfonic acid, covalent and ionic active centers were simultaneously observed by 1 H and 19 F NMR spectroscopy. A higher proportion of secondary oxonium ions (these species detected by 19 F NMR were independently observed by proton trapping with R 3 P in the 31 P NMR spectrum). The proportion of ionic species decreases with monomer conversion, indicating a substantial contribution of bimolecular ionization of the monomer. The effective molarity in oxepane polymerization [OXP] eff ⋍ 1 mol ·I ‐1 was found to be lower by a factor of 10 2 than [THF] eff in the polymerization of THF. The rate constant of the covalent propagation in the polymerization of OXP is similar to that measured for THF, however, due to the reduced reactivity of the oxepanium cation, the relative reactivity of the covalent active centers becomes higher than that of the ions. Thus, for OXP, in CH 3 NO 2 at 25°C, K pc = 3 · 10 −4 mol −1 · 1 · s −1 , k pi = 2 · 10 −4 mol −1 · 1 · s −1 whereas for THF k pc = 5 · 10 −4 mol −1 · 1 · s −1 and k pi = 2 · 10 −2 mol −1 · 1 · s −1 under similar conditions. The rates of ionization and temporary termination, measured by the “temperature jump” technique, allow to determine the contributions of inter‐and intramolecular ionizations. These rates becomes equal at [OXP] = 1 mol · 1 ‐1 (= [OXP] eff ).