Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution. THF–CH₂Cl₂ and THF–CH₂Cl₂/CH₃NO₂ systems

Cationic polymerization of tetrahydrofuran (THF) in CH 2 Cl 2 solvent and in mixed CH 2 Cl 2 /CH 3 NO 2 solvent was initiated with 1,3‐dioxolan‐2‐ylium cations with AsF and SbF anions. Dissociation constants of the polytetrahydrofuranium ion pairs into ions were measured (e.g., K D = 1.5 × 10 −5 M at 25°C and [THF] 0 = 7.0 M ; CH 2 Cl 2 solvent) and were found to be more than 100 times lower than in CH 3 NO 2 solvent at the same [THF] 0 and temperature. The rate constants k and k , measured for degrees of dissociation ranging from 0.03 to 0.35 in CH 2 Cl 2 , were the same within an experimental error of measurements (±15% of the value of k p ). Dependence of k ( = k = k ) on the dielectric constant was a monotonous function in three different solvents, namely, CCl 4 , CH 2 Cl 2 , and CH 3 NO 2 , which covered a large range of dielectric constants of the medium (from D = 5 to D = 22) and degrees of dissociation of the macroion pairs, α (from 0.03 to more than 0.70). Thus a decrease in the dielectric constant increases the rate constant k in the whole range of studied polarities of the medium. This result confirms an earlier conclusion that the rate constant of propagation does not depend on the state of aggregation of ions and k = k .