Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution: THF‐CH3NO2 system

Polymerization of tetrahydrofuran (THF) in CH3NO2 solvent was initiated with 1,3‐dioxolan‐2‐ylium cations with AsF and SbF anions, as well as with esters of FSO3H and CF3SO3H acids. Polymerization shows in this solvent a living feature: values of kp (determined directly from the semilogarithmic kinetic plots) were the same for all of the listed above initiators; thus kp is the same for AsF , CF3SO , FSO , and SbF anions. The identity of the kp values for complex and noncomplex (ester‐forming) anions comes from the fact that in CH3NO2 solvent equilibrium between macroesters and macroion pairs is shifted almost completely (Ke = 33.0 at 25°C and |THF|0 = 7.0M) to the macroions side. Dissociation constants of the polytetrahydrofuranium ion pairs (CF3SO and SbF anions) were measured (e.g., KD = 2 × 10−3 M at 25°C and |THF|0 = 7.0M; i.e., at D = 22.8, ΔHD = −3.8 ± 6 kcal mole; ΔSD = −25 ± 2 eu). On the basis of the known values of KD, and therefore dissociation degrees α, rate constants of propagation on the free and paired THF cations (k and k ) were determined for a large range of degrees of dissociation (α from 0.15 to 0.52). The rate constants k and k were found to be the same within an experimental error of measurements (± 15% of the value of kp). Apparently, the polytetrahydrofuranium cations are highly solvated or even separated from their anions by molecules of THF itself. At these conditions the reactivities of the solvated “free” and solvated (or separated) paired cations became undistinguishable.