Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution. I. THF–CCI4 system

Polymerization of THF in CCl4 solvent was initiated with 1,3‐dioxolan‐2‐ylium eations with AsF6−, PF6−, and SbF6− anions as well as with esters of fluorosulfonic and trifluoromethanesulfonic acids. With these esters polymerization proceeds with a marked acceleration period, due to slow initiation. The corresponding rate constants of initiation and their dependence on the polarity of the THF/CCl4 mixture were determined. The rate constant of propagation on the macroion‐pairs (kp±) of the polytetrahydrofurylium cation with AsF6−, PF6−, and SbF6− and CF3SO3−, anions was found to be independent in CCl4 solvent on the anion structure and given by the expression: kp± = 2.93 × 10−2 exp {−4.7 × 103/T} at [THF]0 = 8.0M. This constant depends on the polarity of the polymerization mixture, and at 25°C for the THF‐CCl4 system, kp± = 1.78 × 10−2 exp {−4.9/D}; thus, in CCl4 at [THF]0 = 8.0M, and at 25° kp± = 4.0 × 10−21/mole‐sec. In the polymerization with derivatives of CF3SO3H (able to form the corresponding macroester) the overall polymerization rate is much lower than that with complex anions because of the reversible conversion of the macroion‐pairs into the macroester (internal return). The macroester is much less reactive than the macroionpair (102–103 times) in the monomer addition reaction. At [THF]0 = 8.0M and at 25°C, 96.5% of the growing species exists in the macroester form. Polymerization of THF initiated with derivatives of CF3SO3H is a subject of a strong special salt‐effect. At a sufficiently high ratio of [AgSbF6] to [I]0, where the initiator I is C2H5OSO2CF3, the overall polymerization rate is equal to that observed for the polymerization of THF on the macroion‐pairs, since the internal return within the triflate ion‐pair (the macroester formation) is eliminated and polymerization proceeds on the macroion‐pairs with SbF6‐ anions exclusively.