KINETICS AND MECHANISM OF THE CATIONIC POLYMERIZATION OF TETRAHYDROFURAN IN SOLUTION - THF-CH3NO2 SYSTEM

In the reported experimental study, polymerization of tetrahydrofuran (THF) in CH//3NO//2 solvent was initiated with 1,3-dioxolan-2-ylium cations with AsF//6** minus and SbF//6** minus anions, as well as with esters of FSO//3H and CF//3SO//3H acids. Polymerization shows in this solvent a living feature: values of k//p (determined directly from the semilogarithmic kinetic plots) were the same for all of the listed above initiators; thus k//p is the same for AsF//6** minus , CF//3SO//3** minus , FSO//3** minus , and SbF//6** minus anions. On the basis of the known values of K//D, and therefore dissociation degrees alpha , rate constants of propagation on the free and paired THF cations (k//p** plus and k//p** plus or minus ) were determined for a large range of degrees of dissociation ( alpha from 0. 15 to 0. 52). The rate constants k//p** plus and k//p** plus or minus were found to be the same within an experimental error of measurements ( plus or minus 15% of the value of k//p). 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 indistinguishable.