ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Polymerization of tetrahydrofuran (THF) in CH3NO2 solvent was initiated with 1,3-dioxolan-2-ylium cations with AsF6- and SbF6- 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 AsF6-, CF3SO3-, FSO3-, and SbF6- 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 (CF3SO3- and SbF6- 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 (kp+ and k+±) were determined for a large range of degrees of dissociation (α from 0.15 to 0.52). The rate constants kp+ and kp± 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.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1979.170170108
Permalink
