Cationic Copolymerization of Propylene Oxide with Tetrahydrofuran. XI. Calculation of Individual Rate Constants

Abstract

A B S T R A C TRate constants (ki, kll, k12, k22, kZ1, and k ) for various steps involved in the copolymerization of propylene oxide (PO) with tetrahydrofuran (THF) have been calculated from reaction rate data obtained with the following catalyst system: (a) triphenylmethyl cations ((C& )sC') associated with hexafluorophosphate (PFa-), hexafluoroarsenate (As&-) and hexafluoroantimonate (SbFe-) gegenions; (b) antimony pentachloride (SbCl5 ); and, (c) boron trifluoride etherate, BFs:(C2Hs )aO. The latter two systems were studied in the presence of cocatalysts. The effects of several parameters (the cocatalyst concentration and bulk size, the nature of the solvent, and the reaction temperature) on the rate constants are highlighted. The role of entropy in the initiation, propagation and termination steps is discussed in terms of solvation and desolvation processes. Based on termination activation energy considerations, the order of t 1317