Polymerization of THF induced by initiators bearing anions able to form covalent bonds (i. e. macroesters) proceeds according to the kinetic scheme proposed by us recently'):In principle, scheme (1) might be supplemented by a process in which the macroester En is formed by recombination of the unpaired macrocation P: with an anion (anions are omitted in the scheme) but the existing experimental data indicate that this "external return" (in Winstein's terminology*)) is less important than the recombination within an ion pair P :.We have shown previously that for both THF3-4) and oxepane k : = k : ( = k$). We determined also the rate constants of interconversions of macroesters into macroion pairs (k,, and k,, in scheme (1)) '). This part of the scheme therefore seems to be quantitatively described.There is, however, in the literature a difference in opinions concerning the proportions of macroions and macroesters in the chain growth and the relative reactivities of these species in propagation (k; vs. k: in scheme (1)). In the present work we measured the upper limit of k: in the cationic polymerization of THF with initiators providing the triflic (CF,OSO 7) anion.
ResultsRemembering that k ; = k ; ( = k;), the apparent rate constant of propagation k i p p , determined from the measurements of the rate of propagation, proceeding simultaneously via both macroions and macroesters, is given by Eq. (2).
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