Rate constants of propagation of THF on macroesters and macroions

Abstract

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).

Covalent and ionic species in cationic polymerizations: Rates of exchange

“…(5) (6) We are considering reactionswiththe rate constants k and kei to PC be covalent propagations, although only the former reforms J i r e c t 1 y covalent species. Thus, the way between ...-R X and ...-Rn+IX in Scheme (6) is exclusively via ionic species, whereas in Scheme(5)there is a direct way.…”

Cyanines comprising barbiturate group facilitate NIR‐light assisted ATRP under anaerobic and aerobic conditions at two wavelengths using Fe(III) catalyst

“…Atom transfer radical polymerization (ATRP) has been one of the most commonly employed method for tailor‐made synthesis of polymeric materials 1–8 . First attempts started with Cu(I) catalysts that remained on a high level requesting to remove excess of heavy metal ion by an additional step 9 .…”

“…From this point of view, polymerization techniques based on photoinitiation offer several advantages in comparison with the aforementioned reducing agents 1,3–8,12–30 . They initiate or stop the polymerization process just by switching the light source ON or OFF, respectively.…”