Kinetics of the anionic polymerization of ϵ‐caprolactone with K⁺ · (dibenzo‐18‐crown‐6 ether) counterion. Propagation via macroions and macroion pairs

Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ϵ‐caprolactone (ϵCL) with K + · (dibenzo‐18‐crown‐6 ether) (K + DB18C6) counterion was studied calorimetrically in THF solution in the temperature range from 0 to 20°C. Dissociation constants of CH 3 (CH 2 ) 5 O − K + DB18C6, modelling the active centers, were determined conductometrically: K D (20°C) = 7,7 · 10 −5 mol · dm −3 , Δ H = 9,3 ± 0,2 kJ · mol −1 , Δ S = −47 ± 2J · mol −1 · K −1 . From kinetic measurements and from measurements of the dissociation constant of CH 3 (CH 2 ) 5 O − K + DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: Δ H = 39,2 ± 0,2 kJ · mol −1 , Δ S = −63 ± 1 J · mol −1 · K −1 , Δ H = 13,7 ± 0,1 kJ · mol −1 , Δ S = −185 ± 2 J · mol −1 · K −1 . At 20°C, k = 3,50 · 10 2 dm 3 · mol −1 · s −1 and k = 5,2 dm 3 · mol −1 · s −1 . Due to the large difference of Δ H ≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point ( k = k ) would appear at −65°C.