ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ∊-caprolactone (∊CL) 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 CH3(CH2)5O-K+DB18C6, modelling the active centers, were determined conductometrically: KD (20°C) = 7,7 · 10-5 mol · dm-3, ΔH0D = 9,3 ± 0,2 kJ · mol-1, ΔS0D = -47 ± 2J · mol-1 · K-1. From kinetic measurements and from measurements of the dissociation constant of CH3(CH2)5O- K+DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: ΔH≠(±) = 39,2 ± 0,2 kJ · mol-1, ΔS≠(-) = -63 ± 1 J · mol-1 · K-1, ΔH≠(±) = 13,7 ± 0,1 kJ · mol-1, ΔS≠(±) = -185 ± 2 J · mol-1 · K-1. At 20°C, kp- = 3,50 · 102 dm3 · mol-1 · s-1 and kp± = 5,2 dm3 · mol-1 · s-1. Due to the large difference of ΔH≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point (kp- = k±p) would appear at -65°C.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1991.021920323
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