#Sodium acetate molar mass for free#

In order to be consistent with the experimental results, and especially with the dependence of the activation parameters on 0 ( Table 1), the aforementioned reaction scheme must include the participation of βPL in the solvation of the active species. A much more negative entropy of activation should result from the necessity of proper orientation of both ion and monomer molecules in the activated complex.

#Sodium acetate molar mass for free#

The enthalpy of activation is, thus, essentially independent of solvation effects, and lower than that for free anions. When the propagation takes place on macroion pairs, the charge distribution and the related solvation ability are quite similar in both the ground state and the activated complex ( Figure 2b).

Therefore, the formation of the activated complex from the carboxylate anion requires a desolvation step, which increases the activation energy and makes the entropy of activation less negative. The solvation efficiency of the free carboxylate anion is much higher than that of the activated complex, in which that negative charge is greatly delocalized ( Figure 2a). From the dependence of In ( k p − ) and In ( k p ± ) on T −1 ( Figure 1), activation parameters have been calculated ( Table 1) and interpreted as follows. 9 The ratio of the related rate constants, k p − / k p ±, which amounts to 150 at 35 ☌, falls, however, down to 5.6 at −20 ☌. 9Īs would be expected, macroions are more reactive propagating species than are mecaroion pairs. This behavior is most probably due to the bulkiness of the complexed potassium counterion. These values correlate with the existence of loose ion pairs which are subjected to only a small change in their solvation when becoming free ions. Moreover, the entropy of dissociation is equal to −92 and −75 JK −1 mol −1 at initial β-PL concentration () of 1 and 3 mol l −1, respectively. In dichloromethane, the dissociation constant is found to be largely independent of temperature, therefore the enthalpy of dissociation of the macroion pairs is close to zero.

9–15 From the dissociation constant of the crowned potassium carboxylate ion pairs (calculated approximately from conductometric data), the proportion of macroion pairs and macroions has been established, and the rate constant of propagation on these species determined.

This particular situation has enabled Penczek and co-workers to quantify the contribution of specific active species, rather than to report global propagation rate constants. 9 Another advantage of complexing the alkali metal cations is that it provides systems in which well-defined active species are present, i.e. 8 As well as providing a noticeable rate enhancement, crowned cations also eliminate transfer reactions, resulting in a living process. Nowadays, the addition of macrocyclic ligands, which act as complexing agents for the alkali metal cations, allows β-PL to be polymerized by carboxylate anions under conditions that would not usually lead to polymers. 7 Its reactivity at room temperature was especially low, and transfer reactions were usually reported. Sodium acetate has been used as a weak nucleophile in the anionic polymerization of β-propiolactone (β-PL). Potassium hydroxide uses in agriculture.Robert Jerome, Philippe Teyssié, in Comprehensive Polymer Science and Supplements, 1989 34.2.1 β-Propiolactone