Dissociation of Macroion Pairs

Detailed studies of the dissociation of macroion pairs, includii thermodynamic parameters of dissociation, are avaUable only for THF and oxepane Dissociation constants and the corresponding enthalpies and entropies of dissociation are given in Table 8 below. 

Measurements of Kq were performed for polymeric chains differing in DPn, but it has recently been shown for the macromotecular ammonium salts 

Monomer [MJo (mole - 1-1) Solvent Dielectric constant of solution Kd. (mole r ) AH (kcal mole-1) AS (cal mole 1 K i) Ref. 

The dissociation of poly-THF macroion pairs in THF/solvent mixtures is more exothermic than the dissociation of macroion pairs of polyoxepane under similar conditions (dielectric constant, solvent structure, temperature). In both cases, however, the exothermicity is very low and typical of parated rather than of contact ion pairs. It has to be remembered that the positive diarge ist not concentrated on the oxygen atom but distributed on the three carbon atoms and that, moreover, the anions with their diffused charge are large. Hie estimated dimensions of the poly-THF growing ion pair are shown below for SbFg anion  

The small differences in AHj) and ASp between poly-THF and polyoxepane macroion pairs in CH2CI2 solvent (the dissociation of poly-THF macroion pairs is more exothermic and accompanied by a higher loss of entropy) stem from the higher nucleophilicity of THF. THF, as a 

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Table 8. Dissociation constants and thermodynamic parameters (AH and AS0) of dissociation of macroion pairs... 

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