Solvent clustering, polar network density, and thermodynamic interactions in coordination polymers: an inverse gas chromatography study of metal-ion-containing polyesters of poly(diethylene glycol-co-succinic acid)

The spatial distribution of toluene and THF in the polyester poly(diethylene glycol-co-succinic acid) and its Mg 2+ -containing "telechelic" derivative was described by Kirkwood–Buff–Zimm (KBZ) cluster integrals. The values of KBZ integrals as a function of the volume fraction of solvent in the polymer–solvent systems were obtained from finite concentration inverse gas chromatography measurements utilizing the elution-on-a-plateau technique. The results show that toluene has a higher self-affinity to form clusters in the pure polyester than THF, which is more homogeneously distributed in the polymer. Data for preferential solvation indicate that a segregation of parts of the polymer chains is present in the toluene–polyester system. When metal ions are introduced, the self-affinity of the solvent molecules to gather increases, whereas solvent clusters of toluene form in the free volume, and the gathering of the THF is likely to take place close to the metal ions. Based on the electron donacity values of the various donor groups present in the metal-ion-containing polymer it was assumed that THF in the Mg 2+ -containing polyester will be bound to the central metal ion while the apolar toluene will participate in the solvation of the apolar parts of the polymer and will be "repelled" from the ion-containing regions. The concentration of these ionic centres, which act as effective cross-links in the coordination polymer, was determined from measurements of thermodynamic activity. A comparison of the experimental and estimated effective cross-link density values indicates a nearly atomic dispersion of Mg 2+ in the metal-ion-containing polyesters.