Preparation of ion-exchangers by cross-linking of starch or polygalacturonic acid with 1,3-bis(3-chloro-2-hydroxypropyl)imidazolium hydrogen sulphate

The reaction conditions for cross-linking of starch (S) or polygalacturonic acid (PGA) with 1,3-bis(3-chloro-2-hydroxypropyl)imidazolium hydrogen sulphate (BCHIHS) in the presence of NaOH and water were studied in terms of the molar ratio of the reaction components, the yields of water-insoluble product, the nitrogen content and the BCHIHS conversion. The optimum for S-derivatives was at the molar ratio of S/BCHIHS/NaOH/H2O=0.01:0.02:0.04:0.333 with 348% yield on the amount of used S, 7.71% nitrogen content and 78% conversion of BCHIHS. Analogically on PGA the optimum was at PGA/BCHIHS/NaOH/H2O=0.005:0.005:0.1:0.2 with 125% yield, 7.99% nitrogen content and 63% conversion. The linkage of dihydroxypropylimidazolum (DHPI) groups was confirmed by NMR in solution on water-soluble products as well as by 13C solid-state NMR and FTIR on insoluble products. Under the used conditions much more NaOH is consumed on PGA while the yields of water-insoluble materials are lower than on S. The calculated T1ρ(H) relaxation times gave similar values obtained previously on different polysaccharides cross-linked with different cross-linkers. The elemental composition of samples in different cycles confirmed the ionic interaction between the quaternary ammonium group and the PGA carboxyls.