Synthesis and characterization of amide linkage‐incorporated polyethyleneimine‐based chelating resins and studies of the crosslink density and surface properties on metal ion uptake

Abstract

SYNOPSISThe chelating resins incorporating amide linkages were synthesized in open reaction vessels (OV) by polycondensing different proportions, uiz., 1 : 1, 1 : 1.3, and 1.3 : 1 of polyethyleneimine (PEI) and diethylenetriaminepentaacetic acid (DTPA) , respectively, at 145-155"C, and at varying curing times (15 h and 22 h). For the proportion 1 : 1, the synthesis was performed in a closed reaction vessel (CV) as well. The resins were characterized by FTIR, elemental, and thermogravimetric analysis, apart from sarptometric surface studies, The extent of crosslinking was evaluated by swelling measurements and the chemical stability was assessed by acid and alkali treatment. The effect of the mode of heating and curing times on the extent of crosslinking and pore structure modifications were evaluated. The influence of these factors on the capacities, the kinetics, and the break through curve trends of these resins were studied using zinc and cadmium metal ions as references. The reproducibility of the resins were ascertained by assessing the extent of change in the break through curve trends of their different batches, synthesized under identical conditions. 0 1993 John Wiley & Sons, Inc. INTRODUCTIONAn important new class of synthetic multifunctional substrates, with enhanced molecular/ ionic recognition,' is the chelating ion exchange resins, which, due to their complexing abilities and enhanced selectivities, play important roles in the preconcentration' and separation3 of metal ions from a variety of matrices. Included among these polymers are the promising PEI-based resins, 4,5 because PEI with low molecular weight per monomer unit provides a high content of functional groups per unit weight. The presence of primary and secondary amino groups allows suitable modifications through polycondensation and crosslinking by simple methods.Crosslinked PEI resins, obtained from reactions between PEI and a variety of crosslinking agents, have been rep0rted.6'~ Since nitrogen-and oxygencontaining resins are more effective, due to their extended utilities, for a wide variety of metal ions, modifications of PEI resin matrix necessitated a further careful choice from the incorporating groups. The simple introduction of carboxyl functions can be achieved by treating PEI with 4-chloro 2,6-pyridine dicarboxylic acid' and subsequent crosslinking with epichlorohydrin. In this respect, condensation of PEI with other potent groups, as explained in our studies, is another useful pathway to useful modification of PEI. One of the earlier studies, based on polycondensation, involved an amine-isocyanate reaction, using toluene diisocyanate as the second reactant, which led to a product with a comparatively low capacity for the metal ions, since the urea linkages formed could not participate in the complexation process.To overcome this drawback, in the present study, 1195 1196 THIAGARAJAN AND SUBBAIYANcondensation of PEI with a polyamino polycarboxylic acid [ Diethylenetriaminepentaacetic acid ( DTPA) ] was attempted, keeping in view ...

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