Synthesis of anion exchange resins for selective complexation of pertechnetate ion

Anion exchange resins were synthesized by functionalizing polymer supports with different crosslink densities. A variety of amines, including trialkylamines, with different alkyl-chain lengths were used as the ligands in the synthesis of monofunctional and bifunctional resins. The resins were characterized by total anion exchange capacities (TAEC), percent solids of the resins, chlorine and nitrogen elemental analyses. The results show that as the alkyl-chain length of the trialkylamine increases, the degree of functionalization decreases. An increase in alkyl-chain length also contributes to an increase in hydrophobicity, resulting in slow accessibility. Bifunctional resins were synthesized with two different trialkylamines on a 5% crosslinked poly(vinylbenzyl chloride) polymer support in a two step reaction. Each step is similar to the monofunctionalization reaction.

Metal-ion studies of the resins were performed with a simulated ground water solution consisting of pertechnetate and other potentially interfering anions. The distribution coefficients were determined by batch processes with varying equilibrium time. The results indicate selectivity of the resin toward pertechnetate increases with an increase in alkyl-chain length and varies with the microenvironment. The increase in alkyl-chain length, however, increases the time needed to reach equilibrium. Optimum selectivity was achieved using tripropyl and tributyl ammonium groups on a crosslinked poly(vinylbenzyl chloride) polymer support. Copolymers incorporating methyl methacrylate show poor selectivity for pertechnetate. Styrene copolymers show remarkable selectivity over those with methyl methacrylate and butyl methacrylate. These results indicate the microenvironmental effect plays an important role in the selectivity of the resins.