Ion-exchange resins. III. Functionalization-morphology correlations in the synthesis of some macroporous, strong basic anion exchangers and uranium-sorption properties evaluation

The synthesis and characterization of a series of macroporous, strong basic anion exchangers (SBAEs), with an average pore radius higher than 50 nm, and the evaluation of their sorption properties for uranyl chlorocomplexes from HCl solutions are reported. Finely divided macroporous styrene-divinylbenzene (S-DVB) copolymers with a narrow distribution of beads sizes, diameters within the range of 90-200 mum, were prepared for this purpose with 2-ethyl-1-hexanol as a porogen, at a high dilution of monomers (D greater than or equal to 0.55 mL/mL). Chloromethyl groups were introduced with (CH2O)(n)/Me3SiCl as a chloromethylation agent in the presence of a Lewis acid as a catalyst (TiCl,, SnCl, and FeCl3) in CHCl3 as a reaction medium. SnCl4 and FeCl3 gave comparable chloromethylation degrees in the same reaction conditions. TiCl, was not efficient as a catalyst in the chloromethylation with this reagent. Diethyl-2-hydroxyethylamine was used as a tertiary amine to prepare SBAEs. Structural and morphological characteristics were determined after every functionalization step of the macroporous network. Both the chloromethylation, in the presence of FeCl3 as a catalyst, and the amination reactions determined a significant decrease of the pore volume, in the whole range of the nominal crosslinking degree, comparative with the starting copolymer. The specific surface area and the average pore radius varied in a different way as a function of the nominal crosslinking degree. Thus, the specific surface area increased and the average pore radius decreased after chloromethylation and amination for copolymers with a DVB content lower than 10 wt %. Small decreases of the specific surface area and the average pore radius were observed after chloromethylation and amination reactions for copolymers with a DVB content higher than 10 wt %. SBAEs were also characterized by thermogravimetric analysis and sorption capacity for uranyl chlorocomplexes. (C) 2004 Wiley Periodicals, Inc.