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1. A process for the preparation of a crosslinked amine polymer, the process comprising (i) swelling a preformed crosslinked amine polymer with a swelling agent, wherein the preformed crosslinked amine polymer is a copolymer comprising the residues of (a) 2-Propen-1-ylamine or a salt thereof and (b) 1,3-Bis(allylamino)propane or a salt thereof and (ii) further crosslinking the preformed crosslinked amine polymer with a crosslinking agent comprising 1,2-dichloroethane to form the crosslinked amine polymer in a reaction mixture comprising the crosslinking agent and the swelling agent, wherein the preformed crosslinked amine polymer has an absorption capacity for the swelling agent, the amount of swelling agent in the reaction mixture is less than the absorption capacity of the preformed crosslinked amine polymer for the swelling agent, the weight ratio of the swelling agent to the preformed crosslinked amine polymer in the reaction mixture is less than 1:1, and the swelling agent is water, and wherein the crosslinked amine polymer has a chloride ion binding capacity of at least 4 mmol/g, and a phosphate ion binding capacity of less than 2 mmol/g, in a Simulated Small Intestine Buffer (“SIB”) assay wherein, in the SIB assay, the crosslinked amine polymer is combined with a SIB buffer consisting of 36 mM NaCl, 20 mM NaH2PO4 and 50 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffered to pH 5.5 at a concentration of 2.5 mg/ml (25 mg dry mass of the crosslinked amine polymer) in 10 mL of the buffer, and the combination is incubated at 37° C. for 1 hour with agitation on a rotisserie mixer.
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