Interpenetrating polymer networks (IPNs) comprising weakly acidic and weakly basic cross-linked polymers, namely, poly(acrylic acid-co-ethyleneglycol dimethacrylate) (XPAA) and 80% ethoxylated polyethyleneimine (EPEI) cross-linked with glutaraldehyde, were prepared by the copolymerization of acrylic acid (AA) and ethyleneglycol dimethacrylate by a free-radical method, in the presence of calculated amounts of EPEI in methanol solution, followed by cross-linking with glutaraldehyde. The resulting IPNs, containing carboxylic acid groups and weakly basic tertiary amine groups in close proximity in the same resin bead, exhibited thermally regenerable desalination properties [e.g., sorption of salt at 30 degrees C and desorption at higher temperatures (80 degrees C)], simulating the behavior of the well-known Sirotherm resins. For NaCl and MgCl2, the maximum equilibrium sorption (similar to 0.5 mmol/g of dry resin in 0.1 M salt solution) was exhibited by an IPN with a carboxylic-to-amine (C/A) mole ratio in the range of 3-5. The equilibrium sorption at 30 degrees C for NaCl and MgCl2 on an IPN sorbent with a C/A mole ratio of 4.2 (referred to as Sirosorb) fitted well to both the Langmuir and Freundlich isotherms for single-component sorption and the Butler-Ockrent and Jain-Snoeyink models for bicomponent sorption. Containing both carboxylic and amine groups largely in a free state, Sirosorb exhibited buffer action over a wide range of feed solution pH values (3-8) to give nearly constant sorption of NaCl, although the sorption of MgCl2 increased with increasing pH because of additional sorption by ion exchange at the ionic sites formed by neutralization of the carboxylic acid groups. The sorption rate data showed characteristics of particle diffusion control with a NaCl and MgCl2 diffusivity ratio of 2:1, yielding diffusivity values of (2.5-3.9) x 10(-7)cm(2)/s for NaCl and (1.2-1.7) x 10(-7)cm(2)/s for MgCl2 in the initial period at 30 degrees C, with the diffusivity falling abruptly in both cases at higher conversion. Continuous column operation performed with Sirosorb showed that the quantity of potable water with a NaCl content of less than 1500 mg/L that can be produced is about 4 times the weight (dry) of the resin, when the influent brackish water has a NaCl content of 3000 mg/L. The used resin was regenerated with 1 M NaCl solution at 90 degrees C and used repeatedly with no apparent loss of capacity, as demonstrated in the present work for up to 10 cycles of operation.