It has been found that hydrogels may be formed by microwave irradiation of aqueous solutions containing appropriate combinations of polymers. This new method of hydrogel synthesis yields sterile hydrogels without the use of monomers, eliminating the need for the removal of unreacted species from the final product. Results for two particularly successful combinations, poly(vinyl alcohol) with either poly(acrylic acid) or poly(methylvinylether-alt-maleic anhydride), are presented. Irradiation using temperatures of 100-150 °C was found to yield hydrogels with large equilibrium swelling degrees of 500-1000 g g(-1) . Material leached from both types of hydrogel shows little cytotoxicity towards HT29 cells.
Here we present fundamental studies of a new blending strategy for enhancing water permeability in ionomeric reverse osmosis membrane materials. A random disulfonated poly(arylene ether sulfone) copolymer containing 20 mol percent hydrophilic units (BPS-20) in the potassium salt (-SO 3 K) form was blended with hydroxyl-terminated poly(ethylene glycol) oligomers (PEG, M n = 600-2 000) to increase the water permeability of BPS-20. Blending PEG with the copolymer resulted in pseudoimmobilization of the BPS-20 polymer chains because PEG complexes with cations in the sulfonated polymer matrix. Strong ion-dipole interactions between the potassium ions of the BPS-20 sulfonate groups (-SO 3 K) and the PEG oxyethylene (-CH 2 CH 2 O-) groups were observed via NMR spectroscopy. These interactions are similar to those reported between crown ethers and free alkali metal systems. The PEG oligomers were compatible with the copolymer at 30 °C in an aqueous environment. Transparent and ductile BPS-20_PEG blend films exhibited a Fox-Flory-like glass transition temperature depression as the PEG volume fraction increased. This depression depended on both PEG chain length and concentration. Both ion-dipole interactions and high coordination of -CH 2 CH 2 O-with -SO 3 K yielded a defined and interconnected hydrophilic channel structure. The water permeability and free volume of BPS-20_PEG blend films containing 5 or 10 wt % PEG increased relative to BPS-20. The blend films, however, exhibited reduced sodium chloride (NaCl) rejection compared to BPS-20. Addition of PEG did not significantly alter the material's dry-and hydrated-state mechanical properties. Unlike commercial state-of-the-art polyamide RO membranes, the blend materials do not degrade when exposed to aqueous chlorine (hypochlorite) at pH 4. This comprehensive suite of measurements provides understanding of the molecular and morphological features needed for rational design of next-generation, chlorine-tolerant water purification materials.
The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulfone) (BPS) copolymers have been characterized. Cast BPS membranes of both salt form and acid form with sulfonation levels from 20% to 40% were investigated. Water permeability of BPS films increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while the salt permeability of the corresponding membranes increases two orders of magnitude. Moderate salt rejection (98.2%) was achieved by a BPS salt form membrane with a sulfonation level of 20%.
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