Composite Cationic Exchange Membranes Prepared from Polyvinyl Alcohol (PVA) and Boronic Acid Copolymers for Alkaline Diffusion Dialysis.

Boronic acid copolymers with a large number of functional groups were obtained via a free radical polymerization method. The corresponding composite membranes for alkaline diffusion dialysis (DD) were prepared by a crosslinking reaction between polyvinyl alcohol (PVA) and the as-obtained boronic acid copolymers. The composite membranes possessed water uptake (WR) of 122.1⁻194.4%, ion exchange capacities (IECs) of 0.79⁻1.17 mmol/g, as well as both good mechanical stability (tensile strength of 40.7⁻49.9 MPa and elongation at break of 52.1⁻121.1%) and thermal stability. The as-prepared membranes were stable in 2 M NaOH solution at 65 °C with a swelling degree and mass loss of as-prepared membranes in the range of 305⁻368% and 9.2⁻22%, respectively. A NaOH/Na₂WO₄ mixture was used to investigate the separation properties of as-prepared membranes via the DD process. Results indicated that the dialysis coefficients of OH- (UOH) were in the range of 0.0079⁻0.0150 m/h, while the separation factors (S) were in the range of 26.6⁻53.2. The functional groups from boronic acid copolymer and ⁻OH from PVA were demonstrated to promote the ion transport synergistically.