Quaternization and degradation of block copolymer templates for UF and ED membranes via non-solvent induced and solvent evaporation induced phase separation

Degradable block copolymers are considered as ideal templates to prepare porous membranes with tunable nanostructure. However, most of these templates are hydrophobic and it remains a challenge to make nanoporous and charged membranes using such templates that contain a sacrificial block through phase inversion. Herein, block copolymers poly(ε-caprolactone)- b -poly(4-vinyl pyridine) have served as cross-linkable and degradable templates to prepare porous and dense membranes via non-solvent induced phase separation (NIPS) or solvent evaporation-induced phase separation (SIPS). During NIPS, the prepared membranes showed a dense skin and finger-like or sponge-like sublayer. By controlling the quaternization and degradation of templates, the permeance of pure water and molecular weight cut-off performance tuning were achieved. The above ultrafiltration membranes with well-defined pores exhibited excellent rejection ability towards different dyes based on size exclusion and Donnan effect. Moreover, after being treated with NaOH solution, the membranes fabricated via SIPS showed a unique change from dense to hollow cross-sectional structure, which also demonstrated promising electrodialysis desalination performance and electrodialysis stability.