CO₂-responsive membranes prepared by selective swelling of block copolymers and their behaviors in protein ultrafiltration

Due to the predominance of CO₂ as a new trigger with source abundance, non-toxicity, good reversibility and no byproduct accumulation compared to other triggers, CO₂-responsive membranes recently attract wide interest in stimuli-switchable separation. Here we report on the development of CO₂-responsive nanoporous membranes with poly(2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) block polymer (BCP) under the instruction of selective swelling-induced pore generation strategy, where hydrophilic chains of PDMAEMA can be enriched on the membrane surface and pore walls in the swelling process. The tertiary amine of PDMAEMA can be reversibly switched in conformation and charge property under the stimulation of CO₂/N₂. The CO₂-responsive behavior of PDMAEMA enriched on the surface and pore walls has further enabled as-prepared membranes to feature the tunable pore size by introducing and removing CO₂ gas. As a result, the PDMAEMA-b-PS nanoporous membranes exhibit excellent regulation in separation performances in terms of the permeance and rejection to varied proteins under the stimulation of CO₂/N_2. This work represents a simple and reliable way for making CO₂-responsive membranes.