Free-standing thermo-responsive nanoporous membranes from high molecular weight PS-PNIPAM block copolymers synthesized via RAFT polymerization

The incorporation of stimuli-responsive pores in nanoporous membranes is a promising approach to facilitate the cleaning process of the membranes. Here we present fully reversible thermo-responsive nanoporous membranes fabricated by self-assembly and non-solvent induced phase separation (SNIPS) of polystyrene-poly(N-isopropylacrylamide) (PS-PNIPAM) block copolymers. A variety of PS-PNIPAM block copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and the reaction conditions were optimized. The target copolymers featured: (1) a thermo-responsive PNIPAM block, (2) a majority PS fraction, and (3) a well-defined high molecular weight, which are requirements for successful fabrication of free-standing responsive membranes using SNIPS. The resulting membranes exhibited a worm-like cylindrical morphology with interconnected nanopores. The thermo-responsive character of the membranes was studied by measuring the permeability of the membranes as a function of temperature. The permeability was found to increase by almost 400% upon going from room temperature to 50 °C and this thermo-responsive character was fully reversible.