A Strategy of End Anchoring to Poly(N‑isopropylacrylamide) Chains for the Thermo-Driven Controllable Oil–Water Separation

Poly(N-isopropylacrylamide) (PNIPAM) chain with catechol end group was designed and successfully synthesized by a reversible addition–fragmentation chain transfer (RAFT) procedure, and then, even via a simple one-step soaking method, it could be firmly grafted to many different substrates (e.g., a stainless-steel mesh, a nylon microfiltration membrane, an Al plate, and glass). Moreover, after the end anchoring, the formed thin and uniform coating of PNIPAM onto the surfaces of the stainless-steel mesh and the nylon microfiltration membrane would endow the surfaces with a valuable thermo-driven controllable separation ability for oil–water mixtures and emulsions, respectively. And below PNIPAM’s lower critical solution temperature (LCST) (34 °C), the membranes exhibited hydrophilicity and underwater oleophobicity and thus can be used for the separation of a “light oil”/water mixture and an O/W emulsion through a “removing water” process; meanwhile, above its LCST, the membranes show the opposite properties (hydrophobicity and oleophilicity) and thus are used to separate a “heavy oil”/water mixture and a W/O emulsion through a “removing oil” process. In addition, without changing the morphologies and pore sizes of the substrates, the membranes gave many excellent performances such as excellent recyclability, high separation efficiency and a thermo-driven controllable separation ability. So, the facile and effective strategy presented in this work that is suitable for the coupling of PNIPAM with various substrates would also supply an inspiration to the effect conjunction for heterogeneous materials of other functional polymers and substrates.