Nanoporous Block Copolymer Membranes with Enhanced Solvent Resistance Via UV‐Mediated Cross‐Linking Strategies

In this work, a block copolymer (BCP) consisting of poly((butyl methacrylate‐co‐benzophenone methacrylate‐co‐methyl methacrylate)‐block‐(2‐hydroxyethyl methacrylate)) (P(BMA‐co‐BPMA‐co‐MMA)‐b‐P(HEMA)) is prepared by a two‐step atom‐transfer radical polymerization (ATRP) procedure. BCP membranes are fabricated applying the self‐assembly and nonsolvent induced phase separation (SNIPS) process from a ternary solvent mixture of tetrahydrofuran (THF), 1,4‐dioxane, and dimethylformamide (DMF). The presence of a porous top layer of the integral asymmetric membrane featuring pores of about 30 nm is confirmed via scanning electron microscopy (SEM). UV‐mediated cross‐linking protocols for the nanoporous membrane are adjusted to maintain the open and isoporous top layer. The swelling capability of the noncross‐linked and cross‐linked BCP membranes is investigated in water, water/ethanol mixture (1:1), and pure ethanol using atomic force microscopy, proving a stabilizing effect of the UV cross‐linking on the porous structures. Finally, the influence of the herein described cross‐linking protocols on water‐flux measurements for the obtained membranes is explored. As a result, an increased swelling resistance for all tested solvents is found, leading to an increased water flux compared to the pristine membrane. The herein established UV‐mediated cross‐linking protocol is expected to pave the way to a new generation of porous and stabilized membranes within the fields of separation technologies.