Polyethyleneoxide-b-poly(isopropyl methacrylate) diblock copolymers as novel material for ultrafiltration membranes

Amphiphilic polyethyleneoxide-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers (BCP) with different molar masses are synthesized via atom transfer radical polymerization (ATRP). For that functionalized PEO monomethyl ether with two different molar masses, 10 and 20 kDa, are used as macroinitiator to obtain BCP in a molar mass range relevant for membrane fabrication. The BCP are used in the nonsolvent induced phase separation (NIPS) with the aim to obtain isoporous ultrafiltration membranes due to combination with its self-assembling properties (SNIPS). In various experiments, a strong effect of PEO homopolymer (hPEO) on the membrane formation process can be proven in which fractions of BCP with low molar mass might also play a role. These impurities are left in the BCP after ATRP due to incomplete purification. Under specific conditions, they induce formation of void-like superstructures on the membrane surface and in the cross section by a templating mechanism. Probably, large compound micelles play a key role in this scenario hindering the favored SNIPS process. The superstructure formation can be avoided by extensive purification of the BCP via dialysis or extraction. From the purified polymers, self-supported ultrafiltration membranes with an integrated hydrophilic component are successfully fabricated. Although they do not lead to isoporous surfaces after semiempirical determination of suitable solvent systems for the SNIPS process, there are convincing indications that the trade-off relation between selectivity and permeability can be overcome. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. , 2020 , 58, 2561–2574