Poly(ionic liquid) copolymer blended polyvinyl chloride ultrafiltration membranes with simultaneously improved persistent hydrophilicity and pore uniformity

Persistent hydrophilicity and uniform pore structure are key features of antifouling ultrafiltration membranes. Here, a poly(ionic liquid) copolymer, poly(methyl methacrylate)-b-poly(1-butyl-3-vinylimidazolium tetrafluoroborate) (PMMA-b-PBVImBF4), was designed and synthesized by a simple free radical polymerization method and was employed to manipulate the hydrophilicity and pore structure of polyvinyl chloride (PVC) ultrafiltration membranes through the classic non-solvent induced phase separation. The hydrophobic PMMA segment, which has a carbonyl group, could be twined with the PVC chain, thus ensuring that the copolymer was stably anchored in the PVC skeleton, while the hydrophilic PBVImBF4 segment was segregated on the membrane surface. Membrane hydrophilicity and pore size uniformity were simultaneously enhanced. A 100 % increase in pure water flux, 45.8 % increase in mechanical strength, and 80 % increase in flux recovery rate were achieved when 3.85 wt% PMMA-b-PBVImBF4 was added. After 3 cycles of BSA filtration, the pure water flux of the copolymermodified membrane was 267.0 L.m(-2).h(-1), approximately 4 times that of the pristine PVC membrane. Due to the stable existence of PMMA-b-PBVImBF4 in the membrane, the improved membrane hydrophilicity was maintained after 30 days of continuous washing.

Automated summary

This study designed and synthesized a poly(ionic liquid) copolymer to modify the hydrophilicity and pore structure of ultrafiltration membranes, resulting in improved membrane performance. The modified membranes showed significantly increased pure water flux, mechanical strength, and flux recovery rate. The stable presence of the copolymer in the membrane ensured the maintained hydrophilicity even after continuous washing for 30 days.