(728f) Nanostructured Polysulfone-Based Block Copolymer Membranes

For the first time, self-assembly and non-solvent induced phase separation (SNIPS) was applied to polysulfone-based linear block copolymers, reaching mechanical stability much higher than other block copolymer membranes used in this method, which were mainly based on polystyrene blocks. Poly(tert-butyl acrylate)-b-polysulfone-b-poly(tert-butyl acrylate) (PtBA_30k-b-PSU_14k-b-PtBA_30k) with a low polydispersity of 1.4 was synthesized by combining step-growth condensation and RAFT polymerization.¹ Various advanced electron microscopies revealed that PtBA_30k-b-PSU_14k-b-PtBA_30k assembles into worm-like cylindrical micelles in DMAc and adopts a “flower-like” arrangement with the PSU central block forming the shell. Computational modeling described the mechanism of micelle formation and morphological transition. Asymmetric nanostructured membranes were obtained with a highly porous interconnected skin layer and a sublayer with finger-like macrovoids. Ultrafiltration tests confirmed a water permeance of 555 L m^-2 h^-1 bar^-1 with molecular weight cut-off of 28 kg/mol. PtBA segments on the membrane surface were then hydrolyzed and complexed with metals, leading to cross-linking and enhancement of antibacterial capability. Furthermore, nanostructured membranes were prepared from the hydrolyzed copolymer, poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid), via a novel self-assembly and chelation assisted phase inversion process.² After thermal annealing channels of poly(acrylic acid) could be seen as domains in thin films. In a selective solvent mixture of DMF/THF/acetone (10/45/45), spherical micelles with poly(acrylic acid) corona were formed. They assembled to form membranes by casting the concentrated solution and then immersing it in aqueous Cu²⁺ or Ag⁺ solution. Metal-acid complexation immobilized the micellar morphology in membranes. The ordered space between micelles filled with poly(acrylic acid) as water channels containing Cu²⁺. The pure water permeance of membranes prepared by dip-coating was up to 1.7 L m^-2 h^-1 bar^-1 with magnesium chloride rejection of 83 %. Silver nanoparticle decorated membranes were obtained by NaBH₄ reduction, featuring three distinct layers with different nanoparticle sizes.

1. Xie, Y., et al. Synthesis of highly porous poly (tert-butyl acrylate)-b-polysulfone-b-poly (tert-butyl acrylate) asymmetric membranes. Polym. Chem. 2016, 7(18), 3076-3089.

2. Xie, Y., et al. Membranes prepared by self-assembly and chelation assisted phase inversion. Chem. Commun. 2017, submitted.