Fabrication and structural tailoring of reverse osmosis membranes using β-cyclodextrin-cored star polymers

Here, we designed a new chemistry of fouling-resistant reverse osmosis (RO) membranes using a star polymer (CD-PAH) comprising multiple linear polymer (poly(acryloyl hydrazide), PAH) arms grafted onto a β-cyclodextrin (β-CD) core. The well-defined structure of the β-CD-cored star polymer enabled us to systematically synthesize CD-PAHs with different arm lengths, which were assembled into membrane selective layers via a layered interfacial polymerization technique. Increasing the PAH arm length of CD-PAH enhanced the inter-chain entanglement of PAH arms and thus the crosslinking reaction efficiency by providing a higher density of the crosslinkable amine groups of densely-packed PAH arms. Hence, longer PAH arms of CD-PAH resulted in an enhancement in NaCl rejection with a reduction in the water permeance of the CD-PAH-assembled (CD-TFC) membrane. Importantly, the CD-TFC membranes prepared using CD-PAHs with longer PAH arms exhibited RO separation performance comparable to that of a commercial RO membrane, which is not feasible by other reported branch-structured macromolecules. Furthermore, the CD-TFC membrane displayed lower organic fouling with a higher rinsing efficiency than a commercial RO membrane, because of its more negatively charged and hydrophilic surface combined with its smoother surface, overcoming a performance-fouling trade-off.