Postfunctionalization of Nanoporous Block Copolymer Membranes via Click Reaction on Polydopamine for Liquid Phase Separation

In this work, an azido-modified dopamine derivative was synthesized and subsequently used to postfunctionalize the surface of nanoporous poly­(styrene)-<i>block</i>-poly­(4-vinylpyridine) diblock copolymer membranes. On the basis of this layer a continuative modification was realized by performing a “Click” reaction, namely, the Cu­(I)-catalyzed 1,3-dipolar cycloaddition, with different alkynes. While the Click reaction was monitored by X-ray photoelectron spectroscopy, the morphology of the membranes in the different states of modification was examined with scanning electron microscopy and atomic force microscopy. The membrane properties were characterized by measurements of contact angle and clean water permeance, retention tests, and protein adsorption. Independent from the alkyne applied during the Click reaction, the clean water permeance is approximately 1200 L m^–2 bar^–1 h^–1 and therefore slightly below the permeance of the pristine membrane. While the sharp molecular weight cutoff of the pristine membrane and all modified membranes is similar, antifouling properties as studied on the interaction of two model proteins (bovine serum albumin, hemoglobin) with the membranes turned out to be best for the membranes modified with 1-nonyne

CO₂ Selective PolyActive Membrane: Thermal Transitions and Gas Permeance as a Function of Thickness

It is generally accepted that the melting point of a semicrystalline polymer is associated with the thickness of the crystalline lamellae (Gibbs–Thomson equation). In this study, a commercially available multiblock copolymer PolyActive composed of 77 wt % of poly­(ethylene glycol terephthalate) and 23 wt % of poly­(butylene terephthalate) was dip-coated on top of a multilayer microporous support. The thickness was changed between 0.2 and 8 μm using coating solutions containing 0.75–7.5 wt % PolyActive. The surface temperature of the membrane during dip-coating was monitored using an infrared camera. Single gas permeances of N₂, H₂, CH₄, and CO₂ were measured between 20 and 80 °C at temperature steps of 2 °C. Spherulitic superstructures composed of radially directed lamellae were observed in the polarized light microscope in the prepared membranes. Atomic force microscopy studies showed that the thickness of the crystalline lamellae was in the order of 10 nm or 0.01 μm at the surface of the membrane. Therefore, according to the Gibbs–Thomson equation, the melting point should not change in the thickness range 0.2–8 μm. However, the gas permeance data showed that the melting point of the polyether domains of the 0.2 μm PolyActive layer was 10 °C lower compared to that of the 8 μm layer. The results can be explained by considering that the width of many crystalline lamellae significantly reduces as a function of film thickness, thereby reducing the average fold surface free energy/lateral surface free energy ratio