(277d) Cross-Linked Block Copolymer Membranes

Porous and dense polymer-based films are easily manufactured by conventional large-scale methods and are widely used as membranes. Polymer membranes find their applications in various separation processes in the industry, medicine, or biotechnology. They are mainly produced based on commercially available homopolymers, such as polysulfone, polyacrylonitrile, and polydimethylsiloxane. However, particularly convenient properties can be achieved using block copolymers (BCPs), including commercial ones like polyether-b-polyamide (Pebax®), and sulfonated pentablock copolymers (Nexar^TM) [1,2].

Depending on the composition of the BCP counterparts, such as their length, solvophilicity, and solvent used, different morphologies are formed via self-assembly of these materials in solution. These phenomena can be directly used to control the pore size distribution at the nanoscale when producing the membrane by solution casting and phase inversion [3]. When BCPs are used as dense membranes or coatings, a plethora of possibilities is opened by combining materials with different properties into a single membrane, allowing to finely tune the resulting membrane characteristics. The BCPs can be terminated with different active groups to allow cross-linking either of the self-assembled structure or cross-linking with other matrixes, which can yield a confined membrane structure providing enhanced thermal, mechanical, and chemical resistance.

Here, we present a new strategy demonstrated with polystyrene-block-poly(ethylene oxide) (PS-b-PEO) BCP with a block ratio of ~70 % PS [4]. We study the PS-b-PEO in two versions - double-terminated by functional groups (α, ω-difunctionalized), and monoterminated by functional groups (α-functionalized). The double termination allows cross-linking of the BCP. We explore how the self-assembly changes upon the induced cross-linking in different organic solvents and how it affects the resulting membrane morphology and stability. We utilize this knowledge to produce stable BCP cross-linked membranes to target applications such as gas separation using dense cross-linked BCP films, but also to form porous materials to be applied for liquid processing or as scaffolds for biotechnology and medicine. The scanning electron microscopy micrographs of prepared porous membranes and their respective thermal stability curve obtained by thermogravimetric analysis are presented in Figure 1.

References:

[1] S.P. Nunes, A. Car, From charge-mosaic to micelle self-assembly: Block copolymer membranes in the last 40 years, Industrial and Engineering Chemistry Research. 52 (2013) 993–1003. https://doi.org/10.1021/ie202870y.

[2] L. Upadhyaya, A.Y. Gebreyohannes, F.H. Akhtar, G. Falca, V. Musteata, D.K. Mahalingam, R. Almansoury, K.C. Ng, S.P. Nunes, NEXARTM-coated hollow fibers for air dehumidification, Journal of Membrane Science. 614 (2020). https://doi.org/10.1016/j.memsci.2020.118450.

[3] S.P. Nunes, Block Copolymer Membranes for Aqueous Solution Applications, Macromolecules. 49 (2016) 2905–2916. https://doi.org/10.1021/acs.macromol.5b02579.

[4] G. Polymeropoulos, G. Zapsas, K. Ntetsikas, P. Bilalis, Y. Gnanou, N. Hadjichristidis, 50th Anniversary Perspective: Polymers with Complex Architectures, Macromolecules. 50 (2017) 1253–1290. https://doi.org/10.1021/acs.macromol.6b02569.