Synthesis and utilization of PEO-based AB block copolymers as self-assembling membrane material

Synthesis and utilization of PEO-based AB block copolymers as self-assembling membrane material

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Ultrafiltration is a well-established process with a wide range of applications like fractionation of biomolecules or water purification. Nevertheless, commercially available membranes have a broad pore size distribution and suboptimal porosity, leading to limits in separation performance. An approach to improve the selectivity and flux of ultrafiltration membranes and to overcome the typical trade-off relationship between those two parameters is the application of block copolymers (BCP) with incompatible blocks as membrane material. Due to self-assembly of the BCP, highly ordered structures can be obtained, potentially leading to narrow pore size distribution and high porosity.

In this work, we are focusing on the synthesis of the diblock copolymer poly(ethylene oxide)-b-poly(isopropyl methacrylate) (PEO-b-PiPMA). The BCP is accessible by copolymerization via atom transfer radical polymerization (ATRP). ATRP enables a more straightforward transfer into industrial scale in comparison to ionic polymerization methods. Utilizing BCP, obtained by copolymerizing methacrylates with PEO macroinitiators derived from mono-disperse commercial precursors, offers simplified synthesis and easy structure variation by varying the type of monomer and the block lengths.

The PEO and PiPMA blocks are supposed to have a sufficient incompatibility (as indicated by Hansen solubility parameters) to yield microphase-separated morphologies or to form micellar structures. Ordered structures in the polymer bulk have been proven by Atomic Force Microscopy (AFM) and Differential Scanning Calorimetry (DSC) [1]. Micelle formation in solution is mainly investigated via Dynamic Light Scattering (DLS). When self-assembly is combined with processes such as non-solvent induced phase separation (NIPS), micellar structures in BCP solutions can be transferred to solid polymer films. Direct preparation of ordered nanoporous films via NIPS is well known in literature [2]. In this case, the BCP is used as a single membrane material. In this work, an alternative way to make use of the block copolymer is to apply it as an additive in poly(methyl methacrylate) (PMMA) base membranes. Due to micelle formation and/or surface modification, the porosity and the pore structure in the selective layer can be improved. Recently, this was already shown for PEO-b-PMMA BCP used as an additive in PVDF ultrafiltration membranes [3].

References

  1. S. Chaudhuri, J. Gaalken, J. Meyer, M. Ulbricht, Polymer, 2018, 139, 11
  2. S. P. Nunes, A. Car, Ind. Eng. Chem. Res., 2013, 52, 993
  3. J. Meyer, M. Ulbricht, J. Membr. Sci. 2018, 545, 301

Contact:
Janina Gaalken