Functional amphiphilic diblock copolymers for improved ultrafiltration membranes

Functional amphiphilic diblock copolymers for improved ultrafiltration membranes

In this work, poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers were established as functional additive for polyvinylidene fluoride (PVDF) ultrafiltration membranes and as novel self-assembling membrane material.

The copolymers were synthesized via atom transfer radical polymerization (ATRP) with commercially available poly(ethylene oxide) methyl ether as first block. PEO methyl ether is available with molar masses between 350 and 20,000 g·mol-1, permitting a wide range of block ratios and molar masses of the diblock copolymer.

When the copolymer is used as an additive, the hydrophilicity of PVDF-based membrane is increased, which decreases fouling.

Additionally, it was found that copolymer micelles can be induced by complexing the PEO block with several metal salts. These micelles lead to a higher surface porosity and a more regular barrier pore structure, presumably through microphase separation during the nonsolvent induced phase separation process (NIPS) used for membrane preparation. It was possible to tailor the molecular weight cut-off (MWCO) between 30 kDa and 110 kDa by varying the type and amount of salt in the otherwise identical casting solution. The permeability of the developed membranes was significantly higher than for comparable commercial reference membranes from PVDF [1].

When the copolymer is used as novel membrane material, its self-assembling properties can be used to obtain membranes with a narrow barrier pore size distribution as well as a very high number density of pores, which should lead to a sharp sieving curve and a high permeability. These membranes have been prepared as thin-film composites by spin-coating on PET track-etched support membranes and via NIPS with and without nonwoven support.

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Intended functions of diblock copolymer for UF membranes:

  1. increased surface hydrophilicity of PVDF UF membranes via stable surface segregation
  2. formation of PEO-metal complex to induce microphase separation during NIPS
  3. self-assembly of copolymer micelles to directly form isoporous membranes

[1] J. Meyer, M. Ulbricht, J. Membr. Sci. 2018, 545, 301-311

Funding: This work was partly funded by the European Commission within the Seventh Framework Program (FP7; NANOPUR project – Grant Agreement no. 280595).

Contact:
Prof. Mathias Ulbricht