Tight ultrafiltration membranes of mesoporous phenolic resin filled in macroporous substrates

Mesoporous polymers derived from supramolecules of phenolic resins (PRs) and block copolymers (BCPs) containing highly uniform pores with sizes down to a few nanometers, are expected to deliver promising membrane separation performances. Here we report on the preparation of mesoporous phenolic membranes exhibiting tight ultrafiltration properties through a pore-filling strategy. Solutions of PR/BCP supramolecules are filled into the macropores of polyvinylidene fluoride (PVDF) microfiltration membranes (substrates), followed by thermopolymerization to solidify the solution in the pores. Subsequently, the filled PVDF substrates are treated in hot H₂SO₄ to remove the BCP components, thus producing mesopores in the PR framework. The produced composite membranes are mechanical robust and ductile as mesoporous phenolic resins are tightly embedded in the pores of the PVDF matrix. The mesoscale porosity in the PR phases endow the composite membrane a tight ultrafiltration performance with the molecular-weight-cut-off (MWCO) down to 2350 Da. The separation properties can be tuned simply by adjusting the dosage of supramolecule solutions used to fill the macroporous substrates. Considering the tight and uniform pore sizes and the robustness of phenolic resins, this strategy opens a new avenue to ultrafiltration membranes with low MWCOs or even nanofiltration membranes.