Methacrylate resin membranes by gel-template-leaching: concept and scope

A method of preparation of microporous membranes is described, based on the removal of a crystalline (perfluoroalkyl)alkane [F(CF₂)_m‐(CH₂)_nH] network from a cross‐linked methacrylate matrix. (Perfluoroalkyl)alkanes with a particular (CF₂)_m/(CH₂)_n balance form gels of interconnected long‐needle crystals upon crystallization from dilute solution. A template of this gel structure was prepared employing a mixture of suitable methacrylate monomers as a solvent. The solvent was first cured by low‐temperature UV‐initiated copolymerization/cross‐linking and subsequently the crystalline network was removed by extraction or sublimation. The resulting microporous morphologies were monitored by optical microscopy, scanning electron microscopy and scanning force microscopy. The cylindrical pore sizes could be varied deliberately by changing the (perfluoroalkyl)alkane, its concentration, and the degree of undercooling upon gelation. Maximum pore diameters varied between 12 nm and 145 nm. Flux measurements showed a decrease in pore size upon increasing the operation temperature of the membrane. A change in the temperature coefficient has been correlated with the glass transition temperature of the membrane. After saponification of the pore surfaces, the pores became smaller, which is probably due to swelling of the top layer of the surfaces. Introduction of sodium‐sulfonate groups on the inner pore surfaces resulted in a certain cation selectivity.