Quaternization of a Polystyrene‐block‐poly(4‐vinylpyridine) Isoporous Membrane: An Approach to Tune the Pore Size and the Charge Density

Abstract

Isoporous integral asymmetric membranes derived from the self‐assembly of block copolymers combined with the non‐solvent‐induced phase separation (SNIPS) have gained great attention. To extend their utility, good control over pore size and surface functionality in a facile manner is highly desirable. Here, an approach is proposed to achieve this by quaternization of the poly(4‐vinylpyridine) moiety of a polystyrene‐block‐poly(4‐vinylpyridine) SNIPS membrane using alkyl iodides via a scalable gas‐solid heterogeneous reaction. By changing the size of the alkyl groups of the quaternization agent and the degree of quaternization, the effective pore size of the membrane is tailored in a wide range from the ultrafiltration to the nanofiltration regime. A quaternization of approximately half of the 4VP repeating units of the membranes with methyl iodide, ethyl iodide, or 1‐propyl iodide leads to a retention of methylene blue from a 10 mg L−1 aqueous solution of 96%, 87%, and 83%, respectively.