A Method for the Introduction of Chloromethyl Macroinitiators to Polysulfone Membranes for Grafting Zwitterionic Polymers via Atomic Transfer Radical Polymerization

A novel chloromethylation (CM) approach was developed to graft the macroinitiator -CH₂Cl onto aromatic backbone-bearing polymer materials such as polysulfone (PSf) in the aqueous phase, followed by atomic transfer radical polymerization (ATRP) of zwitterionic polysulfobetaine methacrylate (PSBMA) for antifouling modification. This CM reaction was completed in one step using a mixture of paraformaldehyde, hydrochloric acid, and a phase transfer catalyst (PTC), i.e., 3-(pyridinium-1-yl) propane-1-sulfonate inner salt. Advantages of the described method include: (1) No environmentally hazardous catalysts, such as SnCl₄ and ZnCl₂, were used. (2) The PTC was chemically stable and recyclable, which was superior to the water-sensitive, almost nonrecyclable Lewis acid. (3) The CM reaction occurred in the presence of hydrochloric acid rather than water-sensitive solvents (e.g., chloroform, sulfuric acid) used in the bulk modification method. Membranes were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to verify the presence of -CH₂Cl and PSBMA on the surfaces. Under the optimized CM and ATRP conditions, the obtained polysulfone membranes showed a water contact angle (WCA) as low as 25°, their pure water flux (PWF) and protein rejection were simultaneously enhanced, and the flux recovery ratio improved from 72.6% to 92.6%.