Synthesis of sulfonated poly(styrene‐ co ‐methyl methacrylate) by semicontinuous heterophase polymerization for filtration membranes

Abstract In this study, styrene (St) and methyl methacrylate (MMA) were copolymerized in semicontinuous heterophase using Hitenol‐BC10 (HBC10) as polymerizable surfactant and ammonium persulfate as initiator to obtain copolymers of poly(St‐ co ‐MMA). The effects of St/MMA weight ratio and surfactant concentration on kinetics, and colloidal properties of latexes were studied. Copolymers and latexes were characterized by scanning electron microscopy, thermogravimetric analysis (TGA), gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and X‐ray diffraction analysis. Fast reaction rates under monomer starved conditions and high conversions (>85%) were observed in all cases, with a weight‐average molecular weight in the range of 2.10 × 10 6 to 0.96 × 10 6 g mol −1 , decreasing with the HBC10 concentration due to an effect of chain transference to surfactant. Stable latexes with spherical particles with average diameter in the interval of 65–41 nm and Z ‐potential in the interval of −68.24 to −38.44 mV were obtained. Copolymers were sulfonated using acetyl sulfate as sulfonating agents and subsequently used for filtration membrane fabrication through the phase inversion method. Membranes were tested in simulated seawater filtration (3.5% NaCl) under constant pressure. At a pressure of 20 psia, permeated flux ( J ) of pure water and salt rejection ( R ) varied from 13.8 to 20.5 L m −2 h −1 and 37.8%–50.7%, respectively. It was concluded that membrane's performance is dependent on copolymer composition, the crystallinity of copolymers, and the ionic exchange capacity of membranes, being the best membrane composed of 90/10 of St‐to‐MMA weight ratio and using a monomer‐to‐surfactant weight ratio of 29.9.