Synthesis of poly(vinyl chloride)-g-poly(3-sulfopropyl methacrylate) graft copolymers and their use in pressure retarded osmosis (PRO) membranes

Poly(vinyl chloride) (PVC) was grafted with 3-sulfopropyl methacrylate potassium salt via atom transfer radical polymerization (ATRP) to produce a poly(vinyl chloride)-g-poly(3-sulfopropyl methacrylate) (PVC-g-PSPMA) amphiphilic graft copolymer, as characterized via Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H NMR). Two separated domains and two glass transition temperatures (T_gs) were observed via transmission electron microscopy (TEM) and differential scanning calorimetry (DSC), respectively, indicating a microphase-separated structure in the PVC-g-PSPMA. Small-angle X-ray scattering (SAXS) analysis revealed scattering peaks at q=0.54nm^-1, by which the interdomain distance was determined to be 11.6nm, roughly consistent with the TEM results. The PVC-g-PSPMA graft copolymer was blended with pristine PVC and solution-casted to prepare organized PVC/PVC-g-PSPMA blend membranes, as characterized via scanning electron microscopy (SEM), contact angle measurement and X-ray photoelectron spectroscopy (XPS). The water flux of the PVC/PVC-g-PSPMA blend membrane was approximately 2.20L/m²h (LMH) at 14.7bar, which was much higher than that of the pristine PVC membrane. This is due to the water channels that formed due to the presence of hydrophilic ionic groups, which allow for the passage of water while resisting the passage of salt.