Molecular design of amphiphilic triblock copolymers as additives for high performance poly(vinyl chloride) ultrafiltration membranes

Amphiphilic triblock copolymers (TBCs) of poly(styrene)-b-polyethylene glycol-b-poly(styrene) (PS-b-PEG-b-PS) were synthesized by atom transfer radical polymerization (ATRP) and added to poly(vinyl chloride) (PVC) to prepare ultrafiltration (UF) blend membranes with superior water treatment efficiency. Compared to neat PVC, the blend membranes showed higher surface and bulk porosity, mean pore size, and surface hydrophilicity. These, attributed to the surface segregation of TBCs during membrane preparation, resulted in higher pure water flux (PWF), sodium alginate rejection, and fouling resistance for the blend membranes. The molecular weight (MW) of the hydrophilic (PEG) and hydrophobic (PS) blocks of the TBCs had significant influences on the PWF and fouling resistance of the membranes. Increasing the MW of PEG from 1000 g/mol to 4000 g/mol led to an improvement in the PWF and fouling resistance. However, TBCs containing PS with medium MW resulted in blend membranes with PWF of 1000 L.m^{- 2} h^{- 1} and rejection of 95%, demonstrating the practical efficacy of the approach. This was attributed to the counterbalance of TBC/PVC miscibility and TBC surface segregation effects using TBC with PS block having medium MW. Finally, designing and tuning the MW of hydrophilic/hydrophobic segments of TBC is promising for the development of PVC UF blend membranes with high water purification performance.