Remarkable pH-responsive Microfiltration Membrane from Well-defined PS-b-PDEAEMA Copolymers by ATRP Method

This work presented a detailed study on pH-responsive self-supporting microfiltration membranes via the non-solvent-induced phase separation (NIPS) process from mixtures of THF and DMF. The well-defined pH-responsive polymers polystyrene-block-poly (N,N-diethylaminoethyl methacrylate) (PS-b-PDEAEMA) were synthesized via atom transfer radical polymerization (ATRP) evidenced by ¹H-NMR and GPC studies. Two amphiphilic diblock copolymers were used, St₇₁-b-DEAEMA₃₁ and St₇₁-b-DEAEMA₈₂. The influence of pH value in the coagulation bath, the solvent composition, the “open-time” before immersion into the coagulation bath and the polymer composition onto the membrane morphology were investigated, and flux values obtained for the different membrane systems were compared. The SEM images and polarized optical microscopy revealed that the size and the number of pores in the membranes were larger along with the decreasing THF content and “open time”. For the copolymer with the longer PDEAEMA block, St₇₁-b-DEAEMA₈₂, the flux values were lower than that of St₇₁-b-DEAEMA₃₁ under different “open time”, which meant that the total area of the pores in the membranes was smaller, respectively. The optimum preparation conditions for microfiltration membrane were as follows: the polymer was St₇₁-b-DEAEMA₈₂, the “open time” was 20s, the non-solvent bath was the pH = 2 distilled water, and the solvent composition was 25% THF and 75% DMF. Both polymers were shown to form self-supporting membrane systems that were able to react onto pH stimuli in terms of water flux.