Water and salt transport properties of zwitterionic poly (arylene ether ketone) for desalination membrane applications

A series of novel poly (arylene ether ketone) with pendant zwitterion groups were designed. Three molecules, 1,4-butane sultone, sodium 2-bromoethanesulphonate and sodium bromoacetate were selected to quaternize with tertiary amine-containing poly (arylene ether ketone) to prepare sulfobetaine poly (arylene ether ketone) (PAEK-SB4 and PAEK-SB2) and carboxylbetaine poly (arylene ether ketone) (PAEK-CB) with controllable content of zwitterion group. The fundamental water and salt transport properties in zwitterionic PAEKs were characterized. Except PAEK-SB2, the water and salt diffusivity and permeability of PAEK-SB4 and PAEK-CB increase with the increase of water sorption, which follows the trend of Yasuda's free volume theory. Salt diffusivity and permeability in PAEK-SB2 were suppressed relative to PAEK-SB4 and PAEK-CB with comparable water sorption, which is due to shorter distance between positively charged group (-N+(CH3)(2)-) and negatively one (SO3-) in SB2 group leading to stronger self-association interaction between zwitterions. The water/salt permeability selectivity of PAEK-SB2 and PAEK-CB change little with the increase of diffusive water permeability, which break through the trade-off between them. The permeability selectivity of zwitterionic PAEKs is more than one order of magnitude higher than sulfonated polysulfone (BPS), and its orders is PAEK-SB2>PAEK-CB > PAEK-SB4>BPS at the comparable diffusive water permeability. This study suggests that shorter distance between positively charged group and negatively one in zwitterion group benefits water/salt selectivity of zwitterionic PAEKs.

Automated summary

A series of novel poly (arylene ether ketone) with pendant zwitterion groups were designed and the water and salt transport properties were characterized. The study showed that the zwitterionic polymers exhibited higher water/salt permeability selectivity compared to sulfonated polymers.