Thiol-containing zwitterionic polymers for polymeric membrane surface modification in wastewater treatment
Lai, Cheng Kee
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A series of copolymers based on disulfide-containing monomer 2-(methacryloyloxy) ethyl lipoate (MAEL) were synthesized by reverse addition-fragmentation chain transfer (RAFT) polymerization with three different zwitterionic monomers, namely (i) sulfobetaine methacrylate (SBMA), (ii) carboxybetaine methacrylate (CBMA), and (iii) phosphobetaine methacrylate (PBMA) at 70 °C for 22 hours, with 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CTP) and 4,4’-azobis(4-cyanovaleric acid) (ACVA) as the chain transfer agent and initiator respectively. Among the resulting well-defined disulfide-containing zwitterionic polymers, p(PBMA 160 - co -MAEL 42 ) was then reduced to p(PBMA 160 - co -DTMAEL 42 ) (a thiol-containing zwitterionic polymer) by using reducing agent, tris(2-carboxyethyl)phosphine hydrochloride (TCEP). The chemical structures of both the zwitterionic polymers and thiol-containing zwitterionic polymer were confirmed by the 1 H NMR spectra. The thiol-containing zwitterionic polymer was then used to graft onto the polydopamine (PDA) coated polyethersulfone (PES) membrane. Both the water flux permeability and contact angle measurement showed that the hydrophilicity of the surface modified membrane was increased through its lower water permeability and lower contact angle respectively compared to these of an unmodified membrane. Moreover, the study of the antifouling property through dead-end filtration cell by algae solution revealed that the water permeability of surface modified membrane decreased to a lower value compared with that of an unmodified membrane even for short filtration periods. Thus, the thiol-containing zwitterionic polymer could serve as an active layer for the membrane, especially for PES membrane, for surface modification in wastewater treatment.