Grafting of zwitterion polymer on polyamide nanofiltration membranes via surface-initiated RAFT polymerization with improved antifouling properties as a new strategy

Special radical grafting strategies, e.g. surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization, are considered as promising techniques for the purpose of not only uniformly modifying nanofiltration (NF) membranes with the functional polymers but also preventing nonspecific protein adsorption. In this research work, we decide to report for the first time an efficient approach to stabilize RAFT initiators on the surface of polyamide NF membranes and study the effect of the chain length of the polymer on the membrane fouling performance. For this purpose, using interfacial polymerization between trimesoyl chloride (TMC) and a mixture of diamines (i.e. 1,3-phenylenediamine (MPD) and (3,5-diamino phenyl) methanol (DAPM), polyamide thin film composite NF membranes were synthesized. Afterward, the reaction between the polyamide thin film composite layer and alpha-bromoisobutyryl bromide (BIBB) was carried out. It was found that the stabilized amount of BIBB on the surface of the prepared membranes could be efficiently enhanced by using the DAPM treatment. Finally, using RAFT polymerization technique, a zwitterionic polymer, poly[(2-methacryloyloxy)ethyl]dimethyl [3-sulfopropyl]ammonium hydroxide (pMEDSAH), was successfully grafted on the membrane surface. It is noteworthy that the irreversible adsorption amount of proteins on the prepared pMEDSAH-grafted membrane appreciably decreased to > 96%. All the provided results indicate that all the pMEDSAH-grafted membranes, which were prepared using a facile and efficient method, have proved promising for practical applications.