Branch length and density have critical effects on membrane performances; however, it is regarded to be traditionally difficult to investigate the relationship due to the uncontrolled membrane modification methods. In this study, zwitterionic polymer with controlled grafting branch chain length(degree of polymerization) and grafting density(grafting chains per membrane area) was tethered to the microporous polypropylene membrane surface based on the combination of reversible addition-fragmentation chain transfer(RAFT) polymerization technique with click reaction. The modified membranes were tested by filtrating protein dispersion to highlight the correlations of branch chain length and grafting density with the membrane permeation performances. The pure water flux, the flux recovery ratio are positively and significantly, and the irreversible fouling negatively and significantly correlated with grafting density. These results demonstrate that the larger the coverage of the membrane with poly{[2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl) ammonium hydroxide}(PMEDSAH), the higher the pure water flux and the higher the flux recover ratio, and the lower the irreversible fouling, which shows that high grafting density is favorable to fouling reducing.
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