Poly(methyl methacrylate)-<i>block</i>-polysulfone-poly(methyl\nmethacrylate) Triblock Copolymer-Modified Support Layers for Forward\nOsmosis Membranes

Abstract

In this work, poly­(methyl methacrylate)-<i>block</i>-polysulfone-poly­(methyl\nmethacrylate) (PMMA-<i>b</i>-PSf-<i>b</i>-PMMA)\nas an amphiphilic block copolymer, which is appropriate for support\nlayer modification of forward osmosis (FO) membranes, was prepared\nvia an atom transfer radical polymerization (ATRP) method using a\nbromo-terminated PSf as a macroinitiator. First, the Br-terminated\nPSf macroinitiator was synthesized by esterification of the phenolic\ngroups with α-halo-ester. Second, the PSf-Br macroinitiator\nwas used to start the ATRP process of the MMA monomer, resulting in\na PMMA-<i>b</i>-PSf-<i>b</i>-PMMA block copolymer.\nThis block copolymer was combined with PSf during the phase inversion\nprocess. Using the PMMA-<i>b</i>-PSf-<i>b</i>-PMMA-modified\nsupport layers, we constructed thin film composite (TFC) membranes\nby interfacial polymerization. The effect of the PMMA-<i>b</i>-PSf-<i>b</i>-PMMA block copolymer content on the porosity,\nmorphology, hydrophilicity, and polyamide layer (PA) properties was\ncarefully studied using several characterizations. The results showed\nthat the support layer characteristics including porosity, hydrophilicity,\nand pure water flux were considerably improved after PMMA-<i>b</i>-PSf-<i>b</i>-PMMA incorporation. In addition,\nthe best performing TFC₂₀ (modified with 20 wt % PMMA-<i>b</i>-PSf-<i>b</i>-PMMA) membrane exhibits a satisfactory\nFO performance: a high water flux of 34.09/17.52 LMH (pressure-retarded\nosmosis (PRO)/FO configuration) and a minimum specific reverse salt\nflux of 0.09/0.1 g/L (PRO/FO configuration) using DI water as the\nfeed solution and 1 M NaCl as the draw solution. Furthermore, the\nwater permeability was significantly improved with an optimal addition\nof the PMMA-<i>b</i>-PSf-<i>b</i>-PMMA block copolymer,\nwhich should be related to an increase in the PA layer roughness.\nMeanwhile, the structural parameter (<i>S</i>) value severely\ndeclined to 625.2 μm for TFC₂₀ from 1925.6 μm\nfor the control TFC. Therefore, the modification of the PSf substrate\nwith the PMMA-<i>b</i>-PSf-<i>b</i>-PMMA copolymer\nis an effective method to alleviate the internal concentration polarization\nduring the FO process.