Effect of amine spacer of PEG on the properties, performance and antifouling behavior of poly(piperazineamide) thin film composite nanofiltration membranes prepared by in situ PEGylation approach

Abstract

In continuation of work (Gol et al., J. Membr. Sci., 2014, 455, 271–282) for in situ PEGylation of thin film composite (TFC) membrane, herein, effect of polyethylene glycol (PEG) end-group on the properties and performance of PEGylated TFC nanofiltration (NF) membranes is reported. In situ PEGylation of conventional poly(piperazineamide) TFC NF membranes was performed by interfacial polymerization between TMC and PIP+PIP-terminated polyethylene glycol (PIP–PEG–PIP), PIP+m-phenylenediamine-terminated PEG (MPD–PEG–MPD) and PIP+alkyl amine terminated-PEG (H2N–PEG–NH2) mixtures respectively. Among these three processes, PEGylated membranes prepared with TMC and PIP+PIP–PEG–PIP mixture exhibited excellent antifouling property, similar performance, close pore radius and pore structure factor compared to conventional poly(piperazineamide) TFC NF membrane. This is attributed to the closer reactivity of PIP and PIP–PEG–PIP towards TMC. Membranes prepared with TMC and PIP+MPD–PEG–MPD mixtures exhibited superior antifouling property compared to conventional TFC NF membrane, nevertheless, rejection and permeate flux were decreased. TFC membranes prepared with PIP+H2N–PEG–NH2 mixtures/TMC exhibited similar performance compared to conventional membrane with low degree of PEGylation and hence showed only marginal improvement of antifouling property. Conceptual Density Functional Theory (DFT) and average local ionization potential energy calculations performed on the lowest energy conformations of PIP and different amines (PIP, MPD and alkyl amine) terminated PEG type of molecules indicated closer reactivity of PIP and PIP-terminated PEG type of molecule compared to PIP and other amines terminated PEG type of molecules towards TMC.