Synthesis and characterization of highly branched, functional poly(arylene ether sulfone)s for water purification membranes

Official URL: https://risc01.sabanciuniv.edu/record=b2486352 _ (Table of contents)

Recovery of wastewater is a global and environmental matter on the sustainability of water sources. Pressure-driven membrane technology is one of the best options for wastewater treatment because of no need for chemicals. Poly(arylene ether sulfone)s (PAES) are widely used in membrane technology due to their unique chemical and thermal characteristics. Yet, the linear structure of PAESs limits their functionality, while branched polymers come with a multitude of terminal groups, which may be used to introduce unique functionalities to the polymer backbone. Highly branched polymers typically have a lower hydrodynamic volume; consequently, their solubility in organic solvents is higher than linear analogous. However, they have lower mechanical properties. Therefore, the terminal groups of branched polymers can be fully or partially designed to be cross-linkable end-groups, which can enhance their thermal and mechanical properties while retaining the functionality. The investigation of the effect of degree of branching and the distance between branch points on the thermo-mechanical features and water purification performance of membranes fabricated from novel HBPAES synthesized via using the A₂+B₃ polymerization method forms the basis of this Ph.D. dissertation. These investigations have focused on three different types of materials, namely, (i) blend films of linear and highly branched PAES, (ii) UF membranes fabricated from linear and branched PAESs and (iii) TFC membranes prepared from sulfonated HBPAES (SHBPAES). In the A₂+B₃ polymerization methodology employed in this study, A₂ species were difunctional reagents such as 4,4'-dichlorodiphenyl sulfone (DCDPS) or 3,3'-disulfonate-4,4'-dichlorodiphenyl sulfone (SDCDPS) type monomers or in-house synthesized PAES-based linear oligomers with varying degrees of polymerization (DP). 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) was chosen as the B₃ monomer with three phenolic functionalities. The type of A₂ species, either a monomer or a difunctional oligomer with varying DPs enabled tailoring of the degree of branching and the average distance between branch points. Additionally, various strategies were developed to further introduce functional groups such as silane and phenolate on the chain ends of synthesized HBPAES products, which were characterized by Fourier Transform Infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopies, Size Exclusion Chromatography (SEC), Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC) and stress-strain tests. Silane functionalities of HBPAESs offered the ability to crosslink final polymeric films or membranes in the presence of moisture and heat. These films and membranes were found to possess inorganic domains upon the crosslinking via the silane terminal groups of HBPAES, which generally have heat and chemical resistance. In order to enhance the thermal and mechanical properties of PAES-based UF membranes, the designed HBPAESs were proportionately blended with a commercially available linear PAES (LPAES). Lastly, the A₂+B₃ polymerization in the presence of SDCDPS as one of the A2 reagents resulted in SHBPAES, which was observed to be soluble or dispersible in water depending on the SDCDPS content and allowed SHBPAESs in water-based applications such as the fabrication and characterization of novel TFC membranes having poly(arylate sulfone) active layer for the first time in the literature