The Synthesis Of PSf And PSf-b-PEG Block Copolymer And The Development Of The Integrated Process Of Membrane Preparation

In recent years,polysulfone（PSf）has been widely used to prepare separation membranes due to its excellent chemical inertness,thermodynamic stability,and processability.However,both the processes of PSf material synthesis and the PSf membrane preparation need a lot of organic solvent and water,which produces a significant amount of the heavily polluted waste liquid.The post-treatment process of the PSf synthesis is to obtain PSf material from the reaction solution by precipitation,purification,and drying.The process of PSf membrane fabrication is to dissolve PSf in an organic solvent to prepare the casting solution,and then to precipitate in water through the nonsolvent induced phase separation（NIPS）method.Obviously,the post-treatment process of PSf synthesis is very similar as that of the PSf membrane preparation.Therefore,it is important to develop the integrated green process of PSf synthesis and membrane preparation to save organic solvents and water,and also reduce water pollution.In addition,because of the inherent hydrophobicity,PSf membrane faces challenges of membrane fouling and poor permeability during its practical application.Hydrophilic PSf materials are highly desired.The main research contents and results of this study are as follows:（1）The integrated green process of PSf synthesis and PSf membrane fabrication.According to the principle of step-growth polymerization,Bisphenol A and 4,4’-Dichlorodiphenyl sulfone were used as monomers to synthesize PSf materials.Firstly,the reaction kinetics of PSf synthesis were studied and the number average molecular weight（M_n）of PSf was tailored in the range of 2 kDa-100 kDa by changing the polymerization time and the monomer ratio.The casting solution was obtained for membrane fabrication by filtrating the viscous PSf solution from the polymerization reaction using PTFE membrane with 5 micrometer pore diameter without PSf precipitation,drying,and re-dissolving processes.It is fully proved that the PSf ultrafiltration membrane prepared by the integrated green process and from the commercial PSf had the similar membrane structure and separation performance,demonstrating the feasibility of the integrated green process of PSf synthesis and membrane fabrication.（2）Synthesis of PSf-b-PEG block copolymer and the development of the integrated process of PSf-b-PEG synthesis and membrane preparation.Upon the synthesis of PSf,a series of PSf-b-PEG block copolymers with different PEG contents were synthesized through a one-pot approach using different lengths（M_w:400,2000,6000 Da）of PEG as the end-capping reagents.Subsequently,the PSf-b-PEG membranes with dense sponge-like pore structure were prepared by the NIPS method.Results show that the longer PEG chain in the PSf-b-PEG block copolymer,the larger surface pore diameter formed in the PSf-b-PEG membrane.The average effective pore diameters of PSf-b-PEG membranes are 4nm,5nm,and 10nm,respectively,when the M_W of PEG is 400 Da,2000 Da,and 6000 Da in the PSf-b-PEG block copolymer.The membrane made by PSf-b-PEG with PEG₂₀₀₀ exhibits a very high pure water permeance of 266Lm^-2h^-1bar^-1 and a precise separation of dyes with high rejection above 99.1% for Congo Red and 69.1%for Acid Fuchsin.In addition,it was demonstrated that the integrated process of material synthesis and membrane fabrication was applicable to prepare PSf-b-PEG membranes.In this work,we develop an integrated green process of material synthesis and membrane fabrication for PSf and PSf-b-PEG.Besides,the effect of the PEG chain length on the pore size and pore structure of PSf-b-PEG membranes was illustrated.This work offers an avenue to eco-friendly fabricate high-performance PSf and PSf-b-PEG membranes with low costs.