Synthesis Of PES-b-PEG Block Copolymer Material And Preparation Of Its Nanofiltration Membran

Polyethersulfone(PES)has been widely used to prepare separation membranes due to their excellent mechanical strength,membrane-processing properties,thermal stability,oxidation resistance and acid and alkali resistance.Phase inversion is easy to prepare membrane on a large scale and suitable for a variety of membrane materials.At the same time,it has a simple process for preparing membranes.However,the PES nanofiltration membrane prepared by the phase inversion has some disadvantages such as thick skin layer and low porosity,which lead to low perm-selectivity of the nanofiltration membrane.Considering the material structure design,the amphiphilic polyethersulfone-b-polyethylene glycol(PES-b-PEG)block copolymer was synthesized by using hydrophilic block as the end capping agent of polyethersulfone in order to improve the perm-selectivity of phase inversion nanofiltration membranes.High performance nanofiltration membranes were prepared by phase inversion method by using PES-b-PEG block copolymer as the membrane material.This work mainly focuses on the following:(1)Synthesis and characterization of amphiphilic PES-b-PEG block copolymers.In this work,PES and PES-b-PEG block copolymer were synthesized by“one pot”polycondensation with bisphenol S and 4,4’-dichlorodiphenylsulfone as monomers and polyethylene glycol with molecular weight of 2000 Da as capping agent.The molecular weight and molecular weight distribution of PES and PES-b-PEG block copolymer and PEG content of PES-b-PEG block copolymer were characterized.The best reaction conditions for the synthesis of PES-b-PEG block copolymer were determined by investigating the effects of different reaction temperature and reaction time on the molecular weight and molecular weight distribution of PES and PES-b-PEG block copolymer and the composition proportion of each block in PES-b-PEG block copolymers.The molecular weight,distribution and PEG content of PES-b-PEG block copolymers were characterized by gel permeation chromatograph and thermogravimetric respectively.The test results showed that the number average molecular weight,PDI and PEG content of PES-b-PEG block copolymer were 1.7×10~4 g/mol,2.43 and 12.1%,respectively.(2)Preparation and characterization of amphiphilic PES-b-PEG block copolymer nanofiltration membrane.In this work,PES-b-PEG nanofiltration membrane was prepared by adjusting the composition of casting solution(polymer concentration,porogen,volatile solvent ratio)and air bath time by phase inversion using PES-b-PEG block copolymer as the membrane material.The surface morphology and cross-section structure of PES-b-PEG nanofiltration membrane were characterized and analyzed.Meanwhile,the sieving performance of PES-b-PEG nanofiltration membrane was tested and evaluated.The results show that the structure of PES-b-PEG membrane becomes dense,the pure water permeance decreases and the rejection of inorganic salts increases with the increase of PES-b-PEG polymer concentration,Li Cl content and the proportion of acetone in the casting solution.In addition,the cross-section structure of PES-b-PEG membrane transformed from loose finger-like structure to dense spong-like structure,the pore diameter of PES-b-PEG membrane reduced from 2.7 nm to 1.5 nm,the pure water permeance of PES-b-PEG membrane decreased from 21.4 LMH/bar to 3.2 LMH/bar and the rejection of divalent salt increased from 21.8%to 61.1%with the increase of air bath time.The pure water permeance of the optimal PES-b-PEG membrane is 3.2LMH/bar and the separation factor of the membrane for monovalent/divalent salts is9.7,which is higher than the value reported in the literature(1.8～7.1).In this work,amphiphilic PES-b-PEG block copolymer was synthesized by condensation polymerization.Amphiphilic PES-b-PEG block copolymer has unique microphase separation characteristics.Highly selective PES-b-PEG nanofiltration membrane was prepared by Phase inversion by using PES-b-PEG block copolymer as the membrane material,PES-b-PEG nanofiltration membrane has the potential to be prepared on a large scale.