Synthesis Of Amphiphilic Polymer PLA-PEG-PLA And The Modification Of Pes Membrane

Polyethersulfone(PES)is one of the most widely used membrane materials because of its high mechanical strength,good thermal and chemical stability,wide scope of pH application and strong oxidation resistance.Even it can be used at the highest temperature of 120?.However,the intrinsic hydrophobicity of PES always makes the membrane preferentially interact with the natural organic material(NOM)like humic substance or biomolecules in the feed solutions,and it becomes fouled,which result in the decrease of separation efficiency and difficult to wash and recycle.Therefore,it is necessary to modify PES membrane surface to improve its hydrophilicity and biocompatibility.In this study,the amphiphilic copolymers PLA-PEG-PLA were synthesized by ring-opening polymerization of L-lactide using PEG as a macro-initiator.Then the hydrophilicity and biocompatibility of PES ultrafitration membranes were improved by blending with PLA-PEG-PLA amphiphilic triblock copolymers.PES membranes were prepared by an immersion precipitation phase inversion method using DMAc as solvent and PLA-PEG-PLA as hydrophilic modification agent.Firstly,the effect of PLA-PEG-PLA amount added into the casting solution on the structure and properties of PES UF membrane was investigated.The membrane surface was characterized by Attenuated total reflection Fourier transform infrared spectrometer(ATR-FTIR).The results indicated that PLA-PEG-PLA had embedded into PES block membrane.Scanning electron microscope(SEM)bservation indicated that the structure of modified PES membrane changed obviously.The water contact angle(CA)test indicated that the hydrophilicity of the modified PES membrane increased with the content of PLA-PEG-PLA modifier in the casting solution increasing.The ultrafiltration performance of the membranes was investigated by dynamic filtration of bovine serum albumin(BSA).The permeation flux and anti-fouling properties of modified membrane were improved obviously.And the membrane modified with 4wt%PLA-PEG-PLA displayed the highest permeation flux and the best antifouling properties.The blood compatibility of the membrane was also evaluated by protein adsorption,platelet adhesion and hemolysis test.The results revealed that the modified PES membranes presented relative better blood compatibility featured by the lower platelet adhesion,protein adsorption and a little hemolysis.Secondly,the effect of PLA chain length on the structure and properties of PES/PLA-PEG-PLA blending membrane was further researched.Three amphiphilic copolymers with different PLA chain length were synthesized by changing the mole ratio of L-lactide to PEG.PLA-PEG-PLA with different PLA chain length was blended with PESat the same condition.The results suggested that some amphiphilic copolymer molecules acted as pore-forming agent and some amphiphilic copolymer molecules acted as hydrophilic modification agent in the immersion precipitation phase inversion process.Meanwhile,the shorter of the PLA chain length was,the higher the water flux of modified membranes would be.However,for all the modified PES membranes,considering,hydrophilicity,anti-fouling ability and biocompatibility,when the mole ratio of L-lactide to PEG is 30:1 and the dosage is 4wt%(M33)the modified PES membrane present the best performance.