Synthesis Of Amphiphilic Copolymers Based On MMA And Their Effects On The Hydrophilization Of PVDF Porous Membrane

Poly(vinylidene fluoride) is one of the most popular materials for microporous membranes.However,high driving force,as well as proteins absorbtion fouling,will be the disadvantages in the process where PVDF membranes are applied,due to the strong hydrophobility of PVDF.Thus,it is urgent to find an effective method to improve the hydrophilicity of PVDF membranes.Ever attempts revealed that the water-soluble polymers,such as PEG and PVP,have been studied as the additives for hydrophilization of PVDF membranes.Unfortunately,they are much likely to be washed out either in the membrane preparation process or the practical application. And thus,a stable hydrophilicity can not be realized for the PVDF membranes by using these polymers.To settle the problems above,a novel triblock amphiphilic copolymer PVP-PMMA-PVP and a diblock amphiphilic copolymer PMMA-b-PMAA had been synthesized via reversible addition-fragmentation chain transfer(RAFT) radical polymerization,where methyl methacrylate(MMA) was chosen as the hydrophobic monomer,while N-vinyl-2-pyrrodlidone(NVP) and methacrylic acid(MAA) were hydrophilic monomers.And the blend membranes PVDF/PVP-PMMA-PVP and PVDF/PMMA-b-PMAA were fabricated via immersion precipitation phase inversion process,by blending PVP-PMMA-PVP and PMMA-b-PMAA with PVDF, respectively.The structure,composition,molecular weight and polydispersity index(PDI) for the two amphiphilic copolymers were characterized by FTIR,~1H NMR and GPC.It was found that the PDI of the synthesized triblock and diblock copolymers were low (＜1.7 or＜1.5).These results indicated the successful synthesis of these two amphiphilic copolymers via RAFT polymerization route.XPS was applied to study the compositions in the surfaces of the PVDF/PVP-PMMA-PVP and PVDF/PMMA-b-PMAA blend membranes.It was found that amphiphilic copolymers obviously enriched in the surface layer of blend membranes.The enrichment of amphiphilic copolymers had an important effect on improving the hydrophilicity of the PVDF membranes.SEM images indicated the pore diameter and porosity had remarkably increased for the PVDF membrane as the addition of amphiphilic copolymers.Compared with pristine PVDF membrane,the contact angles of the blend membranes had decreased greatly(from 98°reduced to about 70°).The water flux of the blend membranes measured under 0.1MPa were considerable improved to 1800 L/(m~2·h),while that of the pristine PVDF membrane was 0 L/(m~2·h).Besides,to investigate the stability of the amphiphilic copolymers in the blend membranes,blend membranes PVDF/PVP-PMMA-PVP and PVDF/PMMA-b-PMAA had been leached for days in a thermostat water bath at 60℃. The hydrophilicity of the leached membranes was studied by contact angle measurement.The leached membranes still showed low contact angles,which suggested modified PVDF membranes were endowed with stable hydrophilicity by the synthesized amphiphilic copolymers.The results of this dissertation had proved that when the triblock amphiphilic copolymer PVP-PMMA-PVP,as well as the diblock amphiphilic PMMA-PMAA, was blended into PVDF porous membranes,it would not only influence the structure of the membranes,but also enrich on the membranes surfaces and be stable in the membrane base.It could be concluded that PVP-PMMA-PVP and PMMA-PMAA contribute the potential materials to prepare high performance PVDF porous membrane with stable,perfect hydrophilicity.