Preparation Of Enviroment-responsive Pet Track-etched Membranes By Surface-initiated Atom Transfer Radical Polymerization

In this paper, atom transfer radical polymerization (ATRP) as one of thecontrolled/‖living‖radical polymerization methods was used on the surfacemodification of PET track-etched membranes. By grafting differentfunctional polymers: pH-responsive polymer PHEMA andP(HEMA-co-DMAEMA), photo-sensitive polymer PHEMA/CA andP(HEMA/CA-co-DMAEMA) via ATRP to prepare various functionalmembranes for application.PET track-etched membrane was first reacted with the ethylenediamineto introduce the active amino group and hydroxyl group. Then the modifiedmembrane was reacted with ATRP initiator2-bromoisobutyryl bromide(2-BIB) to immobilize it onto membrane surface, followed by controlledgrafting of the poly(2-hydroxyethyl methacrylate)(PHEMA) andpoly(2-(dimethylamino) ethyl methacrylate-co-2-hydroxyethyl methacrylate)P(DMAEMA-co-HEMA) to prepare pH-responsive membranes. The X-rayphotoelectron spectroscopy (XPS), fourier transform infrared spectroscopy in attenuated total refection (ATR-FTIR), thermogravimetric analysis(TGA), grafting degree measurement and contact angle measurement wereused to prove that the PHEMA and P(HEMA-co-DMAEMA) weresuccessfully grafted onto PET membranes surface. Scanning electronmicroscopy (SEM) was employed to characterize the surface morphology ofgrafted membranes, and demonstrated that the diameter of membrane poresreduce gradually with grafting time increasing. Membrane water fluxmeasurement studied the pH-responsive of grafted membrane. The waterfluxes of membrane were small in neutral solution, and increased sharply inacidic solution with the critical pH among4to5. The PET-g-P(HEMA-co-DMAEMA) membrane had different pH responsive property.The responsive region of PET-g-P(DMAEMA-co-HEMA) membraneincrease according to the increased mole ratio(<0.5) of HEMA in thecopolymer chains. When the mole ratio of HEMA was0, the responsiveregion of PET-g-PDMAEMA membrane was pH=4~6. When the mole ratioof HEMA was0.4, the responsive region of PET-g-P(DMAEMA-co-HEMA)membrane rised to pH=9~11.Based on the grafted membranes, the hydroxyl of HEMA could bereacted with cinnamoyl chloride (CA) to produce cinnamate esterifiablephoto-sensitive grafting chains and prepare photo-sensitivePET-g-PHEMA/CA membrane and PET-g-P(HEMA/CA-co-DMAEMA)membrane. ATR-FTIR, TGA were used to demonstrate that the cinnamate esterification and photo-cross-linking were successfully accomplished. SEMcharacterized the membrane surface and cross-section morphology, andwater flux measurement characterized the permeability of membrane beforeand after photo-cross-linking. The results showed that, after UV inducedcross-linking, the pore size and porosity of PET-g-PHEMA/CA membraneincreased sharply, and its water flux was twice as high as that before UVirradiation. The effect of different solvents on the process of UV inducedcross-linking of P(HEMA/CA-co-DMAEMA) chains was discussed. Thegrafted chains had different states (collapse or swelling) in different solvents,resulting in the various membrane surface morphologies after UV inducedcross-linking. When grafted membrane was immersed in strong polaritysolvents DMF and NMP, the interaction force between solvent and graftedchains is strong. So the grafted chains were well swelling and stretching overthe pores of membrane, resulting in the dense smooth thin layer onmembrane surface after UV induced cross-linking. When grafted membranewas immersed in water, the grafted chains were collapsed because of theweak interaction force between water and grafted chains. So the collapsedchains adhered to the pore wall, and porous membrane was formed after UVinduced cross-linking.