Study On PH Responsive Membrane By Sequential Photoinduced Living Graft Polymerization

pH responsive membrane is one kind of environmentally responsive membrane, its permeability can be tuned by altering the surrounding pH value. Because pH responsive membrane can be sensitive to pH value, it can be used in many fields such as controlled drug delivery, separation, chemical sensors, water treatment et al. Therefore much attention has recently been focused on the development of pH responsive membrane.Ultraviolet (UV) induced grafting polymerization method is a popular way to improve the performances of membranes. It is easy to operate continuously, and the cost of the whole reactive equipments is low. Meanwhile, exposure to ultraviolet is of little influencing on the host materials'properties. However the simultaneous UV induced grafting polymerization can produce a considerable amount of homopolymers, which result in the wastes of raw materials. Therefore, a sequential photoinduced living graft polymerization method was used in the study. In this method, the amount of homopolymer can be reduced significantly. Also, initiator formation and graft polymerization occur independently in the successive steps, so grafting density (number of grafting sites) and grafted polymer chain length can also be controlled independently, which is very important to the research of the pH responsive membrane.In the present work, polypropylene (PP) membrane was used as the host membrane, and the pH responsive membranes were prepared by the sequential photoinduced living graft polymerization method when benzphenone (BP) was used as the photoinitiator and acrylic acid (AA) was used as the monomer. The influences of the concentration of photoinitiator, the concentration of monomer, the reaction time and the reaction temperature on the grafting yield including grafting density and grafted polymer chain length, were discussed detailedly. Also, the effects of different polymerization conditions on the pH responsibility of the grafted membrane were studied and the optimum polymerization conditions were obtained. In the second step of the reaction, differing from the traditional solvent ethanol, the solvent of water and the mixed solvent of water and ethanol were discussed. At the end, a particular ratio of mixed ethanol and water was selected as the optimum reaction solvent.ATR-FTIR technique was used to verify the chemical composition of the membranes, and it indicated that the acrylic acid groups had been grafted onto the host membranes. Thermal analysis showed that the acrylic acid groups had been grafted to the host membranes too, and the composite membranes have excellent thermal stability. The surface and cross-sectional morphology of the membranes were observed by SEM, and the results found that the grafting had happened on both surface and cross section of the membranes. The pH responsibility of grafted membranes were evaluated by measuring the water filtration flux changes on different pH values(3～8). Also, the thickness and the pore size distribution of grafted membranes were evaluated respectively. The study showed that pH responsive membranes can be made by the sequential photoinduced living graft polymerization method when benzphenone (BP) was used as the photoinitiator. And the effect of grafting yield on pH responsibility is great. pH responsibilities had been observed when grafting yields were in the range of 1%～30%, and the pH responsive coefficient reached 15 with the grafting yield of 15%. In the end, pH responsive mechanism and the flux modal of the pH responsive membrane were discussed simply, which is helpful for taking an ulterior investigation.