The Grafting Polymerization Of Poly(N-isopropylacrylamide) Onto Superfine Silica Surface By ATRP And Its Application In HPLC

Thermosensitive composites were prepared through Atom Transfer Radical Polymerization(ATRP) of N-isopropylacrylamide(NIPAM) on the surface of ultrafine silica beads in the present work.. The synthetic procedure included the connection of silane coupling agentγ-glycidylpropyltrimethoxysilane(KH-560) with the superfine silica particles, reaction of diethanolamine with glycidyl group of KH-560, and reaction of 2-bromoisobutyryl bromide with hydroxy groups respectively, and finally the ATRP reaction of NIPAM grafting on the superfine silica particle surface. In the synthetic procedure the branch point and the active position on the silica surface increased due to participating of the intermediate diethanolamine. The effects of some synthetic conditions such as the types of ligands and dosages of monomers on the grafting ratio and the molecular weight were investigated.The composite particles were characterized by infrared spectra(FTIR), thermogravimetry(TG), scanning electron microscope(SEM), and differential scanning calorimetry(DSC) and so on. The analysis of FTIR gave the structure of the composite. The grafting ratio of PNIPAM on the silica surface was measured by TG and calculated. The images of SEM revealed that a homogeneous and smooth PNIPAM layer was formed on the surface .The diagram of DSC indicated the composite silica particle was thermosensitive. The PNIPAM had successfully been cleaved from the composite silica particles(silica-g-PNIPAm) through chemical method in this paper. The measurement of GPC for the PNIPAM cleaved from the composite silica particles gave the average molecular weight and the molecular weight distribution and the GPC analysis showed that the molecular weight distribution of polymer on the silica surface was very narrow. The results of these studies showed that a thermosensitive polymer had been successfully grafted onto the silica surface.The thermosensitive composite was used as a packing material in high performance liquid chromatography(HPLC) for separating amino acid mixtures and phenolic mixtures. The result indicated that satisfactory separation was successfully achieved by controlling temperature of the column. The HPLC separation results revealed that satisfactory separation could be attained only by controlling column temperature, instead of by changing composition of the mobile phase.This separationg system had strongpoints such as less pollution, lower cost, easy control and high efficiency of separation. So the research about temperature controllable separation system had gradually become focus of application of HPLC in recent years.