Silica particles containing surface-bound free radical initiators have been used as supports for the grafting of thin films of molecularly imprinted polymers (MIPs). This technique offers a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity in chromatographic or sensor applications. Thus prepared MIPs imprinted with L-phenylalanine anilide, have been characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis, fluorescence microscopy, and scanning electron microscopy (SEM), providing evidence concerning the reproducibility in each step and the quantity and quality of the grafted films. The chromatographic properties of the materials have been investigated with respect to the average layer thickness of the polymer on the surface, the solvent, the support pore diameter, the cross-linker concentration, and the composition of the mobile phase. For the porous particles, the column efficiency depended strongly on the amount of grafted polymer. Thus, polymers grafted as thin films (ca. 0.8 nm as average film thickness) on silica with 10 nm average pore diameter showed the highest column efficiency giving plate numbers (N) for the imprinted enantiomer of ca. 700 m -1 and for the antipode ca. 24 000 m -1 . This resulted in baseline resolutions on a 33 mm long column in less than 5min. On the other hand the sample load capacity and separation factor increased up to 7.0 nm layer thickness and dropped again for larger amounts of grafted polymer. A support with an average pore diameter of 100 nm and a 3.8 nm layer thickness showed a far higher saturation capacity than values previously determined for the conventional monolithic materials.
Wide pore silica (D P ~100 nm) and gel-type or macroporous (12% nominal crosslinking density) Merrifield resins were modified with iniferter groups for grafting of crosslinked molecularly imprinted or non-imprinted polymer layers through quasi-living polymerisation. Prior to iniferter coupling, the silica supports were premodified by silanisation with p-(chloromethyl)phenyl trimethoxysilane. The iniferter groups were then introduced by reacting the resin-bound chloromethyl groups with sodium N,N-diethyldithiocarbamate. It was shown that the coupling yield, measured as the conversion of the chloromethyl groups, could be varied between 5 and 85% through kinetic control, with the fastest conversions observed for the macroporous resins. This allows the density of radical generating groups to be finely adjusted. Ultraviolet light-initiated copolymerisations of ethyleneglycol dimethacrylate and methacrylic acid in toluene resulted in grafting of 0.2-1.9 g of polymer per gram of support, where the grafted amount increased with reaction time, iniferter content and monomer concentration. The dry-state texture of the composite beads prepared from the gel-type resin depended strongly on the amount of grafted polymer. According to the scanning electron micrographs, the beads with the lower grafted amounts (0.4 g polymer per g support) were deformed exhibiting a peculiar folded structure, whereas the beads containing more grafted polymer (1.6 g polymer per g support) were spherical, with an appearance similar to the precursor particles. None of these materials exhibited permanent porosity. Only the composites obtained from the porous precursor particles also exhibited porosity after grafting. Among these, the silica-based composites also showed recognition for their templates when assessed in the chromatographic mode, whereas no imprinting effects could be demonstrated for the polystyrene-supported materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.