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We prepared surface-grafted polystyrene (PS) beads with comb-like poly(ethylene glycol) (PEG) chains. To accomplish this, conventional gel-type PS beads (35-75 microm) were treated with ozone gas to introduce hydroperoxide groups onto the surface. Using these hydroperoxide groups, poly(methyl methacrylate) (PMMA, Mn= 22,000-25,000) was grafted onto the surface of the PS beads. The ester groups of the grafted PMMA were reduced to hydroxyl groups with lithium aluminum hydride (LAH). After adding ethylene oxide (EO) to the hydroxyl groups, we obtained the PS-sg-PEG beads, which had a rugged surface and a diameter of 80-150 microm. We could obtain several kinds of the PS-sg-PEG beads by controlling the chain lengths of the grafted PMMA and the molecular weights of the PEG chains. The grafted PEG layer was about 30-50 microm thick, which was verified from the cross-sectioned views of the fluorescamine-labeled beads. These fluorescence images proved that the beads possessed a pellicular structure. Furthermore, we found that the surface-grafted PEG chains had the characteristic property of reducing non-specific protein adsorption on the beads.

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Cover: The picture on the cover presents surface-grafted polystyrene (PS) beads with comblike poly(methacrylate) (PMMA) and poly(ethylene glycol) (PEG) chains. The resulting PSsg-PEG beads consist of a PS core and a flexible PEG shell layer and show good swelling properties in various solvents ranging from toluene to water. The grafted hydrophilic PEG chains on the surface of the PS beads overcome the limitations posed by hydrophobic PS beads, such as non-specific protein adsorption.Further details can be found in the Full Paper by