Structure and molecular motion of poly(ethylene oxide) chains tethered on silica, depended on grafting ratio by the spin labeled method

Electron spin resonance (ESR) spectroscopy of spin-labeled poly(ethylene ox ide) (SL-PEO) tethered on silica was studied to characterize the conformati on and local dynamics of the chain end. The e.s.r spectra could be interpre ted in terms of two components from two different kinds of spin labels atta ched to "train" and "tail" segments, which were strongly and weakly interac ted with the silica surface. The structure and molecular motion of the chai ns are strongly dependent on the grafting ratio. The fractional amount of t he "train" segment decreases remarkably with an increase in the grafting ra tio. From the temperature dependence of the e.s.r. spectra, it was found th at the molecular mobility of the "tail" segment was higher and that of the "train" segment was extremely lower than the PEO chains in the homopolymer bulk. These facts suggest that the "tail" segments are protruding from the silica surface and having a low segmental density, whereas the "train" segm ents are trapped near the silica surface. It can be also considered that th e fractional amount of the "tail" segment increases abruptly with an increa se in the grafting ratio after the tethered chains of a coiled structure fo rm one monolayer.