Structure and Molecular Motion of Poly(ethylene oxide) Chains Tethered on Silica, Depended on Grafting Ratio by the Spin Labeled Method

Abstract

Electron spin resonance (ESR) spectroscopy of spin-labeled poly(ethylene oxide) (SL-PEO) tethered on silica was studied to characterize the conformation and local dynamics of the chain end. The e.s.r. spectra could be interpreted in terms of two components from two different kinds of spin labels attached to “train” and “tail” segments, which were strongly and weakly interacted with the silica surface. The structure and molecular motion of the chains are strongly dependent on the grafting ratio. The fractional amount of the “train” segment decreases remarkably with an increase in the grafting ratio. From the temperature dependence of the e.s.r. spectra, it was found that 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” segments are trapped near the silica surface. It can be also considered that the fractional amount of the “tail” segment increases abruptly with an increase in the grafting ratio after the tethered chains of a coiled structure form one monolayer.