Structure and molecular motion of poly(ethylene oxide) chains tethered on silica by the spin label method: effect of polystyrene adsorption

Abstract

Electron spin resonance (e.s.r.) spectroscopy of spin-labelled poly(ethylene oxide) (SL-PEO) tethered on silica was studied to characterize the conformation and local dynamics of the chain end. Non-labelled polystyrene (PS) with narrow molecular weight distributions, having weight-average molecular weights ( M w ) of 9.64 × 10 4 (PS-96) and 3.84 × 10 5 (PS-384), were adsorbed on the surface of the silica-tethered PEO with 1.9% grafting ratio in carbon tetrachloride solution at 35°C. E.s.r. spectra of the tethered SL-PEO were observed at various temperatures after the samples were completely dried. The structure and molecular motion of the PEO chains are strongly dependent on the M w of PS. From the temperature dependence, it was found that the molecular mobility of the tethered PEO chains increased when the large PS-384 molecules were adsorbed on the surface. The chain ends of the PEO chains were mobile even at − 196°C. These facts suggest that the PS chains spread out the PEO chains and are adsorbed on the silica surface as ‘train’ segments, whereas the PEO chains protrude from the surface as ‘tail’ segments. On the other hand, when the small PS-96 molecules are adsorbed, the rate of motion of the tethered PEO chains is slowed down by the PS chains. This suggests that the PS chains are distant from the silica surface and entangled with the PEO chains.