Photochromic properties and microstructures of poly (tetramethylene oxide)/tungsten trioxide hybrid materials

Tungsten trioxide (WO3) was incorporated in silica end-capped poly(tetramethylene oxide) (PTMO) using the sol-gel process involving ion exchange of sodium tungstate dihydrate. When the hybrid was irradiated with a low-pressure mercury lamp, the transmittance at 620 nm in the UV-visible spectra decreased and the color changed from pale yellow to blue. This means that amorphous WO3 have changed to the tungsten bronze structure. After irradiation the films bleached with elapsed time in the dark. Temperature dependence of the dynamic viscoelasticity of the PTMO/WO3 hybrid was measured. A sharp peak at about -55 degrees C in the tan delta curves is due to micro-Brownian motion of PTMO segments. The peak position did not change below 15 wt% of WO3 content, but above 30 wt% it shifted to a higher temperature and the peak broadened. The storage modulus of the hybrids at the rubbery region increased with increasing amount of WO3. A broad peak in small-angle X-ray scattering profiles was caused by the interference between terminated silica domains. The peal; position shifted to a lower angle, and the peak disappeared with increasing amount of WO3. These results suggest thar the WO3 domains may be formed in the vicinity of silica domains below 15% of WO3 content, but dispersed in the PTMO matrix above 30% WO3 and strongly restricts the molecular motion of the PTMO segments.