Morphology,phase transitions and viscoelastic properties of poly(oxybisdimethylsilylene). A mesophase in a silicon analogue of a polyether

Poly(oxybisdimethylsilylene) (POBDMS)

1 System. name: poly[oxy(tetramethyldisilane-1,2-diyl)].

has been studied by differential scanning calorimetry, polarizing microscopy, wide-angle X-ray scattering and dynamic mechanical measurements. The polymer shows a weakly marked glass transition near 154 K and three first-order transitions: a crystal-to-crystal transition at 256 K, a crystal-to-mesophase transition at 294 K and a transition to the isotropic melt at 325 K. These transitions are correlated with the mechanical relaxations measured as a function of temperature. The rheological behaviour of the polymer in the isotropic liquid state and in the mesophase has been studied, as well. The properties of POBDMS are discussed in comparison with liquid-crystalline polymers with mesogenic groups.