The dynamic mechanical properties of double chain polyphenylsilsesquioxane were studied with a torsion pendulum between -150° and 450℃ at 1 Hz. The natures of the loss peaks were investigated by studying the effects of thermal treatment and plasticizer on the shear modulus and damping. We found that the loss peak at -120℃ is due the local movement of the siloxane chain

loss peak at - 40℃ is the characteristic feature of the double siloxane chain

and at 300℃ the decomposition of the double chain begins.