Decoupling of time scales of motion in polybutadiene close to the glass transition

Studying the dynamic structure factor of polybutadiene in the first valley of S(Q) we observed a decoupling of microscopic and macroscopic time scales about 40^∘{} above Tg. At higher temperatures the time scale set by the viscosity scales with the microscopic scale, while at lower T strong decoupling effects occur. We present evidence that the decoupled low-temperature relaxation is distinctly different from the high-frequency ``{β} process.'' The decoupling temperature coincides with the critical temperature of the mode coupling theory.