The failure behavior and its mechanism of time-temperature superposition (TTS) poly(vinyl chloride) (PVC)/dioctylphthalate (DOP) (100/70) system were studied from low to high temperatures with a step of 10 degrees C. Arrhenius equation, WLF equation, mathematical nonlinear fitting, and manual shift were applied for TTS fitting. None of these methods could obtain the well-superposed master curves with either single horizontal shift or two-dimensional (horizontal and vertical) shift. The rheological data and differential scanning calorimeter (DSC) results were used to explain the failure mechanism of the TTS fitting. The curves of storage modulus versus frequency were well fitted to an empirical equation G' = G(0)' + K omega(n). The yield behavior was used to analyze the influence of test temperature on the dynamic rheological behavior for the PVC/DOP (100/70) system. A transition of rheological behavior from the solid-like to the linear viscoelastic could be observed at 190 degrees C because of the gradual melting of microcrystallites and the destruction of gel networks, which were confirmed by DSC analysis. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012