Dielectric study of linear low density polyethylene using thermally stimulated depolarization currents techniques

The TSDC spectra of LLDPE functionalized with diethylmaleate polar groups has three main peaks labeled α, β and γ with decreasing temperature. The γ and β relaxations have been alternatively attributed in the literature to the manifestation of the glass rubber transition, and to a localized conformational bond rotation perturbed by the environment. The α relaxation has been related to processes occurring in the crystalline phase. These peaks have been carefully recorded and the γ peak also shows a broad shoulder on its low temperature side. We analyzed these relaxations using the Simulated Annealing Direct Signal Analysis (SADSA) procedure where we decompose each peak into its elementary excitations which are monoenergetic and have either an Arrhenius or Vogel-Fulcher relaxation time dependence. This model is fitted to the experimental curves by utilizing Monte Carlo Simulated Annealing method and the result is the energy spectra for the relaxations. In particular the clean γ peak was found to have Vogel-Fulcher relaxation times and the sub-γ shoulder could only be fitted using Arrhenius relaxation times, confirming that the γ transition is indeed the T_g relaxation and that at these low temperatures both localized motions of the polar groups and cooperative motions of the chain occur