Studies of the enthalpy relaxation and the ''multiple melting'' behavior of semicrystalline poly(arylene ether ether ketone) (PEEK)

We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes in the amorphous phase of semicrystalline PEEK - enthalpy relaxation below the glass transition (T-g) and secondary crystallization above T-g. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer - the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained from small strain creep studies of ''physical aging'' of semicrystalline PEEK below and above T-g.