The effect of thermal history on the phase behaviour and viscoelastic relaxations of poly(triethylene glycol p,p’-dibenzoate) (PTEB) was studied. The mesophase of PTEB can be converted into a three-dimensional crystal by annealing at appropriate temperatures and for appropriate times. Three PTEB samples were analysed, one of them freshly quenched from the melt and the other two annealed under different conditions (room temperature and 85-degrees-C). The phase structure was investigated by differential scanning calorimetry and X-ray diffraction, both at wide and low angles (using synchrotron radiation in the latter case). This structure affects slightly the beta and gamma relaxations, whereas the glass (alpha) transition is more intense and narrow and appears at a lower temperature for the sample freshly quenched from the melt, which exhibits only the liquid crystalline phase.