In this article, piezo- and pyroelectric signals are used for the photothermal characterization of the thermomechanical properties of polymers as a function of temperature. The potentialities of the proposed technique are explored using poly(ethylene terephthalate) as the test sample. The influence of the sample thermal aging on the polymer physical properties is also discussed. The sensitivity of the proposed photothermal technique is tested by comparing its results with complementary dielectric response measurements and X-ray diffraction.