Scanning nanocalorimetry at high cooling rate of isotactic polypropylene

A wide set of cooling scans and subsequent melting behavior of isotactic polypropylene (i-PP) were investigated using differential scanning calorimetry and nanocalorimetry at very high cooling rate. The latter technique offers, indeed, the distinctive possibility to perform heat capacity measurements at rates of more than 1000 K/s, both in cooling and in heating, to characterize the crystallization. When the i-PP sample was solidified with cooling rate larger than 160 K/s, a novel enthalpic process was observed that was related to the mesomorphic phase formation. Furthermore, at cooling rates higher than 1000 K/s, the i-PP sample did not crystallize neither in the alpha nor in the mesomorphic form. The subsequent heating scan starting from -15 degrees C showed an exothermic event, between 0 and 30 degrees C, ascribed to the mesophase cold crystallization.