Heat of Fusion of the Local Equilibrium of Melting of Isotactic Polypropylene

• Published in: Macromolecules 2001-11, Vol.34 (23), p.8384-8387
• Main Authors: Androsch, R, Wunderlich, B
• Format: Article
• Language: English
• Subjects: Applied sciences; Crystallization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma011118i

Temperature-modulated differential scanning calorimetry (TMDSC) is a useful tool to measure the apparent, reversible heat capacity in the absence of nonlinear, irreversible processes. This condition is best reached using the quasi-isothermal mode in which one can delay the measurement until any slow, irreversible processes such as annealing, crystallization, or melting are completed and a local, structural equilibrium has been achieved. If the measured, apparent, reversible heat capacity is still larger than the thermodynamic, vibrational heat capacity, this increase may be caused by the temperature dependence of the concentration of crystal defects, an equilibrium melting and crystallization of molecules of sufficiently low mass so that no molecular nucleation is necessary, and the reversible melting, i.e., crystallization and melting of macromolecular segments that do not need molecular nucleation. In the present paper, we attempt to compare the reversible change of crystallinity of iPP probed by temperature-resolved WAXS and TMDSC to check whether the two independent observations refer quantitatively to the same effect and involve the same crystallinity.