Journal of Thermal Analysis and Calorimetry, Vol. 75 (2004) 233–248 CRYSTALLIZATION AND MELTING OF ISOTACTIC POLYPROPYLENE IN RESPONSE TO TEMPERATURE MODULATION A. Genovese and R. A. Shanks * Department of Applied Chemistry, RMIT University, GPO Box 2476V, Melbourne, Victoria 3001, Australia (Received July 27, 2003; in revised form September 30, 2003) Abstract Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scan- ning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool–heat modu- lation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool–heat method lead to an increase in the peak melting temperature and the final traces of melt- ing. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crys- tal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible. Keywords: crystallization, DSC, isotactic polypropylene, melting, TMDSC Introduction The crystallization and melting of polyolefin’s has been a subject of much interest, par- ticularly in the case of isotactic polypropylene (iPP). Multiple melting endotherms are commonly observed in differential scanning calorimetry (DSC) experiments. The origin of the multiple melting peaks in iPP has been attributed to factors such as crystallization temperature [1–4], heating rate, orientation [3], the presence of different crystal modifica- tions (α, β and γ-forms) and the transformation of the different structures [2, 5, 6, 7]. 1388–6150/2004/ $ 20.00 © 2004 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: robert.shanks@rmit.edu.au