Influence of molecular characteristics on non-isothermal melt-crystallization kinetics of syndiotactic polypropylene

Non-isothermal melt-crystallization and subsequent melting behavior for six syndiotactic polypropylene (sPP) resins having different molecular characteristics were investigated by differential scanning calorimetry (DSC). For a given sPP resin, the crystallization exotherm became wider and shifted towards a lower temperature with increasing cooling rate. Among all of the sPP resins investigated, the crystallization exotherm of sPP#11 was found to locate at the highest temperature range, followed by that of sPP#14, sPP#10, sPP#13, sPP#12, and sPP#9, respectively. Based on the absolute temperature scale, sPP#11 showed the highest tendency to start crystallizing during a cooling scan. The ability of these resins to start crystallizing was found to be very similar when the difference in the equilibrium melting temperature of the resins was taken into account. The non-isothermal melt-crystallization kinetics of these sPP resins was well described by the Avrami, Urbanovici-Segal, Ozawa, and Ziabicki models. The subsequent melting behavior of these sPP resins exhibited either a single melting endotherm or double melting endotherms. (C) 2004 Elsevier Ltd. All rights reserved.