The multiple melting behavior and morphologies of isotactic polystyrene (iPS) isothermally crystallized from the glassy state have been investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).The combination of thermal analysis and morphological results indicates that two lamellar populations are responsible for the so-called double melting behavior in iPS.The low-temperature melting peak is attributed to the melting of less perfect (thinner or defect containing) subsidiary lamellae formed in the framework of the dominant (thicker or more perfect crystalline) lamellae upon isothermal crystallization.The high-temperature one is mainly due to the melting of the dominant thicker lamellae, and to some less extent,the melting of a recrystallized population coming from the melted defect lamellae during the heating process in DSC.

Analysis of the nonisothermal melt and cold crystallization kinetics of poly (aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC).The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK.And,the Ozawa analysis,when applied to this polymer system,failed to describe its nonisothermal crystallization behavior.A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation.By evaluating the kinetic parameters in this approach,the crystallization behavior of PEEKK was analyzed. According to the Kissinger method,the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization,respectively.