Morphology, structure, and kinetic analysis of nonisothermal cold- and melt-crystallization of syndiotactic polystyrene

Nonisothermal cold- and melt-crystallization of syndiotactic polystyrene (sPS) were carefully carried out by Perkin-Elmer Diamond differential scanning calorimetry, polarized optical microcopy (POM), and wide angle X-ray diffraction. The experimental data subjected to the two types of processing were thoroughly analyzed on the basis of Avrami, Tobin, Ziabicki, and combination of Avrami and Ozawa models. Avrami, Tobin, and Ziabicki analyses indicate that nonisothermal cold-crystallization (A) characterizes smaller Avami and Tobin exponent and larger Ziabicki kinetic crystallizability index G than those obtained from nonisothermal melt-crystallization (13) possibly due to the existence of partially ordered structures in the quenched samples. Kissinger and the differential isoconversional method (DICM) of Friedman's were utilized to obtain effective energy barrier of A, in good agreement with that obtained by using Arrhenius equation to analyze the isothermal cold-crystallization, indicating that Kissinger and Friedman equations can be applied to obtain activation energy from A of sPS. X-ray diffraction analysis indicates that cold-crystallization mainly produces alpha-type crystal but for melt-crystallization the contents of alpha-type and beta-type crystals depend on the cooling rates. The POM also indicates the difference of end morphology of the sample between A and B. At the same time, the DICM of Friedman's was applied to analyze experimental data of B, which were divided into two groups with 20 K/min as the threshold, and it was found that the formation of beta-type crystal possesses larger absolute value of effective activation barrier than the formation of alpha-type crystal. (c) 2006 Wiley Periodicals, Inc.