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

Abstract

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 meltcrystallization (B) 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 a-type crystal but for melt-crystallization the contents of a-type and b-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 b-type crystal possesses larger absolute value of effective activation barrier than the formation of a-type crystal.

Elastic Light Scattering Studies on Cold-crystallization Behaviors of Syndiotactic Polystyrene

“…n 值依赖于结晶成核过程和晶体生长过程, 对于线性一维 生长, n 值为 1 或者 2; 盘状二维生长, n 值为 2 或者 3; 而 球晶三维生长模式, n 值则为 3 或 4 [22] . 许多实验结果表 明, 由于分子链结构的复杂性, 以及受壁面、杂质等外 部因素影响, 计算得到的 Avrami 指数往往不是整数 值 [23,24] , 甚至 n 值出现大于 4 的情况 [25] . 根据实验中得 到的 n 值大小, 可以推测 s-PS 在结晶过程中可能同时存 在均相成核与异相成核, 晶核生长方式会出现从线性一 维生长到球晶三维生长模式的转变.…”