Non-isothermal crystallization and multiple melting behavior of syndiotactic polystyrene-pre-melting temperature effects

• Published in: Polymer engineering and science 2000-11, Vol.40 (11), p.2397-2406
• Main Authors: Chiu, Fang-Chyou, Peng, Chi-Gong, Fu, Qiang
• Format: Article
• Language: English
• Subjects: Applied sciences; Crystallization; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Polymer industry, paints, wood; Polymers; Polystyrene; Technology of polymers; Thermal properties
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.11371

This work investigated how pre‐melting temperature (Tmax) and cooling rate (C) affected the non‐isothermal melt crystallization, melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) techniques. Experimental results indicated that raising Tmax or C decreased the crystallization peak temperature (Tp) and crystallization initiating temperature (Ti). The crystallization kinetics was analyzed through the Ozawa equation. Although the Ozawa exponent n and cooling function K(T) were determined for Tmax = 340°C and Tmax = 315°C specimens, for Tmax = 290°C specimens, the Ozawa equation was not applicable. Activation energies for the non‐isothermal crystallization processes of different Tmax specimens were estimated to be approximately 418 kJ/mol. As Tmax was raised the nucleation rate of sPS became slower. The multiple melting peaks were associated with different polymorphs as well as recrystallized crystals that formed during heating scans. The percentage content of α polymorph formed in the crystals under various crystallization conditions was estimated through WAXD experiments.