A comparison of induction time and crystallization rate for syndiotactic polystyrene

Abstract

One objective of this study was to measure the crystalkation parameters for syndiotactic polystyrene (M, = 244,000) to support a computer simulation of this material in an injection molding application. A second objective was to introduce a new crystallization rate equation that adequately predicts crystallization rates over a broader temperature range than the Hofhnan-Lauritzen equation. A third objective was to establish a new clearly defined method for determining the true induction time of a semicrystalline polymer as a function of temperature. The new uystallization rate equation introduced in this study has been formulated to give appropriate crystallization rate constants for all the temperatures currently usable with the Hoffinan-Lauritzen equation. In addition, this new equation also predicts appropriate crystallization rate constants outside the range of the Hofhnan-Iauitzen equation from temperatures significantly below the glass transition temperature, Tg. to temperatures sigmficantly above the melting point, T , . Interestingly, the isolation of the true isothermal induction times from apparent induction times in this study nicely mirrored the isothermal crystallization rates at each specific temperature. Both the true induction time and the crystallization rate curves were found to be similarly unsymmetrical as a function of temperature. Also, the temperature at the minimum induction time and the temperature at the peak crystallization rate determined from nonisothermal crystallization rate measurements were found to be nearly identical. Consequently, the results from this study strongly suggest that there is a significant and potentially very useful relationship between induction time analysis and crystallization rate kinetics.

Correlating the crystallization kinetics of syndiotactic polystyrene

“…Also indicated in Figure 3 are experimental results for T 1/2 versus φ from five sources in the literature,4, 7–10 as documented in Table II. In particular, it is noted that the nine data points (Δ) from Chiu et al9 agree extremely well with the solid curve in Figure 3, with an rms deviation of 0.5°C over the extensive cooling‐rate range of 1 to 80°C/min.…”

“…In addressing the above discrepancy, it is noted that of the five experimental investigations4, 7–10 reported in Figure 3, only Chiu et al9 corrected their data for the effects of thermal lag. Although results for their own experimentally determined thermal–lag correction are not explicitly presented by Chiu et al,9 one might refer to earlier work by Monasse and Haudin,18 dealing with polypropylene, in which the thermal–lag correction was determined experimentally and fitted with a linear dependence upon cooling rate, namely According to this result, the actual specimen temperature would be higher than the instrument reading by 1.07°C at φ = 10°C/min and by 10.7°C at φ = 100°C/min.…”

“…Syndiotactic polystyrene (sPS), a fairly recently developed polymer1, 2 which exhibits enhanced properties and excellent processibility, has been receiving considerable attention. In the present article, consideration is given to available cumulative data concerning the crystallization kinetics of sPS under isothermal3–7 as well as nonisothermal4, 7–10 conditions. Making use of the Nakamura11 model, which includes the Avrami12 limit (under isothermal conditions) and the Ozawa13 limit (under constant‐cooling/heating‐rate conditions), a correlation is developed which describes the cumulative data very well and clearly demonstrates the need to correct for thermal lag in the case of nonisothermal DSC measurements at high cooling/heating rate.…”

Heterogeneous polyamide 66/syndiotactic polystyrene blends: Phase structure and thermal and mechanical properties

“…New polymer materials with remarkable properties, such as high glass‐transition temperatures ( T g 's), high melting temperatures ( T m 's), heat resistance, chemical resistance to common solvents, low moisture uptake, high water barriers, good mechanical properties, and transparency, are traditional objects of basic and applied material science. Syndiotactic polystyrene (sPS) is a semicrystalline polymer that attracts much attention1–8 because of its high T m (≅285°C), rapid crystallization, and high crystallinity and modulus; on the other hand, its T g (≅100°C) is approximately equal to that of atactic polystyrene (PS). Mainly, the heat resistance and chemical stability allow potential applications of sPS at elevated temperatures.…”

“…Mainly, the heat resistance and chemical stability allow potential applications of sPS at elevated temperatures. The crystalline phase of sPS has been the subject of many studies,1–8 which have shown the coexistence of several crystalline modifications (polymorphism), although under ordinary conditions, the α modification (a planar all‐trans form with a planar zigzag backbone structure) dominates 3. The stiffness of crystalline sPS has been ascribed to intrachain interactions involving bond bending and stretching.…”