Effect of Tacticity on Viscoelastic Properties of Polystyrene

• Published in: Macromolecules Vol. 44; no. 15; pp. 6155 - 6161
• Main Authors: Huang, Chien-Lin, Chen, Yu-Chen, Hsiao, Ting-Jui, Tsai, Jing-Cherng, Wang, Chi
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.08.2011
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Rheology and viscoelasticity; Molten state; Shear flow; Molecular weight viscosity relationship; Styrene polymer; Experimental study; Syndiotactic polymer; Activation energy; Comparative study; Atactic polymer; Rheological properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma200695c

The viscoelastic properties of a series of syndiotactic polystyrene (s-PS) melts with high stereoregularity and different molecular weights (M w = 134–1160 kg/mol) are measured in a wide achievable temperature range (270–310 °C) to determine the entanglement molecular weight (M e ) and flow activation energy (E a ). In addition, four actactic polystyrenes (a-PS, M w = 215–682 kg/mol) and one isotactic polystyrene (i-PS, M w = 247 kg/mol) are also studied to elucidate the tacticity effect on the corresponding properties. Using a reference temperature of 280 °C, the master curves of dynamic storage and loss modulus are constructed according to the time–temperature superposition principle. On the basis of the classic integration method, the M e values are determined to be 14 500 and 17 900 g/mol for the s-PS and a-PS, respectively, which are significantly lower than that for the i-PS, ∼27 200 g/mol, derived from the Wu’s empirical equation. Owing to the difference in M e , at a fixed M w, the viscosity of i-PS is about 1 order of magnitude lower than that of s-PS and a-PS. However, when double-logarithmic plotting of the melt viscosity against the M w/M e is performed, a self-consistent behavior is seen for all the PS used despite of the differences in the M w and chain tacticity; the derived exponent is 3.61. According to the Arrhenius plot, the determined E a for the s-PS is 53 ± 5 kJ/mol, which is apparently lower than that for the other two isomers possessing a similar value of 90–107 kJ/mol.