Effect of Tacticity on Viscoelastic Properties of Polystyrene

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• 作者：Chien-Lin Huang ; Yu-Chen Chen ; Ting-Jui Hsiao ; Jing-Cherng Tsai ; Chi Wang
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：August 9, 2011
• 年：2011
• 卷：44
• 期：15
• 页码：6155-6161
• 全文大小：815K
• 年卷期：v.44,no.15(August 9, 2011)
• ISSN：1520-5835

文摘

The viscoelastic properties of a series of syndiotactic polystyrene (s-PS) melts with high stereoregularity and different molecular weights (M_w = 134鈥?160 kg/mol) are measured in a wide achievable temperature range (270鈥?10 掳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鈥?82 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 掳C, the master curves of dynamic storage and loss modulus are constructed according to the time鈥搕emperature superposition principle. On the basis of the classic integration method, the M_e values are determined to be 14鈥?00 and 17鈥?00 g/mol for the s-PS and a-PS, respectively, which are significantly lower than that for the i-PS, 27鈥?00 g/mol, derived from the Wu鈥檚 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 卤 5 kJ/mol, which is apparently lower than that for the other two isomers possessing a similar value of 90鈥?07 kJ/mol.