Universal Relaxation Behavior of Entangled 1,4-Polybutadiene Melts in the Transition Frequency Region

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• 作者：Seung Joon Park ; Priyanka S. Desai ; Xue Chen ; Ronald G. Larson
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：June 23, 2015
• 年：2015
• 卷：48
• 期：12
• 页码：4122-4131
• 全文大小：531K
• ISSN：1520-5835

文摘

Linear viscoelastic G鈥?and G鈥?master curves for linear, star, H, and comb 1,4-polybutadienes from the literature are compared and found to agree well in the transition frequency region, where G鈥?and G鈥?exceed the plateau modulus, irrespective of molecular weight and branching structures. A value of 蟿_e = (3.7 卤 0.93) 脳 10^鈥? s for the equilibration time at T = 25 掳C can therefore be determined from fitting Rouse predictions to the transition frequency data, after subtracting effects of glassy modes represented by the Kohlrausch鈥揥illiams鈥揥atts (KWW) expression. Good agreement among multiple data sets was obtained in the transition region despite large variations in low-temperature shift factors, evidently due to small sample-to-sample variations in 1,2 content. These variations in 1,2 content can also cause small changes the plateau modulus G_N⁰ and the entanglement molecular weight M_e, which should have only a small effect on linear polymers but for long-chain branched polymers could lead to large variations in terminal relaxation time predicted by tube models. The small variations in G_N⁰ can, however, be inferred from the dependence of shift factor on temperature, allowing all three tube model parameters 蟿_e, G_N⁰, and M_e to be obtained from high-frequency data for 1,4-polybutadienes, thus in principle removing these as parameters that can be adjusted to fit specific data sets for linear or branched 1,4-polybutadienes.