Glassy and Highly Crystalline Polymers

Multiple Viscoelastic Mechanisms with Different Temperature Dependences 

It has already been noted in Section A5 that the temperature reduction factors in the transition and terminal zones may be somewhat different. An example of a very complete study by Plazek on a polystyrene with almost uniform molecular weight 46,900 is shown in Fig. 11-14. The creep compliance Jp t) reduced to a reference temperature of 100° by shift factors ar calculated from the viscosity—i.e., from equation 13—provides satisfactory superposition of data in the terminal zone, but in the transition zone the reduced data diverge. Alternatively, the recoverable compliance Jp(t) — t/rjo can be satisfactorily reduced in the transition zone with a slightly different set of reduction factors these, however, appear to give a slight divergence in the terminal zone (Fig. 11-15). Both sets of shift factors follow the WLF equation, equation 21, but with slightly different coefficients in Fig. 11-14, 

Creep measurements on a polystyrene with molecular weight 46,900, reduced from different temperatures as indicated to 100 C with shift factors calculated from steady flow viscosity. (After Plazek.25) Subscript p denotes multiplication by Tp/Topo. 

An exaggerated form of the deviations illustrated for polystyrene, but in the opposite direction, has been observed in some methacrylate polymers and their solutions.2 2 When dynamic data are reduced with ay values derived from the transition zone, they fail to superpose in the plateau and terminal zone, as exemplified for solutions of poly( -butyl methacrylate) by plots of J in Fig. 11-16. With increasing temperature, the maximum in J shifts upward and to the left. 

l 1-15. Recoverable creep compliance from data of Fig. 11-14 reduced to 100° by shift factors chosen empirically in the transition zone and Fitted to equation 21. (The small rise to the right of 8 on the abscissa scale is attributed to a very small proportion of species of much higher molecular 

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Figure 2.23 Volume-temperature dependence for glassy and highly crystalline polymers.

For the very lightly cross-linked polymer (curve VII), there is a subsidiary maximum at lower frequencies associated with the losses involved in entanglement slippage as discussed in connection with J(t) and J". In this case, also, the maximum in J" lies to the left of that in tan d. Smaller maxima occur in the curves for the glassy and highly crystalline polymers, reflecting other dissipative mechanisms. 

E.g., glassy and highly crystalline polymers, or soft polymers at such high frequencies that the moduli approach glasslike magnitudes. 

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