Dynamic Mechanical and Dielectric Results

The relaxation map of PMMA obtained from E and s is shown in Fig. 111. It shows a good agreement between the two types of investigations, in agreement with the fact that the same motional groups are involved in the response of both techniques. 

Furthermore, the activation energies (83 =t 5 kj mol-1 from mechanical analysis and 82 2 kj mol-1 from dielectric relaxation) as well as the activation entropies (51 3 J K-1 mol-1 from mechanical analysis and 58 33 J K-1 mol-1 from dielectric relaxation) are identical, confirming that the processes are the same. 

the mechanical loss generated at the a transition is much larger than the dielectric one. 

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Finally, it is worth comparing the dynamic mechanical and dielectric results. For this purpose, Fig. 130 shows the temperature dependence of the mechanical loss modulus, E", and the dielectric loss modulus, m", at 1 Hz, obtained by superposing the low-temperature part of the P transition. 

Non-linear mechanical properties were observed for rubber eomposites and referred to as the Payne effect. The Payne effeet was interpreted as due to filler agglomeration where the filler clusters formed eontained adsorbed rubber. The occluded rubber molecules within filler elusters eould not eontribute to overall elastic properties. The composites behaved similarly to rubber composites with higher filler loading. Uniform and stable filler dispersion is required for rubber composites to exhibit linear viscoelastic behaviour. Payne performed dielectric measurements on SBR vulcanizates containing silica or carbon black. The dielectric data were used to construct time-temperature superposition master curves. The reference temperature increased with crosslinking but not significantly with filler. Comparison of dynamic mechanical and dielectric results for the SBR blended with NR was made and interpreted. ... 

Without using any motional model, the temperature positions of T and Tip minima can be assigned an appropriate frequency 90 MHz at 120 °C from Ti and 43 kHz at - 34 °C from T r These two results fit quite well on the relaxation map of BPA-PC obtained from dynamic mechanical and dielectric relaxation. They support the fact that phenyl ring motions are involved in the /3 relaxation of BPA-PC. Furthermore, the Ti and T f> data can be simulated by considering the Williams-Watts fractional correlation function [33] ... 

The various solid-state NMR results (Sects. 8.1.4.1 and 8.1.4.2), lead to the following understanding of the motions performed by the ester groups and associated with the /3 transition observed in dynamic mechanical and dielectric investigations. 

Results of dynamic-mechanical and dielectric studies of PSF and PES are summarized in Table 13.6. Results for PSF indicate a well-defined y relaxation located near 162-229 K. There is substantial evidence that the intensity of the y-relaxational peak increases with sorbed water content [49,77,79]. Substitutions that hinder phenylene mobility increase the temperature of the y relaxation [78]. There is controversy concerning the existence of a /3 relaxation located around 330-360 K that is sensitive to thermal history as has been reported for polycarbonate [18,19,80]. The dynamic-mechanical behavior of PES, which has a slightly lower Tg, is similar to that of PSF with a prominent y relaxation that is also water sensitive [49] and is located in the region from 163 to 265 K. 

Dynamic-mechanical and dielectric data have been widely reported for most aliphatic polyamides, especially poly(g-caprolactam) (nylon-6 or PA-6 rg 313K) and poly(hexamethylene adipamide) (nylon-6,6 or PA-6,6 Tg 323 K). Results of dynamic-mechanical and dielectric measurements of PA-6 and PA-6,6 (Table 13.8) provide evidence for three relaxations (/3, y, and 8) in these polymers at temperatures below their crystalline-melting temperature Tni (487-506 K for PA-6 and 523-545 K for PA-6,6) [8]. The /3 relaxation (located at above 310-347 K for PA-6,6 and 357-370 K for PA-6,6) is associated with high... 

The purpose of this paper is to present some of the results of studies on structure and properties of poly(amino acid) solids. Methods employed in this work include X-ray diffraction, broad-line nuclear magnetic resonance, electron spin resonance, dynamic mechanical, and dielectric methods. Poly(amino acid)s studied here are mostly poly(glutamate)s which include poly(y-benzyl L-glutamate), poly(y-methyl L-glutamate), and others. 

The dielectric relaxation of bulk mixtures of poly(2jS-di-methylphenylene oxide) and atactic polystyrene has been measured as a function of sample composition, frequency, and temperature. The results are compared with earlier dynamic mechanical and (differential scanning) calorimetric studies of the same samples. It is concluded that the polymers are miscible but probably not at a segmental level. A detailed analysis suggests that the particular samples investigated may be considered in terms of a continuous phase-dispersed phase concept, in which the former is a PS-rich and the latter a PPO-rich material, except for the sample containing 75% PPO-25% PS in which the converse is postulated. 

The quasi-static modelling of the dynamics of the ester group flip in an amorphous cell of atactic PMMA has yielded information complementary to that derived from dynamic mechanical analysis, dielectric relaxation and, mainly, multidimensional 13C and 2H solid-state NMR. The main results are ... 

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