Rubbery plateau region

As one example, in thin films of Na or K salts of PS-based ionomers cast from a nonpolar solvent, THF, shear deformation is only present when the ion content is near to or above the critical ion content of about 6 mol% and the TEM scan of Fig. 3, for a sample of 8.2 mol% demonstrates this but, for a THF-cast sample of a divalent Ca-salt of an SPS ionomer, having only an ion content of 4.1 mol%, both shear deformation zones and crazes are developed upon tensile straining in contrast to only crazing for the monovalent K-salt. This is evident from the TEM scans of Fig. 5. For the Ca-salt, one sees both an unfibrillated shear deformation zone, and, within this zone, a typical fibrillated craze. The Ca-salt also develops a much more extended rubbery plateau region than Na or K salts in storage modulus versus temperature curves and this is another indication that a stronger and more stable ionic network is present when divalent ions replace monovalent ones. Still another indication that the presence of divalent counterions can enhance mechanical properties comes from... 

It is possible that either Me has increased by degradation of the network structure or the resin is internally plasticized by free chain ends. If Me has increased, then the modulus in the rubbery plateau region for irradiated specimens should be less than that of a control. As discussed above, E (Tg+40) decreases up to a dose of 5000 Mrads. Between 5000 and 10,000 Mrads, E (Tg+40) increases but remains 6% below the control. For the 73/27 and 80/20 samples (10,000 Mrads) which have been sorbed/desorbed, E (Tg+40) is 18.5% greater than the control. 

The molecular weight between crosslinks (Me) was determined for each epoxy/amine ratio of the neat resin from the rubbery plateau region of the modulus curve following the Tg region. This can be seen in Figure 13 for several epoxy/amine ratios. The Me values were calculated from the following equation ... 

Figure 8 presents the storage and loss-modulus master curves obtained on all five samples of interest. The dashed lines indicate extensions of the master curves, using appropriately reduced data from the Rheovibron experiments in tension. Storage-modulus data in the rubbery plateau region vary systematically with composition, i.e., the... 

Figure 3.3 Variation of elastic modulus of a polymer with temperature. As the degree of crystallinity increases, the extent of rubbery plateau region decreases.

Increasing filler loading broadens the relaxation spectrum of the cure reaction. Broadening the relaxation spectrum by filler loading also has been found in the mechanical spectrum of cured rubber from the glass transition region to rubbery plateau region [15]. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

If 60°C is a glass transition, then heating the polymer slowly past 60°C would take it to the rubbery plateau region (region III in Fig. 2.24), where the modulus E, and hence hardness, would remain fairly constant with increase of temperature. For a melting transition, however, the modulus would drop rapidly and the polymer would become increasingly softer in a similar experiment. 

Region IE (c to d) in Fig. 2.21 is described as-the rubbery plateau region. The modulus after a sharp drop, as described above, again becomes nearly constant in this region with typical values of 2x10 dyne/cm (2x10 Pa) and polymers exhibit significant rubber-like elasticity. 

The E value for cured samples In the rubbery plateau region... 

This approach to viscoelastic theory is reasonably successful in the low modulus regions, but it requires considerable modification if the high modulus and rubbery plateau regions are to be described. 

Above the glass transition lies the rubbery plateau region, region 3. The equations of state for rubber elasticity (see Section 1.5.4) apply here if the material is crosslinked, these equations may apply up to the decomposition temperature (see dashed line. Figure 1.12). 

In the rubbery plateau region, the modulus is also increased by the presence of a filler. For example, Maewaka et al. (1967) reported increases in both and " (storage and loss moduli, respectively) as a function of filler content in rubber-calcium carbonate systems. However, the Kerner... 

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