Polycarbonate secondary losses

Dynamic mechanical response spectra of elastin145 (insoluble protein of vessels and ligaments), poly(ethylene terephthalate)141 and polycarbonate based on Bisphenol A (4,4 -dihydroxydiphenylmethane)141 show that incorporated water brings about enlargement of the existing secondary loss peak and its displacement toward lower temperatures. In conformity with the latter result, the activation energy of the relaxation process of elastin decreases. So far, no detailed data on this type of relaxation have been collected so that the copartidpation of water in the molecular motion cannot be specified more accurately. 

An enhanced dielectric loss maximum was observed at -85°C when a polysulfone sample which contained 0.76 wt. % unassociated water and no detectable level of clustered water (<0.01 wt. %) was run (Fig. 6, curve A). An apparent low temperature broadening of the dielectric loss dispersion was noted for another polysulfone specimen with 0.76 wt. % unassociated water and an additional 0.04 wt. % clustered water (Fig. 6, curve B). However, when a polysulfone sample which contained the same amount of unassociated water as the two prior samples but had 0.16 wt. % clustered water was analyzed, it had a significantly more intense loss peak centered near -105°C (Fig. 6, curve C). We believe that this shift in loss maximum and increase in loss intensity is caused by the development of an additional secondary loss peak about 20° below the 3-transition (Figure 6). In earlier work we had observed the same phenomenon in polycarbonate where the new loss peak occurred about 40 below its 3-transition as a separate loss peak. 

The dielectric loss behavior of both polyethylene s Y transi-tion and polycarbonate s 0-transltion was enhanced by the presence of unassociated water. The area under the associated loss peak was found to increase in direct proportion to the concentration of unassociated water. In addition a secondary dielectric loss peak associated with frozen clustered water occurred in polycarbonate about 40°C below Its g-transition. Liquid clustered water at... 

The dielectric strength. As, which is proportional to the area under the loss peak, is much lower for the secondary processes, relative to the a relaxation analysed in the next section. This is a common pattern foimd in both polymer materials and glass formers. The P secondary process is even more depleted in linear polymers that contain the dipole moment rigidly attached to the m chmn, such as polycarbonate [78-80] and poly(vinyl chloride) (the behaviour of this polymer was revisited in ref [81] where the secondary relaxation motions are considered as precursors of the a-relaxation motions). Polymers with flexible polar side-groups, like poly(n-alkyl methacrylate)s, constitute a special class where the P relaxation is rather intense due to some coupling vnth main chain motions. 

Intermediate - Temperature Relaxations. Secondary relaxations in the glassy state at temperatures intermediate between those of the a- and P- relaxations have been reported, but workers disagree as to their nature, location and origin. Confusion arises in part from a failure to recognize the existence of two separate processes. Krum and MUller [19] observed an intermediate relaxation only for injection-moulded or cold-drawn polycarbonate samples. Since the magnitude was diminished by annealing and the loss was not detected in fully annealed samples, they concluded that the intermediate process is a non-equilibrium effect associated with residual stresses. 

Certain macroscopic properties of materials sometimes show major changes near the secondary transitions detected by the loss modulus spectrum. It is well known that the toughness of certain resins, such as polycarbonate, suddenly disappears and the material becomes brittle below the... 

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