Glassy polymers definition

We shall conclude with some remarks on the structure of glassy polymers. If one frequently speaks of glass structures, this does not mean that there exists one definite glass structure similar to a crystal. In a macromolecular solid-e.g., the polystyrene-plasticizer system, entirely different glasses are obtainable, the macroscopic composition of which is always the same (8). In Figure 10 the full... 

Argon and Salama have demonstrated that this form of the expression accoimts for the measured craze growth kinetics in homogeneous glassy polymers very well, giving for values in the range of 1.5-2.0, which is quite consistent with the definition of this quantity in Eq. (51) and the known extension ratio of 4 in craze matter and back stresses that correspond to this extension ratio. 

The solubility in glassy polymers is usually described by the so-called dual-mode model, which implies that there is a need for a more detailed definition of the sorption, c, in the flux Equation 4.1. Equations 4.20 and 4.21 illustrate this and can relate to... 

Table 14.4, which lists some requirements for CDs, allows the elimination of some contending plastics. Polystyrene has too low a resistance to crazing and stress cracking, and the disc birefringence would be too high because the relatively elastic melt has a high stress-optical coefficient (defined in Eq. 9.9). Values for melts differ from values for glassy polymers given in Table 11.5. PVC has too low a heat distortion temperature, and its lack of thermal stability makes the injection moulding of high definition surfaces difficult. Silicate glass cannot be moulded with sufficient surface detail, and is brittle.

Membrane technologists are well aware that the most permeable glassy polymers are those which possess a very high free volume, where the term free volume refers to the intermolecular voids within a material [1], Scientists who work with molecular sieves, such as zeolites, commonly use the term microporous material to describe those materials which contain pores or channels less than 2nm in width, a definition that arises in the context of gas adsorption studies [2],... 

Let us consider two limiting cases of the adduced in Fig. 4.15 dependence at = 0 and 1.0, both at d = 3. In the first case (d = 2) the value dU = 0 or, as it follows from dU definition (the Eq. (4.31)), dW = dQ and polymer possesses an ideal elastic-plastic deformation. Within the frameworks of the fractal analysis d =2 means, that (p, = 1.0, that is, amorphous glassy polymer structure represents itself one gigantic cluster. However, as it has been shown above, the condition d =2 achievement for polymers is impossible in virtue of entropic tightness of chains, joining clusters, and therefore, d > 2 for real amorphous glassy polymers. This explains the experimental observation for the indicated polymers dU 0 or dW dQ [57], At Vg, =... 

In previous work (i, 13, 14) we considered the comparison between the predictions of the model and the experimental results for the solubility of pure gases and vapours in glassy polymers, and concluded that NELF is a definitely reliable model. In this work the comparison is extended to the case of solubility of mixed gases, by considering the solubility of CO2/C2H4 mixtures in PMMA reported Koros and co-workers 4,15, 76). The model correctly represents the value and the trend of the penetrants solubility when the partial pressure of the penetrants changes. The results are obtained via a completely predictive procedure the comparison is limited to the low pressure range since experimental data for the dilation of the... 

The nonequivalence of the rates of photosensitized reactions in heterogeneous nanophases of glassy polymers is proved in experiments with naphthalene phosphorescence decay. For example, it is shown [13] that in aerated PMMA films fluorescence of singlet-excited naphthalene molecules N can be decayed by tinuvin P, but this does not affect the rate of naphthalene dissociation. The latter is consumed in the process, the rate of which is not defined by the concentration of particles responsible for fluorescence. Under such conditions, according to definition by the authors [13], primary chemical acts are inevitable. However, in the absence of oxygen tinuvin P slows the photochemical process down in accordance with a decrease of singlet-excited naphthalene molecule concentration. 

The character of the polymethyl methacrylate data is essentially similar to that found for systems atactic polystyrene-benzene at 25°, 35°, and 50° C. [Kishimoto, Fujita, Odani, Kurata and Tamura (1960) Odani, Kida, Kurata and Tamura (1961)] and also atactic polystyrene-methyl ethyl ketone at 25° C. [Odani, Hayashi and Tamura (1961)], and appears to be fairly general for amorphous polymer-solvent systems in the glassy state. On the other hand, the cellulose nitrate data shown in Fig. 8 appear to manifest features characteristic of crystalline polymer-solvent systems. For example, the earlier data of Newns (1956) on the system regenerated cellulose-water (in this case, water is not the solvent but merely a swelling-agent) and recent studies for several crystalline polymers all show essentially similar characters [see Kishimoto, Fujita, Odani, Kurata and Tamura (I960)]. To arrive at a more definite conclusion, however, more extensive experimental data are needed. 

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