Glassy polymers determination

Wang D, Liu Y-H, Nishi T, Nakajima K. Length scale of mechanical heterogeneity in a glassy polymer determined hy atomic force microscopy. Appl Phys Lett 2012 100 251905 (4pp). 

The properties of glassy polymers such as density, thermal expansion, and small-strain deformation are mainly determined by the van der Waals interaction of adjacent molecular segments. On the other hand, crack growth depends on the length of the molecular strands in the network as is deduced from the fracture experiments. 

Since glassy polymers tend to become plasticized by C02, it is important to determine the magnitude to which CO2 effects plasticization. This is achieved in monitoring nonlinear effects of gas permeability of mixtures containing CO2. CO2 shows a higher sorption than expected. This is attributed to the presence of acrylonitrile moieties in the ABS copolymer. 

Secondary Transitions in Glassy Polymers and Methods of Their Determination 120... 

Of the thermodynamic quantities just mentioned, only the determination of the expansion coefficient or other quantities reflecting its change have assumed practical importance for the identification of secondary transitions in glassy polymers. The most efficient methods for the investigation of the dynamics and intensity of molecular motions have so far been those based on the interference between molecular motion and the oscillating magnetic, electric or mechanical force field. In recent years, methods which employ various probes or labels in the study of molecular mobility have increasingly been used. 

The second key factor determining permeability in polymers is the sorption coefficient. The data in Figure 2.18 show that sorption coefficients for a particular gas are relatively constant within a single family of related materials. In fact, sorption coefficients of gases in polymers are relatively constant for a wide range of chemically different polymers. Figure 2.25 plots sorption and diffusion coefficients of methane in Tanaka s fluorinated polyimides [23], carboxylated polyvinyl trimethylsiloxane [37] and substituted polyacetylenes [38], all amorphous glassy polymers, and a variety of substituted siloxanes [39], all rubbers. The diffusion... 

Figure4.4 Effect of thickness on aging rate of glassy polymer films determined by change in oxygen permeability at 35 °C [46]. Reproduced with permission of Elsevier.

The general features of the D vs. Cj relations for amorphous polymer-solvent systems slightly above or below Tg° are not fully elucidated. This is mainly due to the fact that, as will be explained in the next section, the sorption processes in glassy polymers are not Fickian and hence the methods for the determination of D (cj) presented in the previous section can no longer be applied. In principle, D values of such systems could be determined from steady-state permeation measurements, but Kishimoto (unpublished) has shown that the analysis of permeation data on glassy systems is complicated by factors which are not yet fully resolved. 

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