Physical and Chemical Basis for Interactions

Molecules of gases, vapors, and other low molecular weight substances can dissolve in polymers, diffuse through the polymers, and then travel to a contacting substance. The extent and speed of these occurrences depends on the chemical and physical structure of the polymer, and on the nature of the traveling molecule. The driving force for net transfer of penetrant molecules from one location to another is the natural tendency to equilibrate the chemical activity of the species. Chemical activity will be discussed in more detail in Section 14.4. 

In semicrystalline polymers, as discussed in Chapter 3, there are both amorphous and crystalline regions within the polymer. If the polymer is above its Tg, the chain segments in the amorphous regions have mobility, as in the case of a completely 

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