Data from Diffusion of Small Foreign Molecules

Correlation of with Data from Diffusion of Small Foreign Molecules 

Though fo is normally determined by mechanical measurements, it is evident from its definition that it is related in a simple manner to translatory diffusion, and in principle it can be determined from self-diffusion measurements in a polymer with sufficiently low molecular weight to avoid entanglements. Some data of this sort have been obtained from diffusion 6f radioactively tagged molecules - and spin-echo nuclear magnetic resonance measurements, as well as from diffusion of deuterated molecules whose concentration can be followed by infrared absorption. They yield the product Pfo. since the frictional resistance for the entire molecule is measured. 

Some information collected from the literature for this purpose - is given in Table 12-VI. In some cases, the chemical similarity between foreign molecule and polymer is not very close because of the paucity of available data. However, it appears that for temperatures far above as in the polyisobutylene and rubber, the 

Additional examples of for n-hexadecane in various rubbers, most of them studied far above Tg. are given in Table 12-VII and compared with the corresponding values of fo- Here the penetrant has 3 to 4 times the molecular weight of the chain unit, but fo and are quite similar over a range of nearly four powers of 10. Even the 1,2-polybutadiene, which is fairly near Tg, shows no great discrepancy. That they are so similar in magnitude is somewhat unexpected, but that 

Molecular Friction Coefficients from Diffusion in Polymers Compared with Monomeric Friction Coefficients 

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