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� Polymeric materials may have very
large molecular weights compared to other solids.
� Small impurity atoms may diffuse in polymers in the manner
discussed previously.
� Self diffusion
of the large molecules involves moving the molecule through a crystalline
or amorphous matrix of other large molecules.
� In the "Reptation" model of this macro-molecular transport, the
moving molecule translates as a unit through an imaginary tube defined by neighboring
chains. As the molecule moves the conformation of the tube changes.
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