Phase Structure and Ordering

Dynamics of Solid Polymen.—Various aspects of relaxation in PE have been examined. In an extensive study of H and Ty, relaxatbn, four 

Measurements of the frequency and temperature dependence of the H T, in poly(dimethyl siloxane) revealed relaxations due to methyl rotation and segmental motions and also an oxygen impurity effect The experimental data could not be fitted using thermally activated Arrhenius behaviour, as was also true of backbone motions in poly(vinyl chloride). Multiple side-group motions have also been observed in poly (diethyl siloxane) and poly(L-histidine). Backbone motions have been observed in poiy(diethyl siloxane), poly(oxymethylene), poly(ethylene terephthalate), poly(p-phenylene sulphide), aromatic polyamides, and PTFE. A close similarity between the effects of entanglements and radiation cross-linking on the of cis-polyisoprene has been found.  

Molten Polymers.—A few other studies of molten polymers have been made in addition to those mentioned above. Inequalities between the values of nT, for the backbone C nuclei in CH groups (n = 1 or 2) in molten trans-buta-l,4-diene/propene copolymer and cis- and trans-polyisoprene have been 

Finally, two groups have studied the diffusion of small molecules in a polymer matrix using the field-gradient technique. Zupancic et a/. have pointed out that because the n.m.r. method measures diffusion over small distances, it gives a true microscopic diffusion constant. For butane in PE, diffusion occurs through the amorphous regions. The diffusion of oil in rubber obeys free-volume behaviour, with no barriers to diffusion over distances of several fim. 

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