Polymer contraction

Slow diffusion of molecules and radicals in polymer contracts the interval of the observed rate constants of bimolecular reactions. 

Yeager suggests that the major factor involved in the ion exchange selectivity of Nafion is the positive entropy change associated with the replacement of H+ with the metal ion, which is accompanied by water release and polymer contraction. 

Micrometer measurements of thickness were made on the solidified PE samples. Errors due to polymer contraction on solidification were small, as the process of solidification generally results in a net volume change of the solid in the absence of constraints. As the polymer samples were not constrained in any dimension, contraction occurred along the length and width of the specimen as well as the thickness. That portion of the contraction resulting in a decrease in sample thickness was observed to be non-uniform across the face of the sample micrometer measurements on this face were taken as true melt thickness. 

Adachi and Kotaka report Ae and relaxation times for 8.6 and 164 kDa cis-polyisoprene in the good solvent benzene and in the Theta solvent dioxane(6). Figure 7.2a shows (r ) inferred from Ae. In the good solvent, the 164 kDa polymer contracts markedly over the full range of solution concentrations in the Theta solvent, the 164 kDa polymer apparently does not contract a great deal with increasing c. From the limited number of points, in either solvent (r ) of the 8.6 kDa polymer does not appear to depend strongly on c. These results are consistent with fundamental expectations that chain-chain and chain-solvent interactions in Theta solvents substantially eliminate excluded-volume-driven chain expansion, and that excluded-volume-driven expansion is not substantial for small chains. 

Final Report, Specific heat of high polymers. Contract No. DA-11-022-ORD-996,1958. Dept, of Chem. Northwestern University, Evanston, Illinois. 

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