K. Saalwächter, J.-U. Sommer.
NMR Reveals Non-Distributed and Uniform Character of Network Chain Dynamics.
Macromol. Rapid Commun. 28, 1455–1465 (2007).
Results of different NMR investigations of elastomers are reviewed with respect
to their significance for statistical models of rubber elasticity. In contrast
to earlier work based on lineshape analysis and relaxometry, results of recent
multiple-quantum experiments indicate that the NMR-detected dynamic chain order
parameter, which reflects the conformational space of individual monomer units
at which the signal is detected locally, is a rather narrowly distributed
quantity. Constraints to the dynamics and the conformations of a network chain
thus act uniformly and appear as a dynamic average over chains of different
length and with different end-to-end separations. All our findings are in good
agreement with large-scale computer simulations. Anomalies on swelling such as
chain desinterspersion at the early stages and the appearance of
heterogeneities, are also discussed.