K. Saalwächter, J.-U. Sommer.
NMR Reveals Non-Distributed and Uniform Character of Network Chain Dynamics.
Macromol. Rapid Commun. 28, 1455–1465 (2007).
Abstract
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.