NMR Observations of Entangled Polymer Dynamics: Focus on Tagged Chain Rotational Dynamics and Confirmation from a Simulation Model

Molecular-level insights into the entangled dynamics of high-molecular-weight chains, in particular of slower chain modes in regimes II–IV of the tube model, are still rare due to the lack of methods resolving the rather long associated time scales. On the theoretical side, new computer simulation methods are just reaching the relevant time scales in sufficiently large systems. Here, we confront results from a recent multiple-quantum proton NMR method with results from a novel lattice model. We address the concern that proton NMR, relying on the dipole–dipole couplings between nearby nuclei, is intrinsically sensitive not only to intrachain rotational motions which reflect the desired details of the tube model or possibly necessary modifications, but also to the translational diffusion of chains past each other via interchain dipole–dipole couplings. In order to critically assess the influence of the latter, we here present results of isotope-dilution experiments, in which the data reflect mainly tagged-chain dynamics. We find overall weak effects of interchain dipole–dipole couplings on the shape of the extracted orientation autocorrelation function and very good agreement of the experimental and the computer simulation data. We conclude that the NMR method as well as the novel lattice model faithfully reflects the universal features of entangled chain dynamics and in particular the deviations from simple tube-model predictions on a microscopic level.