Chain-order effects in polymer melts probed by 1H double-quantum NMR spectroscopy

Double-quantum NMR experiments are presented, elucidating the nature of the polymer chain dynamics in a polybutadiene melt far above the glass transition. The obtained experimental information about the rotational dynamics of spin pairs allows the translational dynamics as well as the long-term stability of the topological constraints on a microscopic scale to be probed. The results are shown to support some but not all aspects of the reptation model. For short times, the local chain order reflecting the time averaged configurations is much larger than expected, indicating strong packing effects.