The junction dynamics in a selectively deuterated model polymer network containing junctions on every 21st chain carbon is studied by solid state 2H echo NMR. Polymer networks are prepared via acyclic triene metathesis of deuteron‐labeled symmetric trienes with deuteron probes precisely placed at the alpha carbon relative to the junction point. The effect of decreasing the cross‐link density on the junction dynamics is studied by introduction of polybutadiene chains in‐between junctions. The networks are characterized by swelling, gel content, and solid state 1H MAS NMR. Line shape analysis of the 2H quadrupolar echo spectra reveals that the degree of motion anisotropy and the distribution of motion correlation times depend on the cross‐link density and structural heterogeneity of the polymer networks. A detailed model of the junction dynamics at different temperatures is proposed and explained in terms of the intermolecular cooperativity in densely‐packed systems.
