Chain dynamics in thermoreversible polybutadiene networks were studied in comparison to linear polybutadiene using field-cycling NMR (nuclear magnetic resonance) relaxometry. The effect of rapidly fluctuating cross links on the chain mode relaxation time is shown to result in dynamics rescaled according to a new effective segmental friction coefficient. The frequency dependence of the spin-lattice relaxation time consists of a sequence of three regions characterized by power laws with exponents 0.5 +/- 0.05, 0.25 +/- 0.05, and 0.44 +/-0.05 from high to low frequencies (and low to high temperatures). Thermoreversible cross-linking shifts the crossover frequencies toward lower values. In our previous work on linear polymers these frequency dependences were shown to be a consequence of the once (or twice) renormalized Rouse theory. The same formalism can be used for the thermoreversible polybutadiene networks by rescaling the segmental relaxation time. (C) 1997 American Institute of Physics.