The intermediate dynamic light scattering function has been computed for a single A-B diblock copolymer chain in dilute and many-chain solutions, assuming a nonrefractive solvent (i.e., setting opposite contrast factors for the A and B units). Theoretical calculations, based in the Pecora scheme for the Rouse model, have been compared with the results obtained with a dynamic Monte Carlo algorithm for chains with nonoverlapping units placed in a cubic lattice. These numerical functions are also compared with the prediction of a single exponential described by the first cumulant method, which is consistent with the application of the linear response theory. The homopolymer case is also discussed.