Excimer formation was used as a tool to probe the dynamics in tetrahydrofuran solution of two ethylene propylene copolymers labeled with pyrene. The excimer kinetics were analyzed by a new model. This model considers that the polymer chain can be divided into equivalent blobs. The fluorescent probe is assumed to be distributed randomly among the blobs. As a consequence, the occupancy probability of chromophores inside a blob follows a Poisson distribution. We can describe the kinetics of the system in terms of the theory of excimer formation in micellar systems. In this way we can obtain the blob size and the magnitude of the first-order rate constant for excimer formation in the blob. The model is applicable to polydisperse polymer systems and provides information by shifting the focus of attention from chain-length-dependent to blob-size-dependent behavior.