A series of phenanthryl and methylmethacrylate copolymers were synthesized and investigated by means of nanosecond laser kinetic spectroscopy. Laser-induced absorption changes (in the 400-500-nm spectral region) were attributed to the triplet state and to radical ions of phenanthrene, whose disappearance could not be explained by conventional homogeneous kinetics. Accordingly, a model was developed in which each transient species (X, say) was divided into two categories : mobile (X(m)) and trapped (X(t)). The observations could be interpreted in terms of a mechanism involving, apart from unimolecular decay (if any), two types of encounters : X(m) - X(m) and X(t) - X(t). The bimolecular rate constant for the annihilation process, X(m) + X(m) --> products, was found to increase with rising phenanthrene content. The rate constant for the pseudounimolecular decay of the triplet also increased with loading, an effect attributed to migration of charge and electronic excitation, and quenching of the latter by doublet-state ionic species.