The influence of molecular oxygen and a common slip agent, erucamide, on the selectivity of pyrene attachment to polyethylene chains has been investigated. Films with covalently attached pyrenyl groups are useful to follow microscopic changes that occur when the bulk material is perturbed. Selectivity increases when pyrene-doped low-density polyethylene (PE37) films are thoroughly degassed (< 10(-5) Torr) prior to irradiation. Surprisingly, an increase in selectivity also increases with erucamide content in pyrene-doped PE37 films. Films were characterized using UV/Vis spectroscopy, steady-state and time-resolved fluorescence techniques, differential scanning calorimetry, and X-ray diffraction.