A maleated ethylene-propylene (EP) random copolymer was labeled with the fluorescent dye 1-pyrene-butanoicacid hydrazide to yield EP-Py. Fluorescence spectroscopy was used to determine the microstructure of EP-Py (i.e., the distribution of the pendants along the chain) in THF where little association is expected to occur between the polar pendants. In hexane, an apolar solvent, associations take place between the polar pendants acid the association level of EP-Py (i.e., fractions of pendants, which are associated and unassociated) was estimated by analyzing quantitatively both the monomer and the excimer fluorescence decays. The ability of pyrene to form an excimer was used to carry out this study. The excimer formation process was monitored by using a combination of two models, namely the sequential model and the blob model. Both monomer and excimer decays were analyzed in order to completely describe the distribution of pyrene groups. It was found that 70% of all pyrene groups are located at small distances from one another and form excimer readily. In apolar hexane, 87% of all pyrene groups are involved into loose pyrene aggregates, held together via polar interactions between the succinic anhydride groups.