Abstract A pyrene fluorescence probe was grafted onto EP copolymer backbone by reacting 1-pyrenebutyrylhydrazine with pendant succinic anhydride groups. Behavior of the pyrene-labelled EP in methylcyclohexane and tetrahydronaphthalene (tetralin) was studied as a function of copolymer concentration. Ratios of pyrene excimer intensity to its monomer intensity were determined for copolymer solutions with concentrations ranging from 0.02% to 0.6%. The lower ratios in methylcyclohexane than tetralin agreed with viscosities indicating that methylcyclohexane is a better solvent. The plots of the ratio vs. copolymer concentration in both solvents were nonlinear. From these plots, C* can be estimated. The fine structure of pyrene monomer fluorescence spectra revealed that the copolymer is loosely coiled in both solvents.