To monitor polymer-polymer coupling reactions between two different monofunctional polymers in dilute polymer blends, fluorescence-labeled anhydridefunctional polystyrene (PS) and poly(methyl methacrylate) (PMMA) were prepared by conventional anionic polymerization. Sequential trapping of lithiopolystyrene by 1-(2anthryl)-1-phenylethylene (APE) and then di-t-butyl maleate (4) provided, after pyrolysis, anhydride-functional fluorescent PS. Fluorescent PMMA anhydride (8) was synthesized with sec-butyllithium/APE as an initiator for the anionic polymerization of methyl methacrylate, trapping by 4, and pyrolysis. These polymers could be reacted with amine-functional polymers by melt blending, and the reaction progress could be monitored by gel permeation chromatography coupled with fluorescence detection. This technique not only allows monitoring of the coupling reaction with high sensitivity (ca. 100 times more sensitive than refractive index detection) but also permits selective detection because unlabeled polymers are invisible to fluorescence detection. This highly sensitive and selective detection methodology was also used to monitor the coupling reaction of 8 with PS-NH 2 at a thin-film interface, which was otherwise difficult to detect by conventional methods.