Fluorescent PMMAs containing a phthalic anhydride (PA) group at the chain ends were prepared using the newly developed initiator 7 by atom transfer radical polymerization and subsequent pyrolysis. These polymers allowed for the detection of inter-macromolecular reaction in reactive polymer blends at a low concentration by the use of fluorescence-gel permeation chromatography. The PA-amine coupling reaction proved to be efficient in reactive blending studies for the compatibilization of PS-PMMA blends at low concentration (less than or equal to8%) giving a morphology where the average PMMA drop size is 0.6 mum. With 7-nitrobenz-2-oxa-1,3-diazole (NBD) groups as the fluorescent label, the blend morphologies could be visualized in three dimensions by laser confocal microscopy.