Subsequent treatment of branched poly(ethylene imine) with N,N,N-trimethyl-3-({[(2-oxo-1,3-dioxolan-4-yl)methoxy]carbonyl}amino)pro pan-1-ammonium iodide and either (2-oxo-1,3-dioxolan-4-yl)methyl-(oxiran-2-ylmethyl)carbamate or 4-[(oxiran-2-ylmethoxy)methyl]-1,3-dioxotan-2-one yielded 'quat-prinler polymers' bearing quarternary ammonium and cyclic carbonate groups covalently linked to the macromolecule. H-1 and C-13 NMR spectroscopy with model reaction mixtures and the macromolecular products revealed that the quaternary ammonium groups were selectively attached to the primary amino groups of the polymeric educt. The new functional macromolecules were characterized further by means of DSC and TGA. Upon spin coating the cyclic carbonate groups containing cationic polymers on oxygen/argon plasma-pretreated highly oriented pyrolytic graphite (HOPG), scanning force microscopy revealed the presence of a 3 nm thick film covering the substrate. This ultrathin coating was persistent against extraction with methanol, demonstrating the adherence of the polymer on the substrate. Applied on carbon fibers the polymer layer improved the interfacial shear strength between the carbon fiber and an epoxy resin matrix by 35% with respect to nontreated carbon fibers as demonstrated by single-fiber fragmentation tests.