Randomly branched (arboreseent) cationic polyelectrolytes were synthesized by self-condensing vinyl copolymerization (SCVCP) of a methacrylic AB* inimer, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM), with (diethylamino)ethyl methacrylate (DEAEMA) via atom transfer radical polymerization (ATRP), followed by quaternization. Homopolymerization of DEAEMA with the CuBr/hexamethyltriethylenetetramine (HMTETA) catalyst system gave a linear polymer having controlled molecular weights and narrow molecular weight distribution, which were evaluated by conventional GPC, GPC-viscosity, and MALDI-TOF mass spectrometry. The catalyst system could be applied to self-condensing vinyl polymerization (homo-SCVP) of BIEM in bulk and in solution to provide hyperbranched architectures, as confirmed by H-1 and C-13 NMR and GPC-viscosity measurements. SCVCP with CuBr/HMTETA in solution gave a series of tertiary amine methacrylate-based branched polymers, in which the molecular weights, the composition of the DEAENU segment, and the branched structure can be adjusted by an appropriate choice of the comonomer composition, gamma. Quaternization reaction of the branched poly(DEAEMA)s with methyl iodide led to water-soluble cationic polyelectrolytes with branched structures.