A novel potential cationic polymeric gene vector, PCT, was synthesized by copolymerizing 3-chloro-1,2epoxypropane (CEP) and tetraethylene pentamine (TEPA). The protonizable nitrogen content of PCT is 17.7 mmol/g at 1: 1. of CEP to TEPA, lower than 23.3 mmol/g of polyethylenimine (PEI) but higher than 7.8 mmol/g of polylysine, which indicates PCT is a candidate of polycation with high-content but discrete charge after protonation. PCT has many hydrophilic quaternized amino and hydroxy groups contributing to hydrophilicity. Acid base titration showed that PCT was protonated in both pH 7.4-11 and pH 5.0-7.4 and had "proton sponge effect." In aqueous solution, PCT complexed with weak anionic polymer, poly(acrylic acid) (PAA), into nanoparticles. Fourier transform infrared spectroscopy proved the formation of complex. Particle size is first increased and then decreased as increasing mass ratio theta of PCT to PAA from 0.1 to 1.7, as shown by dynamic light scattering. At theta values of more than 1.7 or less than 0.2, complex particles with mean diameter less than 200 nm were obtained. At theta of 0.5, the UV-Vis absorbance of complex solution at first day was obviously higher than that at 7 day, while at theta of 1.7, two absorbance curves at these two time points had slightly smaller change, indicating that small complex particles were more stable than large ones because of electrostatic repulsion. (c) 2007 Wiley Periodicals, Inc.