A novel degradable cationic polymer with discrete charge based on water-soluble poly(P-amino ester) was synthesized by Michael addition of tetraethylene pentamine (TEPA) to ethylene glycol diacrylate (EGDA), which is denoted as PTE. There are primary, secondary and tertiary amines in PTE molecule as branched polyethylenimine. The nitrogen content of PTE is 13.9 mmol/g at molar feed ratio of 1: 1, lower than that of polyethylenimine mine of 23 mmol/g, so PTE is a polycation with discrete charge relative to polyethylenimine with excess high charge density. acid-base titration indicated that PTE was protonated in the ranges from both pH 5.0 to pH 7.4 and pH 7.4 to pH 11. The changes of pH, viscosity and H-1 NMR spectra showed that PTE was degraded in water first rapidly and then slowly. In aqueous solution, PTE self-assembled with weak anionic polymer, poly(acrylic acid) (PAA), into nanoparticles. The particle size first increased and then decreased with increasing the mass ratio of PTE to PAA, which is defined as theta, from 0.1 to 2. At theta of more than 0.8 or less than 0.6, complex particles with diameter less than 200 nm were obtained. At 0 of 0.8. the UV-vis absorbance of complex solution at first day was obviously higher than that at seventh day, while at 0 of 0.2. two absorbance curves at these two time points were almost superimposed, indicating that small complex particles were more stable than large ones because of electrostatic repulsion. (c) 2007 Elsevier Ltd. All rights reserved.