Two kinds of polyaspartic acid (PAsp) derivates, i.e. PEG-g-PAsp and PEG-g-PDEA, were prepared through the ring-opening reaction of polysuccinimide by CH3O-PEG-NH2, followed by alkaline hydrolysis and aminolysis, respectively. Utilizing the electrostatic interaction between them, polyion micelles with PEG shell and PAsp complex core were formed in phosphate buffer. The results showed that the polyion micelles are spherical with an average diameter of about 70 nm, and the size distribution is narrow. However, the stability of polyion micelles was strongly affected by pH and ionic strength. Crosslinking of primary amine contained in PEG-g-PDEA by glutaric dialdehyde could effectively improve the stability of polyion micelles to pH and ionic strength.

Key words: polyion micelles, polyaspartic acid, polysuccinimide, cross-linked, core-shell structure