Preparation of cationic comb-type copolymers having high density of PEG graft chains for gene carriers

A series of poly(L-lysine)-graft-polyethylene glycol (PLL-g-PEG) was prepared by a reductive amination reaction of PLL with aldehyde modified PEG using NaBH3CN as a reductant. The high coupling efficacy observed in the 8o% acetonitrile aqueous solution led to the grafting polymers with abundant PEG chains (more than go wt % and 30 mol %). By the method, we can retain high cationic charge density of the polymer backbone, because the resulting secondary amino groups are still protonated. By controlling the primary structure of the copolymer, we can also regulate the ionic interaction with nucleic acids and other biological components for gene delivery purpose.