Figure 2. Synthesis of hyperbranched PEG–H20–PEI co-polymer.

First, the hydroxyl groups of hyperbranched polyester (H20) were converted into carboxyl groups through succinic anhydride at room temperature. Then, the selected PEG chains reacted with a carboxyl group through condensation to attach on the hyperbranched bis-MPA polyester core. At the same time, certain azido groups also reacted with the carboxyl groups on the hyperbranched bis-MPA polyester. Then, PEI-yne reacted with azido groups on the hyperbranched bis-MPA polyester via a click reaction.