Amphiphilic hyperbranched copolymers bearing a hyperbranched core and dendritic shell: synthesis, characterization and guest encapsulation performance

The 2,2-bis(hydroxymethyl) propionic acid (BHP)-based generation 1 dendron with two palmitate tails (D1-C16) and the generation 2 dendron with four palmitate tails (D2-C16) were synthesized. The coupling of D1-C16 or D2-C16 with hyperbranched polyethylenimine (PEI) through the amidation reaction resulted in amphiphilic hyperbranched copolymers bearing a hyperbranched PEI core and a dendritic D1-C16 shell or dendritic D2-C16 shell. The structure of the obtained copolymers was verified through Fourier transform infrared (FTIR) and 1 H nuclear magnetic resonance (NMR) characterization. Differential scanning calorimetry (DSC) measurement demonstrated that the existence of the branching units in the shell pronouncedly reduced the crystallinity of the hyperbranched copolymers, and the copolymers with less branched shells had a higher melting temperature and melting enthalpy. These novel amphiphilic hyperbranched copolymers could be used as nanocarriers to efficiently accommodate the hydrophilic guests, including Methyl Orange (MO), Congo Red (CR) and Direct Blue 15 (DB), into the hydrophilic amidated PEI core. Each nanocarrier with a branched shell could accommodate a much higher number of guests than the corresponding nanocarriers with linear shells, which indicated that the dendritic structure of the shell played a key role in significantly enhancing the encapsulation capacity of the nanocarriers. As far as the weight ratio of the encapsulated guests to the nanocarriers was concerned, the nanocarriers with branched shells could be modulated to have a similar encapsulation capacity for the small MO with a mono-sulfonate group, but a much superior encapsulation capacity for the large CR and DB guests with multi-sulfonate groups to the nanocarriers with linear shells.