Dendrimers are highly branched,symmetrical macromolecules of nano-sized dimensions,consisting of a central core,repeating units and terminal functional groups.When used as drug nanocarriers,the dense and compact dendritic structure of dendrimers avoids chain entanglement and reduces hydrodynamic radius in comparison with the linear copolymers with identical molecular masses.Moreover,they could have higher drug loading content (LC) and drug encapsulation efficiency (EE).Boltorn H40,a dendrimer-like aliphatic polyester with a large number of terminal hydroxyl groups,may be a satisfactory macro-initiator (inner core) of ring-opening polymerization,which can thus be employed to formulate hydrophobic anti-cancer drugs of high drug loading and high drug encapsulation efficiency due to its globular architecture [1].