Thermo- and pH-responsive poly[(diethylene glycol methyl ether methacrylate)-co-(2-diisopropylamino ethyl methacrylate)] hyperbranched copolymers: self-assembly and drug-loading

Abstract

We present the synthesis of a new series of thermo- and pH-responsive poly[(diethylene glycol methyl ether methacrylate)-co-(2-diisopropylamino ethyl methacrylate)], P(DEGMA-co-DIPAEMA), hyperbranched copolymers and studies regarding their self-assembly in aqueous media. Three P(DEGMA-co-DIPAEMA) hyperbranched copolymers, with different ratios of hydrophobic to hydrophilic segments, are synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization using the branching agent ethylene glycol dimethacrylate (EGDMA). By employing several physicochemical characterization techniques, it was possible to determine the properties of self-assembled nanostructures, which are responsive to changes in aqueous solution temperature and pH. Dynamic light scattering (DLS) verified the formation of nano-aggregates in aqueous media, in particular at pH 3 and at both low and high temperatures (25 °C, 55 °C), where all hyperbranched copolymers form the largest aggregates compared to the other two pH conditions investigated (i.e., pH 7 and pH 10). In addition, the hyperbranched copolymers were able to encapsulate the hydrophobic drug indomethacin (IND) at different loading ratios. IND release experiments were performed at pH 7, and revealed that a high amount of the entrapped IND is strongly attached to the hydrophobic domains of the hyperbranched copolymer aggregates. The acquired data are encouraging for the potential of these novel hyperbranched copolymers to be used as nanocarrier systems for medicinal applications.