Poly(oligoethylene glycol methacrylate) Star-Shaped Copolymers with Hydroxypropyl Methacrylate Cores

Star-shaped copolymers with crosslinked hyperbranched cores, varying in both number and length of the arms, are prepared by the reversible addition-fragmentation chain transfer (RAFT) polymerization technique. Star synthesis is conducted via a simple, “core-first” method. Hydroxypropyl methacrylate monomer is used for the formation of the hyperbranched/crosslinked core, with ethylene glycol dimethacrylate used as a bifunctional monomer in the role of the cross-linker. Two different cross-linker/chain transfer agent ratios are chosen to manipulate the number of the arms in the final star nanostructure. Oligoethylene glycol methacrylate (OEGMA₅₀₀) is used as a biocompatible and hydrophilic component for the creation and extension of the arms. Arm length is controlled by the amount of OEGMA monomer used in the second polymerization step. Molecular characterization of the four synthesized stars is achieved via size exclusion chromatography and nuclear magnetic resonance, which provides information regarding the molar mass, dispersity, and composition of each star-shaped copolymer. Dynamic light scattering (DLS) studies of copolymers in N,N-dimethyl formamide solutions provide sizes of individual copolymer molecules in the size range of 8–20 nm. Aqueous dispersions of copolymers are investigated by DLS, cryogenic transmission electron microscopy, and atomic force microscopy, which show the formation of spherical aggregates with diameters of 60–350 nm, dependent on the arm number and length of star copolymers. The obtained sizes and size distributions, along with the hydroxyl-group-bearing cores, indicate that the star copolymer can be used as potential nanocarriers for drugs or bioimaging agents.