Hydrophilic Stars, Amphiphilic Star Block Copolymers, and Miktoarm Stars with Degradable Polycarbonate Cores

A facile one-pot synthetic approach toward the realization of star polymers made of degradable carbonate cores is reported. The synthetic strategy involved triethylborane-activated anionic copolymerization of a difunctional epoxide with CO2 initiated by bis(triphenylphosphine)iminium chloride (PPNCl).Vinyl cyclohexene dioxide (VCD) was, thus, used as a difunctional cross-linker, and core compositions with 80−90% carbonate content were achieved. Poly(ethylene oxide) (PEO) arms were grown from these in-situ generated polycarbonate core anions to build a range of star polymers, including hydrophilic PEO stars and star-shaped block copolymers. Poly(propylene oxide) (PPO) precursors were used in a second approach as macroinitiators to form carbonate cores through the arm-first method; miktoarm stars having a large number of arms, both hydrophilic and hydrophobic, could be derived by this method. The carbonate cores of the synthesized stars were readily degraded through hydrolysis of the core carbonate linkages to yield PEO and PPO chains. Potential applications of these types of systems are manifold, especially for PEGbased drug delivery vehicles.