Photocontrolled bromine–iodine transformation reversible-deactivation radical polymerization: facile synthesis of star copolymers and unimolecular micelles

The ideal particle size and high stability of unimolecular micelles (UIM) formed from star copolymers make them less susceptible to microenvironment changes in vivo, giving them unique advantages in many applications such as drug delivery and molecular probes. Photocontrolled bromine–iodine transformation reversible-deactivation radical polymerization (BIT-RDRP) is considered to be an efficient and environmentally friendly polymerization method which is supposed to synthesize a variety of functional and topological polymers. In this work, a convenient and facile strategy of synthesizing star copolymers was established via photocontrolled BIT-RDRP under irradiation with blue LED light at room temperature by using hydrophobic methyl methacrylate (MMA) and hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA). The obtained star copolymers have narrow molar mass dispersity (Đ ≤ 1.35), and have well-defined four-arm structures and porphyrin functional groups. The amphiphilic copolymers can form unimolecular micelles below their critical aggregation concentration (CAC) in water with particle sizes ranging from 9.8 nm to 21.9 nm, which can be stable from 25 °C to 61 °C.