Synthesis of Light-Responsive Miktoarm Copolymers via Aqueous Polymerization-Induced Self-Assembly

Traditional linear block copolymers often suffer from structural collapse or irregular transitions under external stimuli. To overcome these limitations, we report the design and synthesis of a novel photo-responsive miktoarm copolymer using an aqueous Polymerization-Induced Self-Assembly (PISA) technique.

Here, a thiophene-based dithienylethene (DTE) derivative is synthesized as the central junction core of the miktoarm architecture. Unlike conventional approaches incorporating photo-responsive groups along polymer side chains, localizing the photoswitch at the miktoarm junction allows precise physical manipulation of the arm angle upon irradiation. From this core, we construct a miktoarm copolymer using poly(ethylene glycol) (PEG) and poly(2-hydroxypropyl methacrylate) (PHPMA).

The synthesis is conducted via an aqueous PISA approach, offering significant advantages over traditional solvent-switch methods. It enables highly efficient, one-pot in-situ synthesis at high solid concentrations without causing macroscopic aggregation or requiring toxic organic solvents. Furthermore, combining the miktoarm architecture and specific polymer blocks is highly synergistic. PEG serves as a highly stable water-soluble corona, while HPMA—soluble as a monomer but highly hydrophobic upon polymerization—forms the core. The inherently bulky side groups of PHPMA induce a rapid volume increase of the hydrophobic segment even at short chain lengths. This dramatically alters the packing parameter, making self-assembled nanostructures highly sensitive and facilitating versatile transitions among various morphologies directly visualized by cryo-TEM.

Ultimately, the successful PISA synthesis of this thiophene-based miktoarm copolymer establishes a robust and scalable platform for engineering dynamic nanomaterials, paving the way for advanced structural controls such as reversible gated pores without structural degradation.