Brush‐First Synthesis of Core‐Photodegradable Miktoarm Star Polymers via ROMP: Towards Photoresponsive Self‐Assemblies

This report describes the synthesis of miktoarm brush‐arm star polymers (BASPs) from branched and linear norbornene‐terminated macromonomers (MMs) via the brush‐first ring‐opening metathesis polymerization (ROMP) method. First, a polystyrene (PS)‐ branch ‐poly(lactic acid) (PLA) MM is synthesized via a combination of atom transfer radical polymerization (ATRP), tin(II)‐mediated ring opening polymerization, and copper‐catalyzed azide‐alkyne cycloaddition reactions. Graft‐through ROMP of this MM followed by in situ cross‐linking with a photo‐cleavable bis‐norbornene derivative provided nanoscopic BASPs with photodegradable cores and a precise 1:1 PS:PLA arm composition. Three‐miktoarm BASPs are prepared in an analogous manner via copolymerization of the same PS ‐branch‐ PLA MM with a poly(ethylene glycol) (PEG) MM prior to cross‐linking. Intramolecular phase segregation of these miktoarm BASPs is characterized by transmission electron microscopy (TEM); a UV‐induced structural rearrangement from three‐faced Janus particles to micelles is observed.