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

Abstract

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.

Structure, function, self-assembly, and applications of bottlebrush copolymers

“…Johnson et al developed a series of bottlebrush star polymers and copolymers as degradable drug carriers using a two-step synthesis approach [134][135][136][137] (Fig 14). The approach involves the preparation of living, end-functional bottlebrush arms by ROMP that are then coupled in a second reaction step with bis-norbornene crosslinker.…”

“…In another study using the brushfirst approach, Johnson et al demonstrated the preparation of mikto-arm bottlebrush star polymers. Analysis by TEM showed the intramolecular phase separation of the various polymer arms to form Janus nanoparticles 135 .…”

Synthesis of Acid-Labile PEG and PEG-Doxorubicin-Conjugate Nanoparticles via Brush-First ROMP

“…6,7 The remarkable efficiency and functional group tolerance of ROMP 8 enables the benchtop synthesis 7 of diversely functionalized BASPs within hours. We have used the brush-first ROMP method to prepare degradable BASPs with various sizes and corona compositions, including multidrug-loaded poly(ethylene glycol) (PEG)-based BASPs, 9 two- and three-miktoarm BASPs, 10 and chloride-functional BASPs 11 for subsequent azide exchange and copper-catalyzed azide–alkyne cycloaddition (CuAAC) “click” 12−14 chemistry.…”

One-pot synthesis of end-functionalised soluble star-shaped polymers by living ring-opening metathesis polymerisation using a molybdenum-alkylidene catalyst

“…31,34 The conditions for the rst and the third ROMPs with NBE (4 and 15 minutes, respectively) were unchanged, because the NBE consumption should be completed based on our previous study. 31 The results are summarised in 26,27); it becomes more difficult to control the molecular weights (as well as to obtain the reproducibility).…”