title: 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.
authors.affiliation: 77 Massachusetts Ave., Room 18-296, Cambridge, MA, 02116, USA.
authors.forename: Alan O
authors.initials: AO
authors.lastname: Burts
authors.affiliation: 77 Massachusetts Ave., Room 18-296, Cambridge, MA, 02116, USA.
authors.forename: Angela X
authors.initials: AX
authors.lastname: Gao
authors.affiliation: 77 Massachusetts Ave., Room 18-296, Cambridge, MA, 02116, USA.
authors.forename: Jeremiah A
authors.initials: JA
authors.lastname: Johnson
mesh_terms: D046529:Microscopy, Electron, Transmission; D010782:Photolysis; D011108:Polymers / Q000138:chemical synthesis*; D014466:Ultraviolet Rays
chemical_list: D011108:Polymers
keywords: ROMP; graft-through; macromonomers; miktoarm; star polymers