“Brush-First” Method for the Parallel Synthesis of Photocleavable, Nitroxide-Labeled Poly(ethylene glycol) Star Polymers

Abstract

We describe the parallel, one-pot synthesis of core-photocleavable, poly(norbornene)-co-poly(ethylene glycol) (PEG) brush-arm star polymers (BASPs) via a route that combines the "graft-through" and "arm-first" methodologies for brush polymer and star polymer synthesis, respectively. In this method, ring-opening metathesis polymerization of a norbornene−PEG macromonomer generates small living brush initiators. Transfer of various amounts of this brush initiator to vials containing a photocleavable bis-norbornene cross-linker yielded a series of water-soluble BASPs with low polydispersities and molecular weights that increased geometrically as a function of the amount of bis-norbornene added. The BASP cores were cleaved upon exposure to UV light; the extent of photo-disassembly depended on the amount of cross-linker. EPR spectroscopy of nitroxide-labeled BASPs was used to probe differences between the BASP core and surface environments. We expect that BASPs will find applications as easy-to-synthesize, stimuli-responsive core−shell nanostructures.

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 contrast to similar "brush-first" approaches using controlled radical polymerization reactions 141 , there is no residual unreacted macromonomer after the first step, and the bottlebrush star molecular weight can be controlled by varying the length of the bottlebrush arms and the molar ratio of crosslinkers. The group also incorporated a UV-responsive nitrobenzyloxycarbonyl (NBOC) crosslinker which led to bottlebrush star polymer degradation upon UV irradiation 134 . Johnson et al prepared photo-responsive drug carriers using their brush-first approach.…”

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

“…[1][2][3][4][5][6][7][8][9][10] Reported examples for the synthesis by adopting living ring-opening metathesis polymerisation (ROMP) [11][12][13][14][15][16][17][18][19][20][21][22][23] via arm (brush) rst [24][25][26][27][28][29][30] and core rst (in-out) [31][32][33][34][35] approaches by sequential addition of monomers/cross linkers (CLs) are known. Moreover, related examples for synthesis of cross-linked polymers (which are insoluble in common organic solvents) by ROMP are also known, 36-39 especially in terms of application as monolith materials for separation.…”

Importance of Macromonomer Quality in the Ring-Opening Metathesis Polymerization of Macromonomers

“…Grubbs and co-workers synthesized a series of GC-MMs by "click" coupling of ATRP polymers with alkynyl norbornene, which then produced brush homopolymers and brush BCPs with a high molecular weight (MW) (200−2600 kDa) and a very low Đ M of <1.1. 6,7 Premade polyolefins, 18 conjugated polymers, 22 and poly(ethylene glycol)s [28][29][30][31][32]40 have also been coupled to functionalized norbornenes like GC-MMs, which were subsequently ROMPed to synthesize brush polymers.…”