EPR Study of Spin Labeled Brush Polymers in Organic Solvents

Xia, Yan; Li, Yongjun; Burts, Alan O.; Ottaviani, M. Francesca; Tirrell, David A.; Johnson, Jeremiah A.; Turro, Nicholas J.; Grubbs, Robert H.

doi:10.1021/ja2085349

Cited by 80 publications

(84 citation statements)

References 75 publications

(93 reference statements)

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“…Xia et al studied the dynamics of the side-chains and backbone using electron paramagnetic resonance (EPR). 92 They placed nitroxide radical probes at different locations along a PLA bottlebrush -either in the middle of the backbone, at the backbone ends, or on the side-chain ends. Rotational correlation times were roughly two orders of magnitude shorter for side-chain ends compared with the backbone, indicating much faster dynamics of side-chain ends.…”

Section: Synthesis Of Bottlebrush Polymersmentioning

confidence: 99%

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

et al. 2015

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Bottlebrush polymers are a type of branched or graft polymer with polymeric side-chains attached to a linear backbone, and the unusual architecture of bottlebrushes provides a number of unique and potentially useful properties. These include a high entanglement molecular weight, enabling rapid self-assembly of bottlebrush block copolymers into large domain structures, the self-assembly of bottlebrush block copolymer micelles in a selective solvent even at very low dilutions, and the functionalization of bottlebrush side-chains for recognition, imaging, or drug 2 delivery in aqueous environments. This review article focuses on recent developments in the field of bottlebrush polymers with an emphasis on applications of bottlebrush copolymers.Bottlebrush copolymers contain two (or more) different types of polymeric side-chains. Recent work has explored the diverse properties and functions of bottlebrush polymers and copolymers in solutions, films, and melts, and applications explored include photonic materials, bottlebrush films for lithographic patterning, drug delivery, and tumor detection and imaging. We provide a brief introduction to bottlebrush synthesis and physical properties and then discuss work related to: i) bottlebrush self-assembly in melts and bulk thin films, ii) bottlebrushes for photonics and lithography, iii) bottlebrushes for small molecule encapsulation and delivery in solution, and iv) bottlebrush micelles and assemblies in solution. We briefly discuss three potential areas for future research, including developing a more quantitative model of bottlebrush self-assembly in the bulk, studying the properties of bottlebrushes at interfaces, and investigating the solution assembly of bottlebrush copolymers.

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Section: Synthesis Of Bottlebrush Polymersmentioning

confidence: 99%

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

et al. 2015

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“…Furthermore, surface-or core-functionalized star polymers and miktoarm star polymers could be prepared via arm-first crosslinking of appropriate telechelic or branched MMs. [10][11][12][13]53 ■ RESULTS AND DISCUSSION In Matyjaszewski's work, (meth)acrylate-terminated MMs, an alkyl bromide initiator, cross-linker (e.g., divinylbenzene), and copper catalyst are typically combined at the outset of polymerization. As a result, star cores are formed rapidly via a statistical combination of star+star and star+linear reactions between MM, cross-linker, and newly formed stars.…”

Section: ■ Introductionmentioning

confidence: 99%

“…53,64,65 Figure 10C shows EPR spectra for BASPs c and p before and after irradiation. The increased spectral broadening for c compared to p is indicative of the hindered environment experienced by the core-bound nitroxide label.…”

Section: ■ Introductionmentioning

confidence: 99%

“…We previously demonstrated that quenching rates are faster for peripherally-labeled poly(lactide) brush polymers in organic solvents compared to core-labeled analogues. 53 Here we describe the first application of this method to aqueous BASP systems. To explore quenching under these conditions, water-soluble, polymeric quencher Q was designed ( Figure 9).…”

Section: ■ Introductionmentioning

confidence: 99%

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

et al. 2012

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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.

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“…[5] Such coalescence of the nitroxide's three hyperfine lines into a single line due to strong dipolar coupling has been observed in poly(vinyl ether) thin film with TEMPO covalently attached to the polymer side chains. [22] Also, nitroxides in some organic solvents with carbon-coordinating oxygen, such as tetrahydrofuran or ether, have shown a single line [23][24][25] EPR spectrum, where the 3 hyperfine peaks are constantly exchanged.Having identified that different nitroxide derivatives probe different local environments in Nafion, the next question is whether the local water diffusivity spatially varies with the nitroxide's location. This can be assessed by ODNP measurements.…”

mentioning

confidence: 99%

Nanometer‐Scale Water‐ and Proton‐Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

Song

Han

2015

Angewandte Chemie

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Nafion, the most widely used polymer for electrolyte membranes (PEM) in fuel cells, consists of fluorocarbon backbones and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. While the effects of the channel structures and the acidic groups on water/ion transport have been studied before, the surface chemistry or the spatially heterogeneous diffusivity across water channels has never been shown to directly influence water/ion transport. Using molecular spin probes that selectively partition into heterogeneous regions of PEM and Overhauser dynamic nuclear polarization relaxometry, this study reveals that both water and proton diffusivity are significantly faster near the fluorocarbon and the acidic groups lining the water channels compared to within the water channels. The concept that surface chemistry at the (sub-)nanometer scale dictates water and proton diffusivity invokes a new design principle for PEM. Keywordselectron paramagnetic resonance spectroscopy; Overhauser dynamic nuclear polarization relaxometry; water and proton dynamics; polymer electrolyte membrane; heterogeneous structure A polymer electrolyte membrane (PEM) placed between a cathode and an anode in a fuel cell, which is a device that converts chemical energy of fuel into electricity through an electrochemical reaction, should be a good conductor for protons but not for electrons and the molecular constituents of the fuel. Nafion's success as PEM stems from the good ionic conductivity through water channels, [1] as well as high chemical and mechanical stability for a wide operating temperature range between 50°C and 100°C. [2] Nafion is composed of a Correspondence to: Oc Hee Han, ohhan@kbsi.re.kr; Songi Han, songi@chem.ucsb.edu. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript poly(tetrafluoroethylene) backbone with side arms decorated with sulfonic acid groups, as illustrated in Figure S1 of Supporting Information (SI). Nafion is known, upon hydration, to swell to form percolated channels through which water, protons and ions diffuse. [3] Nafion's hydrophobic domains are known to have ordered helical fibers with crystallinity similar to that of pure poly(tetrafluoroethylene) at elevated temperatures. [4] However, the exact structure and ordering of the water channels lined by the sulfonic acid groups is still a subject of controversy. Crucially, the channel dimension was found to increase linearly with the water volume fraction [3] indicating locally flat structures of the channels, [5] while scattering patterns are consistent with rod-like shapes for hydrated Nafion membrane at water volume fraction < 50%. [6][7][8] The structure and connectivity of the water channels has been thought to play an important role in the proton and water diffusivity through Nafion membranes, although a firm relationship between structure and transport function has not been established. At a hydration level of ~20 water molecules per sulfonic acid in Nafion 11...

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EPR Study of Spin Labeled Brush Polymers in Organic Solvents

Cited by 80 publications

References 75 publications

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

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

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

Nanometer‐Scale Water‐ and Proton‐Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

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