Category Archives: Polymers

Improved Structural Elucidation of Synthetic Polymers by Dynamic Nuclear Polarization Solid-State NMR Spectroscopy #DNPNMR

Ouari, Olivier, Trang Phan, Fabio Ziarelli, Gilles Casano, Fabien Aussenac, Pierre Thureau, Didier Gigmes, Paul Tordo, and Stéphane Viel. “Improved Structural Elucidation of Synthetic Polymers by Dynamic Nuclear Polarization Solid-State NMR Spectroscopy.” ACS Macro Letters 2, no. 8 (August 20, 2013): 715–19.

https://doi.org/10.1021/mz4003003

Dynamic nuclear polarization (DNP) is shown to greatly improve the solid-state nuclear magnetic resonance (SSNMR) analysis of synthetic polymers by allowing structural assignment of intrinsically diluted NMR signals, which are typically not detected in conventional SSNMR. Specifically, SSNMR and DNP SSNMR were comparatively used to study functional polymers for which precise structural elucidation of chain ends is essential to control their reactivity and to eventually obtain advanced polymeric materials of complex architecture. Results show that the polymer chain-end signals, while hardly observable in conventional SSNMR, could be clearly identified in the DNP SSNMR spectrum owing to the increase in sensitivity afforded by the DNP setup (a factor ∼10 was achieved here), hence providing access to detailed structural characterization within realistic experimental times. This sizable gain in sensitivity opens new avenues for the characterization of “smart” functional polymeric materials and new analytical perspectives in polymer science.

DNP NMR Studies of Crystalline Polymer Domains by Copolymerization with Nitroxide Radical Monomers #DNPNMR

Verde-Sesto, Ester, Nicolas Goujon, Haritz Sardon, Pauline Ruiz, Tan Vu Huynh, Fermin Elizalde, David Mecerreyes, Maria Forsyth, and Luke A. O’Dell. “DNP NMR Studies of Crystalline Polymer Domains by Copolymerization with Nitroxide Radical Monomers.” Macromolecules 51, no. 20 (October 23, 2018): 8046–53.

https://doi.org/10.1021/acs.macromol.8b01665

Dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) spectroscopy is increasingly recognized as a powerful and versatile tool for the characterization of polymers and polymer-based materials. DNP requires the presence of unpaired electrons, usually mono- or biradicals, and the method of incorporation of these groups and their distribution within the structure is crucial. Methods for covalently binding the radicals to the polymer and controlling their location (e.g., exclusively within a specific phase or at an interface) can allow the selective enhancement of a particular region or the measurement of domain sizes. We have prepared a series of polyurethanes by copolymerization of a nitroxide radical monomer with poly(ethylene glycol) (PEO) and diisocyanate linkers. The PEO is shown to form crystalline domains with the radical monomers in a separate phase, providing DNP enhancements of around 10 and allowing the domain size and morphology to be probed with the aid of X-ray scattering data. Additionally, electron paramagnetic resonance is used to estimate the inter-radical distances and density functional theory calculations are used to refine the PEO crystal structure.

[NMR] PhD position in EPR & NMR at IPF Dresden

PhD position on EPR and NMR at the Leibniz Institute of Polymer Research Dresden, Germany

The Institute of Physical Chemistry and Polymer Physics, department Polyelectrolytes and Dispersions, at the Leibniz Institute of Polymer Research Dresden offers a position for a research assistant / PhD student (Chemist/Physicist). 

Project: Investigations on the dynamics of polyelectrolyte multilayers by spin-labeling and EPR spectroscopy (funded by Deutsche Forschungsgemeinschaft)

Salary 2/3 position TV-L EG 13 (26 hours/week). 

Start: asap

Duration: 31.03.2020

Qualification: MSc degree/diploma in Chemistry or Physics

Project description: Subject of the project are polyelectrolyte multilayers that can be prepared by alternating adsorption of polyanions and polycations using the Layer-by-layer technique on various substrates. It is a general and broadly applicable technique that enables manufacturing numerous different tailored structures. Polyelectrolyte multilayers find increasing attention in the targeted modification of surfaces and membranes. 

Various aspects, such as the growth mechanism, the internal structure of the layers as well as the dynamics are of fundamental interest for practical applications. While many details of the structures are known, there is much less knowledge for no less important dynamics of polymers in the multilayers. 

The aim of the project is to gain new insights into the mobility of chain segments of polyelectrolytes in multilayers and to show correlations between the internal structure and dynamics in these multilayers and resulting properties. 

In order to achieve this goal polyelectrolyte molecules are equipped with spin labels and incorporated in a defined manner in the PEM. The EPR spectroscopy offer the potential to study the rotational diffusion of the spin label linked to the macromolecule and to gain quantitative information about the mobility of polymer segments, which are complemented by NMR data,which are sensitive to longer time scales. 

The experimental investigations aim at the relationships between the chemical structure of the polyelectrolytes used, the conditions at the preparation of the PEM and the parameters of the surrounding medium (ionic strength, pH) and the mobility of polymer segments in different zones of the multilayer. 

The internal dynamics of the polyelectrolytes in the multilayers has an influence on the transport in the multilayer and through the multilayer when it is used as a membrane. The correlation of the temperature dependence of the polymer dynamics and the diffusion of small guest molecules results in insights in the mechanism of transport.

The Leibniz Institute of Polymer Research Dresden (IPF) is one of the largest polymer research facilities in Germany. As an institute of the Leibniz Association, the IPF is committed to carrying out application-oriented basic research. The focus of activities at the IPF is directed toward the advancement of basic scientific knowledge for the development of functional polymer materials and polymer materials with new or improved characteristics. Leading scientists of the IPF are at the same time appointed professors at the Technische Universität Dresden (TUD). Since 2011 the TUD has been one of the excellence universities in Germany. The IPF offers a stimulating working atmosphere for outstanding interdisciplinary research in one of the most beautiful cities of Germany. 

Dresden, the capital of Saxony, possesses an extraordinarily high density of research facilities which have made Dresden a leading research site, particularly in the fields of material research, microelectronics, and biotechnology. 

Applications including motivation letter, CV, should be submitted by e-mail as a single PDF document to the Department of Human Resources (with the No. 083-2017):

Leibniz-Institut für Polymerforschung Dresden e.V.

Frau Susanne Otto

Leiterin Personal und Soziales

Hohe Straße 6

01069 Dresden

otto-susanne@ipfdd.de

Queries about the lab and the research project should be directed by e-mail to:

Ulrich Scheler Scheler@ipfdd.de or Uwe Lappan Lappan@ipfdd.de .

Job offer (in German)

https://www.ipfdd.de/fileadmin/user_upload/jobs/AUSS%20083%20PD%20WiMi.pdf

Best regards,

Ulrich Scheler

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Dr. Ulrich Scheler

Leibniz-Institut für Polymerforschung Dresden e.V.

Hohe Strasse 6

D-01069 Dresden, Germany

phone +49 351 4658 275

fax +49 351 4658 231

www.ipfdd.de

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Nanometer-scale water- and proton-diffusion heterogeneities across water channels in polymer electrolyte membranes

Song, J., O.H. Han, and S. Han, Nanometer-scale water- and proton-diffusion heterogeneities across water channels in polymer electrolyte membranes. Angew Chem Int Ed Engl, 2015. 54(12): p. 3615-20.

http://www.ncbi.nlm.nih.gov/pubmed/25630609

Nafion, the most widely used polymer for electrolyte membranes (PEMs) in fuel cells, consists of a fluorocarbon backbone and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. Although 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. By the use of molecular spin probes that are selectively partitioned into heterogeneous regions of the 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 than 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 PEMs.

Visualizing Specific Cross-Protomer Interactions in the Homo-Oligomeric Membrane Protein Proteorhodopsin by Dynamic-Nuclear-Polarization-Enhanced Solid-State NMR

Maciejko, J., et al., Visualizing Specific Cross-Protomer Interactions in the Homo-Oligomeric Membrane Protein Proteorhodopsin by Dynamic-Nuclear-Polarization-Enhanced Solid-State NMR. J Am Chem Soc, 2015.

http://www.ncbi.nlm.nih.gov/pubmed/26102160

Membrane proteins often form oligomeric complexes within the lipid bilayer, but factors controlling their assembly are hard to predict and experimentally difficult to determine. An understanding of protein-protein interactions within the lipid bilayer is however required in order to elucidate the role of oligomerization for their functional mechanism and stabilization. Here, we demonstrate for the pentameric, heptahelical membrane protein green proteorhodopsin that solid-state NMR could identify specific interactions at the protomer interfaces, if the sensitivity is enhanced by dynamic nuclear polarization. For this purpose, differently labeled protomers have been assembled into the full pentamer complex embedded within the lipid bilayer. We show for this proof of concept that one specific salt bridge determines the formation of pentamers or hexamers. Data are supported by laser-induced liquid bead ion desorption mass spectrometry and by blue native polyacrylamide gel electrophoresis analysis. The presented approach is universally applicable and opens the door toward analyzing membrane protein interactions within homo-oligomers directly in the membrane.

In Situ Determination of Tacticity, Deactivation, and Kinetics in [rac-(C2H4(1-Indenyl)2)ZrMe][B(C6F5)4] and [Cp2ZrMe][B(C6F5)4]-Catalyzed Polymerization of 1-Hexene Using (13)C Hyperpolarized NMR

Chen, C.H., W.C. Shih, and C. Hilty, In Situ Determination of Tacticity, Deactivation, and Kinetics in [rac-(C2H4(1-Indenyl)2)ZrMe][B(C6F5)4] and [Cp2ZrMe][B(C6F5)4]-Catalyzed Polymerization of 1-Hexene Using (13)C Hyperpolarized NMR. J Am Chem Soc, 2015. 137(21): p. 6965-71.

http://www.ncbi.nlm.nih.gov/pubmed/25961793

The stereochemistry, kinetics, and mechanism of olefin polymerization catalyzed by a set of zirconium-based metallocenes was studied by NMR using dissolution dynamic nuclear polarization (DNP). Hyperpolarized 1-hexene was polymerized in situ with a C2 symmetric catalyst, [(EBI)ZrMe][B(C6F5)4] (EBI = rac-(C2H4(1-indenyl)2)), and a C2v symmetric catalyst, [(Cp)2ZrMe][B(C6F5)4] (Cp = cyclopentadienyl). Hyperpolarized (13)C NMR spectra were used to characterize product tacticity following initiation of the reaction. At the same time, a signal gain of 3 orders of magnitude from (13)C hyperpolarization enabled the real time observation of catalyst-polymeryl species and deactivation products, such as vinylidene and a Zr-allyl complex. The compounds appearing in the reaction provide evidence for the existence of beta-hydride elimination and formation of a dormant site via a methane-generating mechanism. The presence of a deactivating mechanism was incorporated in a model used to determine kinetic parameters of the reaction. On this basis, rate constants were measured between 0.8 and 6.7 mol % of catalyst. The concentration dependence of the rate constants obtained indicates a second-order process for polymerization concomitant with a first-order process for deactivation. The simultaneous observation of both processes in the time evolution of (13)C NMR signals over the course of several seconds underlines the utility of hyperpolarized NMR for quantifying early events in polymerization reactions.

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