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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
¹H NMR: Pople Notation01:09

¹H NMR: Pople Notation

The Pople nomenclature system classifies spin systems based on the difference between their chemical shifts. Coupled spins are denoted by capital letters with subscripts indicating the number of equivalent nuclei. When the coupled nuclei have well-separated chemical shifts, they are assigned letters that are far apart in the alphabet, such as A and X. When the difference in chemical shifts is small, coupled nuclei are named using adjacent letters of the alphabet (AB, MN, or XY).
A proton...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Mass Spectrometry of Amines01:15

Mass Spectrometry of Amines

In mass spectroscopy, amines undergo fragmentation to give parent ions with odd molecule weights. This observed mass spectrum follows the nitrogen rule; a molecule with an odd number of nitrogen atoms produces a molecular ion with an odd molecular weight. Amines undergo fragmentation through α cleavage, producing nitrogen-containing cations—iminium ions—and alkyl radicals. Mass spectra of aromatic and cyclic aliphatic amines exhibit strong molecular ion peaks, but acyclic aliphatic amines show...

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MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups
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MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups

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Universal polymer analysis by (1)H NMR using complementary trimethylsilyl end groups.

Michael Päch1, Daniel Zehm, Maik Lange

  • 1Fraunhofer Institute of Applied Polymer Research, Geiselbergstrasse 69, D-14476 Potsdam-Golm, Germany.

Journal of the American Chemical Society
|June 10, 2010
PubMed
Summary

New degenerative chain transfer agents with trimethylsilyl (TMS) markers enable universal polymer analysis using (1)H NMR spectroscopy. These agents provide accurate molar mass and end-group determination for controlled radical polymerization, simplifying polymer characterization.

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Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures
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Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures

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MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups
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Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry
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Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures

Published on: January 7, 2019

Area of Science:

  • Polymer Chemistry
  • Organic Synthesis
  • Analytical Chemistry

Background:

  • Controlled radical polymerization techniques like reversible addition-fragmentation chain transfer (RAFT) polymerization are essential for synthesizing polymers with defined properties.
  • Accurate characterization of polymer molar mass and end-group functionality is crucial for understanding polymer behavior and applications.
  • Conventional analytical methods can be challenging for simultaneously determining these parameters, especially for diverse polymer structures.

Purpose of the Study:

  • To design and synthesize novel degenerative chain transfer agents for controlled radical polymerization.
  • To demonstrate the utility of these new agents for universal polymer analysis via (1)H NMR spectroscopy.
  • To enable facile determination of absolute molar masses and end-group content in polymers.

Main Methods:

  • Design and synthesis of two-fold labeled degenerative chain transfer agents with complementary trimethylsilyl (TMS) markers.
  • Application of these agents in reversible addition-fragmentation chain transfer (RAFT) polymerization of various monomers (n-butyl acrylate, styrene, inimers).
  • Analysis of resulting polymers using conventional (1)H NMR spectroscopy to determine molar mass and end-group content.

Main Results:

  • Polymers with low polydispersities and high molar masses were obtained using the new RAFT agents.
  • Routine (1)H NMR spectra allowed accurate determination of molar masses up to 10(5) g/mol and end-group content (>95%).
  • Complementary TMS end-group markers revealed solvent-dependent differences in RAFT polymerization suitability.

Conclusions:

  • The newly developed RAFT agents are powerful tools for universal polymer analysis by (1)H NMR spectroscopy.
  • These agents facilitate the determination of absolute molar masses and end-group content, crucial for synthesizing high-quality polymers like telechelics and block copolymers.
  • Preliminary results suggest potential applicability in analogous atom transfer radical polymerization (ATRP) systems.