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Polymers: Defining Molecular Weight01:01

Polymers: Defining Molecular Weight

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Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight.  So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
The number average molecular weight (Mn) is the summation of the number...
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Polymers: Molecular Weight Distribution01:10

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For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
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Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion03:48

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Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...
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Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
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Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
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When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
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Using the GELFREE 8100 Fractionation System for Molecular Weight-Based Fractionation with Liquid Phase Recovery
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Using Fractionation and Diffusion Ordered Spectroscopy to Study Lignin Molecular Weight.

James R D Montgomery1, Priory Bazley1, Tomas Lebl1

  • 1School of Chemistry and Biomedical Sciences Research Complex University of St Andrews and EaStCHEM St Andrews, Fife KY16 9ST UK.

Chemistryopen
|May 22, 2019
PubMed
Summary

Determining lignin molecular weight is crucial for its applications. A new method using 2D DOSY NMR provides consistent and accessible measurements for this important biopolymer.

Keywords:
DOSY NMRbiomassfractionationligninmolecular weight determination

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Area of Science:

  • Biopolymer Chemistry
  • Analytical Chemistry
  • Materials Science

Background:

  • Lignin applications benefit from specific molecular weight fractions.
  • Current methods for determining lignin molecular weight are inconsistent and inaccessible.
  • Accurate molecular weight measurement is key to optimizing lignin utilization.

Purpose of the Study:

  • To introduce a reliable method for measuring lignin molecular weight.
  • To address the limitations of existing lignin characterization techniques.
  • To facilitate the broader application of lignin through improved analysis.

Main Methods:

  • Utilized 2D DOSY NMR (Diffusion Ordered Spectroscopy Nuclear Magnetic Resonance) analysis.
  • Applied a well-established Nuclear Magnetic Resonance (NMR) technique.
  • Tested the method across a diverse range of lignin samples.

Main Results:

  • The 2D DOSY NMR approach provides a direct measure of lignin molecular weight.
  • Consistent and reproducible results were achieved using this NMR technique.
  • The method proved effective for various types of lignin.

Conclusions:

  • 2D DOSY NMR offers a robust and accessible solution for determining lignin molecular weight.
  • This technique can enhance the understanding and application of lignin.
  • The findings pave the way for more standardized lignin characterization.