Metrology for the Characterization of Branch Architecture in Polymers
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Motivation/Objective |
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| Determination of molecular branching is one of one of the most difficult measurements to make in polymer science.
After molecular mass distribution, it is chain branching that controls the mechanical, rheological, and solution properties of macromolecules.
We seek new methods to measure chain branching that will be used by industry to understand how single-chain topology influences processing and service properties.
Currently determination of chain branching are performed indirectly primarily by measuring bulk properties (e.g., melt rheology, solution viscosity, crystallization).
Nuclear magnetic resonance and vibrational spectroscopy can be used to give support to the modeling efforts by providing qualitative average values for number of branch points per chain and average branch length provided that the branches are short.
What is missing is a molecular-mass dispersive measurement of either the number of branches per chain or branch length.
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NIST Role/Approach |
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We will develop three novel approaches to measure chain branching:
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Chemically modify end groups and determine the number of end-groups per molecule as a function of molecular mass •
- Use radiation-induced gas-phase fragmentation to stimulate scission at branch points •
- Use gas-phase chemical reactions that preferentially seek out branch points •
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Highlights |
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Example: Gene Therapy via DNA Transfection using Branched Polyethyleneimine Proton Sponges
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- Transfection is the process of introducing nucleic acids into the target cells
- It requires the use of carrier molecules to transport the therapeutic material into the cell nuclei.
- Synthetic cationic polymer systems, such as polyethylenimine (PEI), are used as vectors to optimize gene therapy.
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Polyethyleneimine Polymerization
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Customers and Impact |
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- We have developed a method to methylate the primary amines of PEI.
- By using mass spectrometry to measure the molecular mass before and after methylation we can determine the number of branches per molecular as a function of molecular mass.
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Contributors: |
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W. E. Wallace
C. M. Guttman
K. M. Flynn
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Collaborators: |
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Dr. Charles Birse, Celera
Dr. Philip Price, Dow |
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