Positronium annihilation in amine-cured epoxy polymers
| ISSN: |
0887-6266
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|---|---|
| Keywords: |
Chemistry ; Polymer and Materials Science
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| Source: |
Wiley InterScience Backfile Collection 1832-2000
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| Topics: |
Chemistry and Pharmacology
Physics
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| Notes: |
Positronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of amine-cured epoxy polymers. We have determined the free-volume “hole” sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between -78° and 250°C. The free-volume holes for these polymers are found to range from 0.025 to 0.220 nm3. Two important transition temperatures were found: one corresponds to the glass transition temperature Tg determined by differential scanning calorimetry (DSC), and the other occurs about 80-130°C below Tg. The sub-Tg transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for positronium trapping or else the onset temperature for local mode or side-chain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.
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| Additional Material: |
8 Ill.
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| Type of Medium: |
Electronic Resource
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| URL: |