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Positronium annihilation in amine‐cured epoxy polymers

1986; Wiley; Volume: 24; Issue: 6 Linguagem: Inglês

10.1002/polb.1986.090240605

1099-0488

Y. C. Jean, T. C. Sandreczki, D. P. Ames,

Membrane Separation and Gas Transport

Abstract 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 nm 3 . Two important transition temperatures were found: one corresponds to the glass transition temperature T g determined by differential scanning calorimetry (DSC), and the other occurs about 80–130°C below T g . The sub‐ T g 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.