Open spaces and molecular motions of acrylic epoxy-based network polymers probed by positron annihilation

Lifetime spectra of positrons have been measured for acrylic epoxy-based network polymers. For the specimens with the different permeability coefficients to water vapor C_p, the lifetime of ortho-positronium (o-Ps) τ₃ increased with increasing C_p. This fact suggests that the permeability increases with an increase in the size of open spaces. From measurements of temperature dependencies of τ₃ and the intensity of o-Ps, three onset temperatures for the change in the temperature gradient of these parameters were determined. The highest onset temperature (T_α = 300–325 K) was identified to be the glass transition temperature, and others (T_γ = 90–180 K and T_β = 160–205 K) were associated with the onset temperatures for limited local motions of molecules; those molecular motions were found to be affected by both the number of crosslinks and the presence of free side chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2875–2880, 1999