Influence of structure of a crosslinked epoxy resin on its properties studied by positron annihilation and other methods

Positron annihilation has been applied to study samples of two crosslinked epoxy resins: onglycidyl ether of bisphenol A (Epikote 828) and polyglycidyl-ether of phenol-formaldehyde novolac (Epikote 155) cured with 4,4-diamino-diphenylo-methane (MDA), phenol-formaldehyde novolac resin (Novolac Z) and bisphenol A (formaldehyde resin). Results of measurements of positron lifetime spectra were compared with the ones coming from DMTA, flexural strength testing and density measurements. The most important features of samples (glass transition temperature, storage modulus, flexural strength, crosslinking density and tan proved to be correlated with the product, proportional to the fractional free volume in samples. Values of have been estimated from the values of ₃, the longest lifetime in positron lifetime spectra.I₃ corresponds to the intensity of the longest-lived component in them. Distributions of free volume radii reconstructed on the basis of PAL measurements are given for all samples. The influence of structure of both cured resin and the curing agent on the properties of the crosslinked products is clearly seen from the presented results.