INFLUENCE OF STRUCTURE OF A CROSS-LINKED EPOXY-RESIN ON ITS PROPERTIES STUDIED BY POSITRON-ANNIHILATION AND OTHER METHODS

Positron annihilation has been applied to study samples of two crossli nked epoxy resins: diglycidyl ether of bisphenol A (Epikote 828) and p olyglycidyl-ether of pbenol-formaldehyde novolac (Epikote 155) cured w ith 4,4'-diamino-diphenylo-methane (MDA), phenol-formaldehyde novolac resin (Novolac Z) and bisphenol A (formaldehyde res in). Results of me asurements of positron lifetime spectra were compared with the ones co ming from DMTA, flexural strength testing and density measurements. Th e most important features of samples (glass transition temperature, st orage modulus, flexural strength, crosslinking density and tan delta) proved to be correlated with the product I-3.(v) over bar proportional to the fractional free volume in samples. Values of (v) over bar have been estimated from the values of tau(3), the longest lifetime in pos itron lifetime spectra I-3 corresponds to the intensity of the longest -lived component in them. Distributions of free volume radii reconstru cted on the basis of PAL measurements are given for all samples. The i nfluence of structure of both cured resin and the curing agent on the properties of the crosslinked products is clearly seen from the presen ted results.