Hyper-cross-linked polystyrene sorbents with various degree of cross-linking ranging from 25% to over 100% were studied using positron annihilation lifetime (PAL) spectroscopy. Long-lived components of the lifetime distribution of positron annihilation, orthopositronium (o-Ps) lifetimes, give information on the effective size of elementary free volumes (unoccupied spaces), responsible for the properties of sorbents. Experiments were carried out in a vacuum, in air and also in oxygen and nitrogen. Narrow size distribution of elementary free volumes having radius of about 1.5 nm and concentration estimated as ∼10 19 cm -3 , were found in the samples with cross-linking higher than 40%. Some of the hyper-cross-linked samples gave positronium lifetime τ5 > 50 ns, which is among the highest values ever measured for organic polymer compounds. Positronium quenching (shortening of o-Ps lifetime) due to Ps exchange interaction with oxygen, dissolved in sorbents, gave information about the character of distribution of elementary free volumes in polymers.

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SYNOPSISPositron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned to ortho-positronium located in amorphous regions. This component was shown to be sensitive to the defects in high-density polyethylene introduced in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma-ray irradiation was also examined. Although the intensity (Z4) of the longest lived component was reduced by the irradiation, correlation between Z4 and the free radical concentration was poor, and the reduction in I4 caused by the irradiation is considered to be due to structure change and not to chemical reasons. Keywords: positron annihilation in polyethylene, before and after irradiation polyethylene, positron annihilation in, effect of radiation on 517