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Poly-2,6-dimethylphenylene oxide (PPO) film samples with varying degrees of crystallinity (from 0 to 69%) were obtained by means of different techniques. The films were studied by various physicochemical methods (Fourier-transform infrared spectroscopy, positron annihilation lifetime spectroscopy, X-ray diffraction, and 1H nuclear magnetic resonance relaxation). Solubility coefficients of gases in the PPO samples were measured via sorption isotherms of gases by volumetric technique with chromatographic detection. The apparent activation energy of permeation and the activation energy of diffusion of all gases were estimated based on temperature dependences of gas permeability and diffusivity for amorphous and semi-crystalline PPO in the range of 20–50 °C. The peculiarities of free volume, density, and thermal properties of gas transport confirm the nanoporosity of the gas-permeable crystalline phase of PPO. So, the PPO can be included in the group of organic molecular sieves.

Positron annihilation technique as a probe of subatomic vacancies is described for non-positron polymer scientists.Although positronium (Ps) is an unparalleled unique probe of inter-molecular vacancies in insulating materials, with both its intensity and mean lifetime carrying information about the free volume, the processes that lead to these physical quantities are not simple. The state-of-the-art understandings of how Ps is created and how its mean lifetime is determined in vacancies are described, and examples of the unique feature as well as the problems and precautions are illustrated.

The structure of isotactic polypropylene (PP) and its blends with ethylene-propylene-diene terpolymer EPDM (0-100%) containing the unvulcanized and the vulcanized rubber phase were studied using positron annihilation lifetime (PAL) spectroscopy technique and thermostimulated luminescence (TSL). Cross-linking in the polymer blends is one of the effective ways to create novel materials with effective industrial properties. Meanwhile, composition of such systems is very complicated since it contains microphases of the dispersed components, cross-linked or not, elements of the cross-linking agents, which have some distribution between the blend components. This distribution, heterogeneity and also variation of elementary free volumes due to cross-linking are the points of interest in the study of polymer blend structures.

Positron annihilation lifetime spectroscopy (PALS) is a recognized instrument for the studies of size-distribution of nanopores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of “alien” pores, produced by swelling of poly (hexafluoro propylene) PHFP in the gas (CO2) in super-critical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.