N.N. Semenov Research Center of Chemical Physics Russian Academy of Sciences, 119991 Moscow
This paper is not a usual review and is written to illustrate the scientific activity of the outstanding researcher Yuri Pavlovich Yampolskii in one of the fields of interest: the creation and investigation of the new amorphous polymeric materials with chosen characteristics of gas separation and permeation. In this review, the specific property of the free volume number densities and the effective size of polymers determined using positron annihilation will be described. The exciting results will be highlighted, touching on several points of the research, such as the relations between permeation properties and elementary free volume characteristics, the multimodality of the distribution of ortho-positronium lifetimes, the dependence of the size of elementary free volumes on the conformation rigidity of the polymer chain, the relation between local rigidity and multimodality and the experiments with thermostimulated luminescence, and the low-temperature gas sorption connected to the free volume elements. These studies' importance for solving chemistry and ecology problems is obvious.