ABSTRACT
This chapter discusses highly permeable polymers, both rubbery and glassy and considers main chain and side chain structure peculiarities of the polymers as responsible for transport parameters, physicochemical properties, and the free volume values. It describes the search for correlation between polymer structure, free volume as estimated through macroscopic or microscopic behavior of polymer-gas systems, and transport properties. The chapter provides the discussion of structure-properties relationships in rubbers by considering poly(dimethyl siloxane), which is well known as the most permeable rubber. It shows how the size of the side group in polysiloxanes influences the glass transition temperature and the permeability coefficient. An interesting feature of polyphosphazenes is a wide range of permeability coefficients reported for the same polymer-gas systems. The most interesting property of poly(vinyltrimethyl silane) that at once drew attention to it is the high permeability. Positron annihilation has been applied to characterize the free volume of glassy polymers.
