Technique for the study of diffusion of large molecules in polymers based on infrared microdensitometry

Abstract

THE diffusion of small molecules (in the gaseous, vapour or liquid phases) through polymeric matrices has been the subject of much study¹, and the techniques for such studies are, by and large, well established. Similar studies in the case of large molecules (broadly speaking, those forming solids at room temperature) in polymers, including polymeric self-diffusion, have been more rare^2–5. Existing techniques for measurements of the diffusion of large molecules in synthetic polymers rely mainly on radioactive labelling of the diffusants. Nuclear magnetic resonance (NMR) has been used⁵, but is limited to measurements of diffusion in the melt, and also to relatively high diffusion rates⁵. Measurements involving radioactively labelled diffusants have two major shortcomings, in addition to the necessity of having to obtain the required labelled material : they fail with diffusants which are surface active with respect to the polymer², and they may involve significant interfacial resistance which the method does not reveal^2,3.