The factor group splitting phenomenon: a vibrational spectroscopy approach to assess polymer crystallinity and crystalline density

This paper gathers a number of relevant recent findings where Raman spectroscopy has been successfully applied by the author and coworkers to gain a unique structural picture about the crystalline phase present in isotropic and cold-drawn polyethylenes and in a range of aliphatic polyketone materials. In these semicrystalline polymers a relatively well-known spectroscopic phenomenon called factor group splitting (or correlation field splitting) is thought to occur. By careful analysis of the behaviour of this splitting phenomenon, chiefly in the -CH₂- bending range of the spectrum and in terms of alterations in band intensity and position, a valid approach to asses crystallinity content and morphology, crystalline polymorphism, and crystalline density is displayed. The potential of this spectroscopic phenomenon to yield information about the crystalline phase present in these polymers can therefore be regarded as analogous to that gained by wide-angle X-ray scattering.