Because of the structural use of polymers, it is important to understand the origin of their strength, elongation to break, elasticity, flexibility, and so on. It is in the very low frequency region (the so called “terahertz” range) where it is believed that the real indicators for crystallinity appear.
This introduction to two-dimensional correlation spectroscopy (2D COS) illustrates how to understand the structural changes occurring in polyester molecules in the fibers as they are annealed under tension.
We show Raman spectra of polymeric fibers acquired as a function of increasing stress and temperature. With knowledge of Raman band assignments, it becomes possible to understand, in detail, the molecular changes that are responsible for polymer orientation and crystallization.