Polarization modulated infrared spectroscopy: A pragmatic tool for polymer science and engineering

In the area of polymer crystallization, the most widely used techniques to quantify structure, morphology and molecular orientation are fundamentally based on light or X‐ray scattering and absorption. In particular, synchrotron X‐rays are used for detailed studies on the semicrystalline structure in polymeric materials. The technical requirements for such techniques, especially when high spatial resolution is essential, make the application of X‐ray diffraction not straightforward. Direct information on the chain orientation in different semicrystalline morphologies requires rather complex sampling and analysis procedures. Surprisingly, a simple yet versatile technique based on infrared spectroscopy is hardly applied in the field of polymer crystallization. By modulating the polarization of the incident light, local anisotropy can be studied in real time on a submolecular length scale. In this article, we provide the relevant details of the polarization modulated infrared microspectroscopy technique for the study of semicrystalline materials from an engineering perspective. We demonstrate the essence of the method using as model systems spherulitic and transcrystalline morphologies and present its applicability to polymer/fiber composite technology and the study of injection‐molded parts. The results provided in the present work serve to illustrate the applicability of this informative technique in the field of semicrystalline polymer science. Properties of polymeric materials are to a large extent determined by their microstructure. In semicrystalline polymers the crystal structure, morphology and molecular orientation are generally quantified using optical techniques, in particular synchrotron X‐ray scattering and diffraction. A versatile technique based on infrared spectroscopy is emerging. By modulating the polarization of the incident light, local anisotropy can be studied in real time on a submolecular length scale. This polarization modulation method is applied to several orientation related challenges in the crystallization of isotactic polypropylene.