Crystal polymorphism: Polymorphism occurs when a molecule is able to exist in more than one crystalline state. Many crystalline materials can form different polymorphs to minimize their crystal lattice energy under specific thermodynamic conditions. While the chemical nature remains the same, physical properties (solubility, dissolution, nucleation and growth kinetics, bioavailability, morphology, and isolation properties) can vary between polymorphs. Raman spectroscopy is ideal for recording the differences in forms and in measuring the forms while optimizing the crystallization process.
Polymerization: Raman spectroscopy tends to provide a stronger signal (than IR) from the molecular backbone, especially double and triple carbon bonds. For this reason, Raman can be a better choice for identifying polymers and monitoring polymerization reactions. Extrusion chemistry, microstructure analysis during polymerization, and polyethylene density (LDPE/HDPE) calculations are just a few practical applications where Raman spectroscopy is used.
Chemical Synthesis: In-situ Raman spectroscopy is a useful technique to monitor key reaction variables of chemical syntheses where infrared spectroscopy may not be as sensitive (e.g., silicone, thiol, disulfide, etc.). Key reaction variables such as initiation, endpoint, kinetics, transient intermediate(s), and mechanistic information are vital aspects to know and fully characterize to ensure a safe and robust process development method.