This work reviews principles of Raman and infrared imaging, as well as applications of the art to understand physiochemical phenomena in polymer systems. Image sequences may be assessed in terms of spatial or spectral changes that occur over time, either within a specific region or across the field of view. As such, the methods have enabled the analysis of diffusion and dissolution processes at polymer interfaces, drug release from polymer matrices, and structural transitions among others. Despite analytical limitations imposed by resolution (spectral or spatial) and sample preparation, Raman and infrared imaging are powerful tools for relating performance attributes to molecular‐level characteristics.magnified image

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Fourier transform infrared (FT-IR) imaging was used to study dissolution of stereoregular poly(methyl methacrylate) (PMMA) films in toluene, benzene, chloroform, acetic acid, and 2-ethoxyethanol. Images of the polymer-solvent interface showed that syndiotactic (sPMMA), atactic (aPMMA), and isotactic (iPMMA) samples dissolved in acetic acid and chloroform; only iPMMA dissolved in benzene, toluene, and 2-ethoxyethanol. Concentration profiles allowed quantitative comparison of each polymer-solvent system. In the cases of chloroform and acetic acid, the rate of polymer dissolution increased with increasing isotacticity. Dissolution of PMMA in chloroform was observed to coincide with development of strong polymer-solvent interactions. The results of systems containing toluene, benzene, and 2-ethoxyethanol reflect kinetic effects on dissolution, including solvent size and stiffness of the polymer backbone.

Hyperspectral chemical imaging technologies are frequently applied in the pharmaceutical industry to assess the distribution of ingredients in product intermediates and finished products. This article discusses two recognized measures of spatial uniformity in the context of pharmaceuticals. Synthetic images are used to introduce the utility of Ripley's K-function and the Herfindahl-Hirschman index (HHI) for describing image content. These metrics were applied to a commercial-like product to demonstrate the practical interpretation for product development. The simple approaches presented here offer the possibility of reporting objective measures of intra-tablet compositional uniformity with minimal supervision.