Analysis of synthetic polymers by near-infrared spectroscopy

Abstract

As the role of the polymeric materials in industry broadens, it becomes increasingly important to provide rapid quality evaluation of these materials. Existing quality evaluation methods, such as physical testing, FT-IR spectroscopy, Differential Scanning Calorimetry, and X-ray scattering, cannot be used for rapid quality evaluation, because they require substantial sample preparation and long analysis times, and are usually destructive. In contrast, near-infrared (NIR) spectroscopy requires minimal sample preparation and is not destructive. Therefore, NIR spectroscopy can be used for rapid analysis of polymers, if it is periodically calibrated with a reference analytical method.The success of NIR methods depends on the ability of NIR spectroscopy to determine important compositional and structural properties of polymers. Earlier NIR analyses have demonstrated successful determinations of a few properties, but these studies were very limited in scope, and did not utilize newly-developed NIR instrumentation and multivariate calibration techniques. In this work, the ability of NIR spectroscopy to determine several important compositional and structural properties of polymers is demonstrated, with the aid of multivariate calibration methods. Results indicate that NIR spectroscopy can determine composition in styrene-butadiene copolymers, Reaction Injection Molded (RIM) polyurethanes, polyurethane foams, and EPDM terpolymers, microstructure of poly(butadiene) and styrene-butadiene copolymers, crystallinity in poly(ethylene terephthalate) and Ethylene-Propylene-Diene (EPDM) terpolymers, phase separation in RIM polyurethanes, and adsorption of poly(octadecyl methacrylate) to alumina. Other effects, such as $\pi$-$\pi$ interactions and sequencing effects in polymers, can also be detected by NIR spectroscopy.