Polymer Characterization by Combined Chromatography-Infrared Spectroscopy

Infrared spectroscopy is widely used in the analysis and characterization of polymers. Polymer products are not a singular species, but rather, they are a population of polymer molecules varying in composition and configuration plus other added components. This paper describes instrumentation that provides the benefit or resolving polymer populations into discrete identifiable entities, by combining chromatographic separation with continuous spectra acquisition. The technology also provides a way to determine the mass distribution of discrete components across the chromatographic distribution of a sample. Various examples of application of this technology to polymer products are described. Examples include additives analysis, resolution of polymer blends, composition characterization of copolymers, analysis of degradation byproducts, and techniques of analysis of reactive polymer systems. 1. Introduction “The primary motivation for determining the structure of a polymer chain is to relate the structure to the performance properties of the polymer in end use. If a polymer chain is completely characterized and the structural basis of its properties is known, the polymerization can be optimized and controlled to produce the best possible properties from the chemical system” [1]. This paper addresses hyphenated chromatography-IR spectrometry instrumentation and the data processing and presentation techniques that can reveal the compositional and molecular structural properties of polymer materials. In analysis of polymers, no single technique can provide as much information as can Fourier transform infrared spectrometry (FTIR). Many commercial polymer products are not simply a single homopolymer, but rather are multicomponent systems. To obtain maximum information regarding the product, one must utilize some fractionation process prior to spectroscopy. Polymer products are quite complex. They may consist of mixtures of discrete components. The polymerization process typically yields variations in structure and composition as polymerization proceeds. These variations dictate the physical properties (strength, flexibility, melting point, and glass transition temperatures, to name a few) in the resulting product. In some cases, it is desirable to have invariant structure and composition throughout the population of polymer chains, while in other cases, such variations are specifically generated by the manipulation of the polymerization process. Characterization of distributed composition and structural properties, therefore, is essential to physical properties