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Infrared Spectroscopy in Analysis of Polymers and Rubbers

Polymers and Rubbers

  1. John M. Chalmers

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a2015

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Chalmers, J. M. 2006. Infrared Spectroscopy in Analysis of Polymers and Rubbers. Encyclopedia of Analytical Chemistry. .

Author Information

  1. University of Nottingham, Nottingham, UK

Publication History

  1. Published Online: 15 SEP 2006

Abstract

The infrared spectrum of a polymer or rubber is a profile of its absorption characteristics plotted against infrared wavenumber (or frequency). It is generated when infrared radiation interacts with the molecular moieties that constitute the polymer or rubber material. It is a distinctive property (a “fingerprint”) of the polymer or rubber sample in the form, manner and environment in which it is being examined. It is based on the absorption of infrared radiation at frequencies that match those of the normal modes of vibration within the macromolecule. These absorption features are characteristic of the molecular configuration, sequencing and conformation, and state of order. Absorptions by internal vibrations predominate in the mid-infrared region (ca. 4000–400 cm−1); they involve a few selected atoms in a molecular (functional) grouping, which is a sub-set of those constituting the macromolecule. External vibrations, such as lattice vibrations, which involve segments of macromolecules in crystalline regions, tend to occur at low wavenumbers (<400 cm−1). The intensity of an absorption band is, to a first approximation, proportional to the number density of vibrating species giving rise to that band. The intensity of an absorption band is related to the dipole moment change associated with the molecular vibration; if it is large then the band intensity will be high. Infrared spectroscopy is highly specific. For some quantitative analyses, it can be very precise and sensitive (<0.1%). It is complemented with Raman spectroscopy, for which the selection rules are different and relate band intensity to the change of polarizability occurring during a molecular vibration. Infrared spectroscopy can be used to identify and analyse the molecular structure, composition, order and morphology, both qualitatively and quantitatively, of polymers, copolymers and rubbers and their products. However, for heavily filled and plasticized formulations the spectral interferences may be too high to allow direct or adequate interpretation of a spectrum, and separation of the components will be necessary for unambiguous identifications.