Infrared Spectroscopy in Analysis of Polymers and Rubbers

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.

Contributions of Fourier transform infrared spectroscopy in microplastic pollution research: A review

“…Because each different polymer material is a unique combination of atoms, no two compounds produce exactly the same infrared spectrum. Therefore, the chemical structure of a polymer molecule can be determined by FTIR (Chalmers, 2006). The IR region of the electromagnetic spectrum is divided into three regions: (1) the higher energy near infrared (NIR) region with wavenumbers of 14,000-4000 cm À1 (0.78-2.5 mm wavelength) range, which is sensitive to overtone and combinations of vibrations, (2) the mid infrared (MIR) region with wavenumbers of 4000-400 cm À1 (2.5-30 mm wavelength) range to study the fundamental vibrations and (3) the far infrared (FIR) region with wavenumbers of 400-10 cm À1 (30-1000 mm wavelength) range to study rotations (Mukherjee & Gowen, 2015).…”

Fingerprint analysis of FTIR spectra of polymers containing vinyl acetate

“…However, this area is almost never discussed because of its complexity due to the large number of signals that appear in it. In the literature, we find IR analysis for homopolymers such as rubber and poly (methyl methacrylate) (PMMA) [11][12]. However, there are few studies related to the fingerprint region analysis of a copolymer such as ethylene-vinyl acetate (EVA) [13][14].…”

Remarkable Role of Experimental Olefin-Maleic-Anhydride Copolymer Based Compatibilizing Additives in Blends of Waste PET Bottles and Polyamide

“…For comparison 3000-2800 cm −1 wavenumber range (Fig. 4) was investigated, asymmetric stretching vibrations of methyl and methylene groups appeared at 2967 cm −1 and 2920 cm −1 , respectively, besides symmetric stretching vibration of methylene group at 2851 cm −1 [21]. Ratio of CH 2 /CH 3 belonging to the typical wavenumbers were calculated to be 0.03, 4.85 and 1.48 for 50% ABS, PC and PA respectively.…”