Characterizing chemical composition of polyolefin-based copolymers from spectral features in the C-H stretching region

J.P. TOMBA; L.I. SILVA; M. GARCIA GENGA; G. BARRERA GALLAND; C. J. PÉREZ

JOURNAL OF RAMAN SPECTROSCOPY

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2019 vol. 50 p. 576 - 586

0377-0486

The comonomer content of a series of commercial ethylene?octene (Engage®,Infuse®), ethylene?butene (Engage), and ethylene?propylene (Versify®, Nordel®)copolymers is investigated using the Raman spectroscopy. The analysis reliesupon the different content of methyl, methylene, and methine groups ofeach copolymer and focuses on the spectral features of the C―H stretchingregion. Raman spectra of a series of molecules with well‐defined content ofmethyl, methylene, and methine groups (alkanes and well‐defined polymerchains) are first addressed to rationalize the complex spectral features arisingfrom different stretching modes, their Fermi resonance, and the differentmolecular conformations. Results are interpreted on the base of recent workon the topic. A curve‐fitting procedure is proposed to resolve contributionsarising from CH2 and CH3 groups. The sum of intensity of bands at 2,855and 2,865 cm−1 (symmetric C―H stretching and Fermi resonance) correlateslinearly with CH2 content whereas that at 2,880 cm−1 (symmetric C―Hstretching) does with CH3 content. With that base, Raman spectra of ethylene‐based copolymers are analyzed to quantify comonomer content. Results arecompared with independent results from 13C nuclear magnetic resonanceanalysis with good agreement between the methods. Overall, it highlights theimportance of Raman spectroscopy as versatile tool for process monitoring,quality control, or sample identification not only at academics but also inindustrial environments.