Quantitative Analysis of Monomer Composition in Ethylene-Propylene Block Copolymers by FT-IR Spectroscopy

Abstract

The quantitative analysis of ethylene (or propylene) in the commercially important ethylene-propylene (EP) copolymers has been the subject of considerable research. Although NMR is the most useful method, it does present certain problems such as solubility and cost. IR is therefore still preferred from the industrial point of view. In IR, most of the work has been done on high-ethylene-content EP copolymers, with the use of conventional grating spectrophotometers. The two IR regions usually employed are at 1460–1380 and 1160–720 cm−1, and these have been studied for blends of homopolymers ranging from 0–100 wt % polyethylene (PE) and for random copolymers containing 42–66.7 wt % PE. The analyses are based on measurements of the ratios of absorbances at 1380–1460 and 1160–720 cm−1, as well as the ratios of peak areas for the two IR regions. Difficulties arise when one is attempting to accurately measure absorbance or peak area ratios at the two extremes of the concentration ranges.