Near-Infrared Analysis of Ethylene Propylene Copolymers

Abstract

Abstract A number of block and random copolymers of ethylene and propylene have been synthesized using C14 labeled ethylene. Using the radio-assay results of these materials, a near-infrared analysis for ethylene content was developed. The 2.275 micron (4396 cm−1) and 2.312 micron (4325 cm−1) near-infrared combination bands are useful for determining monomer ratio concentrations in the 0 to 40% ethylene range regardless of copolymer type. They are superior to the fundamental infrared bands because they are much less sensitive to slight differences in crystallinity. Other advantages include internal thickness calibration by relative peak height measurements on peaks of more nearly equal intensities than the fundamental bands and greater convenience in sample preparation techniques. The fundamental 720 cm−1 band intensity is a good indication of ethylene content in crystalline block copolymers but requires the accurate measurement of sample thickness for an analysis. The 968 cm−1 and 1163 cm−1 bands, ratioed with the the 720 cm−1 band, show definite correlation with monomer concentration but are less precise than the near-infrared data because of sensitivity to randomness and crystallinity.