The carbonyl species present in oxidized polyethylene are qualitatively and quantitatively determined through the use of infrared measurements on the polymer. The method described makes use of a carbon monoxide/ethylene copolymer wedge in the reference beam of the infrared spectro photometer to compensate the large 1720 cm −1 ketone absorbance. This allows one to observe the 1710 cm −1 and 1735 cm −1 carbonyl absorbances as distinct peaks rather than as shoulders on the 1720 cm −1 peak. This is a significant advantage over other published infrared methods for this analysis. The absorbances obtained at 1710 cm −1 and 1735 −1 are then used in an equation to calculate the absorbance at 1720 cm −1 due to ketonic carbonyl only. Our results confirm Cooper and Prober's assignment of both the 1710 cm −1 and 1735 cm −1 absorbances in the infrared spectra of oxidized polyethylene to acid functionality. Our quantitative results are comparable to those reported by Cooper and Prober, and our method represents a significant reduction in the time required for the analysis (1.5 hr vs. ∼45 days). The carbonyl distribution in a commercially oxidized polyethylene wax was determined as being ∼11.0 ketone CO/2000 C and ∼21.7 acid CO/2000 C (with a σ of 1.8 CO/2000 C and 3.0 CO/2000, respectively). A high‐density polyethylene, oxidized with air in the laboratory, contained ∼1.91 ketone CO/2000 C and 2.19 acid CO/2000 C (with a σ of 0.08 CO/2000 C and 0.16 CO/2000 C, respectively).
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Benham et al. (1976) studied this question.
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