Analysis of the types and amounts of carbonyl species present in oxidized polyethylene

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).