1.1 ,This test method covers the determination of methyl groups (that is, comonomer content) in polyethylenes by infrared spectrophotometry. The test method is applicable to copolymers of ethylene with 1-butene, 1-hexene, or 1-octene having densities above 900 kg/m³. High-pressure low-density polyethylenes (LDPE) and terpolymers are excluded.