This practice covers infrared spectrophotometry procedures for determining the molecular structural features such as types and number of branches in polyolefins and polyolefin copolymers. The structural features expressed by these determinations affect the ultimate polymeric properties and are useful in showing correlations with many performance properties. The apparatus is comprised of double beam or Fourier transform infrared spectrophotometer, hot plate, microscope slides, compression molding press, metal plates, brass shims, micrometer, and film mounts. Materials shall include polyethylene terephthalate, aluminum, or matte finished teflon-fiberglass sheet. The concentration shall be calculated using either the Beer-Lambert law with the appropriate molar absorptivity or an appropriate calibration curve.