Infrared spectroscopy is a powerful technique for studying the microstructure and determining the short-chain branch distribution of polyethylene. In this work, the types and amounts of short-chain branches in low-density polyethylene were investigated with Fourier transform infrared spectroscopy, and a new and simple method for the determination of butyl short branches was discovered. The amount of each unsaturated species in low-density polyethylene was also determined with Fourier transform infrared after the bromination of samples. Furthermore, the resin was fractionated by preparative temperature rising elution fractionation, and the branch distribution and melting endotherm of each fraction were analyzed with attenuated total reflectance/Fourier transform infrared and differential scanning calorimetry. (c) 2008 Wiley Periodicals, Inc.