To characterize butene polymers, rapid and precise small- and large-scale column fractionation techniques have been developed for low molecular weight pure polyisobutenes and for mixed butene polymers. Fractionation results have been used to determine molecular weight distribution curves of typical commercial butene polymers. Narrow distribution fractions obtained from fractionation have been used to investigate viscosity–molecular weight correlations for both pure polyisobutenes and for mixed butene polymers. Molecular weights were predominantly determined with the relatively new technique of vapor pressure osmometry. Molecular weights and distributions were also checked with cryoscopic and light scattering molecular weights. The chemical composition of several fractions was determined by high resolution nuclear magnetic resonance. The Huggins' constant was measured for several bulk polymers and established for low molecular weight butene polymers.