Thermal fractionation of ethylene polymers in packaging applications

In the past 5 years, new ethylene copolymers have found their way into a wide variety of applications. The new polymers have a unique combination of properties not typically found in conventional elastomeric or thermoplastic ethylene polymers. The characterization of these polymers by new and improved analytical techniques is of great interest. We describe a thermal fractionation method which sorts the crystalline ethylene sequence lengths of the polymer into groups. The ethylene lengths are estimated using melting points of known hydrocarbons. Three statistical terms are introduced to describe ethylene sequence length distribution: the arithmetic mean <(L)over bar(n)>, the weighted mean <(L)over bar(w)> and the broadness index <(L)over bar(w)>/<(L)over bar(n)>. We demonstrate the technique by comparing ethylene polymers produced with different catalyst systems, decipher ethylene components in unidentified ethylene blends and track changes in crystalline fractions with grafting.