| Abstract: | The temperature rising elution fractionation (TREF) technique makes use of the differential crystallizabilities, introduced by short chain branches (SCB), to fractionate polyethylenes (PE) on the basis of the SCB level of any one chain. This allows one to probe the SCB distribution of a polymer. The TREF technique has been applied to blends of PE by recognizing that the two commercial types of low density polyethylene, high pressure (HP-LDPE) and linear low density (LLDPE), have different short chain branching distributions. Other common copolymers of ethylene, like ethylene vinyl acetate (EVA) or terpolymers like ethylene/propylene/hexadiene (EPDM), also have different SCB types, levels, and distributions and therefore have different TREF behavior. We have constructed a TREF apparatus that can be used in a number of different types of blend studies. The first is an Analytical-TREF, which gives a profile of the amount of polymer with a given SCB level and can be used to quantify HP-LDPE/LLDPE blends. We have also modified the technique to construct a stop-flow TREF apparatus, which enables one to separate fractions on the basis of the branching levels. The fractions can then be analyzed by size exclusion chromatography, IR, 13C NMR, or DSC. The use of these TREF techniques to characterize blends of HP-LDPE/LLDPE, LLDPE/EVA, PE/EPDM, and PE/polyisobutylene is discussed. |
