MODELING THE FRACTIONATION PROCESS IN TREF SYSTEMS .3. MODEL VALIDATION WITH LOW-MOLECULAR-WEIGHT HOMOPOLYMERS

Low molecular weight semicrystalline homopolymers are used as a model system for temperature rising elution fractionation (TREF) analysis. A n already proposed thermodynamic model for TREF analysis is used to ch aracterize TREF fractions from low molecular weight polyethylenes M(n) = 500 to 3000 and some of their mixtures. In this molecular weight ra nge it is possible, under appropriate crystallization conditions, to f orm extended-chain crystals, and therefore lamellar thicknesses become comparable to extended-chain lengths. Lamellar thicknesses calculated from TREF spectra permit calculations of the molecular weights of the fractions, up to a limit of about 142 CH2, where partially folded-cha in crystallites appear under these operating conditions. Also homopoly mers blends are fractionated and the TREF spectra analyzed to test mod el predictions. It is shown that appearance of chain folding may set a resolution limit to the analysis of commercial copolymers by TREF. (C ) 1996 John Wiley & Sons, Inc.