Abstract
Abstract The fractionation by temperature rising elution fractionation (TREF) of poly(propylene-ethylene) copolymers containing a minor fraction of ethylene was described. A method was developed to determine the ethylene concentration distribution in these copolymers. A poly(propylene-ethylene) copolymer containing 29% wt. ethylene was fractionated by preparative TREF. The fractions were analyzed by analytical TREF, and by 13C NMR spectroscopy to determine the average ethylene concentration in each fraction. A calibration curve relating analytical TREF elution temperature and ethylene concentration was established. It was shown that the weight-average TREF elution temperature was the appropriate average elution temperature to correlate with the weight percent ethylene determined by 13C NMR spectroscopy. This calibration curve was used to obtain the ethylene concentration distribution for a series of poly(propylene-ethylene) copolymers from their analytical TREF elution temperature chromatograms. The average ethylene concentration was calculated from these ethylene concentration distributions and found to be in good agreement with the ethylene concentration determined by 13C NMR. Extrapolation of the calibration curve to 0% ethylene yielded a predicted analytical TREF elution temperature of 108.7°C, which was in excellent agreement with the experimental elution temperature for isotactic polypropylene of 108.7°C.
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