Tacticity distribution of isotactic polypropylene prepared with heterogeneous Ziegler–Natta catalyst. 1. Fractionation of polypropylene

Two polypropylene samples, one with relatively low isotacticity and the other with high isotacticity were fractionated using a series of solvents and temperatures. For both samples 4–9 fractions were collected and characterised with differential calorimetry, size exclusion chromatography and 13C NMR spectroscopy. The collected fractions showed typical characteristics of a fractionation based on isotacticity, but also similarities to results from temperature rising elution fractionation (TREF), even though a separate controlled crystallisation step was not used. The melting temperatures of the fractions were found to increase linearly as a function of the meso diad fraction. A calibration, which can be used to convert DSC melting curves to wt% curves of isotacticity, was constructed for the temperature range 108–165 °C. The calibration enables quick analysis of samples in polypropylene manufacturing processes.