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

摘要

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 ~(13)C 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 108-165degC. The calibration enables quick analysis of samples in polypropylene manufacturing processes.