Five isotactic polypropylenes produced with different processes and different heterogeneous Ziegler-Natta catalyst systems were fractionated using n-heptane extraction in a Soxhlet apparatus. The unfractionated polymers and their heptane-soluble and heptane-insoluble fractions were analysed with size exclusion chromatography, ~3C nuclear magnetic resonance (n.m.r.), differential scanning calorimetry and Fouriertransform infra-red spectroscopy. The composition of the heptane-soluble fraction was somewhat dependent on the molecular structure of the original polymer. On the other hand, the heptane-insoluble material was not completely isotactic, and some syndiotactic and heterotactic polymers were found in it. Heptane extraction as a method for isotacticity determination is discussed and compared with other methods. One of the samples was also divided into four fractions using successive extractions with n-heptane, n-octane and xylene. Based on the 13C n.m.r, spectroscopic pentad analysis carried out on the fractions, possible structures for stereoblock polymers are suggested. Fractionation results are also compared with an earlier fractionation performed on the same sample using fractional solution with solvent/non-solvent mixtures and vibromixer agitation.
Посилання на статтю:
Fractionation of polypropylenes using Soxhlet extraction methods / Ritva Paukkeri and Arja Lehtinen // Polymer. – 1994. – Vol 35. – P. 1673-1679.