Molecular Characterization of Polypropylene Heterophasic Copolymers by Fractionation Techniques

摘要

Molecular microstructure, thermal properties and morphology of three polypropylene heterophasic copolymers (PHC) with similar comonomer content were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), analytical and preparative temperature rising elution fractionation (TREF), scanning electron microscopy (SEM), and carbon nuclear magnetic resonance spectroscopy (~(13)C NMR). These results indicate that there are no differences in solution and thermal properties between unfractionated copolymers. Nevertheless, a physical fractionation by crystallization of these copolymers was developed to carry out a detailed study. Four fractions at different temperatures were collected. The results showed that the PHC's copolymers are composed by polypropylene, ethylene-propylene rubber (EPR) and, crystallisable sequences with different propylene and/or ethylene comonomers distribution. Despite the similar thermo-chemical properties shown by the raw PHC's copolymers, the characterization of fractions displayed significant differences between them. These results suggest that the fractionation by crystallization allows the different components in which the PHC's copolymers are based to be distinguished clearly, and obtain a more comprehensive sense of the molecular structure characterization.