Branched polyethylenes fractionated in supercritical propane

Abstract

A series of polyethylenes (PEs), were synthesized in the presence of a palladium catalyst containing bulky diimine ligands (VERSIPOL TM ) yielding amorphous PEs. The different PE samples were characterized by Size Exclusion Chromatography (SEC) with on line light scattering, NMR, viscometry or small angle neutron scattering (SANS) techniques to assess the molar mass, molar mass distribution (MMD), radius of gyration (or hydrodynamic radius) and degree of branching. Selected PE samples were fractionated in supercritical propane by isothermal increasing the pressure profile. In most cases, PE fractions with a sharper MMD than the original PEs were obtained. The average absolute molar masses of the resulting fractions increased steadily with increasing extraction pressure. Their dilute solution properties were compared with those of unfractionated PEs. Structural analyses confirmed the homogeneity of the degree of branching within a raw PE sample.

Applications of Supercritical Fluids in Latin America: Past, Present and Future Trends

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