Rheological Characterization of molten ethylene a-olefins copolymers

MARCELO VILLAR; MARCELO D. FAILLA; RAÚL QUIJADA; RAQUEL SANTOS MAULER; ENRIQUE M. VALLÉS; GRISELDA BARRERA GALLAND; LIDIA M. QUINZANI

POLYMER

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2001 vol. 42 p. 9269 - 9279

0032-3861

The rheological behavior of copolymers of ethylene with 1-hexene, 1-octene, 1-decene and 1-octadecene prepared with Et[Ind]2 ZrCl2/MAO is analyzed.  The linear viscoelastic behavior of the copolymers was characterized by measuring the dynamic moduli in small-amplitude oscillatory shear flow.  The copolymers with a-olefin concentration greater than approximately 14 mol% have the simple rheological behavior that may be associated to linear polyethylenes with short chain branches.  On the other hand, the polymers having comonomer concentration lower than approximately 14 mol% are thermorheologically complex materials.  The rheological behavior of these copolymers may not be explained solely by the presence of long chain branching.  A dendritic molecular structure with branches-on-branches has to be considered to explain the complexity observed in the case of the ethylene copolymers with low comonomer concentration and ethylene homopolymer.  The complex chain structure would be the result of the incorporation of branched macromonomers in the polymers produced by single-site catalysts. The level of branching and complexity of molecular structure increases as the comonomer concentration decreases.  No dependence with the length of the a-olefin was found in any of the analyzed parameters