A combined study of microstructure and mechanical properties for a series of single‐site metallocene ethylene/1‐hexene copolymers is presented. The analysis of the results focuses on the effect of branching, which in turn modulates crystallinity and density, on the values of the elastic modulus obtained in tensile‐deformation experiments. An extensive literature review is done in order to compare our own results with previous studies. The typical variation found in the elastic modulus is discussed in terms of the existence of a rigid amorphous phase. This rigid phase controls the macroscopic mechanical behavior of the materials, giving rise to an increase of the elastic modulus as the crystallinity does. Mechanical coupling models for heterogeneous systems are applied in order to describe the experimental results of the elastic modulus as a function of the variation of three different phase fractions, i.e., crystalline, rigid amorphous (or interfacial), and mobile amorphous. The phase fraction values obtained from the analysis of the mechanical properties are in qualitative agreement to those found experimentally in our group by Raman infrared spectroscopy and from the literature by positron annihilation lifetime spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The processability of a metallocene‐catalyzed polyethylene blended in the melt with low amounts of ultra‐high molecular weight polyethylene was evaluated. Our morphological and thermal studies revealed that the blends were structurally heterogeneous, formed by a matrix of metallocene polyethylene and homogeneously distributed particles of ultra‐high molecular weight material. The visible particles were smaller than those of the reactor powder. Also observed was some degree of interaction between both phases. Rheological data indicated an intense effect of morphology on viscoelastic functions, beyond that expected for a system composed of noninteractive phases. Collectively, our findings suggest the existence, to some extent, of a homogeneous phase at the molecular level composed of a fraction of ultra‐high molecular weight species and metallocene polyethylene. This gives rise to a striking behavior during processing in that the blends show improved extrusion performance the higher their ultra‐high molecular weight polyethylene content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2963–2971, 2005

No abstract

No abstract

In this work, we investigate the linear viscoelastic response of high molecular weight ethylene/1-hexene copolymers, characterized by a narrow molecular weight distribution and comonomer content in the range from 0 to 10 mol %. A variation in the entanglement plateau modulus has been found in agreement with the recently developed packing length model. The packing model applied to viscoelastic data suggests decreased values of the characteristic ratio, accordingly with recent computer simulation results. The flow activation energy increases as the side chain content increases. This feature is thought to be related to the mobility of the molecules. The presence of side branches due to the comonomer hinders the mobility of the molecules, and increases the thermal barrier for the segmental motion. Then in the comonomer content range studied, the increase of the flow activation energy goes parallel with a decrease in the characteristic ratio. This result suggests that more parameters than only the stiffness of the chain modulate the thermal dependence of viscoelastic properties. A more refined study is necessary combining experiments with computer simulations in order to elucidate these aspects.