Showing papers by "Rosario Benavente published in 1999"
TL;DR: In this article, an elastomeric poly(propylene) with low percentages of isotactic pentads and high molecular weight was synthesized using unbridged "oscillating" metallocenes.
Abstract: Elastomeric poly(propylene) with low percentages of isotactic pentads and high molecular weight was synthesized using unbridged “oscillating” metallocenes. The polymer sample with the highest [mmmm] content (22%) shows a small amount of crystallinity, which is highly influenced by the thermal history, and differs significantly in stress-strain and dynamic mechanical properties from all other samples. Polymers with lower isotacticity index, although lacking crystallinity in thermal analysis, differ in their viscoelastic behaviour from those of atactic poly(propylene). In dynamic mechanical analysis the γ relaxation at low temperature shows high sensitivity to low isotactic contents.
57 citations
TL;DR: The copolymerization of ethylene and 1-octadecene using a bridged metallocene was studied in order to observe the effect of the comonomer on the catalytic activity.
Abstract: The copolymerization of ethylene and 1-octadecene using a bridged metallocene was studied in order to observe the effect of the comonomer on the catalytic activity. A noticeable increase in activity is seen as the concentration of 1-octadecene in the reaction medium increases. 13 C NMR analysis shows 6.4 mol-% incorporation of comonomer at the highest 1-octadecene concentration in the feed used here. The molecular weight of the copolymers shows a drastic decrease that may be attributed to chain termination by transfer or β-elimination of the comonomer. As to the molecular weight distribution, it remains within a narrow range, as expected with metallocene catalysts. The melting temperature and the enthalpy of melting of the copolymers show a decrease with increasing comonomer content. As usual for ethylene copolymers, the X-ray crystallinities are higher than those determined from the enthalpy of melting.
47 citations
TL;DR: A series of high density polyethylenes (HDPE) were synthesized via homogeneous polymerization with metallocene catalyst in two different reactors (glass and stainless steel) as discussed by the authors.
Abstract: A series of high density polyethylenes (HDPE) were synthesized via homogeneous polymerization with metallocene catalyst in two different reactors (glass and stainless steel). The thermal and mechanical properties of the polyethylenes, synthesized with two types of reactor and different reaction parameters, are discussed.
11 citations