Thermal and mechanical analysis of metallocene‐catalyzed ethene–α‐olefin copolymers: The influence of the length and number of the crystallizing side chains

Abstract

Copolymers of ethene and 1-octene, 1-dodecene, 1-octadecene, and 1-hexacosene were carried out with [Ph 2 C(2,7-ditert BuFlu)(Cp)]ZrCl 2 /methylalumoxane as a catalyst to obtain short-chain branched polyethylenes with branch lengths of 6-26 carbon atoms. This catalyst provided high activity and a very good comonomer and hydrogen response. In this study, the influence of the length and number of the side chains on the mechanical properties of the materials was investigated. The crystalline methylene sequence lengths of the copolymers and lamellar thicknesses were calculated after the application of a differential scanning calorimetry/successive self-annealing separation technique. By dynamic mechanical analysis, the storage modulus as an indicator of the stiffness and the loss modulus as a measure of the effect of branching on the a and b relaxations were studied. The results were related to the measurements of the polymer density and tensile strength to determine the effect of longer side chains on the material properties. The hexacosene copolymers had side chains of 24 carbons and remarkable material properties very different from those of conventional linear low-density polyethylenes. The side chains of these copolymers crystallized with one another and not only parallel to the backbone lamellar layer, depending on the hexacosene concentration in the copolymer. The side chains crystallized even at low hexacosene concentrations in the copolymer. A transfer of these results to 16 carbons

Lattice sizes, crystallinities, and spacing between amorphous chains - characterization of ethene-/ɑ-olefin copolymers with various comonomers and comonomer contents measured by wide angle X-ray scattering

“…It might be either an intralamellar or a lamella boundary crystallization. Piel et al [8] reported that this crystallization accounts for an additional mechanical transition around +45 °C, which roughly coincides with the additional melting peak in DSC, i.e. this transition is the side-chain crystallite melting temperature.…”

“…One part of the question what happens to those longer side chains was already answered by Piel et al [8] by finding a weak crystallization of the tetracosene branches (C24) from the hexacosene comonomer. The question remains, however, where this crystallization is taking place.…”

“…Many others were synthesized by Piel et al [8]. Several mHDPEs with different molar masses were also measured whose synthesis, molecular and rheological characterization was published elsewhere [12].…”

“…Piel et al [8] reported that the use of hexacosene (C 26 H 54 ), however, increases the density of the copolymer distinctly, because of the crystallization of the long side chains. This results in a specific relaxation in the dynamic-mechanical analysis (DMTA) and an additional melting peak in the DSC.…”

“…The high affinity of single-site catalysts towards higher olefins is used for producing ethene-/-olefin copolymers with a very high comonomer incorporation [3] and very long comonomers [4,5]. Usually butene, hexene, or octene are used as comonomers, but also longer olefins were utilized in recent years as comonomers, although such copolymers are not commercially available yet [4][5][6][7][8]. Another advantage of the single-site catalysts are their tendency to produce samples with a very homogeneous comonomer incorporation, which is not given for materials synthesized with ZN-catalysts or via the high pressure process [9][10][11].…”