Entanglement network and relaxation temperature dependence of single‐site catalyzed ethylene/1‐hexene copolymers

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.

The influence of short-chain branching on the morphology and structure of polyethylene single crystals

“…These samples are similar to model homogeneous copolymers reported in the literature . Please refer to previous works for details about molecular characterization and physical properties …”

“…In fact, no systematic studies exist in the literature about the effect of molecular architecture on the shape, morphology, and structure of single crystals obtained from dilute solutions of branched samples with high‐molecular weight. Some of us, have extensively studied the effect of SCB on the physical properties of well characterized samples of ethylene/1‐hexene copolymers obtained from single site catalysts, from both experimental and computer simulation techniques. In the present work, the effect of SCB on the crystallization of well characterized branched PE samples from dilute solution is systematically studied.…”

Predicting experimental results for polyethylene by computer simulation

“…In the case of PE, the model predicts that the decrease in ⟨R g 2 ⟩/M with the side chain weight fraction (S c ) or, alternatively, with the average molecular weight per backbone bond (m b ), causes an increase in p and consequently a decrease in G N 0 , an experimental fact repeatedly reported in the literature for model HPB samples [22,79] and single-site ethylene/-olefin copolymers [132][133][134][135][136]. This empirical fact is especially valuable in the case of polyolefins for which unperturbed dimensions remains unmeasured [131], as knowledge of m b gives a direct estimation of G N 0 and thus of M e = RT/G e , with G N 0 = (4/5)G e in the tube theory [137].…”

“…Effectively, García-Franco et al [134,135] and Chen et al [136] obtained  e values for different model polyolefins including different single-site ethylene/-olefins and HPB. This comparison is shown in Figure 5B for a temperature of T = 463 K and requires shifting of computed and experimental data using proper values of the flow activation energy of each material [132,133,136]. The results obtained are promising for values of m b up to 18 g/mol, and prompt future simulations involving higher SCB contents.…”

New habits in branched polyethylene single crystals

“…The molecular and physical properties were obtained by 13 C-Nuclear Magnetic Resonance, Size Exclusion Chromatography and CRYSTAF-TREF analysis. Please refer to previous works for details about molecular and physical characterization [13,[17][18][19][20][21][22].…”